How much current safe for 30m extension?

[Jerry G.]

As long as the maximum current load does not exceed the current rating of
any of the cables that are used in the extension, it will be safe. There
should not be very much loss over a few hundred feet of extension. If there
is a loss, you can then change the extensions for ones that are of a larger
gauge.

I have run extensions of up to 400 feet. These were 10 Amp rated. I had no
performance loss in the loads that I was using. The load was about 4 to 5
amps. I am working with 120 VAC at my location. I took a voltage reading, at
the outlet, and one across the load. There was a drop of about one or two
volts. But, the total voltage at the extension output was still in specs
while under the load. The source voltage at the outlet was about 118 VAC.
Across the load, if I remember correctly, it was about approximately 116
VAC.

In areas that are using 220 VAC, the current is about 1/2 for the same
wattage, as when compared to 120 VAC. This would lead to less loss when
using an extension cord.

Most devices here in North America are rated at 105 to 125 VAC. Some are
rated from about 105 to 135 VAC.

--

Jerry G.
======


"Ian Stirling" <root@mauve.demon.co.uk> wrote in message
news:420dfa9a$0$45677$ed2e19e4@ptn-nntp-reader04.plus.net...
In uk.d-i-y Sammo <noone@no-where.com> wrote:

I am in the UK (so mains voltage is about 230V or 240V).

I have a reel of main extension cable made of 3-core 1.0 mm^2 wire
rated at 10 Amps. So the nominal power rating would be about 2,400
Watts. (Link to tech reference for the cable is below.)

It's always going to be safe, as it's got a fuse.

Ok...
Copper has a resistivity of 0.7*10^-8 ohms/meter.

Or, for a 1mm^2 wire, 0.7*10^-2 ohms/meter.
Or for 2 wires, 1.4*10^-2 ohms.
Or for 60m, 8.4*10^-1 ohms, or .84 ohms.
At 10A, 8.4V, or heating by 84W.
If at the plug end is 240V, at the socket end will be 232V, which is
(232^2/240^2)= .93444444444444444444

So, you lose 7% of the power for a heater, for example.

 

[John Rumm]

Jerry G. wrote:

As long as the maximum current load does not exceed the current rating of
any of the cables that are used in the extension, it will be safe. There
should not be very much loss over a few hundred feet of extension. If there
is a loss, you can then change the extensions for ones that are of a larger
gauge.

The other issue to beware of is as the length of wire increases, so does
it fault loop resistance (i.e. path from line to earth / ground). This
will reduce the maximum current that can be passed to earth in the event
of a fault, and hence extend the time between the fault occuring and the
circuit protective device (fuse, circuit breaker etc) opening to
disconnet the power. Obviously if *you* are forming part of this earth
fault loop, the sooner the power goes off the better!

Out of interest, are US style plugs fitted with fuses?

(An extension lead running outside ought to have RCD protection anyway
of course, to negate the problem)

--
Cheers,

John.

/=================================================================\
| Internode Ltd - http://www.internode.co.uk |
|-----------------------------------------------------------------|
| John Rumm - john(at)internode(dot)co(dot)uk |
\=================================================================/

 

[John Rumm]

Paul Miller wrote:

The big problem is going to be earth loop impedance, I know it sounds
trivial
because it will work fine, but you did quote a PSC figure of 120A......must
be
a TT instalation. Please make sure you have a RCD on this circuit..

If you do the sums for 1mm sq cable that is the PSC you get *without*
including the supply impedance - it only gets worse in reality.

(not sure what significance the supply being TT would have on PSC mind you)

--
Cheers,

John.

/=================================================================\
| Internode Ltd - http://www.internode.co.uk |
|-----------------------------------------------------------------|
| John Rumm - john(at)internode(dot)co(dot)uk |
\=================================================================/

 

[Sammo]

Jerry G. wrote:

As long as the maximum current load does not exceed the current
rating of any of the cables that are used in the extension, it
will be safe. There should not be very much loss over a few
hundred feet of extension. If there is a loss, you can then
change the extensions for ones that are of a larger gauge.

On 13 Feb 2005, John Rumm wrote:

The other issue to beware of is as the length of wire increases,
so does it fault loop resistance (i.e. path from line to earth /
ground). This will reduce the maximum current that can be passed
to earth in the event of a fault, and hence extend the time
between the fault occuring and the circuit protective device
(fuse, circuit breaker etc) opening to disconnet the power.
Obviously if *you* are forming part of this earth fault loop,
the sooner the power goes off the better!

Out of interest, are US style plugs fitted with fuses?

(An extension lead running outside ought to have RCD protection
anyway of course, to negate the problem)

I am the original poster with two 30m extension cables. You refer to
RCD protection.

I have got a plug-in RCD device but I know nothing about earth fault
loops. It is similar to the one in this illustration.
http://www.argos.co.uk/wcsstore/argos/images/9828331A59IFN104773M.JPG

Where should my RCD device be plugged in to best avoid the problem of
earth fault loops:

(1) At the mains supply end where the first extension goes into the
mains socket.
(2) In the middle of the two 30m extensions.
(3) At the far end of the two extensions where the appliciance I am
using is plugged in?

 

[Dimitrios Tzortzakakis]

cable is not that expensive, it's copper after all.I can see in an invoice
that I paid 28 cents a meter for a 3G1.5 mm^2 A05VV-U cable.A 2.5 mm^2
conductor, single core, which we generally use to connect washing machines,
costs 9 cents a meter .Or 6 mm^2, for ranges, 22 cents a meter.Why don't you
ask an electrician to construct you an extra heavy duty extension cable,
with industrial-grade plugs?I did in college, when doing my Practicum, for a
high-temperature oven, three-phase, 25A, which plug tended to overheat.Cost
was negligent.

