redundant water heater circuit - ok for new combi boiler

[Mike]

Hi all

Wondering if i need to change anything about an existing water heater circuit before using it to power a new combi boiler? (corgi guy starts monday) I know i need to fit a 3 amp fused connection unit at he boiler end but not sure about the consumer unit which has a 16a mcb and is on the non rcd protected side of the unit. Do i need to change rcd rating or move to rcd protected? (and if so maybe it would be easier just to run a spur off another existing curcuit with correct rating and protection, unless boilers need their own circuit like immersion heaters?) Thanks in advance for any help

[David Hansen]

On Thu, 4 Dec 2008 04:25:41 -0800 (PST) someone who may be Mike wrote this:-

Boilers do not need to be on a separate circuit, though there are some slight advantages to doing so.

Assuming the existing cable is correctly sized I would do nothing with the existing circuit other than fit a *switched* fused connection unit at the boiler.

Depending on how the existing circuit is installed one could argue that it should be put on an RCD due to the 17th Edition. I think that requirement is a way of bunging money to equipment manufacturers and I would ignore it. However, I am prepared to argue deviations from the Wiring Regulations [1] in court against the box tickers if necessary [2], you may not be prepared to do that.

In reality the CORGI [3] bod is unlikely to know very much about electrical installations and object to the installation. I suggest providing suitable heat resistant cable, otherwise the boiler may be wired with bog standard cable which may not be suitable. I take it you have contracted them to connect the boiler to the electrical system.

[1] the IET's paperwork has areas to note such deviations. [2] I wouldn't argue it in that way, my arguments would be rather longer. [3] I see from that Crapita's new scheme is to start on April Fool's Day 2009. Given the way Crapita lie to and abuse the public about the BBC Tax, I expect a lot more FUD from them.

[Andy Wade]

Any *new* wiring which is added to the circuit (e.g. to move the FCU to a more convenient location) will need to comply with the 17th ed. Hence new wiring in T&E that is buried at less than 50 mm depth in a wall will need to be 30 mA RCD-protected - either by moving the whole circuit to the RCD side of the CU, or by using an RCD spur. There is no requirement to RCD-protect pre-17th ed. work or any new surface wiring.