OT: house fires - electrical fault

One often hears in the news about a house burning due to an electrical
fault, with no further details, like whether it was old insulation
perishing or a DIY bodge.
I bought a house in which somebody installed an extra power socket in
the kitchen, spliced into the nearby electric stove feed. Now that had
a 40 A breaker. So if the toaster had a short, it could have gone up
in shower of sparks.

 

[noel]

On Tue, 08 Mar 2016 01:21:16 -0800, bruce56 wrote:

One often hears in the news about a house burning due to an electrical
fault, with no further details, like whether it was old insulation
perishing or a DIY bodge.
I bought a house in which somebody installed an extra power socket in
the kitchen, spliced into the nearby electric stove feed. Now that had
a 40 A breaker. So if the toaster had a short, it could have gone up in
shower of sparks.

That's a good point, but, this is Australia, the media are just clueless
bunnies and don't know how to ask technical questions, if it didn't
happen on facebook, they they have no idea who to ask, or what to ask

I'd love facebook to die a slow painful death, even for just a week, then
these piss poor excuse for journos we seem to have today would have to
get off their arses and do some REAL journalism.

 

[Sylvia Else]

On 8/03/2016 8:21 PM, bruce56@topmail.co.nz wrote:

One often hears in the news about a house burning due to an electrical
fault, with no further details, like whether it was old insulation
perishing or a DIY bodge.

Or incompetence by a qualified electrician.

Sylvia.

 

[David]

On 3/8/2016 8:21 PM, bruce56@topmail.co.nz wrote:

One often hears in the news about a house burning due to an electrical
fault, with no further details, like whether it was old insulation
perishing or a DIY bodge.
I bought a house in which somebody installed an extra power socket in
the kitchen, spliced into the nearby electric stove feed. Now that had
a 40 A breaker. So if the toaster had a short, it could have gone up
in shower of sparks.

Note that the Circuit Breaker is there to protect the fixed wiring,
*not* the appliance connected to the socket outlet. Indeed AS/NZS3000
does indeed permit the connection of 10A socket outlets to a circuit
protected by a 40A circuit breaker, provided that the wiring is 10mm2
(See table C8).

Note that in most cases this would be very impractical, as you can not
normally get 10mm2 cable into a 10A socket outlet.

However 25A and even 32A breakers can be used to protect the wiring to a
10A socket outlet, providing the wire size and voltage drop are
considered.

 

[Phil Allison]

Adrian Jansen wrote:

However 25A and even 32A breakers can be used to protect the wiring to a
10A socket outlet, providing the wire size and voltage drop are considered.


That might be what the rules say, but it seems to me that its pretty
illogical to have a socket and wiring which is rated for a max load of
10 amps 'protected' by a 32 amp breaker.

** The 10A rating of domestic outlets is not a *maximum* but merely a safety rating that equates to a modest temp rise in the conductors. Same goes for 10A rated cables.

That said, by far the most likely fault is a short circuit, in which
case the current goes sky-high, and hopefully the breaker opens long
before the wiring blows up.

** A short on a domestic AC outlet supply generates upwards of 200amps.

Fuses blow and breakers trip instantly.

Similar arguments apply to any external appliance.

** Not really.


..... Phil

 

[Phil Allison]

Clocky wrote:

What is to stop the cord to the toaster from turning into a heater
element otherwise?

** The wire element inside is a reliable fuse at currents less than rating of the attached cable.



..... Phil

 

[Phil Allison]

Sylvia Else wrote:

In the UK, where I used to live, the appliance plugs contain a fuse.
That's 13A by default (the maximum current for an appliance), but can
easily be changed to suit lesser rated wiring. That seems a sensible
idea, but I've not seen it elsewhere (I think there are a few other
places that use the UK style plug).

* The UK commonly uses a "ring mains" system with a 32A fuse or breaker in each circuit. Appliance cables are protected by the fuse inside the plug which has massive conductors. This allows the use of some very thin appliance cables ( rated down to 2 or at 3 amps )that would not be allowed elsewhere.

Over-fusing the plug is a fire hazard in the UK that we do not have.


..... Phil

 

[Adrian Jansen]

On 8/03/2016 11:37 PM, David wrote:

On 3/8/2016 8:21 PM, bruce56@topmail.co.nz wrote:
One often hears in the news about a house burning due to an electrical
fault, with no further details, like whether it was old insulation
perishing or a DIY bodge.
I bought a house in which somebody installed an extra power socket in
the kitchen, spliced into the nearby electric stove feed. Now that had
a 40 A breaker. So if the toaster had a short, it could have gone up
in shower of sparks.


Note that the Circuit Breaker is there to protect the fixed wiring,
*not* the appliance connected to the socket outlet. Indeed AS/NZS3000
does indeed permit the connection of 10A socket outlets to a circuit
protected by a 40A circuit breaker, provided that the wiring is 10mm2
(See table C8).

