Adding to a Wylex breaker box for a 10+kwh shower

[NL]

I know this is a job for a professional and that's fine. It's just that every electrician I've phoned seems to think something a bit different, just had one say I can run a 10.5kwh shower through a 40A breaker which I really don't think is correct.

I have an 8.5kwh leccy shower that's knackered on it's last legs, so looking to move it to 10.5kwh.

To do this I'll need the wiring upgrading (it's 6mm atm) and I'll need to ensure the breaker box is good for it, my question is around the breaker box.

It's as in the attached image, it's a Wylex NHRS6604.

The shower is currently on that NSB40 switch, I believe I'll need to have the shower on a 50amp supply through the box.

So looking at it, it almost looks like those switches are modular and so can be inserted and changed as required.

And if so this might be a relatively straightforward job, it might be a case of picking up an NSB50 "module" (can see some on ebay) and having the sparky drop it in where the NSB40 is and wire it all up with the new wire gauge, as opposed to replacing the box and adding a separate independent breaker just for the shower.

In real terms it seems the 8.5kwh shower would be pulling 35A atm and moving to 10.8kwh would move that to around 45A.

The cooker does 6kw so about 25A so with cooker and shower running I guess it could be pulling around 70A total?

Just looking for opinions, is it a case of switching out the NSB40 for an NSB50? and if so would this box be able to support it?

Thanks

 

[AndyPRK]

That current CU would support it. And new cable.

 

[sparkwright]

Your shower is currently on an MCB that is protected by the 80A RCCB. The green area on the left hand side.

As your new shower is much more powerful, I be inclined to get a 50A RCBO for the shower, and fit it on the unprotected red side.

By using an RCBO on the unprotected red side, you dtill have RCD protection, and you won't risk putting too much load on the 80A RCCB.

 

[EFLImpudence]

I know this is a job for a professional and that's fine. It's just that every electrician I've phoned seems to think something a bit different, just had one say I can run a 10.5kwh shower through a 40A breaker which I really don't think is correct.

No - 45A.

To do this I'll need the wiring upgrading (it's 6mm atm)

6mm² will be adequate if it does not run through any thermal insulation or in a wall or floor space with thermal insulation.

and I'll need to ensure the breaker box is good for it, my question is around the breaker box.
It's as in the attached image, it's a Wylex NHRS6604.
The shower is currently on that NSB40 switch, I believe I'll need to have the shower on a 50amp supply through the box.

Ok.

So looking at it, it almost looks like those switches are modular and so can be inserted and changed as required.

Yes.

And if so this might be a relatively straightforward job, it might be a case of picking up an NSB50 "module" (can see some on ebay) and having the sparky drop it in where the NSB40 is and wire it all up with the new wire gauge, as opposed to replacing the box and adding a separate independent breaker just for the shower.

Yes.

In real terms it seems the 8.5kwh shower would be pulling 35A atm and moving to 10.8kwh would move that to around 45A.

10.5kW @ 240V is 43.75A

The cooker does 6kw so about 25A so with cooker and shower running I guess it could be pulling around 70A total?

Well, yes, nothing out of the ordinary.

Just looking for opinions, is it a case of switching out the NSB40 for an NSB50? and if so would this box be able to support it?

Yes.

Is it worth it? Is it that much better than 9.5kW which is 39.6A?

 

[EFLImpudence]

Good point about the RCBO.

 

[NL]

Your shower is currently on an MCB that is protected by the 80A RCCB. The green area on the left hand side.

As your new shower is much more powerful, I be inclined to get a 50A RCBO for the shower, and fit it on the unprotected red side.

By using an RCBO on the unprotected red side, you dtill have RCD protection, and you won't risk putting too much load on the 80A RCCB.

I'm not an electrician but if I read you correctly you're suggesting an RCBO on the red right hand side, this means I'm not pushing the left hand side neart the 80A limit which might be a problem down the line. (We are at a place where EVs, heat pumps are coming in and lots is moving to electric) The right hand side has 100A (I'm assuming it covers the left side too, so really it's providing an additional 20A headroom?) and so sticking it there is sensible but to do so safely I can't just stick in an NSB50, I must get a RCBO?

Do you mean something like this : https://www.superlecdirect.com/7175-wylex-50amp-rcbo-type-b-30ma/

Any ideas if this would be compatible with what I have.

The description says "The Wylex NHXSBS Type B Single Module RCBO's are part of the Wylex NH range and provide protection for final circuits." which implies it should fit?

I could investigate the wiring a bit more, but assuming all ok there, just grab one of those and hire an electrician to fit it all.

 

[NL]

6mm² will be adequate if it does not run through any thermal insulation or in a wall or floor space with thermal insulation.

