consumer unit capacity

[rumpole]

I want to install an electric shower, there is a spare way for the radial circuit in the consumer unit and I understand I need a 45 amp fuse (cartridge). However on the front of the consumer unit it says total load not to exceed 100 amps. There are already two 30 amp fuses, two 15 amp fuses and two 5 amp fuses for circuits already connected to the consumer unit. Does this mean I can't put a 45 amp fuse cartridge and circuit in or does it mean any one circuit cannot exceed 100 amps?

Does anyone have any suggestions?

 

[MANDATE]

It means the total load should not exceed 100 amps, not what fuses you have got.
A 8.5 kw shower draws 35 amp but will have a fuse of 40 amp
It's the same with all your circuits the fuse will be higher than the max current,( well not quite a ring main circuit will have many socket outlets but you don't use them all at once and a fuse ensures this circuit is not over loaded) the problem arises when you have the oven on plus four rings ,all the lights on in the house, the wifes ironing ,the toasters on ,3 TVs on and you decide to have a shower. You could calculate all these loads and I doubt if they total 100, but if they did is it ever likely to happen ? All circuits operating at full capacity. answer No!
Just don't have shower on christmas day
Each circuit comes from the same source in the fusebox and if you had 100 amps per circuit, it would be possible to have 800 amps in you 8 way fusebox, don't forget your main suppliers fuse is approx 100 amps

 

[rumpole]

Thanks mandate, I thought adding up the fuses didnt seem right but better safe than sorry!

 

[ban-all-sheds]

If it's not too late..

Install the fattest cable that you can get into the connectors in your CU & shower. You may think that you only need 6mm to feed an 8K5W shower, and (derating calculations aside) you do.

But showers are getting bigger all the time, and when you come to replace yours (by which time you'll have decided you want a hotter one) you'll be glad that your wiring can cope. You can already get showers which consume 10K5W (and, for all I know, more). Again, ignoring derating, 10mm cable is good for 53A, 12K75W, which is probably enough, but then Bill Gates once thought that 640KB was enough memory for a PC.....

At 70A, 16mm may be a step too far, and even if it fits, it'll be bloody difficult to pull, but if it's practicable, why not?