Note that in most cases this would be very impractical, as you can not
normally get 10mm2 cable into a 10A socket outlet.

However 25A and even 32A breakers can be used to protect the wiring to a
10A socket outlet, providing the wire size and voltage drop are considered.

That might be what the rules say, but it seems to me that its pretty
illogical to have a socket and wiring which is rated for a max load of
10 amps 'protected' by a 32 amp breaker. Surely the breaker should be
the weakest link in the chain.

That said, by far the most likely fault is a short circuit, in which
case the current goes sky-high, and hopefully the breaker opens long
before the wiring blows up.

Similar arguments apply to any external appliance.

 

[Clocky]

On 9/03/2016 6:32 AM, Adrian Jansen wrote:

On 8/03/2016 11:37 PM, David wrote:
On 3/8/2016 8:21 PM, bruce56@topmail.co.nz wrote:
One often hears in the news about a house burning due to an electrical
fault, with no further details, like whether it was old insulation
perishing or a DIY bodge.
I bought a house in which somebody installed an extra power socket in
the kitchen, spliced into the nearby electric stove feed. Now that had
a 40 A breaker. So if the toaster had a short, it could have gone up
in shower of sparks.


Note that the Circuit Breaker is there to protect the fixed wiring,
*not* the appliance connected to the socket outlet. Indeed AS/NZS3000
does indeed permit the connection of 10A socket outlets to a circuit
protected by a 40A circuit breaker, provided that the wiring is 10mm2
(See table C8).

Note that in most cases this would be very impractical, as you can not
normally get 10mm2 cable into a 10A socket outlet.

However 25A and even 32A breakers can be used to protect the wiring to a
10A socket outlet, providing the wire size and voltage drop are
considered.

That might be what the rules say, but it seems to me that its pretty
illogical to have a socket and wiring which is rated for a max load of
10 amps 'protected' by a 32 amp breaker. Surely the breaker should be
the weakest link in the chain.

What is to stop the cord to the toaster from turning into a heater
element otherwise?

 

[Sylvia Else]

On 9/03/2016 9:32 AM, Adrian Jansen wrote:

On 8/03/2016 11:37 PM, David wrote:
On 3/8/2016 8:21 PM, bruce56@topmail.co.nz wrote:
One often hears in the news about a house burning due to an electrical
fault, with no further details, like whether it was old insulation
perishing or a DIY bodge.
I bought a house in which somebody installed an extra power socket in
the kitchen, spliced into the nearby electric stove feed. Now that had
a 40 A breaker. So if the toaster had a short, it could have gone up
in shower of sparks.


Note that the Circuit Breaker is there to protect the fixed wiring,
*not* the appliance connected to the socket outlet. Indeed AS/NZS3000
does indeed permit the connection of 10A socket outlets to a circuit
protected by a 40A circuit breaker, provided that the wiring is 10mm2
(See table C8).

Note that in most cases this would be very impractical, as you can not
normally get 10mm2 cable into a 10A socket outlet.

However 25A and even 32A breakers can be used to protect the wiring to a
10A socket outlet, providing the wire size and voltage drop are
considered.

That might be what the rules say, but it seems to me that its pretty
illogical to have a socket and wiring which is rated for a max load of
10 amps 'protected' by a 32 amp breaker. Surely the breaker should be
the weakest link in the chain.

That said, by far the most likely fault is a short circuit, in which
case the current goes sky-high, and hopefully the breaker opens long
before the wiring blows up.

Similar arguments apply to any external appliance.

In the UK, where I used to live, the appliance plugs contain a fuse.
That's 13A by default (the maximum current for an appliance), but can
easily be changed to suit lesser rated wiring. That seems a sensible
idea, but I've not seen it elsewhere (I think there are a few other
places that use the UK style plug).

Sylvia.

 

[Sylvia Else]

On 9/03/2016 10:53 AM, Clocky wrote:

On 9/03/2016 6:32 AM, Adrian Jansen wrote:
On 8/03/2016 11:37 PM, David wrote:
On 3/8/2016 8:21 PM, bruce56@topmail.co.nz wrote:
One often hears in the news about a house burning due to an electrical
fault, with no further details, like whether it was old insulation
perishing or a DIY bodge.
I bought a house in which somebody installed an extra power socket in
the kitchen, spliced into the nearby electric stove feed. Now that had
a 40 A breaker. So if the toaster had a short, it could have gone up
in shower of sparks.


Note that the Circuit Breaker is there to protect the fixed wiring,
*not* the appliance connected to the socket outlet. Indeed AS/NZS3000
does indeed permit the connection of 10A socket outlets to a circuit
protected by a 40A circuit breaker, provided that the wiring is 10mm2
(See table C8).

Note that in most cases this would be very impractical, as you can not
normally get 10mm2 cable into a 10A socket outlet.

