8.5 KW shower on 40amp mcb and 6mm??

40A is too high for 6mm, should be 32A. Also the length of the cable run has a big impact on whether 6mm is a big enough cable.....! Its generally ok but can struggle for long runs.

14th

 

sorry to disagree 14th but the 40A mcb will be fine as likely as not will also be the cable

 

An 8.5kW shower draws a current of 35.5A.

So, you need an MCB higher than this value. Next size up is 40A. So okay there.

You now need a cable with a higher rating than 40A. BS7671 table 4D2A under ref method C (clipped direct) shows the smallest cable with a rating over 40A is 6mm with a rating of 46A. Table 4D5A gives 6mm flat T&E clipped direct a rating of 47A. So okay there.

So, all okay then!

If at any point the cable needs to pass through the insulation layer in a loft, make sure there is an air space around the cable. I use 100mm waste pipe for this purpose, but if the cable is already in place you could build a plasterboard or chipboard box around the cable.

 

Clipped direct..the cables well in..cripes its showing 4mm @ 12 meters and over @ 8500 Watts..cable on the TLC site shows 40 Amps..

No probs from what I can see..however I am not a sparky so what I say doesn't really count.

 

Do you use Steradent? or do you use a supermarket own brand denture steeper to steep ure gnashers Lucia?

 

Have I missed something here?! I have page 282 table 4D5 [can't find a 5A]. The highest for 6mm t/e is 47 for clipped direct, in my experience extremely unlikely. Much more to be in a wall and or under loft insulation so 27-34 amps.And thats disregarding volt drop.
Agree cable length is rarely a problem but I still think that to protect the cable 32A is better and they rarely trip until that is exceeded by some margin. I think that that is the problem with a 40A mcb it could be running at way over without tripping the mcb.
IMHO

14th

 

The current is limited to the shower rating, in this case around 37 amps.

 

Do you use Steradent? or do you use a supermarket own
brand denture steeper to steep ure gnashers Lucia?


I just use wire wool every fortnight, without fail, JP.

I do have Steradent in the bathroom cabinet, as a stand-by, just in case I'm invited out to dinner and I need that extra sparkle.......



Lucia x

 

Lokkars, aren't we supposed to be protecting the cable....?

14th

 

In this case the mcb will provide short circuit protection to the cable, providing overload protection for the cable by using an mcb isn't required. The reason being that as the load is fixed then an overload is very unlikely to happen. This is all above board, it's a similar situation to the use of light guage flex in pendants, the flexes are often rated less than the 6A mcb

 

Duncan, I can see you point here. You would rather fit a 32A mcb to carry 37A in the knowledge that the mcb would take a few weeks to trip. But we're not supposed to design a circuit where the load exceeds the rating of the mcb, are we?

A 6mm cable will be protected by a 40A mcb, whatever the circumstances - regardless of this loft insulation nonsensense. This shower is a dedicated fixed load. It cannot be added to by other loads. There's only two considerations here: The design current and the short-circuit fault current.


Lucia x

 

Good evening, Lockheart. I seem to have duplicated your reply....


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Good evening Lucia, yes indeed but with that Italian flair of your'un

 

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I cannot beleive how ridiculously long this post has become! 8.5Kw shower, 6mm t/e, 40 amp breaker, no problem at all!

 

Steady on Sen! This is only page 2, dear.......



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