Shower pump connection

[EFLImpudence]

I want to put the pump at ceiling height so would need to spur the fuse outlet.

At risk of tarnishing the Electrics forum with filthy plumbing advice, the pump should be close to the cylinder, on the floor for best results. and in strict accordance with the instructions to validate the warranty. Otherwise additional air vents, anti-gravity loops and negative head pumps become necessary.

I agree with echoes.

If it is a Salamander pump, they are very particular that their instructions are followed to the letter in order to validate the warranty. The installer has to complete their warranty form and sign to the effect that it has been so installed.

 

[acmedone]

If it is a Salamander pump, they are very particular that their instructions are followed to the letter in order to validate the warranty. The installer has to complete their warranty form and sign to the effect that it has been so installed.

It's a motor with two impellers, for goodness sake. They should either manufacture it properly or take it on the chin, not try and escape with wriggle out clauses.

 

[echoes]

If it is a Salamander pump, they are very particular that their instructions are followed to the letter in order to validate the warranty. The installer has to complete their warranty form and sign to the effect that it has been so installed.

It's a motor with two impellers, for goodness sake. They should either manufacture it properly or take it on the chin, not try and escape with wriggle out clauses.

Having recently installed a Salamander pump, the instructions are not particularly onerous, and are consistent with the best plumbing practice. Basically, if you install any maker's pump in such a way that will not prevent air entering, or increases risk of cavitation, it will not work as intended nor will it last.
I've not tried to claim on their warranty though!

 

[echoes]

Back on topic:

However, the cable running under the airing cupboard floor doesn't have enough slack for one junction box. It therefore requires two JBs with a short bridge.

That's OK as long as the JBs remain accessible (i.e. not hidden under the floor again). But as it's an airing cupboard, if the floor boards are not covered with anything, and can easily be unscrewed and lifted again for inspection, I think that would be classed as 'accessible'.

If you're careful, it's possible to insert a single JB on a cable in situ without cutting the cable: just strip the insulation and separate so it drops into the JB. You can then run a short spur to the RCD/FCU or FCU socket for your shower pump.

Or go with EFLImpudence's suggestion of an FCU off the immersion circuit.

 

[JohnW2]

If you're careful, it's possible to insert a single JB on a cable in situ without cutting the cable: just strip the insulation and separate so it drops into the JB. You can then run a short spur to the RCD/FCU or FCU socket for your shower pump.

Indeed - I've often done it. The problem occurs with the CPC ('earth' conductor) - unless one is prepared to trust tape, rather than sleeving, one has to cut it. However, if there's a slight bit of slack available, one can usually arrange the geometry of the conductors within the JB such that only the CPC has to be cut (and sleeved).

Kind Regards, John.

 

[acmedone]

If you're careful, it's possible to insert a single JB on a cable in situ without cutting the cable

Worth a try.

Or go with EFLImpudence's suggestion of an FCU off the immersion circuit.

My preference but wondered because it already has the central heating on it (through an FCU with 3A fuse). The circuit is 2.5mm with 15A in the CU and my understanding is that a radial may only provide 2 outlets. I know a second FCU would be perfectly OK from an electrical pov but what do the rule makers say?

Edit. I notice from another thread that it's probably acceptable to have a 13A FCU feeding several FCUs radially. Agreed?

 

[JohnW2]

Or go with EFLImpudence's suggestion of an FCU off the immersion circuit.

He actually suggested a FCU off a lighting circuit. In theory, an immersion heater circuit should be dedicated to that one load.

Kind Regards, John.

 

[JohnW2]

[

Or go with EFLImpudence's suggestion of an FCU off the immersion circuit.

My preference but wondered because it already has the central heating on it (through an FCU with 3A fuse). The circuit is 2.5mm with 15A in the CU and my understanding is that a radial may only provide 2 outlets. I know a second FCU would be perfectly OK from an electrical pov but what do the rule makers say?

EFLI actually suggested a FCU off a lighting circuit, which would probably be OK (depending on how much current the pump takes, and what lighting load you have on the circuit).

In theory, an immersion heater circuit should supply nothing other than the immersion heater; you already have one other FCU fed from it, so a second one would not be a very good idea. A radial socket circuit can have as many outlets (sockets) as you like, but an immersion heater circuit is a different matter.

Kind Regards, John.

