Electric shower with no fused protection?!

[4StringBass]

Hello forum world This is my first post but I've gleamed a lot of info from here in the past.

My sister rang me up to say her electric shower wasn't working. It appeared to have power, but wouldn't switch on. I knocked off the entire power to the house as the fuse box isn't marked as what's what, and found out it was the water pressure sensor.

Anyhow, after I'd figured that out and ordered the new part, it struck me that there are only three 30A breakers in the fuse box (old Wylex thing with old style fuses). Without pulling them, that sounds like hob/oven, upstairs sockets and downstairs sockets. There is not a larger fuse in the box, and as the shower is rated at 9.5-10.34kW, surely using I=P/V, that's 41.3 - 44.96A.

Without opening the box, it sounds like it's been wired directly to the commons and as such has zero protection. Would that be a reasonable assumption? I haven't got round to fitting the replacement part so it still doesn't work, so it's safe for now.

Any help appreciated.

Cheers

 

[flyingsparks]

More likely it's one of the 30A fuses and the sockets are perhaps all on one circuit. Why don't you pull them out one at a time and see if the shower goes off? 30A fuse wont blow straight away even tho it is allowing 40 ish amps through.

 

[ekmdgrf]

When I did the calculation I got 39.5833A - 43.0833A.

I don't think it's safe to assume anything. The only way to know is to go look. Might be a good idea, if you can to start tracing the cable and see where it goes. You could also try isolating the circuits and see if the shower goes off. Probably quicker to do the old binary chop (pull half, see if it works, put half of the half back or remove another half). Maybe one of those 30A fuses has 40A or 50A fuse wire or more likely, a rusty nail in it.

Likely what you will find is:

Something you weren't expecting
Something you wish you hadn't

 

[Risteard]

I haven't got round to fitting the replacement part so it still doesn't work, so it's safe for now.

Aside from the fact that it's far more likely that all of the sockets are on the one circuit and that the shower is utilising the other 30A fuse, the fact that there is no shower being used wouldn't make it "safe for now" if indeed the cable is unprotected, as the cable would still be unprotected and presumably still energised.

 

[4StringBass]

Thanks for the replies so far

The pull switch in the bathroom has been pulled so the shower is currently isolated, but it won't be getting switched back on until the issue is resolved.

ekmdgrf - I used to 230V, looks like you've used 240V. Anyhow, a third higher than the normal rating of the breaker so something's wrong

 

[ricicle]

Sort it out sooner rather than later as those Wylex boxes have a nasty habit of catching fire with loads greater than 30A !

(Search RF's photos for some evidence)

 

[4StringBass]

Went up and did some fuse pulling. She needs a sparky in to change the board ASAP!

Fuse 1 30A: Half the kitchen, some of the living room, rest of the downstairs
Fuse 2 30A: Upstairs, rest of kitchen and living room
Fuse 3 5A: Lights
Fuse 4 5A: Lights
Fuse 5 30A: Shower - on its own as far as I can tell but still not 40A
Fuse 6: 15A: Oven and ceramic hob!

Time for a pro!

 

[ekmdgrf]

To be fair, having an underrated fuse isn't really an issue if the installation is working. I don't have the graphs in front of me but even a B curve MCB will take a long time to pop under slight overload conditions (up to an hour), fuses will take far more stick. A 15 minute shower probably doesn't quite push it over the edge.

 

[ericmark]

Now I also have two old Wylex boxes with fuses changed for MCB's and feed from two RCD's but this is unusual in the main Wylex box means no RCD so to make safe really does need a upgrade.

 

[EFLImpudence]

When I did the calculation I got 39.5833A - 43.0833A.

You're only half right then.

The 9.5kW will be the equivalent rating at 230V - 41.3A

 

[Risteard]

The pull switch in the bathroom has been pulled so the shower is currently isolated, but it won't be getting switched back on until the issue is resolved.

Ignoring the fact that (as I suspected) the shower is protected by a 30A fuse, if it hadn't been protected then the cable would still have been unsafe even with the pullcord open as under fault conditions (say the cable gets damaged) what would happen?

 

[stillp]

What size is the cable?

 

[conny]

Pulling the pull cord is not an effective means of isolation.
The fuse must be removed and stored securely away from the CU to prevent someone re-fitting it in error.

 

[ekmdgrf]

Pulling the pull cord is not an effective means of isolation.
The fuse must be removed and stored securely away from the CU to prevent someone re-fitting it in error.

Pulling the fuse is not a terribly effective form of isolation either, since it only breaks the line conductor...

 

[winston1]

When I did the calculation I got 39.5833A - 43.0833A.

You're only half right then.

The 9.5kW will be the equivalent rating at 230V - 41.3A

If it is an old shower the 9.5kW will be the rating at 240V.