What are your thoughts on a 32a mcb with a 2.5mm pvc/pvc feed to a 3kw immersion heater via a double pole switch.

Would you class this as overrated ocp for the cable? Even tho the kw rating of the immersion heater means it would never exceed the max current rating of the supply cable.

I personally gave this as a code 3, with recommendation of replacing double pole switch with 13a fused connection unit.

strictly, as the heater is a fixed load, then no overcurrent protection is needed.
sometimes i find that its best to go with the majority (ie an OSG compliant install) as if you dont then you are likely to be bad mouthed to the customer by an electrician following your work.

I would have recommended replacing the 32a mcb with something a bit smaller personally.

As to overcurrent etc, IMO the device is over rated for the cable, however the load is known and therefore I think we could argue that the mcb is providing fault protection only which it will probably comply with.

If it was mine, I'd want to see it on a 16a mcb with a double pole switch. I'm not a fan of 13a fcu's on immersion heaters as they tend to get warm.


Stu

I would definitely advise change the breaker to 16 amps, FCU's are not advisable for immersion heaters, the fuse holders are prone to arcing/burning. I know there's no alternative where the immersion is on the ring circuit but in this case there's no reason to fit an FCU, (i'm assuming this is a dedicated radial and not fed from the ring?)

Dave.

Edited: 30 August 2012 at 08:58 AM by daveparry1

Here we are again. Which regulation are you citing? Is overload possible? Is short circuit protection adequate?

433.3.1 (ii), No, Yes.

Job done.
I think that most of you lads need to spend the next six months studying the big green book properly, and actually having a copy wouldn't be a bad idea either. The OSG is not a guide to that which is allowed, only to a very simplified version which will always be compliant for an install . Inspectors etc need to understand the whole lot properly.
An FCU is unnecessary and not a good idea as stated above.

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David
CEng etc, don't ask, its a result not a question!