Need confirmation of advice given for installation of a water heater

[olderfella]

As our hot water tank is so far from the kitchen sink, for convenience we are considering having one of these water heaters installed under the sink.

I would do the plumbing, but I had two local electrical contractors in to quote for the electrical connection.

One says that it needs a rather costly solution consisting of a new feed all the way back to the mains fuse box. The other says that wouldn't be necessary and that he would change one of our electrical sockets to an isolation switch and connect the wiring to that. He says this is the way to go as (for some reason) our house is wired with a 'Radial' main not a ring main.

I'm a bit confused as to which way to go and wondered if any of the experienced guys here would like to comment.

 

[DetlefSchmitz]

Your first guy is correct. That is too big a load to connect to an existing radial. As a matter of interest, what size fuse or mcb protects this circuit?

 

[securespark]

The one that says you need a new feed is the right guy to go for.

The one that says you can wire a nigh-on 20A heater to a circuit that should only be protected by a 20A device maximum needs to go back to school. To take maths and then back to electrical college.

 

[olderfella]

Thanks for the comments guys.

First - my mistake - the unit we are looking at is not the one I linked, it's this smaller one. Its 3.7KW not 4.5KW.

The fuse on the kitchen circuit is 32A, and I think the cable is 4mm.

I also had this information (which may or may not be relevant) regarding cable sizes.

- 2.5mm² for 3.7 kW & 4.5kW (240V)
- 4 mm² or 2x2.5mm²(ring) for 5.5 kW & 7.3kW - (240V)
- 2.5mm² for 7.5kW these models is two phase no neutral -(400V)

 

[riveralt]

Given what you have now said - the second guy is now also correct.
Nothing to stop you putting anything on its own circuit so first guy is still correct - since it also gives you the option to increase the size of the machine at a later date particularly if he uses 4mm² cable and appropriate sized MCB.

 

[RF Lighting]

Go with the first guy.

 

[DetlefSchmitz]

I think I would ask what else was on the same radial before deciding. You can probably work out what is likely to be the worst case current and compare it to 32A. If in doubt, go for a new radial.

 

[Risteard]

It might be a radial serving only one socket outlet. No point condemning what someone has said without any of us having been there to see the validity or otherwise of the suggestion.

 

[bernardgreen]

Is the unit compliant / approved for use in the UK ?

Instant water heaters have to comply with strict safety requirments.

 

[Taylortwocities]

Good point, Bernard. It seems to be supplied from Poland.

 

[RF Lighting]

I hope the stat never sticks on that heater what with it having no temperature and pressure relief valve

 

[ban-all-sheds]

 

[ban-all-sheds]

I hope the stat never sticks on that heater what with it having no temperature and pressure relief valve

Redring Powerstream has an over-temperature cutout.

 

[kai]

Running a dedicated circuit is the proper option, using the most popular 3kw UK rated heater, a B16 breaker on a 2.5.mm radial often does the trick, with a flex-outlet DP switch within 2 metres of the heater unit itself.

 

[olderfella]

Thanks to all for the responses and comments.

On reflection I have decided that to satisfy our needs I will probably now install one of these instead.

Although it is about twice the price, it appears to offer some benefits over the original choice - namely

- Will give a better water flow as it is not heating the water instantaneously
- has a much smaller reservoir of water to heat compared to our standard hot water cylinder (hence there will be less waste and will heat up a lot quicker)
- can be connected to a standard 13amp socket (and there is one within a few inches of the intended siting) so no expense getting in an electrician to fit new supply (compensates for the extra cost of the unit).

Unless of course I am missing something