power shower feed

I am fitting a power shower in my bathroom, and need a 3A switched supply. Is it ok to spur off my imersion heater supply with a 3A switched fuse? This is the nearest available supply and has its own supply from the consumer unit.
Thanks
Phil
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I believe you can also take a feed from the light circuit this is normally near by as well. I don't see anything wrong in what you plan to do, although I don't know wiring regs.
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Very probably. The immersion is probably a 3kW @ 240V, taking 12.5A. No diversity would be allowed for this. However, I doubt the pump takes more than 2.5A (probably more like 1A continuous), so it should be fine for a 15A circuit. Obviously there is no issue for a 16A circuit either.
Christian.
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stunning, cheers for the info guys.

supply.
15A
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Will you be fitting a pump in the airing cupboard and teeing into existing pipework ?
Hays
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Its one of those all-in-one units from Triton, but the wall I am mounting it on in the bathroom backs onto the airing cupboard through a hollow wall.
I am taking a dedicated feed from the cold water tank in my loft and then teeing into the hot water supply. Is this best practice?
The plan is to make it as clean an installation as possible then upgrade to a separate pump system later and put the pump under the bath.
Phil

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The main issue is one of sucking air through the hot water cylinder vent pipe. It is standard practice to have a separate tapping in the cylinder for the shower called a flange. There are several types.
However, you can sometimes get away with using the standard hot water outlet. If this is to work, you need to have a good flow rate from the cold header tank into the cylinder. This is helped by having large bore pipe (at least 22mm) from a tank sitting directly above with flowed bends rather than elbows and full bore valves. At the other extreme, it is unlikely to be successful if you have 15mm pipe flowing halfway round the house to the cylinder with inline isolator ball valves and elbows aplenty.
It is easy enough to see if it works first and then fit a flange if you get air in the pump (or upgrade a seriously deficient but easily accessed cylinder cold tank supply).
Christian.
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Hi Christian, I'm contemplating much the same exercise (power shower in the distant future) hence I'm interested in this thread):

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So you wouldn't envisage much problems with a 28mm feed to the hot tank from the loft cold storage and a 28mm output which could be teed for the power shower?

get
The symptoms of sucking air being what apart from the noise ?
Mungo
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The pump will surge, and the water coming out of the head may splutter.
Christian.
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Actually this is forbidden in the Regs / On Site Guide. Fixed heating of vessels more than 15l must be supplied by their own dedicated circuit.
In practice though, you may get away with it. The question is that if your immersion *is* taking 12.5A and your pump *does* take 2.5A (or more on startup - could cause nuisance tripping), what happens when they're working at the same time, which is more than likely? The circuit is working "at capacity" for the length of your shower and although this should be fine, if everything was calculated / installed correctly, you leave yourself no leeway.
It's up to you, but I'd be looking for the upstairs socket ring from which to spur or, if desperate, a lighting circuit.
Hwyl!
M.
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Hi Phil,
I would add that strictly speaking, this is not OK. Fixed immersion water heaters > 15 litres should be powered by their own separate circuits.
-- John
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Not to my knowledge. However, you may not apply diversity, so a 3kW @ 240V heater needs to have 12.5A of a circuit dedicated to only its requirements that can't be borrowed by another device. This would preclude it from being installed on a ring main or socket radial circuit. However, a 16A radial circuit with a 13A FCU to the immersion and a 3A FCU to the pump is fine.
Christian.
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Ok, looked it up. The requirement isn't in the regs, per-se, but is in the OSG, Apx 8, p 154. The setup you describe will probably be ok, but given the above probably wouldn't be considered "best practice".
Hwyl!
M.
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