Take it or leave it

[Bubblecraft]

Within the past month I've had 2 customers who were wanting a shower swap, like for like. Both have been 9.5kw but have 6mm2 cable instead of 10mm2. Both customers were advised of the dangers & consequences of having 6mm2 on a 9.5kw such as volt drop, ambient temp's, grouping, and thermal insulation factors, and more so, probably the reason why there old one is defunct.

Both did not want to upgrade their cable so I've said that I would not carry out the work. If I take on the swap, it's me that's got to answer why their new shower is knackered in no time or worse, chance of fire.

What would you guys have done?

 

[telectrix]

check cable run . if it's installed method c then swap shower. leave on 6mm with 32A MCB.

 

[Bubblecraft]

Both houses were 15+m from CU though

 

[telectrix]

around 4.8V volt drop off top of head. acceptable.

 

[Bubblecraft]

Forgot to say, it's method A also which if I'm right is 32a, I could be wrong though

 

[telectrix]

method A as in thermally insulated wall? or is it in masonry?

 

[Bubblecraft]

Masonry mate, sorry

 

[telectrix]

not insulated so i would say method C, or possibly method B , 38A

 

[Deleted member 26818]

By rights, if the load is 45A/50A, the CCC of the cable is 38A and you protect the circuit with a 32A MCB, then whilst not complying with the Regulations, it should be safe.
I would imagine that there will be a lot of nuisance tripping, but that would not be your problem.
Note it as a departure on the Certificate.

 

[Bubblecraft]

I'm confused. Please correct me if I'm wrong but isn't method c clipped direct & these are in sold brick walls behind the tiles?

 

[Bubblecraft]

I would imagine that there will be a lot of nuisance tripping, but that would not be your problem.
Note it as a departure on the Certificate.

But I know what'll happen, after a few trips, they'll be on the blower saying "You couldn't have fitted it correctly. Our old one didn't do it"

I know this would be the way to do it safely but would you do it & put up with the grief from the customer about a tripping shower?

 

[telectrix]

agreed. i estimate the load as 39.5A max. assuming manufacturers claim of 9.5kW is not eggagerated ( as is usual). have seen 9.5kW happily running on a BS3871 30A with no problems.

 

[tony mc]

If you look up ref method c it makes mention of masonary brickwork concrete & plaster!

 

[Bubblecraft]

Either way, I've not took both on so I know I can sleep at night. For the cost of changing it over, I personally don't think it's worth the grief!

 

[telectrix]

I'm confused. Please correct me if I'm wrong but isn't method c clipped direct & these are in sold brick walls behind the tiles?

BS7671 does not have a reference method for T/E in masonry walls. a boffin at the IET told me last year that ref.B would be the closest

 

[telectrix]

If you look up ref method c it makes mention of masonary brickwork concrete & plaster!

so if ref. method c it could be supplied on a 40A MCB then.

 

[Deleted member 26818]

It's not really a problem I have to deal with very often.
Usually when I tell my customers what is required, they accept it and that's that.
Occasionally I get a difficult one, and then I just do it as they request, as long as it's safe.
Then if there's any problems. I just say 'I told you so'.
In your situation, I would explain that the cable and the MCB require uprating, as the shower has a higher rating
I would then explain that if I don't replace the cable, I cannot uprate the MCB, and there is a possibility that the MCB will trip if the shower is used for too long.
Note the departure on the MWC, job done.
In a couple of months time, there will be a very good possibillity that they will be on the blower begging for you to come and replace the cable and the MCB.
More work, more money.

 

[PC Electrics]

I was taught that cable buried directly into standard masonary and plaster is method C. However I've just looked at table 4A2 and it makes mention of cables buried in a thermally insulating wall, but not the more common occurance of cables buried in plaster. As this method is extremely common isn't it odd that 7671 doesn't cover it?

Assuming I was taught correctly and the 6mm cable is clipped direct or buried in plaster or behind normal tiles, then its ccc is 47A and so a 9.5kW shower is fine on this cable with a 40A mcb.

If the cable passes through a loft and you have methods 100 or 101, then that is different. In this instance I would look to re-route this section of cable above the insulation layer and use a 4 inch pipe to maintain an air gap around the cable where it must pass through the insulation.

 

[telectrix]

bearing in mind the safety factors biult in to the rated ccc in BS7671, i would have no hesitation in rating 6mm in a nmasonry wall at 40 - 45A. and protect with a 40A type B MCB.

 

[Bubblecraft]

Thanks for all your thoughts on this guys


Sent from my iPad using Tapatalk - Couple a' Tools