However 25A and even 32A breakers can be used to protect the wiring to a
10A socket outlet, providing the wire size and voltage drop are
considered.

That might be what the rules say, but it seems to me that its pretty
illogical to have a socket and wiring which is rated for a max load of
10 amps 'protected' by a 32 amp breaker. Surely the breaker should be
the weakest link in the chain.


What is to stop the cord to the toaster from turning into a heater
element otherwise?

For that to happen there needs to be a fault that causes excess current
to be drawn, but not enough to trip the breaker. Typically, so much heat
would be generated at the site of the fault that it will quickly either
go open circuit, or to a complete short - hopefully before it sets fire
to something.

Sylvia.

 

[Rheilly Phoull]

On 8/03/2016 7:48 PM, Sylvia Else wrote:

On 8/03/2016 8:21 PM, bruce56@topmail.co.nz wrote:
One often hears in the news about a house burning due to an electrical
fault, with no further details, like whether it was old insulation
perishing or a DIY bodge.

Or incompetence by a qualified electrician.

Sylvia.

I've seen stuff done by people who consider themselves engineers that is
totally dangerous. Normally by those who consider themselves above the
"common" electrician.

 

[F Murtz]

Adrian Jansen wrote:

On 8/03/2016 11:37 PM, David wrote:
On 3/8/2016 8:21 PM, bruce56@topmail.co.nz wrote:
One often hears in the news about a house burning due to an electrical
fault, with no further details, like whether it was old insulation
perishing or a DIY bodge.
I bought a house in which somebody installed an extra power socket in
the kitchen, spliced into the nearby electric stove feed. Now that had
a 40 A breaker. So if the toaster had a short, it could have gone up
in shower of sparks.


Note that the Circuit Breaker is there to protect the fixed wiring,
*not* the appliance connected to the socket outlet. Indeed AS/NZS3000
does indeed permit the connection of 10A socket outlets to a circuit
protected by a 40A circuit breaker, provided that the wiring is 10mm2
(See table C8).

Note that in most cases this would be very impractical, as you can not
normally get 10mm2 cable into a 10A socket outlet.

However 25A and even 32A breakers can be used to protect the wiring to a
10A socket outlet, providing the wire size and voltage drop are
considered.

That might be what the rules say, but it seems to me that its pretty
illogical to have a socket and wiring which is rated for a max load of
10 amps 'protected' by a 32 amp breaker. Surely the breaker should be
the weakest link in the chain.

In Aus power circuits are 2.5sq mm which is in the main 20 amps so lots
of circuits have 20 amp breakers supplying numerous outlets

That said, by far the most likely fault is a short circuit, in which
case the current goes sky-high, and hopefully the breaker opens long
before the wiring blows up.

Similar arguments apply to any external appliance.

 

[Phil Allison]

Chris Jones wrote:

** The 10A rating of domestic outlets is not a *maximum* but merely a
safety rating that equates to a modest temp rise in the conductors.
Same goes for 10A rated cables.


The Australian plugs do sometimes run very hot when used at 10A, and I
have seen them where the plastic around the pins has melted. Perhaps
those were not in ideal condition before they were last used (pins may
have been tarnished, etc.). I regard the 10A rating as being quite
"optimistic" for unattended use, and I am even more dubious about the
similar versions rated at 15A.

** A 10amp Aussie plug and socket in average condition will operate happily at 30amps. The to contact contact resistance is in the order of 100 micro-ohms so self heating from that cause is negligible.

I just tested a 20 year old pair ( Clipsal 415 outlet and 463 plug) to get the above result.

If for some reason a plug and socket is running hot at 10 amps, it definitely needs replacing. The most likely reason is loose or corroded wires in the back of the outlet. Moisture is major contributor to this.

Since there can be many 10amp outlets on a single circuit, the main risk factor is with the cable in the wall and that is well protected by the usual fuses and breakers.

My experience with high current AC supply connectors is that ones that run very hot fail by going open circuit, rather than catching fire.


..... Phil

 

[Sylvia Else]

On 9/03/2016 12:06 PM, Phil Allison wrote:

Sylvia Else wrote:



In the UK, where I used to live, the appliance plugs contain a fuse.
That's 13A by default (the maximum current for an appliance), but can
easily be changed to suit lesser rated wiring. That seems a sensible
idea, but I've not seen it elsewhere (I think there are a few other
places that use the UK style plug).


* The UK commonly uses a "ring mains" system with a 32A fuse or breaker in each circuit. Appliance cables are protected by the fuse inside the plug which has massive conductors. This allows the use of some very thin appliance cables ( rated down to 2 or at 3 amps )that would not be allowed elsewhere.

Over-fusing the plug is a fire hazard in the UK that we do not have.

Or indeed, wrapping the failed fuse with metal foil.

