Some months back, my daughter's electric shower failed in a puff of
smelly smoke. Mindful of part P I sourced an Identically rated
replacement and fitted it. Fortunately the supply cable was long enough
to be shortened back beyond the cooked bit. The electrical installation
looked OK, sleeved earth, double pole isolator, twin+E PVC cable I just
didn't think to check the circuit protection.

Shower performed OK, father pleased at not having to worry about
suitable Christmas pressie until..... 2 months later circuit breaker
starts tripping out occasionally. Parental panic mode on.... ingress of
moisture, unseen junction box in wiring etc.

This is in London and 30 miles away so someone who knows more about
horses than electricity was asked to identify the type and rating of the
circuit breaker.

Ah! ****! The load is 9.5kW, the cable is 6mm and the trip is 32amps. I
suspect someone has fitted a more powerful shower without upgrading the
supply.

Now the question for the team is... where do I go from here?

My electrical education stopped at the fifteenth edition which I see
allows 40 amps for 6mm, load is 39.6 amps at 240v so a bit tight. There
may be considerations of which I an unaware so please comment freely:-)

As yet I don't know anything about the consumer unit or the size of the
feed tails or other loads. Is fitting a 40amp mcb likely to be
practical? Meanwhile I think the shower is being used on a lower output.

The installation is typical of an Edwardian house, converted to shop,
re-converted to flats, i.e.. bits all over:-(

regards
--
Tim Lamb

On Wed, 22 Feb 2006 23:27:49 +0000, Tim Lamb
wrote:

Some months back, my daughter's electric shower failed in a puff of
smelly smoke. Mindful of part P I sourced an Identically rated
replacement and fitted it. Fortunately the supply cable was long enough
to be shortened back beyond the cooked bit. The electrical installation
looked OK, sleeved earth, double pole isolator, twin+E PVC cable I just
didn't think to check the circuit protection.

Shower performed OK, father pleased at not having to worry about
suitable Christmas pressie until..... 2 months later circuit breaker
starts tripping out occasionally. Parental panic mode on.... ingress of
moisture, unseen junction box in wiring etc.

This is in London and 30 miles away so someone who knows more about
horses than electricity was asked to identify the type and rating of the
circuit breaker.

Ah! ****! The load is 9.5kW, the cable is 6mm and the trip is 32amps. I
suspect someone has fitted a more powerful shower without upgrading the
supply.

Now the question for the team is... where do I go from here?

Well... it's 12.7 horse power.... :-)



My electrical education stopped at the fifteenth edition which I see
allows 40 amps for 6mm, load is 39.6 amps at 240v so a bit tight. There
may be considerations of which I an unaware so please comment freely:-)

Cable rating tables are at

http://www.tlc-direct.co.uk/Book/4.3.9.htm




As yet I don't know anything about the consumer unit or the size of the
feed tails or other loads. Is fitting a 40amp mcb likely to be
practical? Meanwhile I think the shower is being used on a lower output.

That probably means that the thermostat is turning the element on and
off at a certain rate and probably is enough to stop the breaker
tripping.




The installation is typical of an Edwardian house, converted to shop,
re-converted to flats, i.e.. bits all over:-(

regards

--

..andy

Tim Lamb wrote:

Ah! ****! The load is 9.5kW, the cable is 6mm and the trip is 32amps. I
suspect someone has fitted a more powerful shower without upgrading the
supply.

Sounds like it...

Now the question for the team is... where do I go from here?

My electrical education stopped at the fifteenth edition which I see
allows 40 amps for 6mm, load is 39.6 amps at 240v so a bit tight. There
may be considerations of which I an unaware so please comment freely:-)

The devil is in the detail. How long is the cable run, and are there any
other derating factors you need to take into account (like being buried
in insulation for part of the run). The cable can be good for over 45A
with favourable conditions - so you may get away with that.

As yet I don't know anything about the consumer unit or the size of the
feed tails or other loads.

You will need to check some other details to make sure it is safe. Most
notably does it have RCD protection, and if not (an RCD is not always
required - although commonly fitted), is the earth fault loop impedance
low enough to ensure rapid disconnection in the event of a fault. Is the
equipotential bonding in the bathroom up to scratch?

Is fitting a 40amp mcb likely to be practical?

Probably, assuming the CU is new enough and suitable MCBs are available.

--
Cheers,

John.

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\================================================= ================/

In message , Andy Hall
writes
On Wed, 22 Feb 2006 23:27:49 +0000, Tim Lamb
wrote:

My electrical education stopped at the fifteenth edition which I see
allows 40 amps for 6mm, load is 39.6 amps at 240v so a bit tight. There
may be considerations of which I an unaware so please comment freely:-)

Cable rating tables are at

http://www.tlc-direct.co.uk/Book/4.3.9.htm

OK Ta. I don't think there is any insulation involved and it is too
short a run for volt drop issues. I will have a proper look next week.

Unfortunately the inter-flat *sound* attenuation has been achieved by
super-imposing 2" of polystyrene and a chip board floor over the
existing. Upping floor boards is not for the faint hearted:-(




As yet I don't know anything about the consumer unit or the size of the
feed tails or other loads. Is fitting a 40amp mcb likely to be
practical? Meanwhile I think the shower is being used on a lower output.

That probably means that the thermostat is turning the element on and
off at a certain rate and probably is enough to stop the breaker
tripping.

Yes. Surprising this did not seem to occur with the original. Perhaps
the local supply voltage is up a bit.

regards

--
Tim Lamb

In message , John
Rumm writes

Now the question for the team is... where do I go from here?
My electrical education stopped at the fifteenth edition which I see
allows 40 amps for 6mm, load is 39.6 amps at 240v so a bit tight.
There may be considerations of which I an unaware so please comment
freely:-)

The devil is in the detail. How long is the cable run, and are there
any other derating factors you need to take into account (like being
buried in insulation for part of the run). The cable can be good for
over 45A with favourable conditions - so you may get away with that.

Unless the cable has been laid within the floor sound insulation, it
should be OK. I doubt if the mcb to switch to load totals 8m but I will
look properly next week.

As yet I don't know anything about the consumer unit or the size of
the feed tails or other loads.

You will need to check some other details to make sure it is safe. Most
notably does it have RCD protection, and if not (an RCD is not always
required - although commonly fitted), is the earth fault loop impedance
low enough to ensure rapid disconnection in the event of a fault. Is
the equipotential bonding in the bathroom up to scratch?

The bathroom is young enough for bonding to have been a requirement.
Unfortunately all pipe work is boxed in so I have not seen any straps. I
can do a simple continuity check but don't have facilities to check
earth impedance. I guess the system will use the supply earth.

Is fitting a 40amp mcb likely to be practical?

Probably, assuming the CU is new enough and suitable MCBs are available.

I'll report back when I know more. Thanks

regards


--
Tim Lamb