Silly me:-(

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! Shit! 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

Reply to
Tim Lamb
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Well... it's 12.7 horse power.... :-)

Cable rating tables are at

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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.

Reply to
Andy Hall

Sounds like it...

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.

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?

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

Reply to
John Rumm

In message , Andy Hall writes

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:-(

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

regards

Reply to
Tim Lamb

In message , John Rumm writes

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.

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.

I'll report back when I know more. Thanks

regards

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Reply to
Tim Lamb

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