DIY Doctor

Two Electric Showers in the House Tripping MCB - Advice Needed

Postby jmdunman » Wed Dec 30, 2015 3:39 pm

I would like to add a second electric shower as I only have an old Radiant combi boiler and the distance of the second shower would result in a long delay in getting hot water to a thermostatic shower. I suspect that the original electric shower was installed before the combi boiler. I've been told (by a plumber) that a second electric shower wouldn't be possible as the MCBs would trip out. If true can anything be done to ensure that wouldn't happen?
Thanks in advance for any advice/suggestions.

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Simply Build It

Postby ericmark » Thu Dec 31, 2015 3:54 pm

Supply to a house can be 60 ~ 100 amp that 13.8kW to 23kW I assume you want to run both together so that's the first hurdle to find out supply size. All main fuse holders say 100A and they are sealed so you can't see fuse size you need the ask the supplier.

Assuming it is 100 then you can't use same cables as in the main largest MCB you can get is 45A which will only feed one shower.

Today all new wiring buried in the wall needs RCD protection and so does the shower so you need to look at consumer unit and work out if it can take the second circuit with RCD protection. Rules have changed so if you want a new consumer unit it must be metal so likely quite expensive.

I will agree with some combi boilers there is a problem with a shower, where there is a hot water store so you get instant hot water the shower uses too much water for this to last so on turning on the shower it starts cold, goes hot, returns to cold then gets hot again. However the output is so much more it is really worth the wait to get a proper shower rather than washing under a trickle of water the electric units deliver.

To have two showers so you have flexibility as to where to shower is OK as long as both not used together. But two showers used together is not really an option.
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