--
Tzortzakakis Dimitri?s
major in electrical engineering, freelance electrician
FH von Iraklion-Kreta, freiberuflicher Elektriker
dimtzort AT otenet DOT gr
? "Peter A Forbes" <diesel@easynet.co.uk> ?????? ??? ??????
news:rpks01dusj3e57g4n976ii30l4ncc1stpj@4ax.com...

On Sat, 12 Feb 2005 10:51:00 -0800, "Watson A.Name - \"Watt Sun, the Dark
Remover\"" <NOSPAM@dslextreme.com> wrote:


"Bob Eager" <rde42@spamcop.net> wrote in message
news:176uZD2KcidF-pn2-pgQf8dbMMKeL@rikki.tavi.co.uk...
On Sat, 12 Feb 2005 12:46:19 UTC, Ian Stirling
root@mauve.demon.co.uk
wrote:

Or for 60m, 8.4*10^-1 ohms, or .84 ohms.

Plus the resistance on the two connections. Not sure whether the earth
fault loop impedance is still OK...

Yeah, true. You 220VAC and 240VAC guys think you got it bad, we have
four times as much of a problem here in 120VAC land. ;-)

Those poor souls that put a hundred feet or so of 18GA (about 1mm sq)
extension cord on their weed wackers soon find that not only does it run
slow, but the motor overheats. So we have extension cords that are 16
or 14 gauge, and can handle the extra current. But people are too cheap
to pay double for the heavy duty extension cord, so they end up eating
their money up in burned out motors.

And then when they get tired of doing that, they go out and buy a weed
wacker with the gas engine. This is on the end of a long pole, so the
engine is right up next to their face, so they go deaf from all the
engine noise. And they put the weed wacker in the garage, where the gas
from the tank runs out and catches on fire!


--
Bob Eager



Why use anything as small as 1mm sq cable???

For 30metres I'd want to see 2.5mm sq at least, if not 4mm sq.

If not for the volt drop or lack of, for the mechanical strength and
resistance
to damage.

Peter

--
Peter & Rita Forbes
Email: diesel@easynet.co.uk
Web: http://www.oldengine.org/members/diesel

 

[The Natural Philosopher]

Sammo wrote:

Jerry G. wrote:


As long as the maximum current load does not exceed the current
rating of any of the cables that are used in the extension, it
will be safe. There should not be very much loss over a few
hundred feet of extension. If there is a loss, you can then
change the extensions for ones that are of a larger gauge.


On 13 Feb 2005, John Rumm wrote:

The other issue to beware of is as the length of wire increases,
so does it fault loop resistance (i.e. path from line to earth /
ground). This will reduce the maximum current that can be passed
to earth in the event of a fault, and hence extend the time
between the fault occuring and the circuit protective device
(fuse, circuit breaker etc) opening to disconnet the power.
Obviously if *you* are forming part of this earth fault loop,
the sooner the power goes off the better!

Out of interest, are US style plugs fitted with fuses?

(An extension lead running outside ought to have RCD protection
anyway of course, to negate the problem)



I am the original poster with two 30m extension cables. You refer to
RCD protection.

I have got a plug-in RCD device but I know nothing about earth fault
loops. It is similar to the one in this illustration.
http://www.argos.co.uk/wcsstore/argos/images/9828331A59IFN104773M.JPG

Where should my RCD device be plugged in to best avoid the problem of
earth fault loops:

(1) At the mains supply end where the first extension goes into the
mains socket.
(2) In the middle of the two 30m extensions.
(3) At the far end of the two extensions where the appliciance I am
using is plugged in?

You can draw the same current through any length of wire, asd long as it
isn't coiled up, because the heat per unit length does not vary with the
length, and that is what causes temp rise.

Which is why cable is rated in amps, not watts. Nor yet amp-meters.

The v drop on even quite extended lengths of extsnion cable is not
likely to be an issue.

 

[Owain]

"Sammo" wrote
| However, if the cable has resistence then presumably current capacity
| (ignoring voltage) gets reduced. I am thinking of W = I^2 * R.

No, because that resistance - and hence the heating effect - is spread along
the length of the cable. If 1m of cable is rated for 10A then 100m of cable
will also be rated for 10A. You will probably need a thicker cable to reduce
the voltage drop, but that is not the same as the current-carrying capacity
of the cable.

| I have got a plug-in RCD device but I know nothing about earth fault
| loops. It is similar to the one in this illustration.
| http://www.argos.co.uk/wcsstore/argos/images/9828331A59IFN104773M.JPG
| Where should my RCD device be plugged in to best avoid the problem of
| earth fault loops:
| (1) At the mains supply end where the first extension goes into the
| mains socket.

Here, because the RCD protection must be applied to the whole extension
flex, because it is in effect a portable appliance.

| (2) In the middle of the two 30m extensions.

No, because that would leave the first flex (or more specifically - someone
handling it) unprotected.

| (3) At the far end of the two extensions where the appliciance I am
| using is plugged in?

No, same reason.

If you were wiring a *permanent circuit* then RCD protection could usually
be applied at the load end, because fixed wiring does not need such a high
standard of protection.

