Hi,

We've got an old style consumer unit, which had a 45A MCB for the electric
shower in it when we moved in a few years ago. I've never tried touching
the MCB or the CU after using the shower, so can't comment on whether it
used to get hot or not.

However, a few days ago, while the shower was running I noticed a sharp
electrical smell, which I'd never smelled before, and opening the cabinet
in which the CU sits, it was clear the smell originated there. The 45A MCB
was hot to the touch, as was the CU surrounding it.

I replaced the 45A MCB with a new 40A MCB (couldn't find a 45A one). A
short run of the shower (60 seconds) proved fine, but a longer run
eventually led to the MCB getting hot, and again, the faint electrical
odor.

The CU did not get hot this time, but the shower didn't run for as long as
it had the first time.

We have an electrician coming out next week to investigate anyway, but
wondered if anyone had any experience of something similar and knew if I
was over-reacting, or if there's likely to be an issue somewhere in the
shower or the wiring between it and the CU.

Nothing has been changed in the last 8 years, but that doesn't mean wiring
hasn't degraded, etc.
--
Tony Evans
Seeking archives for uk.* from 1998 and older. Especially interested
in uk.net.news.* and any groups which preceded uk.net.news.* for
hierarchy management (uk.misc? uk.net?).

In article ,
Tony writes:
Hi,

We've got an old style consumer unit, which had a 45A MCB for the electric
shower in it when we moved in a few years ago. I've never tried touching
the MCB or the CU after using the shower, so can't comment on whether it
used to get hot or not.

However, a few days ago, while the shower was running I noticed a sharp
electrical smell, which I'd never smelled before, and opening the cabinet
in which the CU sits, it was clear the smell originated there. The 45A MCB
was hot to the touch, as was the CU surrounding it.

I replaced the 45A MCB with a new 40A MCB (couldn't find a 45A one). A
short run of the shower (60 seconds) proved fine, but a longer run
eventually led to the MCB getting hot, and again, the faint electrical
odor.

The CU did not get hot this time, but the shower didn't run for as long as
it had the first time.

We have an electrician coming out next week to investigate anyway, but
wondered if anyone had any experience of something similar and knew if I
was over-reacting, or if there's likely to be an issue somewhere in the
shower or the wiring between it and the CU.

Nothing has been changed in the last 8 years, but that doesn't mean wiring
hasn't degraded, etc.

MCB's of any current rating will get warm when running at or near
their max rating. However, they shouldn't smell.

Shower circuits do often fail at the electrical connections, because
the connections are often not made well enough. The sequence is that
a connection or a contact has a slightly higher resistance than it
should and heats up. This heat might start either in the contact or
the terminal, but it gets conducted to both and causes both to
deteriorate, increasing the resistance and rapidly increasing the
operating temperature. The smell results from an insulator nearby or
in contact which is overheating and breaking down.

If this is an old Wylex unit (of the type which originally took
rewirable fuses), the blade contacts on the plug-in breakers can
start increasing their contact resistance, causing the bakalite
support and/or cable insulation to overheat and break down. That's
a common cause for these old CU's to fail.

What's the power rating of the shower? A 40A MCB would be OK for
up to 9kW, but it also depends on the size and routing of the cable.

--
Andrew Gabriel
[email address is not usable -- followup in the newsgroup]

In uk.d-i-y, (Andrew Gabriel) wrote:

In article ,
Tony writes:

We've got an old style consumer unit, which had a 45A MCB for the electric
shower in it when we moved in a few years ago. I've never tried touching
the MCB or the CU after using the shower, so can't comment on whether it
used to get hot or not.

However, a few days ago, while the shower was running I noticed a sharp
electrical smell, which I'd never smelled before, and opening the cabinet
in which the CU sits, it was clear the smell originated there. The 45A MCB
was hot to the touch, as was the CU surrounding it.

I replaced the 45A MCB with a new 40A MCB (couldn't find a 45A one). A
short run of the shower (60 seconds) proved fine, but a longer run
eventually led to the MCB getting hot, and again, the faint electrical
odor.

The CU did not get hot this time, but the shower didn't run for as long as
it had the first time.

MCB's of any current rating will get warm when running at or near
their max rating. However, they shouldn't smell.

Yeh, if it was just heat, I would be less concerned.

If this is an old Wylex unit (of the type which originally took
rewirable fuses), the blade contacts on the plug-in breakers can
start increasing their contact resistance, causing the bakalite
support and/or cable insulation to overheat and break down. That's
a common cause for these old CU's to fail.

Thanks, it is a Wylex, and that's one of the things I was concerned about.

What's the power rating of the shower? A 40A MCB would be OK for
up to 9kW, but it also depends on the size and routing of the cable.

I don't actually know the power rating of the shower, it was in when we
moved in I've not been able to find anything in plain site on the shower
unit which gives me any clues (the name of the unit is mostly worn away). I
do intend to keep investigating that as well however.

Thanks for your response, it gives me additional background info when the
electrician arrives.
--
Tony Evans
Seeking archives for uk.* from 1998 and older. Especially interested
in uk.net.news.* and any groups which preceded uk.net.news.* for
hierarchy management (uk.misc? uk.net?).

