Shower pump and FCU's from immersion heater sockets - again

[dinman]

At the moment, I have an immersion heater in airing cupboard - draws 15 amps. It is currently on a 15A single dedicated circuit protected by 15A MCB at consumer unit. Circuit cable is 2.5 twin and earth.

I would like to change the rating of the circuit - replace 15A MCB with 20A MCB - an electrician will do this. I would then spur off the immersion heater switch to an RCD (30ma) and on to a 5A FCU for the shower pump.

But, this leaves the immersion tank switch/heater potentially vulnerable to a 20amp surge (I think). How do I protect against this?

Can I put a 15A FCU in for the immersion tank, and spur from that?

Please assume that at some point the shower pump and the immersion heater will both be working - and then the draw on the circuit in total 20A...

If I can/should put a 15A FCU at the immersion tank - where can I buy one? I have only seen 13A rated FCU's. I am not sure; would it be ok to put a 15A fuse in a 13A rated FCU? Or would the connections in the FCU burn out when taking 15A? (I leave the immersion tank switch on all of the time).

I noticed some earlier posts on this set up - but am not sure that this question (or state of confused ignorance) was presented...

Airing cupboard is outside of zones.

V Grateful for any help...

Dinman

 

[plugwash]

Are you sure your imersion heater draws more than 13A?

You could use a 2 way CU with a 16A and a 6A breaker to protect the immersion heater and shower pump. This CU could also provide RCD protection (something like http://www.tlc-direct.co.uk/Products/CPR026P.html ).

 

[LoveRocket]

Don't make things complicated.

Just spur off the existing immersion circuit with an FCU fused at 3a for your shower pump. Job's a good 'un!

Your immersion will be 3kW, which will draw no more than 13a, you shower pump will use maybe 1a max.

You'll be fine with what you've got buddy.

 

[Steve]

You could use a 2 way CU with a 16A and a 6A breaker to protect the immersion heater and shower pump. This CU could also provide RCD protection (something like http://www.tlc-direct.co.uk/Products/CPR026P.html ).

An excellent idea. Shame normal MCBs arent DP though.

 

[kai]

It's not just immersions and showers that can make good use of 2 way consumer units.

My shower and fan run off a 2 way unit with 30mA RCD Protection mainswitch, with an 8.5.kW shower on the 40amp breaker, and an 1amp fan on a B6 breaker and a 3amp FCU next to the fan's 12V supply unit just outside the bathroom.

 

[dinman]

Thanks very much for the replies.

Yes - am sure it is a 15A immersion heater - phoned the manufacturer, Backer. (Wish it was 13A !)

2 Way consumer unit seems v good option to me. Never heard of them before - such is my depth of knowledge.

Unfortunately, I bought the RCD and opened it etc. Going to bite the bullet and put in a separate circuit from consumer unit for pump. A steel across downstairs room is in favourable position... (unless there are problems with running wire in conduit by a steel...?...)

2 way consumer unit in mind for various stuff elsewhere.

Thanks,

Dinman

 

[LoveRocket]

Fair enough if you want to do it properly, but you'll have no problems running the shower pump off your existing 15A circuit. That 15A breaker won't trip instantly at 15.1A.

Is there not a socket circuit nearby you can spur from instead of running a new circuit just for the pump.

 

[skenk]

Don't make things complicated.

Just spur off the existing immersion circuit with an FCU fused at 3a for your shower pump. Job's a good 'un!

Your immersion will be 3kW, which will draw no more than 13a, you shower pump will use maybe 1a max.

You'll be fine with what you've got buddy.

Plenty of shower pumps use considerably more than 1 amp

eg: http://www.bathtek.com/shower_pumps.htm

Also this would be poor circuit design and would not comply with BS7671, so not really the kind of advice to be given out on a public forum.

The local CU sounds like the best bet, although a 15A immersion element does sound rather odd

 

[securespark]

It's got a cold?

 

[londonboy]

Ive never seen a 15a immersion either. I work with Backer immersions all the time and they're all standard 3kw jobs.

 

[LoveRocket]

Don't make things complicated.

Just spur off the existing immersion circuit with an FCU fused at 3a for your shower pump. Job's a good 'un!

Your immersion will be 3kW, which will draw no more than 13a, you shower pump will use maybe 1a max.

You'll be fine with what you've got buddy.

Plenty of shower pumps use considerably more than 1 amp

eg: http://www.bathtek.com/shower_pumps.htm

Also this would be poor circuit design and would not comply with BS7671, so not really the kind of advice to be given out on a public forum.

The local CU sounds like the best bet, although a 15A immersion element does sound rather odd

Those are some monster pumps!

In what way wouldn't it comply with BS7671? (Genuine question)

I know it's not great design, but it would work and would be safe. Given what is already in place I think it's a reasonable option.

 

[skenk]

It's not just not great, it's rubbish design. I'm not in a position to make a judgment on whether designing to overload a MCB is safe, are you?

Got a link to a pump using less than 1A?

Circuit already draws 15A on 15A breaker, adding another load would exceed rated capacity of circuit . . . don't have a reg number to hand but the design current should not exceed rated current of CPD, thats basic stuff.

Also no mention of RCD.

Fair enough your original example was based on 13A immersion so would have been ok, assuming the pump as <2A (although fixed loads over 2000w should . . .) but the OP has now reiterated that the immersion uses 15A so the current circuit is at capacity.

So your advice, which you are still proposing, is still bad. Your proposed setup could not be certified to BS7671, which could cause problems with in the future with insurance, PIR's, selling the property, repeated overload of the CPD possibly causing failure . . .

 

[LoveRocket]

Fair enough.

But have you ever known a MCB to be damaged due to overload? Surely the must be designed to tolerate a current that will not trip them? Just asking...