Electric shower wiring

[warco]

I am fitting an electric shower for my father in law. I have notified building control and wish to comply with the law.
The consumer unit fitted at the moment is an old wylex fused type. I intend to fit an additional shower consumer unit with dp rcd and 50 amp mcb with its own 25mm tails. My question is , should this unit have a double pole isolator switch or is the dp rcd enough.

 

[electronicsuk]

The DP RCD is sufficient for isolation purposes.

There has been discussion before as to whether or not such installations should include a single, common isolator that controls the entire installation, although the regulations in this respect are open to interpretation.

Personally, I would retain the RCD as the main point of isolation for the shower installation and leave it at that. If you do want a main isolator, your should be able to arrange to have the DNO fit one for you by going through your electricity supplier. This will probably end nearly as cheap as doing it yourself, and will mean that you can isolate the supply to carry out your work without pulling the main fuse.

 

[riveralt]

I am fitting an electric shower for my father in law. I have notified building control and wish to comply with the law.
The consumer unit fitted at the moment is an old wylex fused type. I intend to fit an additional shower consumer unit with dp rcd and 50 amp mcb with its own 25mm tails. My question is , should this unit have a double pole isolator switch or is the dp rcd enough.

Hi there - couple of issues.

Firstly, the layout of your circuit must also follow the manufactuers instructions. Triton and most of the shower manufacturers have recently changed their instructions to reflect that you Must have an RCD and DP isolating switch fitted - failure to do so will probably invalide the warranty as well as be contrary to BS7671.

Secondly, I seem to remember reading somewhere, it may have been the manufacturers instructions, that your new shower MCB should not exceed half the suppliers fuse. If it does you may have to contact the supplier to have the suppliers fuse uprated. I could be wrong on this and I'm sure if someone knows to the contrary they will highlight it.

 

[Steve]

I am fitting an electric shower for my father in law. I have notified building control and wish to comply with the law.
The consumer unit fitted at the moment is an old wylex fused type. I intend to fit an additional shower consumer unit with dp rcd and 50 amp mcb with its own 25mm tails. My question is , should this unit have a double pole isolator switch or is the dp rcd enough.

Hi there - couple of issues.

Firstly, the layout of your circuit must also follow the manufactuers instructions. Triton and most of the shower manufacturers have recently changed their instructions to reflect that you Must have an RCD and DP isolating switch fitted - failure to do so will probably invalide the warranty as well as be contrary to BS7671.

Secondly, I seem to remember reading somewhere, it may have been the manufacturers instructions, that your new shower MCB should not exceed half the suppliers fuse. If it does you may have to contact the supplier to have the suppliers fuse uprated. I could be wrong on this and I'm sure if someone knows to the contrary they will highlight it.

Firstly, the OP is referring to his mains intake. Though it doesnt say if there will still be a DP switch in the bathroom, its standard to have one.

I have never heard of the half the suppliers fuse story. Though Wylex CU's state they can only supply one circuit with a rating greater than 32A.

 

[Taylortwocities]

Hi, you said that

. I intend to fit an additional shower consumer unit with dp rcd and 50 amp mcb .

That may be OK. What size cable will you be running for the feed to the shower, and what is the rating of the shower?

 

[riveralt]

I am fitting an electric shower for my father in law. I have notified building control and wish to comply with the law.
The consumer unit fitted at the moment is an old wylex fused type. I intend to fit an additional shower consumer unit with dp rcd and 50 amp mcb with its own 25mm tails. My question is , should this unit have a double pole isolator switch or is the dp rcd enough.

Hi there - couple of issues.

Firstly, the layout of your circuit must also follow the manufactuers instructions. Triton and most of the shower manufacturers have recently changed their instructions to reflect that you Must have an RCD and DP isolating switch fitted - failure to do so will probably invalide the warranty as well as be contrary to BS7671.

Secondly, I seem to remember reading somewhere, it may have been the manufacturers instructions, that your new shower MCB should not exceed half the suppliers fuse. If it does you may have to contact the supplier to have the suppliers fuse uprated. I could be wrong on this and I'm sure if someone knows to the contrary they will highlight it.

Firstly, the OP is referring to his mains intake. Though it doesnt say if there will still be a DP switch in the bathroom, its standard to have one.

I have never heard of the half the suppliers fuse story. Though Wylex CU's state they can only supply one circuit with a rating greater than 32A.

Yes I was aware of the fact that the OP was referring to the main intake. I was also aware that the OP was wishing to comply with Part P and presumingly BS7671. The information I gave was specific to the whole insulation and not just the sub-main element. Complying with manufacturers instructions is an element of BS7671.

For example for Triton showers the manufacturer requires the Consumer unit main switch to be rated at least 80Amps preferably 100Amp. I don't think the Wylex has this facility. Nor it seems does the OP hence the submain.

However, the OP has indicated that he intends to create a sub main consisting of a RCD and an 50Amp MCB and seeks advice about the additional introduction of a main isolator switch - For Triton showers at least the manufacturer still wants an 80/100 Amp main switch.

The second issue is more about circuit design and demand. In creating a submain and possibly creating a 40/50Amp load as well as the normal demand from the household through the old 'fusebox' the value of the suppliers fuse becomes critical. Many old Wylex boards are protected by a 60Amp suppliers fuse - do you think it is sufficient for this household?

It is for this reason that the manufacturers instructions also highlight the need to check with the supplier.

 

[warco]

Thanks for all the advice.
You are quite right about the incoming supply fuse. This was 60amp feeding the Wylex board.
I have already had the electricity supply company out and they have uprated this to 80 amp

 

[sparkwright]

It sounds like the old fuse box is the re-wirable type without RCD protection.

If so, you should consider employing an electrician to replace it for up-to-date consumer unit with some spare ways; and connect the shower circuit to this. Subject to the house wiring being in a reasonable condition of course.

 

[PrinceofDarkness]

There's nothing wrong with the O/P's proposal to fit a modern RCD/MCB enclosure alongside the old fuse box. It's far and away the cheapest way to comply - without the liability of checking other unrelated circuits during a complete CU change.

Yes of course, the RCD will give full DP isolation, but that isn't seen as a substitute (by most installers) for additional local DP isolation of the shower.

Lucia.

 

[bunsen]

It sounds like the old fuse box is the re-wirable type without RCD protection.

If so, you should consider employing an electrician to replace it for up-to-date consumer unit with some spare ways; and connect the shower circuit to this. Subject to the house wiring being in a reasonable condition of course.

You'd be more than happy to quote for such a rewire?

 

[ban-all-sheds]

I intend to fit an additional shower consumer unit with dp rcd and 50 amp mcb with its own 25mm tails.

How do you intend to isolate the supply to make it safe to do the work?

 

[PrinceofDarkness]

Oh come come, BAS dear! You know perfectly well that the service fuse will have to removed in order to fit Henley Blocks and tails.

This method might not suit your opinion and that of the supplier, but it's the (unofficial) safe way of doing it.

It's not as though the removal of the seal leads to illegal abstraction of the supply. is it?



Lucia x

 

[ban-all-sheds]

I know that.

I just wondered if the OP does, and if he is aware of the risks he faces.

 

[PrinceofDarkness]

The 'risk' of Danger or prosecution, BAS?


Lucia x

 

[bunsen]

I know that.

No you didn't, stick to IT.