Note, however, that using an RCD plug on only one extension lead raises the
possibility that someone might plug the extension leads togther the wrong
way round, with the result that the first flex would be unprotected. The way
round this is to have an RCD plug on both leads -- this will do no harm, but
either or both may trip in the event of a fault -- or use an RCD socket.

The point remains -- why are you contemplating using 60m extension cables?

Owain

 

[Watson A.Name - \"Watt Su]

"Dimitrios Tzortzakakis" <use@address.below> wrote in message
news:cuqc07$ja0$1@usenet.otenet.gr...

cable is not that expensive, it's copper after all.I can see in an
invoice
that I paid 28 cents a meter for a 3G1.5 mm^2 A05VV-U cable.A 2.5 mm^2
conductor, single core, which we generally use to connect washing
machines,
costs 9 cents a meter .Or 6 mm^2, for ranges, 22 cents a meter.Why
don't you
ask an electrician to construct you an extra heavy duty extension
cable,
with industrial-grade plugs?I did in college, when doing my Practicum,
for a
high-temperature oven, three-phase, 25A, which plug tended to
overheat.Cost
was negligent.

Negligent! Hah-hah-hah-hah!

--
Tzortzakakis Dimitri?s
major in electrical engineering, freelance electrician

 

[Palindr☝me]

Palindr☝me wrote:

Sammo wrote:

I am in the UK (so mains voltage is about 230V or 240V).

I have a reel of main extension cable made of 3-core 1.0 mm^2 wire
rated at 10 Amps. So the nominal power rating would be about 2,400
Watts. (Link to tech reference for the cable is below.)

Presumably the current carrying capacity or power delivery capability
of the unwound 30m length unwound is going to be a bit less than 10
Amps/2,400 Watts due to losses along the length of the cable itself.
Is the reduction in current/power carrying capability significant? If
so, then is there a rough guideline figure for available current/power
which I can use?

If I take *two* of these 30m reels then I can join them with the
standard UK 13 Amp plug and socket supplied on the reels. This gives
me an overall length of 60m. Taking into account losses, what would
be the current carrying or power delivery carrying capability of the
60m length if all the 60m cable is unwound?


30 metres at 10 amperes isn't going to be a problem - so I have
considered just the longer lengths.

Basically, you have two factors to consider:

The first is how hot the wire will get. Now, provided that the cable is
unwound and in the open air, then its length is immaterial. If you coil
the cable up or cover it in something that restricts the flow of heat
from it, that is a different matter. However, for an unwound cable, the
rated current, say 10 amperes, is the maximum that is allowed due to
heat constraints. Pass more current than this and the wire will get too
hot. Pass a lot more current than this and the insulation could fail.

The second is the volt drop. Its resistance is about 0.02 ohms per metre
- so a 60 m length will have a resistance of 1.2 ohms and will drop 1.2
volts per ampere. A 120 m length would drop 2.4 volts per ampere.

Now the equipment at the far end of the cable will have a specified
range of input voltage for which it was designed. You must simply ensure
that it gets the minimum rated voltage, or higher, at the current it
draws. This minimum voltage will depend on the equipment type.

As a rough guide, losing 12 volts in 240 is probably going to be fine.
So, you could use a 60 metre cable at 10 amperes or 120 metre cable at 5
amperes.

If your load is happier with a lower minimum voltage, say 220 volts,
then you could run the 120m cable at about 8 amperes. However, you would
still be limited to 10 amperes for the 60 metre cable, because 10
amperes is the most the cable should be used to carry, irrespective of
length.

Purely resistive loads, like heaters, aren't terribly fussed if their
voltage is a bit low - so you could happily run a 2kW heater at the end
of 120 metres of your cable. If you have a lamp plugged in at the far
end, then it will get noticeably dimmer when the heater is switched on.
This isn't a safety problem, although it might appear so.

Some loads are very fussy about their minimum voltage but even those
should be happy with 10 amperes taken from your 60 metre cable.

OOPs! Yes, I forgot it was twin flex.

Ignore my last post - I clearly shouldn't have got up so
eary this morning...and will now correct that error. Well,
it was a good party last night, from what I remember.

--

Sue

 

[Watson A.Name - \"Watt Su]

<bigcat@meeow.co.uk> wrote in message
news:1108237955.923021.112840@f14g2000cwb.googlegroups.com...
Watson A.Name - "Watt Sun, the Dark Remover" wrote:

"Sammo" <noone@no-where.com> wrote in message
news:95FB7BA1F25441A7D4@130.133.1.4...

I am in the UK (so mains voltage is about 230V or 240V).

I'm in the U.S. and this gives me a flashback on what I was thinking
about trying a few months ago. We have a PBX at work that's on 48V
batteries, but the batteries are 9 yrs old and need replacing. They
cost a bundle

the first logical thought is repair them rather than replace. Lead
acids are often repairable.

Quick repair, doesnt always work:
rinse muck out of cells
fill with new acid
charge, monitor acid conc and adjust as required

This wont fix all cells by any means, but many it will. Those it wont
in some cases may only need replacement plates and acid, which can be
made much cheaper than buying new batts.

No. These cells are 4V each, 12 in all, each is sealed. Well, except
for the one cell that's split open because of internal pressure. :-(
They must be replaced, not repaired. This is a phone system, where it
has to be online during emergencies. Batteries that are working fine,
but over 5 years old are considered unacceptable and must be replaced.

Also they can often be run happily at 24v, if not in all cases. If
yours could, it may be that your present cells would do that as is.

