Loft supply from immersion heater circuit (split thread)

[NELLY64]

Hello all.
I've been reading with interest the posts here because I want to run a socket for a network switch and an old computer to my loft.
My immersion heater and central heating pump are arranged per photo. Immersion heater on the right has a 13 amp fuse and CH pump has a 3 amp.
However, at the CU the immersion heater breaker is 15 amp.
Is this right or should I start worrying more than I am ?
Sorry to jump in like this.
ATB,Nelly

Untitled

• NELLY64
• 24 Oct 2012
• 2

 

[EFLImpudence]

It's fine - although the fuse for the immersion isn't necessary.

The pump will likely be less than 1A.


You shouldn't run anything else on the circuit.

 

[EFLImpudence]

Just realised -

You say the CH pump.
Does that mean that the whole CH system is run from that switched FCU?

If so, THAT would NOT be a problem.


However, if ONLY the pump is supplied by this and the boiler and other things supplied from elsewhere then that could lead to a problem.


OR - do you mean a pump installed because of low water pressure?

 

[kai]

My immersion and central heating system has a similar setup, the immersion has a 13amp fuse (B16 Radial), whilst the CH has a 3amp fuse (B32 Ring).

Perhaps he means a setup similar to mine???

 

[EFLImpudence]

Perhaps, perhaps not.

We don't know. That's why I asked.

 

[NELLY64]

Thanks for the quick replies fellas.
I'll have a good look at everything tomorrow.
But what I do know is the boiler is downstairs in the kitchen.
The Immersion heater and pump are upstairs in the airing cupboard.
The pump is a Grundfos UPS which are "designed for circulation of liquids in heating and air-conditioning systems"
It's beginning to not look good.
Troubled sleep tonight.

 

[ban-all-sheds]

The pump will likely be less than 1A.


You shouldn't run anything else on the circuit.

OK, so you have been asked to install a circuit to support the following loads:

3000W
200W
200W

You wouldn't regard a 15A circuit as a suitable option?


You might well be right, but we need to know the load of the switch and PC to be sure.

 

[securespark]

If you follow advice from the OSG, an immersion heater should have its own dedicated circuit.

I do appreciate however, that a 13A IH + 3A CH = 16A.

 

[ban-all-sheds]

That advice is a shortened over-simplified version of the advice in the Wiring Regulation on how to avoid overloading ring finals.

There is absolutely nothing wrong with designing a radial circuit to supply any mix of loads and load types you like, as long as you are OK for Ib ≤ In ≤ Iz, voltage drop, R1+R2 etc.

 

[EFLImpudence]

The pump will likely be less than 1A.
You shouldn't run anything else on the circuit.

OK, so you have been asked to install a circuit to support the following loads:
3000W
200W
200W
You wouldn't regard a 15A circuit as a suitable option?
You might well be right, but we need to know the load of the switch and PC to be sure.

That would obviously be alright.

I was referring to OP's addition of a socket, albeit initially for a small load.

 

[ban-all-sheds]

ΔIb might make that circuit unsuitable, but that would be because Ib > Iz, not because there's anything special about one of the loads being an immersion heater or because it's a socket being added.

If there was a generic concern that the potential load from sockets might exceed the rating of the protective device then you could never have socket circuits with more than a few outlets and never have fused spurs with more than one outlet, and we know that neither is true.

 

[EFLImpudence]

There is obviously nothing wrong with a properly designed circuit running whatever is required.

However, whilst it is recommended, albeit not in the actual regulations, that immersion heaters not be connected to a 'socket circuit' it does seem somewhat illogical to advise a DIYer it would be acceptable to add a socket to a 16A immersion circuit.