Shower Fuse Size

[loopy66]

We have had a shower for a long while, like most clean people in this modern day. An electrician replaced our old one about 2 years ago to a Triton Sambada. All has been fine until last week the fuse blew. We are still clean, although the shower has not worked for 1 week it blew the day we went on holiday so, first day back. I promise I am not creating this thread with a smelly ass.

Before replacing the fuse I checked inside the shower to ensure there were no obvious signs of something happening, which there aren't but I need to ask a quick question before I go ahead and make it live again.

I am on an old Wylex fuse box, the shower on a 30amp fuse then onto an external box that looks like a 40amp breaker and a 63A / 30mA RCD. Inside the shower the label says the power rating is 7.8 - 8.5 kw. I have been reading around and it seems to look like I can just replace the fuse but there are little bits here and there that make me question, is this set up generally ok?

 

[333rocky333]

A 30 amp fuse is unlikely to blow for no reason, are you sure its blown, if so usually looking at the fuse carrier when removed it shows an indication of the cause.
Replacing 30amp wylex fuses can be hazourdous so be carefull

 

[AndyPRK]

Make sure main switch is off when refitting fuse

 

[loopy66]

The fuse is one of these : https://www.screwfix.com/p/wylex-sfcfl30-30a-cartridge-fuse/42738 ... a 30A cartridge type.

I checked it on a multimeter and it's dead.

There is a bit signs of heat on the fuse holder and the box itself where the fuse plugs in but I cannot say whether it's only just happened or if it's been there forever, I have never looked at it that close before.

 

[EFLImpudence]

I am on an old Wylex fuse box, the shower on a 30amp fuse then onto an external box that looks like a 40amp breaker and a 63A / 30mA RCD.

That would be a silly way to do it. A 40A breaker wired through a 30A fuse.

Inside the shower the label says the power rating is 7.8 - 8.5 kw.

8.5kW @ 240V is 35.5A. If your voltage is a bit higher then it would be more Amps.
Too much for a 30A fuse, but it would take a while to blow.

I have been reading around and it seems to look like I can just replace the fuse

You can. If it goes again, then...

but there are little bits here and there that make me question, is this set up generally ok?

...no it is pointless.

Either the electrician made a mistake - forgot to move the wire - or he doesn't know what he is doing.

 

[333rocky333]

The fuse is one of these : https://www.screwfix.com/p/wylex-sfcfl30-30a-cartridge-fuse/42738 ... a 30A cartridge type.

Ok. I was assuming a Rewirable fuse wire, so you wont see so much looking at it, without breaking it open and looking at the wire link.

Though if its outer shell is discoulered in anyway, that could be a sign of it being overloaded for the 2 years use.
At a quess id say the extra box was used mainly for its RCD function, it just so happened to have a Mcb in it and the installer thought leaving it in was the easiest option/
Did the 40a mcb go off at any time, if not, its possible the shower load has just worn down the fuse

 

[AndyPRK]

Some wylex can’t take over 30A fuse.

Just replace it and it will hopefully last a year.

Buy a couple.

Maybe a new fuse box in order soon or do you rent

 

[loopy66]

Sometimes a picture can speak 1000 words. Attached are the external MCB/RCD and the main fuse box (the missing slot is the 30A fuse I have taken out that was for the shower).

The MCB nor RCD tripped on this circuit, just the fuse blew. The pic of the two fuses shows the brand new one I bought today on the left and the old one of the right... looks older and dirtier but I don't know if that just happens with age or with heat/wear.

Based on the replies so far, I am thinking I can replace the fuse and put this down to wear over time of the fuse but overall, the set up needs an update?

 

[flameport]

Based on the replies so far, I am thinking I can replace the fuse and put this down to wear over time of the fuse but overall, the set up needs an update?

You can replace the fuse and it will very likely work for a length of time, possibly even years.

However the fuse is being run at more than 30A, that fusebox isn't designed for anything over 30A, and the whole lot is well past the time it should have been replaced.
No RCD protection on the other circuits either.

 

[333rocky333]

Now you have the new fuse, you could crack the old one open carefully, squeeze it with pliers, be carefull sand may come out of it, looking at the fusewire inside may help explain whats going on, though it does seem like long term overloading, so the wires likely discouloured, if it had been a major problem it would likely have little round balls of copper inside

 

[loopy66]

I had to put the fuse in a vice to split it, pliers only made a scratch.

This is a picture of what I found inside, apart from white sandy stuff which all spilled out.

 

[Harry Bloomfield]

I had to put the fuse in a vice to split it, pliers only made a scratch.

This is a picture of what I found inside, apart from white sandy stuff which all spilled out.

Difficult to be sure, but that fuse looks as if it has been blown by fault current, rather than an overload. It possibly suggests the shower itself has a dead short internally.

not connected to your immediate problems, but who ever wired that is a numpty. You do not run a B40 MCB, from a 30amp supply, it is just a complete nonsense.

 

[AndyPRK]

now we know (or think) you have an MCB in line.

Just get the new fuse fitted and hopefully you have have a nice shower

As said, could do with a new consumer unit in the next 3 months or so

 

[Harry Bloomfield]

now we know (or think) you have an MCB in line.

Perhaps the OP could confirm that point, once he has fitted a replacement fuse?

 

[loopy66]

I put it all back today, with new 30A fuse and the shower is working. With it running I pressed the test switch for the external RCD and that worked. I also flipped the 40A MCB and that cut the power.

It does all need an update for sure.