How much current safe for 30m extension?

[Sammo]

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?

Thanks for any info.
Sammo


Technical reference for the cable is HAR type H05VV-F3 x 1.00 mm2 -
(details at http://tinyurl.com/7y5xx)

 

[Ian Stirling]

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.

 

[Ian Stirling]

In uk.d-i-y Ian Stirling <root@mauve.demon.co.uk> wrote:

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.

Doh, 1.7.

Or, for a 1mm^2 wire, 0.7*10^-2 ohms/meter.
1.7*10^-2
Or for 2 wires, 1.4*10^-2 ohms.
3.4*10^-2

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

2 ohms.

At 10A, 20V, or the cable heating by 200W.
If at the plug end is 240V, at the socket end will be 220V, which is
(220^2/240^2)= .84027777777777777777

So, you lose 16% of the power for a heater, for example.

 

[Bob Eager]

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...

--
Bob Eager
begin a new life...dump Windows!

 

[Ian Stirling]

In uk.d-i-y Bob Eager <rde42@spamcop.net> wrote:

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...

I took that into account. (but misremembered the resistivity of copper)
See other post for correction.

 

[Dave Plowman (News)]

In article <376fo9F59cjg9U3@individual.net>,
Palindr☝me <sb382638@hotmail.com.invalid> wrote:

OOPs! Yes, I forgot it was twin flex.

3 core, actually. ;-)

--
*Happiness is seeing your mother-in-law on a milk carton

Dave Plowman dave@davenoise.co.uk London SW
To e-mail, change noise into sound.

 

[John Rumm]

Ian Stirling wrote:

Short current is some 120A, plenty to blow a 10A fuse quite prombtly.

You are assuming that the supply impeadance is zero however. If you
factor that in, then you drop the PSC a bit...

(Still ought to be plenty to blow a 13A fuse in under a second though)


--
Cheers,

John.

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

 

[Palindr☝me]

Watson A.Name - "Watt Sun, the Dark Remover" wrote:
<snip>

Presumably, you did the calcs with it in mind that the current runs down
the cable 30M and then back up 30M for a total of 60M of conductor...

Kind of you to put it that way but it was a case of application of
WNTL*. . Otherwise known as SMAFN**

--

Sue
*Write Now Think Later
**Saturday Morning after Friday Night

 

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.

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.

What capacity at 48v is it on?

so 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

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.

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.

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. T&E's
probably far more practical.

I have a reel of main extension cable made of 3-core 1.0 mm^2 wire
rated at 10 Amps.

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?

10A


NT

 

[Mike]

"Watson A.Name - "Watt Sun, the Dark Remover"" <NOSPAM@dslextreme.com> wrote
in message news:110sjq6kis36k05@corp.supernews.com...

And then when they get tired of doing that, they go out and buy a weed
wacker with the gas engine.

One question to somebody presumably residing in the western colonies.

What's a "weed wacker" ?

 

[raden]

In message <110taejtbujdh40@corp.supernews.com>, "Watson A.Name - \"Watt
Sun, the Dark Remover\"" <NOSPAM@dslextreme.com> writes

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

.... colonials !


--
geoff

 

[John Rumm]

Mike wrote:

One question to somebody presumably residing in the western colonies.

What's a "weed wacker" ?

"Strimmer" to us.

--
Cheers,

John.

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

 

[Watson A.Name - \"Watt Su]

"Peter Bennett" <peterbb@somewhere.invalid> wrote in message
news:42jt01h7q5dpasoeufg6gfa0d7mu1qmkcl@news.supernews.com...

On Sat, 12 Feb 2005 17:17:16 -0800, "Watson A.Name - \"Watt Sun, the
Dark Remover\"" <NOSPAM@dslextreme.com> wrote:


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.


I don't know of any 4 volt rechargeable cell chemistry.

I expect that your "4 volt cells" are actually two cell lead-acid
batteries, with each cell good for 2.1 volts.


--
Peter Bennett, VE7CEI
peterbb4 (at) interchange.ubc.ca
new newsgroup users info : http://vancouver-webpages.com/nnq
GPS and NMEA info: http://vancouver-webpages.com/peter
Vancouver Power Squadron: http://vancouver.powersquadron.ca

 

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
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

 

[John Rumm]

Graham W wrote:

disconnet the power. Obviously if *you* are forming part of this earth
fault loop, the sooner the power goes off the better!


I doubt that a *you* of any value would survive if it were to pass
the fusing current of the plug-top fuse!

Depends on if you are in serise or parallel with it!



--
Cheers,

John.

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

 

[Watson A.Name - \"Watt Su]

"raden" <raden@kateda.org> wrote in message
news:Iv0Z3IeHyqDCFwIg@ntlworld.com...

In message <110taejtbujdh40@corp.supernews.com>, "Watson A.Name -
\"Watt
Sun, the Dark Remover\"" <NOSPAM@dslextreme.com> writes


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

... colonials !

Yeah, we call it ground here stateside. And it's Romex.

And it's AC line in every schematic I've seen from the American mfgrs
the likes of HP, Tek, etc., not "mains". Mains are those wires up on
top of the power pole.

Thanks T.A.!!

--
geoff

(That's Thomas Alva, for you right ponders.)

 

[Dave Plowman (News)]

In article <rpks01dusj3e57g4n976ii30l4ncc1stpj@4ax.com>,
Peter A Forbes <diesel@easynet.co.uk> wrote:

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.

Dunno where you'd get 4mm flex, but you'd never get it to fit a 13 amp
plug. 2.5mm is the limit, and not all plugs will have a cord grip suitable.

--
*If a thing is worth doing, wouldn't it have been done already?

Dave Plowman dave@davenoise.co.uk London SW
To e-mail, change noise into sound.

 

[Andy Wade]

Dave Plowman (News) wrote:

Dunno where you'd get 4mm flex,

RS for one, see stock no. 250-1410.

but you'd never get it to fit a 13 amp plug. 2.5mm is the limit, and
not all plugs will have a cord grip suitable.

Actually 1.25 mm^2 is the limit - in the sense that it's the largest
size that BS 1363 requires a plug to accept. Nevertheless _most_ plugs
will accept 1.5 mm^2 without too much difficulty and _some_ will accept
2.5 mm^2.

--
Andy

 

[Peter A Forbes]

On Sun, 13 Feb 2005 12:22:02 -0800, "Watson A.Name - \"Watt Sun, the Dark
Remover\"" <NOSPAM@dslextreme.com> wrote:

I got one for you. I checked the fuse panel of a really old bldg (well
for the U.S., anyway..) - almost 100 yrs - and it had the ground
fused(!) Now _that's_weird.

Was it 3-wire DC originally??

Peter

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

 

**PLONK**

good, itll save me the temptation to reply in future