Yes a cooker doing this to a unit. Eventually traced to a very badly secured
wire end in the unit. Got it in time to stop it melting though. Guy told me
he did not like the wire they had used to fit the cooker as it was aluminium
and very soft and corrosion prone. However we never had the problem again.
Bet you would not get that smell from old ceramic ones, they probably just
burn the house down instead.. grin

Brian

--
Brian Gaff....Note, this account does not accept Bcc: email.
graphics are great, but the blind can't hear them
Email:
__________________________________________________ __________________________________________________ __________


"Tony" wrote in message
...
Hi,

We've got an old style consumer unit, which had a 45A MCB for the electric
shower in it when we moved in a few years ago. I've never tried touching
the MCB or the CU after using the shower, so can't comment on whether it
used to get hot or not.

However, a few days ago, while the shower was running I noticed a sharp
electrical smell, which I'd never smelled before, and opening the cabinet
in which the CU sits, it was clear the smell originated there. The 45A
MCB
was hot to the touch, as was the CU surrounding it.

I replaced the 45A MCB with a new 40A MCB (couldn't find a 45A one). A
short run of the shower (60 seconds) proved fine, but a longer run
eventually led to the MCB getting hot, and again, the faint electrical
odor.

The CU did not get hot this time, but the shower didn't run for as long as
it had the first time.

We have an electrician coming out next week to investigate anyway, but
wondered if anyone had any experience of something similar and knew if I
was over-reacting, or if there's likely to be an issue somewhere in the
shower or the wiring between it and the CU.

Nothing has been changed in the last 8 years, but that doesn't mean wiring
hasn't degraded, etc.
--
Tony Evans
Seeking archives for uk.* from 1998 and older. Especially interested
in uk.net.news.* and any groups which preceded uk.net.news.* for
hierarchy management (uk.misc? uk.net?).

On Friday, August 29, 2014 1:17:04 PM UTC+1, Tony wrote:

Hi,
We've got an old style consumer unit, which had a 45A MCB for the electric
shower in it when we moved in a few years ago. I've never tried touching
the MCB or the CU after using the shower, so can't comment on whether it
used to get hot or not.
However, a few days ago, while the shower was running I noticed a sharp
electrical smell, which I'd never smelled before, and opening the cabinet
in which the CU sits, it was clear the smell originated there. The 45A MCB
was hot to the touch, as was the CU surrounding it.
I replaced the 45A MCB with a new 40A MCB (couldn't find a 45A one). A
short run of the shower (60 seconds) proved fine, but a longer run
eventually led to the MCB getting hot, and again, the faint electrical
odor.
The CU did not get hot this time, but the shower didn't run for as long as
it had the first time.
We have an electrician coming out next week to investigate anyway, but
wondered if anyone had any experience of something similar and knew if I
was over-reacting, or if there's likely to be an issue somewhere in the
shower or the wiring between it and the CU.
Nothing has been changed in the last 8 years, but that doesn't mean wiring
hasn't degraded, etc.

The old wylex fuseboxes are prone to this on 45A circuits. Once the metal bits get hot they can lose their springiness - once that happens the game is over. Don't use the shower on hot until its fixed, its a real fire risk. Probably time for a new CU.


NT

In uk.d-i-y, wrote:

On Friday, August 29, 2014 1:17:04 PM UTC+1, Tony wrote:

Hi,
We've got an old style consumer unit, which had a 45A MCB for the electric
shower in it when we moved in a few years ago. I've never tried touching
the MCB or the CU after using the shower, so can't comment on whether it
used to get hot or not.
However, a few days ago, while the shower was running I noticed a sharp
electrical smell, which I'd never smelled before, and opening the cabinet
in which the CU sits, it was clear the smell originated there. The 45A MCB
was hot to the touch, as was the CU surrounding it.
I replaced the 45A MCB with a new 40A MCB (couldn't find a 45A one). A
short run of the shower (60 seconds) proved fine, but a longer run
eventually led to the MCB getting hot, and again, the faint electrical
odor.
The CU did not get hot this time, but the shower didn't run for as long as
it had the first time.
We have an electrician coming out next week to investigate anyway, but
wondered if anyone had any experience of something similar and knew if I
was over-reacting, or if there's likely to be an issue somewhere in the
shower or the wiring between it and the CU.
Nothing has been changed in the last 8 years, but that doesn't mean wiring
hasn't degraded, etc.

The old wylex fuseboxes are prone to this on 45A circuits.
Once the metal bits get hot they can lose their springiness -
once that happens the game is over. Don't use the shower on
hot until its fixed, its a real fire risk. Probably time for a new CU.

Thanks, appreciate the response. I'll actually be happy if it's only the
CU that's the issue.
--
Tony Evans
Seeking archives for uk.* from 1998 and older. Especially interested
in uk.net.news.* and any groups which preceded uk.net.news.* for
hierarchy management (uk.misc? uk.net?).

On 2014-08-29, Tony wrote:

However, a few days ago, while the shower was running I noticed a sharp
electrical smell, which I'd never smelled before, and opening the cabinet
in which the CU sits, it was clear the smell originated there. The 45A MCB
was hot to the touch, as was the CU surrounding it.

Thanks for everyone's comments. This turned out to be an issue on the
supply side, incorrect fuse due to previous owner not having it updated
when the power shower went in, plus some loose connections and arcing,
had melted some insulation.

All fixed now, no cost in the end.

--
Tony Evans
Seeking archives for uk.* from 1998 and older. Especially interested
in uk.net.news.* and any groups which preceded uk.net.news.* for
hierarchy management (uk.misc? uk.net?).