This is *not* how you run a battery backup system! The idea is to start
out with fully charged batteries, so that when the power fails for a
long period, the voltage of the batteries may drop to 40V or less as the
cells discharge, keeping the PBX online. If you start at anything less,
even 36V, you're not going to have any discharge time before the PBX
system crashes. It would be essentially worthless.

What capacity at 48v is it on?

The rectifier can put out a hundred amps at 54VDC, to charge the
batteries while the PBX is also running. That must be 6 or so kW input.
So I would guess that it's 208V at 30A breakers. But with no batteries,
the load would be more like 3.6kW.

I thought it would be possible to run a power cable
underground to the big UPS we have in our computer room. Problem is
that the PBX's rectifier takes 30A max at 120VAC, or about 3.6kW.

i've no ida how that fits into this

The UPS in the computer room is 150kW, easily capable of handling
another 6 or so kW.

And
the distance between is about 1300 feet or about 400m.

I would guess that the UPS output should go into a transformer and
come
out 480VAC, so the cable losses would be minimized. Then another
transf
on the PBX end to bring it back to 120VAC. But should I expect to
have
a max loss of 5% at max current, or what?

well how much current are you shifting??
And why cant you power your pbx from whatever power source it uses
now?
You havent given us nearly enough information.

The batteries and rectifier are a "UPS" to protect the PBX against
failure of the commercial power. That's what it's being fed from.

I think I came up with 4GA
cable, but at 480VAC, I'm guessing that it would have to be special
insulated underground cable.

standard uk T&E should do that, but shuold be insulation tested to the
required v first. Costs around Ł12 a 100m reel, depending on copper
size.

Assuming that it could be pulled 1300 feet. Probably not without
damage. Heavily insulated cable would be needed. Probably double
jacketed.

Someday I'll have to ask one of the electricians that work on our HV
stuff. We have 4160VAC underground around campus but that's all
specialized switchgear, etc.

rf transmission co-ax is rated pretty high... and its concentric.

RF transmission coax is typically copper clad steel wire center
conductor, which would have much greater I^2R loss than pure copper
cable at 50 or 60Hz. That would be unacceptable.

T&E's probably far more practical.

Thanks, but I've never heard of T&E here in the U.S. I don't know what
that acronym stands for.

[snip]

NT

 

[Watson A.Name - \"Watt Su]

<bigcat@meeow.co.uk> wrote in message
news:1108302344.391913.292380@o13g2000cwo.googlegroups.com...
Watson A.Name - "Watt Sun, the Dark Remover" wrote:

bigcat@meeow.co.uk> wrote in message
news:1108237955.923021.112840@f14g2000cwb.googlegroups.com...

I'm in the U.S. and this gives me a flashback on what I was
thinking
about trying a few months ago. We have a PBX at work that's on 48V
batteries, but the batteries are 9 yrs old and need replacing.
They
cost a bundle

the first logical thought is repair them rather than replace. Lead
acids are often repairable.

Quick repair, doesnt always work:
rinse muck out of cells
fill with new acid
charge, monitor acid conc and adjust as required

This wont fix all cells by any means, but many it will. Those it
wont
in some cases may only need replacement plates and acid, which can
be
made much cheaper than buying new batts.

No. These cells are 4V each, 12 in all, each is sealed.

If youre going to deal with this you'll need a few clues. You will have
2v cells in pairs, 4v lead acid cells dont exist.

Well, except
for the one cell that's split open because of internal pressure. :-(

They must be replaced, not repaired. This is a phone system, where
it
has to be online during emergencies. Batteries that are working
fine,
but over 5 years old are considered unacceptable and must be
replaced.

thats fine if youve got the money, but since they've been there 9
years, and are found dead but still in service, I was guessing you
havent.

Is it April yet?

Also they can often be run happily at 24v, if not in all cases. If
yours could, it may be that your present cells would do that as is.

This is *not* how you run a battery backup system! The idea is to
start
out with fully charged batteries, so that when the power fails for a
long period, the voltage of the batteries may drop to 40V or less as
the
cells discharge, keeping the PBX online. If you start at anything
less,
even 36V, you're not going to have any discharge time before the PBX
system crashes. It would be essentially worthless.

You misunderstood completely, hopelessly, and idiotically. 48v is a

I think I'm talking to a tree here. **PLONK**

very old standard, and many 48v telecomms systems are now run on 24v.
If your equipment were 24v compatible, as some is, you would only need
half the number of cells.

And if you had no money to replace the battery, odds are you'll have at
least 50% of cells still serviceable.

Even if its not 24v compatible, you would get better backup performance
by removing any dead cells from the chain. Whether you remove them or
not you'll run below voltage.

What capacity at 48v is it on?

The rectifier can put out a hundred amps at 54VDC, to charge the
batteries while the PBX is also running. That must be 6 or so kW
input.
So I would guess that it's 208V at 30A breakers. But with no
batteries,
the load would be more like 3.6kW.

3.6kW @ 50v = 72A, so if we take an ultra-vague guess at C/10 charging,
that gives us 700ah capacity @48v. Ouch.

I thought it would be possible to run a power cable
underground to the big UPS we have in our computer room. Problem
is
that the PBX's rectifier takes 30A max at 120VAC, or about 3.6kW.

i've no ida how that fits into this

The UPS in the computer room is 150kW, easily capable of handling
another 6 or so kW.

And
the distance between is about 1300 feet or about 400m.

