Just removed a plastic / glass fibre bath, and the edge of the bath is
slightly melted / warped in front of the electric shower supply cable
that is embedded in the plaster. Does this mean the cable is underrated
? How hot should the cable get ? The bath has probably been there
years, so I cannot tell how long its taken to warp. It would be a pain
to replace the cable, but the run is not too long.
If I removed the bath, would the room no longer be a "bathroom" for
part-P purposes ?!

Simon.

What's the power of the shower? Also, roughly measure the dimensions of
the
cable and post them here.
It sounds like you are absolutely correct: the cable is undersized for
the load
and hence is a fire hazard.

Mungo

P.S. A friend of my wife kept complaining that her electric hob took
ages to
heat things.
When I went round to take a quick look I found that the man of the
house had wired
the new hob via a piece of "flex" to the consumer unit that was about
three feet
away from the hob on the other side of a partition wall.
All attempts to volunteer to replace the wire free of charge (five
years ago) met with
a vacant smile as the lady said she would just persevere with it...
even after I
ranted about the fire hazard!
Some jobs you just gotta walk away from...

wrote:
What's the power of the shower? Also, roughly measure the dimensions of
the
cable and post them here.
It sounds like you are absolutely correct: the cable is undersized for
the load
and hence is a fire hazard.


Well, the shower is 9.5 kW.
I measured the (presumed twin-and-earth) grey cable, approx dimensions
are 6 x 13 mm. I ran the shower for about 10 mins - felt surprising bad
about
the hot water pouring down the drain, and filled up a washing-up bowl !
The cable got noticeably warm in 10 mins, but it would take an awful
long
shower to melt the bath I would have thought. Finally, I melted the
bath back
into shape with a blow-torch, so it would fit snuggly against the wall.
When rating cable sizes, to the regs include length of time passing the
current, as this is surely relevant.

Simon.

On 31 May 2005 12:07:46 -0700, strung together
this:

Well, the shower is 9.5 kW.
I measured the (presumed twin-and-earth) grey cable, approx dimensions
are 6 x 13 mm.

Sounds like 6mm cable, which is too small for a 9.5kw shower in most
circumstances.

Over time, it can melt the bath. Lots of wshort showers, heating and
cooling the bath, little bit at a time etc...
--

SJW
Please reply to group or use 'usenet' in email subject

wrote in message
oups.com...

wrote:
What's the power of the shower? Also, roughly measure the dimensions of
the
cable and post them here.
It sounds like you are absolutely correct: the cable is undersized for
the load
and hence is a fire hazard.


Well, the shower is 9.5 kW.
I measured the (presumed twin-and-earth) grey cable, approx dimensions
are 6 x 13 mm. I ran the shower for about 10 mins - felt surprising bad
about
the hot water pouring down the drain, and filled up a washing-up bowl !
The cable got noticeably warm in 10 mins, but it would take an awful
long
shower to melt the bath I would have thought. Finally, I melted the
bath back
into shape with a blow-torch, so it would fit snuggly against the wall.
When rating cable sizes, to the regs include length of time passing the
current, as this is surely relevant.

Simon.


The cable has probably been installed for a 7.5kW shower in the past, and
then never upgraded to accept the heavier load of the new 9.5kW one.

The cable should be rated to accept current, at the least, half again what
the full load rating would be, for sure safety. So, for a full load rating
of an appliance at 30 Amps, then you'd rate the cable for 45 Amps to be sure
it doesn't do what your cable is doing. This also allows for a small
upgrade in the appliance in the future.

Of course, this also depends on the length and the routing plan of the
cable, but going by a pretty standard install, then this is the safe option.

wrote:
Just removed a plastic / glass fibre bath, and the edge of the bath is
slightly melted / warped in front of the electric shower supply cable
that is embedded in the plaster. Does this mean the cable is underrated
? How hot should the cable get ? The bath has probably been there
years, so I cannot tell how long its taken to warp. It would be a pain
to replace the cable, but the run is not too long.
If I removed the bath, would the room no longer be a "bathroom" for
part-P purposes ?!

I wonder if it's not thermal problems at all, but due to the plasticiser
leaching from the PVC.
Does the cable appear discouloured along its length, or just where it youches
the bath?

wrote:

The cable got noticeably warm in 10 mins

Not the best of signs. When 'fully loaded', conductors of PVC cables are
allowed to reach 70 degrees C (that's the point above which PVC gets too
soft and can start to creep at stress points, reducing its thickness
perhaps all the way to zero). If it's 'noticeably warm', it's probably
up to 50 degrees, at the surface of the insulation, in an area where at
least one side is open to the air. That, and Lurch's '6x13, hmm, sounds
like 6mmsq' diagnosis, suggests to me you're on, or over, the edge for
that shower and that cable. Upping to 10mmsq if you're at 6mmsq would be
worth doing sooner rather than later, I'd-a-thunk.

When rating cable sizes, to the regs include length of time passing the
current, as this is surely relevant.

Not really - it doesn't take long at all for cable to reach its 'final'
temperature. The reasoning behind diversity allows for 'short-term'
overloads, but fixed appliances like showers are treated, as is only
reaonsable, as drawing their full load indefinitely.

