maximum shower size ?

[james beckford]

bit of help please guys,

I have a CU with a 40 amp breaker feeding the electric shower, its on 10mm cable.

My calculation is 8500W div by 230V = 36.9A, therefore 8.5 Kw is the largest shower but mate says 40A with 10mm is fine for 10.5Kw.

Does an electric shower class as water heater therefore no diversity allowed or have i missed a trick somewhere ?

Also the 10mm t+e is running in conduit vertically through a bedroom cupboard alongside the 1.5mm 3core interlink cable for the smoke detectors, the installation method closest to it is B but this is not listed in the current capacity tables as a calculated way of running T+E

Many thanks in advance for my no doubt being incredibly dense tonight

 

[vjsmarwick]

My guess its not in the tables because there is no reason for installing t&e in conduit so there for the writers of the regs make no allowance for this to be done they think they know everything but in fact I would guess most of them would not know which end of the screwdriver to hold and them that have would have done so just after electricity was invented and have little knowledge of the construction of what we fit in these days. As for size of shower on your 10mm cable I would say it depends on length of run also and if you follow all the regs for your 10.5kw shower then I guess you will be looking for a 25mm cable I would go as high as a 9.5kw shower any higher than this and its a waste anyway it will heat the water hotter than you can stand and enough pressure and you will be with in the limits as long as your not living in a palace and running one end to the other

 

[SirKit Breaker]

10mm cable protected by a 40a breaker is fine. the breaker is there to protect the cable only, not the appliance. The appliance (shower) needs protecting in accordance with the manufacturers instructions, if that is not known then calculate by the method you have shown, and go down not up with your protective device rating. Due to the trip curves of a B type, then a 32a for the shower would be ok at 40a anyway for the time that the shower will be on for.

Cheers..........Howard

 

[james beckford]

Cheers for that guys, i thought 10.5 was a no go. Dont want to downrate breaker as already in the board and by my calcs is fine for the circuit.

Cable is in conduit as already installed by previous homeowner as a DIY job instead of pulling up thru cavity wall with rest of wiring.

I added the interlink cable as the easiest way of routing it from hallway to landing.

8.5Kw it is

 

[Guest55]

then use the nearest equivolent current table which is 4D2A , pvc multi core , ref B , which is 52 amps for 10mm , thus In can be 50amps.
50a x 230v = 11500w

therefore the biggest shower you can fit on 10mm cable is 11.5kw so long as there are no other de-rating factors and you fit a bigger mcb.

 

[Lucas]

I've put a 10.5kW shower on a 32A wired in 6mm and i've never had a problem with it.

 

[mydigitalhome]

I like a shower as big as possible 1200 x 900 minimum with lots of power. Pet hate is having controls in the flow of show head really don't like getting my arm wet with cold water prior to having a shower. I like making money from shower installs but would only consider having a plumbed in shower with loads of hot water and lots of pressure. I also like multi point spray positions with oversized fixed shower head. One day the electric versions will catch up and provide a great shower.

 

[MDJ]

I've put a 10.5kW shower on a 32A wired in 6mm and i've never had a problem with it.

Is the Breaker working properly?

 

[Farmelectrics]

10500 divided by 230 = 45.6a

 

[vjsmarwick]

I have seen a 40A mcb handle 125 A so just because it works does not mean its right but what ever floats your boat