 

[echoes]

Oops - it was flameport. Apologies to all concerned, and thanks JohnW2!

Unlimited outlets allowed on a radial circuit by the way.

I've heard it argued both ways regarding an immersion circuit appropriated for other uses - on the one hand it is recommended that a fixed load >2kW such as immersion heater has its own circuit, and on the other that so long as one designs a circuit such that it is not expected to overload then it is OK.

Unless one of the regs gurus can interject otherwise, the designer takes a view that he is happy is compliant.

EDIT: Do you know the current your pump will take? If it's 5A or more then perhaps it's not such a good idea...

 

[JohnW2]

I've heard it argued both ways regarding an immersion circuit appropriated for other uses - on the one hand it is recommended that a fixed load >2kW such as immersion heater has its own circuit, and on the other that so long as one designs a circuit such that it is not expected to overload then it is OK.

Yes, I've heard both arguments, too. As you go on to hint, quite apart from regs and their interpetation, loads are the other issue here. Immersion heaters rated at 3kV at 240V take 12.5A at 240V (and most people get at least 240V), and immersion circuits are usually protected by a 16A MCB or 15A fuse - so that doesn't leave much 'spare'.

The arrangement the OP currently has (with CH run from a spur off immersion circuit) is arguably a particularly unwise design decision - since it presumably means that primary and secondary methods of water heating may 'go down' together.

Kind Regards, John

 

[acmedone]

Or go with EFLImpudence's suggestion of an FCU off the immersion circuit.

He actually suggested a FCU off a lighting circuit.

I did notice that. On a 5A circuit that could already be supplying 2A?

In theory, an immersion heater circuit should be dedicated to that one load.

In theory, two 3kW heaters could be plugged into a radial double socket...
So long as it is only theory and the rules don't actively outlaw connecting small loads to the immersion circuit it must surely be the preferred method? Precedence is that a cooker outlet usually has a 13A socket.

 

[securespark]

My own views are that, personally, I would only have an immersion on its own circuit. Not just because the regs demand it, but because I consider it best practice with regard to separating circuits as much as possible.

If you have a circuit with an immersion and CH and a shower pump on it and something goes short circuit, potentially you'll lose all three.

I would not put a motor on a lighting circuit either.

The OSG suggest putting immersions on their own circuit, the regs don't mention it, save for the "new" appendix concerning appliances >2kW.

 

[echoes]

In theory, two 3kW heaters could be plugged into a radial double socket...

Quite so, and I'm sure people have done it. But in theory, a designer should never install a double socket on a standard 16A or 20A radial knowing that its intended use was 2 x 3kW heaters. His crystal ball would start flashing.

So long as it is only theory and the rules don't actively outlaw connecting small loads to the immersion circuit it must surely be the preferred method? Precedence is that a cooker outlet usually has a 13A socket.

Hmm, but you can't realistically apply diversity to an immersion heater: it's either off or on, and on for long periods. Shower pump on the other hand... 10 mins max?

I think securespark has put it very well: it's certainly not best practice to add these small additonal loads for a number of good reasons, and if there's an easy alternative way of avoiding that, then avoid it.

 

[acmedone]

Yes, I've heard both arguments, too. As you go on to hint, quite apart from regs and their interpetation, loads are the other issue here. Immersion heaters rated at 3kV at 240V take 12.5A at 240V (and most people get at least 240V), and immersion circuits are usually protected by a 16A MCB or 15A fuse - so that doesn't leave much 'spare'.

A mere technical matter of little concern. Wading through the bureaucratic swamp is much, much harder.

The arrangement the OP currently has (with CH run from a spur off immersion circuit) is arguably a particularly unwise design decision - since it presumably means that primary and secondary methods of water heating may 'go down' together.

I can't imagine what sort of fault the CH would have to develop to take down the whole circuit.

 

[echoes]

I can't imagine what sort of fault the CH would have to develop to take down the whole circuit.

A fault with the immersion, shower pump or CH (boiler, pump, valve) might take out a 16A MCB before a local fuse. But all these should be able to be separately isolated, so it's not as if you would have no means of hot water. And your 15A fuse should discriminate with local 3A/5A fuses.

Out of interest, I have my immersion circuit off at the CU, in case young master echoes decides to watch the nice shiny neon on the immersion heater switch come on, and then leave it on. It's there for emergency use only!