I would guess that the UPS output should go into a transformer and
come
out 480VAC, so the cable losses would be minimized. Then another
transf
on the PBX end to bring it back to 120VAC. But should I expect to
have
a max loss of 5% at max current, or what?

well how much current are you shifting??
And why cant you power your pbx from whatever power source it uses
now?
You havent given us nearly enough information.

The batteries and rectifier are a "UPS" to protect the PBX against
failure of the commercial power. That's what it's being fed from.

Why dont you find someone else to discuss this with.

I think I came up with 4GA
cable, but at 480VAC, I'm guessing that it would have to be special
insulated underground cable.

standard uk T&E should do that, but shuold be insulation tested to
the
required v first. Costs around Ł12 a 100m reel, depending on
copper
size.

Assuming that it could be pulled 1300 feet. Probably not without
damage.

You thread it section by section. Regular access points also allow a
section can be replaced if it fails. The T&E also includes a spare
conductor for backup.

Heavily insulated cable would be needed. Probably double
jacketed.

T&E is double insulated, high v rated and cheap - thats why i suggested
it.

Someday I'll have to ask one of the electricians that work on our
HV
stuff. We have 4160VAC underground around campus but that's all
specialized switchgear, etc.

rf transmission co-ax is rated pretty high... and its concentric.

RF transmission coax is typically copper clad steel wire center
conductor, which would have much greater I^2R loss than pure copper
cable at 50 or 60Hz. That would be unacceptable.

obviously it depends what v and i youre running it at, its very much
higher v rated than T&E.

T&E's probably far more practical.

Thanks, but I've never heard of T&E here in the U.S. I don't know
what
that acronym stands for.

twin and earth, its our standard house wiring cable, 2 cores double
insulated plus one single, comes in various copper sizes, is very cheap
and can be bought at thousands of outlets... here, anyway. I dont know
what export would cost.


You would need to get some basic concepts sorted out before youre in a
position to imlpement anything.


NT

 

[Palindr☝me]

Sammo wrote:

On 14 Feb 2005, Owain wrote:


| (1) At the mains supply end where the first extension goes into
| the mains socket.

Here, because the RCD protection must be applied to the whole
extension flex, because it is in effect a portable appliance.

| (2) In the middle of the two 30m extensions.

No, because that would leave the first flex (or more
specifically - someone handling it) unprotected.

| (3) At the far end of the two extensions where the appliciance
| I am using is plugged in?

No, same reason.

If you were wiring a *permanent circuit* then RCD protection
could usually be applied at the load end, because fixed wiring
does not need such a high standard of protection.

Note, however, that using an RCD plug on only one extension lead
raises the possibility that someone might plug the extension
leads togther the wrong way round, with the result that the
first flex would be unprotected. The way round this is to have
an RCD plug on both leads -- this will do no harm, but either or
both may trip in the event of a fault -- or use an RCD socket.

The point remains -- why are you contemplating using 60m
extension cables?



I live in a flat and my car is kept in a garage in a block which is
in the yard. The garages do not have power and sometimes I might
need to use a power drill, electric light, soldering iron, charge a
run-down battery, etc.

This is the layout:

I'm on the third storey and my cable flex would be slung along the
building for about 30 metres and be supported once where it goes
out of my flat and supported again (at about the same height) where
it leaves the building 30m later.

The next 15 metres of cable would be a sort of descent to my garage
roof. The last 5 metres or so takes the power to where I want it.
(I am using 30m + 30m because those are the lengths on my
two extension reels).

In this scenario, I don't really need to protect the cable from
accidental cutting or damage anywhere along its length as it runs
along the building or in the air away from any likely harm.

For my *own* protection as a user of an applicance at the far end of
the cable it seems that it might be better to put an RCD close to
whatever appliance I am using. Is this correct?

OTOH maybe a domestic RCD is so sensitive that it is likely to work
perfectly well at the mains end even when I am chiefly looking to
protect me at the far end?

Basically, the gizmo senses when the current being shoved up
the live wire is greater than what comes back down the
neutral wire. If it is greater, then the difference, instead
of coming back down the wire, is going somewhere else - like
through /you/. If it finds a difference it cuts off the
power, very quickly.

So its sensitivitity will be the same no matter where you
put it - as the same current should be going up the live and
back the neutral - where ever you measure it.

Putting it in the wall socket ensures that the insulation of
the whole length of leads as well as the load is being
monitored. which give the most protection. Plugging it in
after the leads means that the unit doesn't monitor for
faults in the leads themselves, only in the load.

The only thing you gain from plugging it in at the load
end is if you have a piece of hardware that is prone to
tripping rcds on switch-on. Having it near the load makes it
easier to reset the thing if it trips and saves the hike
back upstairs. But you would only plug it in there for that
sort of reason.

Always use the test button each time you set this up. They
are remarkably sensitive devices that have to sense a
difference of a few hundredth's of an ampere in a load of
many amperes. For the cost, as I think another op may have
said, why not fit two - one at each end? Particularly if you
are lying on fairly damp ground under a car, clutching a
mains lamp in your hand.. I have a main one protecting the
sockets for the whole house (excepting a ring main that only
feeds my fridges and freezers - where each socket has an
rcd), but still use an additional plug-in one when doing
anything that makes me nervous.

--

Sue

 

[Owain]

"Sammo" wrote
| > The point remains -- why are you contemplating using 60m
| > extension cables?
| I live in a flat and my car is kept in a garage in a block which is
| in the yard. The garages do not have power and sometimes I might
| need to use a power drill, electric light, soldering iron, charge a
| run-down battery, etc.

