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I have installed a Monsoon U2 shower pump under the HWC in the airing cupboard. Airing cupboard has an electric connection for the immersion heater and the central heating pump and valves. Also, the main control unit for the alarm system has been connected by a fused box from this electric connection in the airing cupboard. I understand you can not run a fused spur from this connection as it is a dedicated supply.
All the nearby sockets are connected by three to four wires and i understand that you can not run a fused spur from any of these connections for the pump. The house is about 40 years old.

Can anyone help with a sound solution to run a fused spur for the pump? Can I use a fused supply from a lighting supply, which is not a preferred method?

Since the lighting circuit will be 6 Amps you do not need a fused connection unit, although it would be advisable for isolation purposes.

Is the immersion heater redundant?

In the main an immersion heater is 3 kW = 13A and the supply is 16A so having a second fused connection unit with a 3A feed to a shower pump is not really a problem unless it is switched off when you want a shower, some immersion heaters can be switched from kitchen.

Depending on model it can draw 1.5 to 5 amp, if 5 amp then can't be used on lights anyway, in the main ceiling roses rated 5 amp so max 5 amp fuse on lights, OK often 6 amp but although you can go to 16 amp for lighting, that would mean no standard ceiling roses so in the main 5 amp limit.

So not difference over load wise with immersion heater or lights, but safety wise if it were to trip a MCB better losing immersion as well than lights as well. Depending on cable used for immersion you may be able to use a 20 amp MCB/RCD do remember the pump recommends use of RCD so if not already fitted a RCD/FCU would be required.

Should not use 13A plug in an airing cupboard as it could over heat, a FCU can get rid of heat into the wall, a plug needs free air around it.

Mr White wrote:Since the lighting circuit will be 6 Amps you do not need a fused connection unit, although it would be advisable for isolation purposes.

Is the immersion heater redundant?

Thanks, Mr. White for a response.
The immersion heater is not redundant, we do use it now and then.
However, I took some floorboards out from nearby (2 meters) the airing cupboard. I found two brown junction boxes under the floorboards. One junction box is rated at 20 AMP (4 x 1.5mmsq) and has four cables connected to it and believes this is for the lighting circuits. The second junction box is rated at 30 AMP and has only two cables connected to it. Can I run a new connection from the second 30 AMP junction box to a fused 3 pin socket spur in the airing cupboard for the pump rather than from a lighting circuit? Please copy and paste this link to see the photos.
https://photos.app.goo.gl/Wm3vKmWtArwKPaEr9

ericmark wrote:In the main an immersion heater is 3 kW = 13A and the supply is 16A so having a second fused connection unit with a 3A feed to a shower pump is not really a problem unless it is switched off when you want a shower, some immersion heaters can be switched from kitchen.
Depending on model it can draw 1.5 to 5 amp, if 5 amp then can't be used on lights anyway, in the main ceiling roses rated 5 amp so max 5 amp fuse on lights, OK often 6 amp but although you can go to 16 amp for lighting, that would mean no standard ceiling roses so in the main 5 amp limit.
So not difference over load wise with immersion heater or lights, but safety wise if it were to trip a MCB better losing immersion as well than lights as well. Depending on cable used for immersion you may be able to use a 20 amp MCB/RCD do remember the pump recommends use of RCD so if not already fitted a RCD/FCU would be required.
Should not use 13A plug in an airing cupboard as it could over heat, a FCU can get rid of heat into the wall, a plug needs free air around it.

Thanks, ericmark for a response. Thanks for informing not to use a three-pin 13A plug in an airing cupboard. I will use an RCD/FCU as you recommend. Further, I do not prefer to use the supply from the lighting circuit or the immersion box. I have found two junction boxes under the floorboard about 2 meters from the airing cupboard. see my further information posted yesterday. I would like to use supply from the 30 AMP junction box, but want to know if it would conform with the regulations. I have not traced the wires to this junction box.