But at least it provides extra protection to people who aren't idiots.

Sylvia.

 

[F Murtz]

Phil Allison wrote:

Chris Jones wrote:



** The 10A rating of domestic outlets is not a *maximum* but merely a
safety rating that equates to a modest temp rise in the conductors.
Same goes for 10A rated cables.


The Australian plugs do sometimes run very hot when used at 10A, and I
have seen them where the plastic around the pins has melted. Perhaps
those were not in ideal condition before they were last used (pins may
have been tarnished, etc.). I regard the 10A rating as being quite
"optimistic" for unattended use, and I am even more dubious about the
similar versions rated at 15A.


** A 10amp Aussie plug and socket in average condition will operate happily at 30amps. The to contact contact resistance is in the order of 100 micro-ohms so self heating from that cause is negligible.

I just tested a 20 year old pair ( Clipsal 415 outlet and 463 plug) to get the above result.

If for some reason a plug and socket is running hot at 10 amps, it definitely needs replacing. The most likely reason is loose or corroded wires in the back of the outlet. Moisture is major contributor to this.

Since there can be many 10amp outlets on a single circuit, the main risk factor is with the cable in the wall and that is well protected by the usual fuses and breakers.

My experience with high current AC supply connectors is that ones that run very hot fail by going open circuit, rather than catching fire.


.... Phil

We also have a problem with unaproved imports with thinner pins(blades)
on leads, chargers,power supplies etc.

 

[Chris Jones]

On 09/03/2016 11:57, Phil Allison wrote:

Adrian Jansen wrote:


However 25A and even 32A breakers can be used to protect the
wiring to a 10A socket outlet, providing the wire size and
voltage drop are considered.


That might be what the rules say, but it seems to me that its
pretty illogical to have a socket and wiring which is rated for a
max load of 10 amps 'protected' by a 32 amp breaker.


** The 10A rating of domestic outlets is not a *maximum* but merely a
safety rating that equates to a modest temp rise in the conductors.
Same goes for 10A rated cables.

The Australian plugs do sometimes run very hot when used at 10A, and I
have seen them where the plastic around the pins has melted. Perhaps
those were not in ideal condition before they were last used (pins may
have been tarnished, etc.). I regard the 10A rating as being quite
"optimistic" for unattended use, and I am even more dubious about the
similar versions rated at 15A.

I have also seen BS1363 plugs that have slightly discoloured after
prolonged use at 13A, though the rewireable ones are usually made from
thermoset materials so they don't tend to melt.

 

[Chris Jones]

On 09/03/2016 16:31, Phil Allison wrote:

Chris Jones wrote:



** The 10A rating of domestic outlets is not a *maximum* but merely a
safety rating that equates to a modest temp rise in the conductors.
Same goes for 10A rated cables.


The Australian plugs do sometimes run very hot when used at 10A, and I
have seen them where the plastic around the pins has melted. Perhaps
those were not in ideal condition before they were last used (pins may
have been tarnished, etc.). I regard the 10A rating as being quite
"optimistic" for unattended use, and I am even more dubious about the
similar versions rated at 15A.


** A 10amp Aussie plug and socket in average condition will operate happily at 30amps. The to contact contact resistance is in the order of 100 micro-ohms so self heating from that cause is negligible.

I just tested a 20 year old pair ( Clipsal 415 outlet and 463 plug) to get the above result.

I don't doubt that. Nevertheless from time to time I do see them melted.
Specifically, it is usually the sort that looks like Clipsal 439 or HPM
100L. The test-and-tag bloke found one on a hotplate at work last year,
where the melted plastic had flowed away from around one pin. The pins
don't seem to fall out, but I don't know if that is because people let
it cool down before unplugging. The fan heater I had in my youth had a
moulded-on plug that got very hot, to the point where you wouldn't want
to touch the pins just after unplugging it, but that one never melted.

 

[Phil Allison]

Trevor Wilson wrote:

Don't you lot have fuses in the plugs?!!!

**Nope. Except for Queensland, Australian wiring rules and licensing is
pretty decent. Plug fuses aren't required.

** The wiring rules are national, what's your beef with Qld?

They have much better regs regarding the compulsory fitting of ELCBs - it must be done whenever a property changes owner. So by now, nearly all homes have them fitted - such is not the case elsewhere.


..... Phil

 

[Ian Field]

<bruce56@topmail.co.nz> wrote in message
news:fa08a388-f594-43f9-95ea-ca58918b4e0d@googlegroups.com...

One often hears in the news about a house burning due to an electrical
fault, with no further details, like whether it was old insulation
perishing or a DIY bodge.
I bought a house in which somebody installed an extra power socket in
the kitchen, spliced into the nearby electric stove feed. Now that had
a 40 A breaker. So if the toaster had a short, it could have gone up
in shower of sparks.

Don't you lot have fuses in the plugs?!!!