[f/u set to uk.d-i-y as getting off-topic for other groups and definately
on-topic for this group; subject line changed]

Ah-ha! "How do I get electricity to my garage" is the real question you
should have asked.

This has been discussed before -- google for threads about garages without
mains power. Suggestions usually include a battery (recharged in the house,
possibly on a trolley for portability) with an inverter, or a small
generator. Photovoltaic (solar) panels are sometimes viable for keeping a
car battery topped up.

Especially as you have a 'block' of garages, it might be financially viable
to have a new public supply laid on to the block, as the cost can be divided
between all the garages, if other owners agree. Power to a garage is useful,
especially if remote from the house, and the cost of the supply would
probably be recouped in sale value. That might not be the case for a new
supply for one garage. A proper fixed supply will also allow garages to be
fitted with mains-powered alarms, which might help persuade your neighbours
to agree with the scheme.

| This is the layout:
| I'm on the third storey and my cable flex would be slung along the
| building for about 30 metres and be supported once where it goes
| out of my flat and supported again (at about the same height) where
| it leaves the building 30m later.

PLEASE STOP RIGHT NOW.

What you are proposing is wholly unacceptable. Ordinary flex and cable is
not designed for being self-supporting over this distance. The flex will be
under considerable mechanical strain at the supports. Have you considered
what happens when 30m of cable comes loose and whips through the air?
Extension lead flex is also not designed for permanent exterior installation
and is not completely waterproof or resistant to abrasion and uv light.

What you are proposing doing is fixed wiring and should be done according to
the regs for a permanent installation -- designed, installed, and inspected
and tested in full compliance with the IEE Wiring Regulations.

As I surmise you will also be running this supply across other people's
property -- even if only the freeholder's -- you will need legal permission
from them to do this.

| The next 15 metres of cable would be a sort of descent to my garage
| roof.

There are strict regulations over the height of suspended cables -- they
have recently been increased following, I think, the death of a BT engineer.

| The last 5 metres or so takes the power to where I want it.
| (I am using 30m + 30m because those are the lengths on my
| two extension reels).

And you are going to waterproof the connection between the two extension
reels how?

| In this scenario, I don't really need to protect the cable from
| accidental cutting or damage anywhere along its length as it runs
| along the building or in the air away from any likely harm.

On a domestic installation "protection by placing out of reach" is not
allowed as a means of protecting either cables or humans.

There are serious public liability issues with what you are proposing. If
anyone is hurt or killed -- even as a result of their own actions eg
vandalising the flex -- you will have to justify your actions in a coroner's
court, and possibly face a charge of manslaughter.

| For my *own* protection as a user of an applicance at the far end of
| the cable it seems that it might be better to put an RCD close to
| whatever appliance I am using. Is this correct?
| OTOH maybe a domestic RCD is so sensitive that it is likely to work
| perfectly well at the mains end even when I am chiefly looking to
| protect me at the far end?

I'm not going to say *anything* which could possibly encourage you to
consider what you are proposing any further. It frightens me

Owain

 

[Sammo]

On 15 Feb 2005, Owain wrote:

"Sammo" wrote
| > The point remains -- why are you contemplating using 60m
| > extension cables?
| I live in a flat and my car is kept in a garage in a block
| which is in the yard. The garages do not have power and
| sometimes I might need to use a power drill, electric light,
| soldering iron, charge a run-down battery, etc.

[f/u set to uk.d-i-y as getting off-topic for other groups and
definately on-topic for this group; subject line changed]

Ah-ha! "How do I get electricity to my garage" is the real
question you should have asked.

Yes I want power in my garage but only on a temporary basis such as
those occassions when I ned to charge my car battery or use power
tools, etc as I described.

This has been discussed before -- google for threads about
garages without mains power. Suggestions usually include a
battery (recharged in the house, possibly on a trolley for
portability) with an inverter, or a small generator.
Photovoltaic (solar) panels are sometimes viable for keeping a
car battery topped up.

Especially as you have a 'block' of garages, it might be
financially viable to have a new public supply laid on to the
block, as the cost can be divided between all the garages, if
other owners agree. Power to a garage is useful, especially if
remote from the house, and the cost of the supply would probably
be recouped in sale value. That might not be the case for a new
supply for one garage. A proper fixed supply will also allow
garages to be fitted with mains-powered alarms, which might help
persuade your neighbours to agree with the scheme.

You talk a lot of sense but my neighbours do not. They are not DIY
or car enthusiasts and have no ineterst in laying on power to the
garage block. :-(

| This is the layout:
| I'm on the third storey and my cable flex would be slung along
| the building for about 30 metres and be supported once where it
| goes out of my flat and supported again (at about the same
| height) where it leaves the building 30m later.

PLEASE STOP RIGHT NOW.

What you are proposing is wholly unacceptable. Ordinary flex and
cable is not designed for being self-supporting over this
distance. The flex will be under considerable mechanical strain
at the supports. Have you considered what happens when 30m of
cable comes loose and whips through the air? Extension lead flex
is also not designed for permanent exterior installation and is
not completely waterproof or resistant to abrasion and uv light.

What you are proposing doing is fixed wiring and should be done
according to the regs for a permanent installation -- designed,
installed, and inspected and tested in full compliance with the
IEE Wiring Regulations.

I was thinking of this arrangement purely on a temporary basis. So
far I have laid the wire on the ground but as it can get damp and/or
dirty then I figured it might be better to suspend it in the air.

