Supply to a one way CU for shower.. please help

[LlandrilloSpark]

Supply to a one way CU for shower.. please help Hi guys I need some help if you would, I feel i should know this but I dont.

New shower going in, there is no provision/circuit existing for 9.5kW shower that is going to be installed.

I'm going to use a 30mA RCD + 45A MCB one way unit

Ive done the calcs, 6mm T&E should carry the current fine as its clipped direct in a loft with no insulation and not grouped, Vold drop will be 6v approx over 20m

My question is where do i feed the one way CU from?, do i use some of the 6mm and connect it to a protective device in the existing BS 3036 rewirable board?, there are only 30A max in there and although ive seen shared 3036's before, is it right?, or can i go into the outgoing side of the main switch?, im just wondering what will be protecting those 6mm tails?

 

[Yooj]

Hi,

What table in the regs did you base your calculation on...was it table 4D2A column 6?

How will the cable get into the loft...will it be clipped direct also, or within the fabric of the building?

I personally do not like the outgoing side of main switches...and I would personally go for a henley block solution, with the tails coming into the henley block, and then splitting out to the existing CCU and also to the new CCU.

What rating is the supply head fuse, and can it take the additional load of the shower?

Yooj

 

[Mark.W]

I don't tend to bother with 6mm cable for shower circuits, I go straight for 10mm.

Agree with Yooj on the Henley bock option.

Mark

 

[maddog]

What about a main isolating switch before the Henly block to Isolate both CU's. Is this a requirement or would you consider the service head fuse as the Isolation?

 

[Mark.W]

You could install an isolator to isolate both CU's but it is not a requirement!

 

[LlandrilloSpark]

Thanks guys

Its a job for a friend who lives 55 miles away, so ive having pics of the board sent to me along with info like the size of the main switch and the total load of the existing board, the make of the board and breakers, plus the circuit approx length.

Then i will know what i need, the Henley block is a cert if i cant get a breaker for the board or the load is to much already.

R.E the cable size, it does, like many showers say use 10mm on the box, but the Ib of the shower is 41.5Amps so all clipped direct and no insulation or grouping, 6mm should be enough by 5 Amps, although it will be in the wall for 1m where it drops from the loft to the shower.

 

[Mark.W]

I'd still use 10mm cable because if your mate wants to put in a bigger shower, he may need to upgrade the cable again. Best to do it all at once, makes life easier. If the box says use 10mm then use 10mm matey!

Mark

 

[Yooj]

I'd have to agree with Mark on this, in that the manufacturer has stipulated that 10mm2 cable should be used for the shower, and the difference between the two in terms of cost is only around a tenner.

Yooj

 

[monkeyelectric]

I always use 10mm for showers too, it makes it future proof incase they want a bigger shower, may also be an oppurtunity to upgrade the c/u if he wants then no need for a c/u just for the shower