6mm on a shower circuit

[macbac]

Been called to have a look at a shower which is being replaced.

The shower which is going in is an 8.5kw but the cable goin to the shower is currently a 6mm2 t+e run in trunking but protected by a 40 amp rcbo, which according to the on regs is not allowed as running it in this way it will only take 38 amps.

So should i go ahead and change the cable or just down size the rcbo, the cable run is about 4/5m long.

 

[bongos]

Is the exisitng shower being replaced with another 8.5kW? If they want one much more powerful then the cable would quite possibly need replacing with 10mm² anyway.

But as you say the only other option is to replace the MCB with a 32A variety.

 

[macbac]

The shower that is going in is also going to be a 8.5kw shower, the only problem i can see with changing the rcbo to a 32 amp is that on full power the shower will draw nearly 37 amp and so i doubt the 32 amp rcbo will take this.

 

[bongos]

Absolutely. Unfortunately there isn't a 38A MCB.

What length of the 4-5m cable run is actually the trunking anyway?

 

[macbac]

Pretty much all of it i'm afraid, i no the cable should be upgraded but if i was to change the rcbo for a 32 what would be they likely hood of this tripping (i.e how often does the shower actually draw 38 amps and will a 32 amp rcbo take much more than 32 amps?)

 

[bongos]

if i was to change the rcbo for a 32 what would be they likely hood of this tripping (i.e how often does the shower actually draw 38 amps and will a 32 amp rcbo take much more than 32 amps?)

Have a look at page 249 in the 17th edition. It looks like a B32 RBCO would hold ~46A indefinately...

Not the right way to install though because the design current (Ib) is higher than the protective device rating (In). Don't know how much you personally charge to run a new length of 10mm² t+e but how much would a 32A RCBO replacemnt cost for the CU anyway? Might go part of the way towards a cable upgrade?

Have you spoken to the customer about this?

 

[macbac]

if i was to change the rcbo for a 32 what would be they likely hood of this tripping (i.e how often does the shower actually draw 38 amps and will a 32 amp rcbo take much more than 32 amps?)

Have a look at page 249 in the 17th edition. It looks like a B32 RBCO would hold ~46A indefinately...

Not the right way to install though because the design current (Ib) is higher than the protective device rating (In). Don't know how much you personally charge to run a new length of 10mm² t+e but how much would a 32A RCBO replacemnt cost for the CU anyway? Might go part of the way towards a cable upgrade?

Have you spoken to the customer about this?

I see what your saying and thanks for your help think the customer is going to have to bite the bullet and have the cable changed. Thanks again.