And it's not only the 'will it melt' factor which determines cable
thickness. We also worry about whether the resistance will be low enough
to blow the fuse/trip the MCB quickly enough in the event of a L-to-N or
L-to-E fault (and we calculate that resistance assuming the cable's at
full temp, when the resistance is higher), and that the poor little
earth conductor won't rise in temperature to the point of irreversible
cable damage during those few seconds. (Yes, we're sad enough to work
this stuff out - or at least, either use software wot works it out, or
(for the ordinary mortal electrician and consciencious d-i-y'er) to look
up the Tabulated Values and plug them into the Sacred Adiabatic Formula.
As someone pointed out to a 'can someone recommend a single simple book
to make me an expert on wiring matters' query, there's a bit more to
electrical installation planning than being able to do a
bulb-switch-battery circuit...)

HTH - Stefek

I wonder if it's not thermal problems at all, but due to the plasticiser
leaching from the PVC.
Does the cable appear discouloured along its length, or just where it youches
the bath?

The cable does not actually touch the bath, it is embedded in plaster
at that point.

Over time, it can melt the bath. Lots of wshort showers, heating and
cooling the bath, little bit at a time etc...

I was amazed at the thermal capacity of the bath plastic. Having heated
it with
the blowtorch to reshape, it was very hot for nearly 10 minutes !
So several showers in a row, and the heat could build in the bath,
which would
not help the cable, etc.
Simon.

BigWallop wrote:
wrote in message

Well, the shower is 9.5 kW.
I measured the (presumed twin-and-earth) grey cable, approx dimensions
are 6 x 13 mm. I ran the shower for about 10 mins - felt

The cable has probably been installed for a 7.5kW shower in the past, and
then never upgraded to accept the heavier load of the new 9.5kW one.

Cables have large overload margins, and 7.5kW of cable running 9.5kW of
shower should not normally be a problem. Bear in mind you can just
about run a 7kW shower on 2.5T&E.* What the problem is, I dont know.


NT

* note to the clueless: dont do that

On 1 Jun 2005 10:20:04 -0700, strung together this:

* note to the clueless: dont do that

*note to clueless tit who posted it, don't post ridiculous ideas like
that, it only gives other numbnuts ideas.
--

SJW
Please reply to group or use 'usenet' in email subject

Lurch wrote:
On 1 Jun 2005 10:20:04 -0700, strung together this:

* note to the clueless: dont do that

*note to clueless tit who posted it, don't post ridiculous ideas like
that, it only gives other numbnuts ideas.

Note to unthinker: censorship does not reduce stupid actions, it in
fact increases them by leaving people uninformed. The best way to
reduce stupid actions is to be honest about what does go on, many a
time, and explain why its a bad idea.

Running a shower on 2.5T&E is a bad idea because under some situations
it will cause a fire, even though under many it wont. It is a real risk
to life, the fact that it often works doesnt change that.


NT

Sorry to butt in on somebody else's topic here, but it's a similar
question...

When I took out my electric oven to install a new (gas) hob, I noticed
some scorch marks in the plaster of the wall behind. This is where the
cooker cable exits the wall en route from the consumer unit to the
cooker switch. (For some strange reason, the cooker is not connected
directly to the cooker switch, but via an unswitched 13A socket.)

Is this common, or should I be worried about it?

TIA

wrote in message
oups.com...
I wonder if it's not thermal problems at all, but due to the plasticiser
leaching from the PVC.
Does the cable appear discouloured along its length, or just where it
youches
the bath?

The cable does not actually touch the bath, it is embedded in plaster
at that point.


It seems to me that you know the cable is inadequate, if it was in my house
I would change it (or the shower).
In your case the cable is buried in the wall which means it should be
derated (as it cannot disipate the heat)
this should help
http://www.tlc-direct.co.uk/Technica...ltageDrop.html

Regards Jeff

"Rich" wrote in message
oups.com...
Sorry to butt in on somebody else's topic here, but it's a similar
question...

When I took out my electric oven to install a new (gas) hob, I noticed
some scorch marks in the plaster of the wall behind. This is where the
cooker cable exits the wall en route from the consumer unit to the
cooker switch. (For some strange reason, the cooker is not connected
directly to the cooker switch, but via an unswitched 13A socket.)

Is this common, or should I be worried about it?

TIA

What gauge is the cabling, and what load rating does the oven have?

It seems to me that you know the cable is inadequate, if it was in my house
I would change it (or the shower).
In your case the cable is buried in the wall which means it should be
derated (as it cannot disipate the heat)
this should help

Yep, I do know. Its just that I only take the odd 10 minute shower. In
the long run
I want to put in a combi/thermostatic shower, so I either leave the
shower till then,
or do it now. I may leave in an electric shower and combi (I'm sure its
been done!)
Simon.

Jeff wrote:
wrote in message
oups.com.

this should help
http://www.tlc-direct.co.uk/Technica...ltageDrop.html

Curious, for a 3kW load clipped direct it recommends 1mm2 cable...


NT

Looks like 6mm sq. There's no rating given anywhere on the oven, but
it's been happily plugged in via a 13A fuse for as long as I've lived
here (3 years).