Boiler and immersion on same MCB?

[dawdle]

Is it bad practice for a 3A supply for a boiler and a 13A supply for a 3KW domestic immersion to be on the same RCD protected 16A MCB?

If ok would it then be advisable to fit a 20A DP switch to the immersion so it could be fully insulated if a fault arose and then the boiler could still operate?

Thanks.

 

[Chri5]

Isn't the immersion on a switch or f/spur anyway

 

[Taylortwocities]

The Electricians Guide to the Building Regulations recommends that an electric water heater for a vessel in excess of 20litres should have its own, dedicated supply.

I don't find this in BS7671 and so, like a lot of things, its guidance.

 

[dawdle]

Of course. Fused switched spur.

 

[londonboy]

Ideally the 16a radial will feed a double pole switch with butyl (or the better modern stuff!) across to the immersion, then you'd spur off the nearby sockets to feed a spur with 3a fuse in just for the boiler. I'm pretty sure that is in the regs but I haven't got them to hand, just seem to remember reading it somewhere

 

[dawdle]

I've had a rethink and will take the supply to the boiler in a spur from the downstairs ring and give the immersion it's own supply as recommended.

I was only considering it as the boiler is below the HW cylinder and I was thinking of using the nearby socket for a spur to something else.

I do have heat resistant flex from the 13A sw spur to the immersion.
But is the 20A DP switch a requirement?

Thanks

 

[londonboy]

Not 100% if the 20a dp switch is a requirement, it certainly is for all my contracts at work. I think its because the immersion draws 13.04 (guesstimate!) amps, i.e. over the 13amps allowed through a fused spur.

 

[dawdle]

So I can assume cable calcs are being made based on 230v now? Used to be 240v and so would have been 12.5A.

 

[TicklyT]

This came up recently ... If the immersion is rated at 3KW @ 240 Volts, then it will only draw about 12 Amps at 230 Volts (OK, 11.979 Amps to the nearest milliamp).

 

[dawdle]

Just took a look at the label on the immersion and it's rated 2.8KW at 230v / 3KW at 240v, which is 12.17A / 12.5A. Still just under 13A

But I still don't know if the 20A DP switch is a requirement?

Thanks.