Shower fitting

[jezhowell]

Hi,

I'm sorry if this repeats a topic that I have been reading about shower installation, but my situation is a little different...

I'm thinking of getting a shower (have not made any purchases yet but I'm thinking 0f a 7.5-8.5 kW unit).

I'm a little concerned about load on the fuse boards that are fitted in my house. I have two crabtree boards.

The top one has in it the master trip (rated 100A). To the right of this is a 63A RCCB 100mA trip with three more trips (32A for the ringmain, 6A for a bathroom wall mounted heater (unused) and 20A for the ringmain to my conservatory). Unless I'm way wide of the mark, this box has a potential load of 52A at any given time (as the 6A trip is never used).

The bottom fuse board has a 63A RCCB with another 3 trips (32A for the cooker, 16A for the immersion heater and 6A for the lighting circuit). Again unless I'm way off, this box has a potential load of 54A at any given time.

My concern is that even though I have spare slots for more trips in either board, placing an extra load of 30-50A (depending on the wattage of the new shower unit) will cause either the main (100A) switch or the relevant 63A RCCB to trip as soon as I try to use it. I understand that the load on each board is likely to be a lot less than the fuse rating at any given time but it still seems a bit on the close side to me.

I'm wondering whether I need another box? Can anyone advise me at all?

 

[Steve]

Do you constantly draw 32A on your ring mains? Are all your lights constantly on and drawing the full 6Amps? Work out typical load on your ring main - things such as TVs computers, table lamps, your typical draw may only be 5A. You probably have a lot more to play with than you think. And instantly putting 50 extra amps on a 100A isolator will not make it trip, unless theres already 60-70 amps already on it (total 110-120)

Dont know why you have 2 fuse boards. If you do get a new one, just get one and have them all put in there. Its not uncommon to find 2 ring mains and a shower on one 63A RCCB (potential total 114A) but because the rings dont pull 32A all the time, there is no problem with this. I think its called diversity.

 

[jezhowell]

Thanks for the great advice - I thought that I would probably be OK - I live in a smallish 2 bedroom bungalow and we don't draw too much power at any one time.

As for the two fuse board deal - I have no idea why whoever installed them did it like that.