When we moved into our flat last year there was a very old electric shower which nevertheless worked okay. It had its own electricity supply - you had to flick a switch outside the bathroom (near the fuse box for the whole flat) to turn on the heat. A few weeks after we started using the shower, it basically exploded - smoke came out and it stopped working. We would like to install a new shower, but have a question: would we be able simply to connect a new electric shower to the electricity supply that fed the old one, or might the problem with the old one have damaged the supply? We don't want to waste our money buying a new shower and getting an electrician/plumber out only to find that the electricity supply to the shower is damaged and won't work. Any advice would be very much appreciated :-)
This is Dangerous Electrical Work, all of which must now be signed off in blood by Tony Blair personally. You can either pay a vastly overcharging sparkie to ignore you for 6 months, or join the rest of us in the criminal classes and sort it yourself. (Search for "Part P")
It won't have "damaged anything", within the bounds of reasonable probablility. But you don't know how competent the original installation was. Many of these were badly bodged, although the presence of an isolator switch suggests that yours was probably OK.
You should _definitely_ check the capacity of the old circuit, particularly by looking at the size of cable it was installed with. Modern instant showers have tended to grow in power, so a legitimate circuit for an old shower might either not be adequate for your new one, or might constrain the size you can fit.
NB - Despite rumours by cowboys, the kilowatt hasn't shrunk over the years. If a 6kW shower was enough for you before, it'll still be enough for you today. Modern showers might well offer 8kW or more, but that's so they can provide more water, not because they "use more power these days" to give you the same shower.
The original circuit was probably supplied by a separate fuseway in the consumer unit. Modern practice would be to fit a 30mA RCD (earth leakage breaker) to a shower circuit. _Even_if_ the CU already has a 100mA RCD fitted to protect the rings. It's worthwhile fitting such an RCD, if there wasn't one already.
Get yourself a good DIY manual, a copy of the electrician's on-site guide (electrical wholesalers, or Amazon), a TLC catalogue and start reading uk.d-i-y. Or else get a sparkie to look at it. But don't just hang a new shower unit onto the old pipe and hope.
Associated tack: Is there any way to determine what the rating of an old MIRA shower is? I'll open it up this weekend to have a gander as my mum's is failing. My dad will have wired it up originally and he tended to over specify the wiring.
It's very unlikely the wiring is damaged. Apart from possibly at the connection to the shower - if this had become loose and overheated. But this should be very obvious by inspection. And with a bit of luck there will be sufficient slack to pull through and make good, or even just re-sleeve.
However, you need to make sure the new unit takes the same current as the old. Showers aren't all the same, power consumption wise, and unfortunately the more powerful ones require larger cable.
Fair enough for a like-for-like replacement, but what happens if a 6kW is replaced by a 9kW and the supply needs upgrading ? What happens if the supply is OK, but you decide it's a good time to fit an RCD too ?
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