Second Electric Shower

[JHCiarrai]

I have an existing electric shower (Triton T90i) in the bathroom. I'm in the process of converting my attic and am planning on having an en-suite up there with another Triton T90i in it.

What's the best solution for preventing any possible overload if both showers were switched on at the same time?

 

[securespark]

Try a search for this - it has been covered before.

 

[Steve]

You can buy changeover switches, but in reality, your service fuse is unlikely to blow if both are on at the same time. (ave. 45A each. 90A altogether. if you have a 100A service fuse, you still have 10A to play with, even if you draw 100A it is unlikely to blow for a long time). Whether the supplying cable is up to this, however, is another matter. Best ask your electricity supplier if the supply is up to this sort of load before you start having them both on at the same time. Why not have a power shower instead? (how and cold feed, pumped)

 

[mapj1]

If you draw a hundred amps through a 100A fuse it must NEVER blow - that is what the rating means. It is allowed to feel warm however, and a typical service fuse swaets off about 5 watts at full load. It blows at substantially more, in a time that depends on the degree of the overload. So 200A for a few mins, 150A for perhaps 20 mins etc. See the curves of fuse characteristics here for the sort of thing I'm waffling about.
http://www.bussmann.co.uk/images/Data Sheets/BS1361/LR85.pdf
BS 1361 and the older BS88 are the common service fuse standards in use.

 

[felix]

It has been covered before because I can remember joining in. The problem with a changeover switch is one of control. By this I mean who gets hot water on demand and which poor mug is left in the cold without warning!

The discussion last time got bogged down in attempts to describe quite complex relay logic circuits without the aid of diagrams. It can be done but would you want to do it. Some day you will move house and whoever inherits your diabolically ingenious switching arrangement won't have a clue if it goes wrong.

 

[securespark]

All this talk of 100A fuses assumes you have one. It may be as low as 40A.....

 

[JHCiarrai]

I did a search on previous topics and eventually found a discussion on the same question, thanks! The changeover switch idea seems to fall down when it comes to coping with power cuts, etc. so it's probably best avoided.

I know in my circumstances that both showers are very unlikely to be used at the same time, but even if it's unlikely, it's still possible and I'd like it to be safe! I can never see myself and a drinking buddy that I dragged home the night before attempting to shower away our hangovers while the missus makes tea and fries up the sausages & rashers for us downstairs, but you never know......

From what mapj1 says, it should be OK to have both showers, each running back to its own MCB on the consumer unit (via isolator switches & shower CUs) provided the supply fuse is 100 amp? I know the shower CUs might be overkill, but I tend to be very cautious when electricity and water are involved!

 

[Steve]

Would splitting the meter tails be a good idea here? Possibly one set going to the existing CU and the other set going to a new 4-way CU with a 100A RCD incomer and 2 50A MCBs. Just to alleviate the strain on the house CU's incomer, should everything come on at once.