Furthermore other might trip on it (even though it is a red colour)
and it seesm better not to inconvenience them.

As I surmise you will also be running this supply across other
people's property -- even if only the freeholder's -- you will
need legal permission from them to do this.

This is unlikely to be an issue as we have a 999 year lease and the
freeholder is an overseas trust fund. This means that we maintain
the flats through our own management company and it holds a lease for
the common parts.

| The next 15 metres of cable would be a sort of descent to my
| garage roof.

There are strict regulations over the height of suspended cables
-- they have recently been increased following, I think, the
death of a BT engineer.

| The last 5 metres or so takes the power to where I want it.
| (I am using 30m + 30m because those are the lengths on my
| two extension reels).

And you are going to waterproof the connection between the two
extension reels how?

No need as I will be using the two extensions in much the same way as
someone might use them for powering a mains hedge trimmer.

| In this scenario, I don't really need to protect the cable from
| accidental cutting or damage anywhere along its length as it
| runs along the building or in the air away from any likely
| harm.

On a domestic installation "protection by placing out of reach"
is not allowed as a means of protecting either cables or humans.

There are serious public liability issues with what you are
proposing. If anyone is hurt or killed -- even as a result of
their own actions eg vandalising the flex -- you will have to
justify your actions in a coroner's court, and possibly face a
charge of manslaughter.

| For my *own* protection as a user of an applicance at the far
| end of the cable it seems that it might be better to put an RCD
| close to whatever appliance I am using. Is this correct?
| OTOH maybe a domestic RCD is so sensitive that it is likely to
| work perfectly well at the mains end even when I am chiefly
| looking to protect me at the far end?

I'm not going to say *anything* which could possibly encourage
you to consider what you are proposing any further. It frightens
me

Heh!

 

[Palindr☝me]

Sammo wrote:

On 15 Feb 2005, Owain wrote:


"Sammo" wrote
| > The point remains -- why are you contemplating using 60m
| > extension cables?
| I live in a flat and my car is kept in a garage in a block
| which is in the yard. The garages do not have power and
| sometimes I might need to use a power drill, electric light,
| soldering iron, charge a run-down battery, etc.

[f/u set to uk.d-i-y as getting off-topic for other groups and
definately on-topic for this group; subject line changed]

Ah-ha! "How do I get electricity to my garage" is the real
question you should have asked.



Yes I want power in my garage but only on a temporary basis such as
those occassions when I ned to charge my car battery or use power
tools, etc as I described.



This has been discussed before -- google for threads about
garages without mains power. Suggestions usually include a
battery (recharged in the house, possibly on a trolley for
portability) with an inverter, or a small generator.
Photovoltaic (solar) panels are sometimes viable for keeping a
car battery topped up.

Especially as you have a 'block' of garages, it might be
financially viable to have a new public supply laid on to the
block, as the cost can be divided between all the garages, if
other owners agree. Power to a garage is useful, especially if
remote from the house, and the cost of the supply would probably
be recouped in sale value. That might not be the case for a new
supply for one garage. A proper fixed supply will also allow
garages to be fitted with mains-powered alarms, which might help
persuade your neighbours to agree with the scheme.


You talk a lot of sense but my neighbours do not. They are not DIY
or car enthusiasts and have no ineterst in laying on power to the
garage block. :-(



| This is the layout:
| I'm on the third storey and my cable flex would be slung along
| the building for about 30 metres and be supported once where it
| goes out of my flat and supported again (at about the same
| height) where it leaves the building 30m later.

PLEASE STOP RIGHT NOW.

What you are proposing is wholly unacceptable. Ordinary flex and
cable is not designed for being self-supporting over this
distance. The flex will be under considerable mechanical strain
at the supports. Have you considered what happens when 30m of
cable comes loose and whips through the air? Extension lead flex
is also not designed for permanent exterior installation and is
not completely waterproof or resistant to abrasion and uv light.

What you are proposing doing is fixed wiring and should be done
according to the regs for a permanent installation -- designed,
installed, and inspected and tested in full compliance with the
IEE Wiring Regulations.


I was thinking of this arrangement purely on a temporary basis. So
far I have laid the wire on the ground but as it can get damp and/or
dirty then I figured it might be better to suspend it in the air.

Furthermore other might trip on it (even though it is a red colour)
and it seesm better not to inconvenience them.



As I surmise you will also be running this supply across other
people's property -- even if only the freeholder's -- you will
need legal permission from them to do this.


This is unlikely to be an issue as we have a 999 year lease and the
freeholder is an overseas trust fund. This means that we maintain
the flats through our own management company and it holds a lease for
the common parts.


| The next 15 metres of cable would be a sort of descent to my
| garage roof.

There are strict regulations over the height of suspended cables
-- they have recently been increased following, I think, the
death of a BT engineer.

| The last 5 metres or so takes the power to where I want it.
| (I am using 30m + 30m because those are the lengths on my
| two extension reels).

And you are going to waterproof the connection between the two
extension reels how?


No need as I will be using the two extensions in much the same way as
someone might use them for powering a mains hedge trimmer.


| In this scenario, I don't really need to protect the cable from
| accidental cutting or damage anywhere along its length as it
| runs along the building or in the air away from any likely
| harm.

On a domestic installation "protection by placing out of reach"
is not allowed as a means of protecting either cables or humans.

