8.5kw Shower on a 6.0mm cable

[Sb8389]

Hi guys,
want your opinion on a issue I have found while changing a consumer unit today.
I came across the shower wired in 6.0mm on a 32amp MCB (8.5KW). I know this will draw just over 35amps and could do with being upgraded to a 40amp MCB, but checking the install of the cable it is going through cavity full of insulation and then through the loft covered in insulation.
i know that the protective device will be overloaded but would you say that this would be a risk to leave on a 32amp MCB and would you be able to tell me how long it would take for the MCB to trip at 35amps as I don't have a regs book to hand to check the time current curve graph.
if you need any more info let us know.

thanks.

 

[Marvo]

8.5KW is about 37A which is approx 1.16 times the MCB rated current. I don't have a chart but the trip time will be hours and depending on the ambient temperature it might never trip so you're looking at a lot longer than it takes to have a shower.

 

[tomspark93]

As marvo said. I'd just point it out to the customer that it potentially could trip and the reason behind it and then just make a note on the certificate.

 

[Sb8389]

Thanks marvo,
It's just my boss is saying it is non compliant as the In is greater than Ib and is therefore a risk and can't be left in place with us doing a board change and that I would need to rewire it in 10mm if they want to keep the shower, I didn't agree with him so wanted an experts opinion on the scenario.

 

[davesparks]

It is non compliant because the regulations require circuits to be designed such that they are not subject to small overloads.

And 35.4 is greater than 32

 

[Simonslimline]

Thanks marvo,
It's just my boss is saying it is non compliant as the In is greater than Ib and is therefore a risk and can't be left in place with us doing a board change and that I would need to rewire it in 10mm if they want to keep the shower, I didn't agree with him so wanted an experts opinion on the scenario.

My 8.5Kw shower has been running on a B32 60898 since i moved in to my flat 9 years ago and has not tripped once while taking a shower.

Just a thought.

 

[Sb8389]

Surely I could just write this in the departures on the certificate as I have not installed the circuit. Surely It's not going to be a risk like my boss is making out and like marvo says the chances of it tripping are very slim.

 

[Marvo]

It is non compliant because the regulations require circuits to be designed such that they are not subject to small overloads.

And 35.4 is greater than 32

Would it be classed as overload if the cable is rated to carry the current even though the mcb is rated marginally less?

Not saying that this is the case here, I'd guess the cable is genuinely overloaded if it's buried under insulation.

 

[davesparks]

Would it be classed as overload if the cable is rated to carry the current even though the mcb is rated marginally less?

Not saying that this is the case here, I'd guess the cable is genuinely overloaded if it's buried under insulation.

Is a 32A mcb with 35A flowing through it subject to a small overload?

 

[Deleted member 78588]

I'd say possibly not because the MCB is rated to 10 thousand Amps

 

[davesparks]

My 8.5Kw shower has been running on a B32 60898 since i moved in to my flat 9 years ago and has not tripped once while taking a shower.

Just a thought.

Remind me which regulation number it is which says that something which has worked for 9 years is automatically considered correct and other regulations can be ignored?

 

[davesparks]

I'd say possibly not because the MCB is rated to 10 thousand Amps

No it's not, it's rated to break a fault current of up to 10kA, it's rated for an operating current of 32A

 

[Marvo]

I'd say possibly not because the MCB is rated to 10 thousand Amps

Oops, I was busy winding up the fluffy moderator in the trainee forum and posted from the wrong account.

 

[Sb8389]

Remind me which regulation number it is which says that something which has worked for 9 years is automatically considered correct and other regulations can be ignored?

Hi davesparks,
would you say the circuit needs rewiring then,I know the circuit has being designed incorrectly but does it mean it's a risk or just not compliant to regs and can be just noted on cert.

 

[Marvo]

No it's not, it's rated to break a fault current of up to 10kA, it's rated for an operating current of 32A

It's also rated for an operating current of 35A for a specific duration of time. I guess our definition of 'overload' might be differing slightly.