Interesting.

Just thinking. I made an mspaint of the wiring, attached.

Essentially the wiring comes out the back of the shower and up through a plaster wall into the loft.

Then across the loft where there obviously will be thermal insulation. (I've added a picture where it goes up and then into the loft.)

Then down, outside the wall inside a cheap cover housing the cables, to the breaker box.

So given what you've said, it seems the up and down bits should be fine at 6mm, but the loft clearly isn't because there's thermal insulation there.

As I say I'm not an electrician and not up on regulations but it seems like there might be various options.

Options here :
1. Wire the whole lot at 10mm gauge (or what is required), this could be difficult with the wire behind the shower in the wall but that will be part of the job
2. Cut the wire at the wall/loft right angle and splice 10mm so it's using 10mm throughout the loft area but 6mm in the vertical only
3. Assuming it's risk of fire in the loft area with 6mm due to it getting warm? Add some plastic tubing to the wiring in the loft to protect the loft from any heat

Any thoughts on those? It seems like (3) might be a nono, (2) is really skirting the regulations, and really I should just bite the bullet and do (1).

Is it worth it? Is it that much better than 9.5kW which is 39.6A?

It's a good question.

To clarify I have 8.5kw right now, so at the moment the obvious choice is stick in another 8.5kw and call it a day.

So I assume you are implying I could go 9.5kw and it's a straight swap? ie no need to worry about wire gauge, perhaps 6mm in the loft is ok? And the breaker box wouldn't need changing? It's very very close to 40A but within spec so should be fine?

 

[EFLImpudence]

The cable is alright above the insulation - or you could fit a batten under the cable.

Do the areas not seen prevent the cable cooling in any way?

It's a good question.

To clarify I have 8.5kw right now, so at the moment the obvious choice is stick in another 8.5kw and call it a day.

A new one might be better.

So I assume you are implying I could go 9.5kw and it's a straight swap? ie no need to worry about wire gauge, perhaps 6mm in the loft is ok? And the breaker box wouldn't need changing? It's very very close to 40A but within spec so should be fine?

Yes,

Very close is good enough.

Just under 40A for the shower and 47A (not 46) for the cable is 15% leeway for a start plus the relatively little time the shower is used is also factor.

 

[AndyPRK]

Is one oven really draw 25A? Or is that oven, Grill which are unlikely to be on at once?

The whole house may only be on a 80A fuse

 

[Harry Bloomfield]

Just looking for opinions, is it a case of switching out the NSB40 for an NSB50? and if so would this box be able to support it?

Yes, and yes.. But rather than a MCB, a 50amp RCD, fitted adjacent to the main isolator switch.

 

[Jurassicspark]

The cooker does 6kw so about 25A so with cooker and shower running I guess it could be pulling around 70A total?

In a real life scenario, certainly not.

 

[sparkwright]

I'm not an electrician but if I read you correctly you're suggesting an RCBO on the red right hand side, this means I'm not pushing the left hand side neart the 80A limit which might be a problem down the line. (We are at a place where EVs, heat pumps are coming in and lots is moving to electric) The right hand side has 100A (I'm assuming it covers the left side too, so really it's providing an additional 20A headroom?) and so sticking it there is sensible but to do so safely I can't just stick in an NSB50, I must get a RCBO?

Do you mean something like this : https://www.superlecdirect.com/7175-wylex-50amp-rcbo-type-b-30ma/

Any ideas if this would be compatible with what I have.

The description says "The Wylex NHXSBS Type B Single Module RCBO's are part of the Wylex NH range and provide protection for final circuits." which implies it should fit?

I could investigate the wiring a bit more, but assuming all ok there, just grab one of those and hire an electrician to fit it all.

Something like that - I am not 100% certain whether an NHX range will actually fit in place of an NSB range - best phone the Wylex technical helpline if in doubt.
Or someone here may know for sure.

There are some NSB Wylex RCBOs on Ebay...

You cannot fit an MCB on the red right hand side, as there is no RCD protection.
An RCBO is basically an MCB with an RCD built into it.

 

[NL]

Is one oven really draw 25A? Or is that oven, Grill which are unlikely to be on at once?

The whole house may only be on a 80A fuse

Oven only, it turned it on and watched the power draw, it was actually nearer 5kw due to existing load so 21ampish.

It burst to 5kwish, then settled back after a few mins to around 2.5kw.

 

[JohnW2]

Yes, and yes.. But rather than a MCB, a 50amp RCD, fitted adjacent to the main isolator switch.

I presume you mean RCBO?

 

[Harry Bloomfield]

I presume you mean RCBO?

Yes, sorry - RCBO!