There are serious public liability issues with what you are
proposing. If anyone is hurt or killed -- even as a result of
their own actions eg vandalising the flex -- you will have to
justify your actions in a coroner's court, and possibly face a
charge of manslaughter.

| For my *own* protection as a user of an applicance at the far
| end of the cable it seems that it might be better to put an RCD
| close to whatever appliance I am using. Is this correct?
| OTOH maybe a domestic RCD is so sensitive that it is likely to
| work perfectly well at the mains end even when I am chiefly
| looking to protect me at the far end?

I'm not going to say *anything* which could possibly encourage
you to consider what you are proposing any further. It frightens
me


Heh!

I must admit to doing much the same when I was living in a
London flat - for very similar sorts of reasons and only to
rig up and put away each time I used it. It obviously
depends on your physical arrangements as to whether it is
totally reckless or not quite totally so.

What I did, however, was to take some polypropylene cord and
tied figure of eight knots on the bight every foot or so,
with the loop big enough to pass the plug through. You have
guessed the rest - one end of the cord was tied to the
window frame and the other to the garage and the power cable
just ran down through the loops. That way, the weight of the
cable was taken by loops in the tensioned cord -
particularly important at the ends, where otherwise the
cable would have had to be tied around something. Where I
had to do a change in direction to avoid the cable rubbing
against anything, I just took a piece of cord from the main
cord and tied it off, to a tree branch, IIRC - and then
tensioned the cords to get the run I wanted..

I don't know your layout and can only advise that doing
things like this is inherently high risk - but, if you are
going to do it anyway, this might help reduce that risk a
little. If it goes wrong, as you have been clearly told -
you will be wishing that you just bought an inverter or a
small genny (IIRC, B&Q do a perfectly good one for under
100GBP) - I have one and it has paid for itself time and
time again. They weren't available at anything like that
price when I played silly games with cables.


If you do think about leaving the cord(s) (but not the
cable) in place - with a pull through extra cord so that you
can pull the cable down as and when you need it, be aware
that man-made cords can be very affected by sunlight, by
relatively modest sudden shock loads, by abrasion, by
pressure at points of sharp change in direction, by the
knots and by a whole lot more. So you need to select the
cord carefully with a very high factor of safety and inspect
it often. Also note that birds will sit on it and do what
birds do to whatever is underneath - so routing it over a
neighbour's patio is not a good idea - unless you live in
London*.

--

Sue
* Where few flat-dwellers even know the names of their
neighbours and then only because of arguments about noise,
parking spaces, children, curtains, etc - you might as well
add the birds' efforts...

 

[Sammo]

On 17 Feb 2005, =?UTF-8?B?UGFsaW5kcuKYu21l?= wrote:

I must admit to doing much the same when I was living in a
London flat - for very similar sorts of reasons and only to
rig up and put away each time I used it. It obviously
depends on your physical arrangements as to whether it is
totally reckless or not quite totally so.

My approach is strictly for temporary use. It will be there for a
day at a time. (Maybe just overnight for a single night if I over-
run the job and I don't want to put the cable and the rest of it all
away in the evening and get it all out again in the morning).

What I did, however, was to take some polypropylene cord and
tied figure of eight knots on the bight every foot or so,
with the loop big enough to pass the plug through. You have
guessed the rest - one end of the cord was tied to the
window frame and the other to the garage and the power cable
just ran down through the loops. That way, the weight of the
cable was taken by loops in the tensioned cord -
particularly important at the ends, where otherwise the
cable would have had to be tied around something. Where I
had to do a change in direction to avoid the cable rubbing
against anything, I just took a piece of cord from the main
cord and tied it off, to a tree branch, IIRC - and then
tensioned the cords to get the run I wanted..

Sue, that appears to be a very neat solution. It sounds simple,
cheap and effective.

I like that and I think I should do the same on a temporary (one day)
basis.

One variation is that I will need to lift and suspend the wire where
is passes the end of the building furthest from my flat and goes off
into the air. At that point I think I will need to mount a pulley in
the wall (with the help of the tennamts in that flat) and then loop
some string around the pulley such that the lower part of the loop
can be reached from the ground. That way I don't need them to be in
when I want to raise the cable up.

The thing I must think about is security. I will never ever hear the
end of it if the string permitted some local ne'er-do-well to pull up
a heavier duty rope and then to scale the wall by using it!

Maybe I will lift up the lower end of the pulley string from my own
third story (top floor) flat by oulling another string to the
pulley's string. IYSWIM!

I don't know your layout and can only advise that doing
things like this is inherently high risk - but, if you are
going to do it anyway, this might help reduce that risk a
little.

Yup, I can see that this if fraught with dangers. In fact I wonder
if it might be easier to go into the loft and thread the wire as far
as I can along the inside (partiton wall permitting) and then seeing
what the down drop requirements are from there onwards!

If it goes wrong, as you have been clearly told -
you will be wishing that you just bought an inverter or a
small genny (IIRC, B&Q do a perfectly good one for under
100GBP) - I have one and it has paid for itself time and
time again. They weren't available at anything like that
price when I played silly games with cables.


If you do think about leaving the cord(s) (but not the
cable) in place - with a pull through extra cord so that you
can pull the cable down as and when you need it, be aware
that man-made cords can be very affected by sunlight, by
relatively modest sudden shock loads, by abrasion, by
pressure at points of sharp change in direction, by the
knots and by a whole lot more. So you need to select the
cord carefully with a very high factor of safety and inspect
it often. Also note that birds will sit on it and do what
birds do to whatever is underneath - so routing it over a
neighbour's patio is not a good idea - unless you live in
London*.