New Shower - Tripping

dt66 · 14 Mar 2007

Folks,
I've been given a new shower and on investigating the electrics I found that although I have 6mm cabling, the fuse is a NSB32 240v.
Although I've never had any problems with my existing 9500 kw shower, I thought I would have needed a 40amp breaker.

The new shower is a 10.5 kw job, so I'm now concerned that it will be too much for the breaker - can you advise if I should get a 40A or greater & if greater, will the 6mm cable still be OK.
Thanks.
DT

davy_owen_88 · 14 Mar 2007

Are you sure the 32A MCB is the right one for the shower?

9500w/240v = 40A MCB
10500w/240v = 45A MCB

CCC for 6mm² t&e clipped direct = 47A

How far from the CU to the shower? Does it run through loft insulation/conduit/high ambient temps?

For the 10.5kW shower I would fit 10mm² cable and a 45A breaker but you might get away with 6mm² cable depending on the distance and de-rating factors - the MCB will need to be upgraded.

Davy

dt66 · 14 Mar 2007

Yep - it's 32. That's what threw me. The Cooker socket is on a similar breaker (but a gas one is installed!)

The house is a small mid terrace. Cable goes from under stairs, up into the attic, 1m through insulation and back down into airing cupboard (no hot water boiler) & through wall to the unit - I'd say 12metres max.

davy_owen_88 · 14 Mar 2007

dt66 said:
1m through insulation

Well that 47A rating for 6mm² cable just went down to 27A. Is there no way the cable can be pulled clear of the insulation and clipped to the loft joists? Failing that you will need to install 16mm² cable.

Davy

dt66 · 14 Mar 2007

Sorry - mis-understood.
The cable is clipped to the joists, but there is also insulation up there - the floor has been boarded, but that could be removed as it's in one corner.
Cheers.

davy_owen_88 · 14 Mar 2007

So the cable is well clear of the insulation? Do the boards cover the cables? Is any part of the cable touching the insulation?

dt66 · 14 Mar 2007

...just been up there.

No, it's a clean hole chased up the wall and then clipped to the joist, for about 1.5m & then straight down into the bathroom.
I've I checked the length and would say it's close to 10m.

The house was gutted & totally re-wired about 10 years ago.
Later I put the insulation between the rafters & boarded over the top. Obviously I didn't realise that this would cause such an important issue - so big lesson learnt there - thanks.

Where do you think that leaves me?

Cheers,
DT

davy_owen_88 · 14 Mar 2007

10500w / 240v = 43.75A

CCC of 6mm² t&e when clipped direct = 47A

So as long as the cable isn't surrounded/covered by insulation at any point along it's run and is clipped directly the the joists or covered with plaster in the walls you can use the cable that is there and upgrade to a 45A MCB.

If the cable is in contact with insulation pull it clear and clip it so it can not become covered.

Davy

dt66 · 14 Mar 2007

Thank you Davy - I really appreciate your giving me your time & experience.
Iechyd da!
DT

securespark · 14 Mar 2007

Sorry to muddy the water, but my rule of thumb is 8.5max on 6mm².

I'd have to be absolutely certain of all factors if rating it higher. Not just insulation, but grouping factors, ambient Tº.....

davy_owen_88 · 15 Mar 2007

I agree with that, for new 10mm² minimum for 10.5kW, but since the OP states that the runs are all clipped/buried direct, I doubt high ambient temps are going to be an issue in a standard house. Plus the OP mentions a separate chase for the shower cable so bunching is taken care of.

Davy

Taylortwocities · 15 Mar 2007

No high ambient temperatures in a standard house?

Have you been in a loft in August?

TTC

dt66 · 15 Mar 2007

If I was to pull in some new 10mm² would it be OK to bring it in under the bathroom floor (clipped to joists) & then up the cupboard to the shower, or are there some regs about doing this?

I'm thinking that 10 years ago, most showers you could buy from the big retailers had much lower power ratings - possibly why the sparkie who did my place only put in a 32amp fuse? although even 7500kw s/240 = 31.75 is a bit tight.
Seems to me, as a layman, that these retailers should be much more proactive about communicating the potential issues with buying these higher powered showers - they put up little notices, but I don't believe they are being responsible enough.

Thanks
DT

EddieCurrent · 15 Mar 2007

Hello All
You may or may not believe this but it happened to me @4 months ago...
A customers sister called me up to wire a shower, I arrived to have a look and asked her on which wall around the bath she was having the shower mounted, she said it "it doesn't matter, either end is ok " I explained that she needed a water pipe to 'feed' the unit, and she replied "oh, it said electric shower, I didn't think of that !

"
I have not been called back and bet the shower has been stashed in the loft next to the x-mas tree, till they sort a 'water man'...

diynot

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New Shower - Tripping

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