Shower is tripping the mcb

[RADabz]

Hi all,

I've been living in my new house now for about a year and the shower tripped out the other morning for no apparent reason while the other half was in it.

My first thought was that she'd stopped the flow of water somehow but it appears she hasn't as it keeps tripping if on full power for about 5 - 7mins.

I took the front off of the shower and nothing in their looks even slightly darkened, in fact it looks like it could be brand new it's that clean.

I replaced the 45a pull cord in the roof but still after running at full power for 5mins it blows. it does however work fine at economy mode but the water flow is crap.

I then went and checked the MCB right after it tripped and it was very hot, it's in a separate box away from the main fuses and has it's own on/off switch. I'm kinda hoping it's busted but I'm also worried that it's getting hot because it's drawing too much power.

It's one of these and I've ordered a replacement which I'm going to try.

http://cgi.ebay.co.uk/ws/eBayISAPI.dll?ViewItem&item=160452828771

All the wiring looks fine and is 10mm copper but with white PVC rather than the normal grey I've seen. It's all earthed as it should be etc.

What do you think my next step should be after replacing the MCB if the fault is still there and more to the point do these things generally fail after a while ?.

Next step I'm thinking is replacing the MCB with something more modern as the tech looks about 6 years old and I'm thinking if I have to go onto ebay to get a replacement then something is way too old.

 

[ban-all-sheds]

What's the rating of the main switch on the box? Those plug-in breakers are often retro fitted to rewirable fuseboards which aren't always designed to take a single load of 45A, so that could explain the overheating.

45A and 10mm² should be fine for a 10+kW shower, so neither should get hot if properly installed.

Loose connections can cause overheating, as can overloading the CU, but then you'd expect to see signs of that on the cable, for it would have to be melting the insulation to create a fault.

 

[RADabz]

Hi,

I should have said the shower is rated 8.5Kw

The box itself has nothing written on it so I was thinking it just holds the MCB itself but I'll check tonight and have a look.

It really does look like the switch on the box just isolates the power to the circuit.

The actual power to the box is from the top of the fuse box and looks like it has been connected straight from the main supply as switching the main off button on the main fuse box does not switch off the shower power.

There was a bit of melting in the 45amp pullcord connection at the live from the source but other than that nothing.

Do you think it might just be the MCB was old and had fried ?

I'm hoping it is as I'm getting married next week and it's 1 less thing I could do with not having to worry about.

 

[LoveRocket]

Take a photo of you consumer unit(s) and uploaded it to here please mate.

 

[RADabz]

I'll do that when I get home from work.

Cheers,

 

[LoveRocket]

And stop surfing the net in work's time!

 

[ban-all-sheds]

I should have said the shower is rated 8.5Kw

35 - 37A.

Something is wrong. I guess maybe it could be an internal fault with the shower but that won't be easy to check.

The box itself has nothing written on it so I was thinking it just holds the MCB itself but I'll check tonight and have a look.

It should have a rating on it somewhere.

The actual power to the box is from the top of the fuse box and looks like it has been connected straight from the main supply as switching the main off button on the main fuse box does not switch off the shower power.

That's could well be wrong.

Not because it doesn't switch it off - you've got the switch on the separate unit for that - but because the terminals in the CU won't be designed to have 2 sets of meter tails going into them. And if they didn't use tails to supply the separate shower unit what did they use? Something large enough to be safely protected by the main service fuse?

There was a bit of melting in the 45amp pullcord connection at the live from the source but other than that nothing.

How far back did you cut the cable before re-fitting it?

Do you think it might just be the MCB was old and had fried ?

Unlikely, as it's only got an 8.5kW shower on it.

I'm hoping it is as I'm getting married next week and it's 1 less thing I could do with not having to worry about.

Get an electrician.

 

[RADabz]

I should have said the shower is rated 8.5Kw

35 - 37A.

Something is wrong. I guess maybe it could be an internal fault with the shower but that won't be easy to check.

There was no sign of any burn out anywhere.

The box itself has nothing written on it so I was thinking it just holds the MCB itself but I'll check tonight and have a look.

It should have a rating on it somewhere.

I'll check.

The actual power to the box is from the top of the fuse box and looks like it has been connected straight from the main supply as switching the main off button on the main fuse box does not switch off the shower power.

That's could well be wrong.

Not because it doesn't switch it off - you've got the switch on the separate unit for that - but because the terminals in the CU won't be designed to have 2 sets of meter tails going into them. And if they didn't use tails to supply the separate shower unit what did they use? Something large enough to be safely protected by the main service fuse?

There are 2 separate multicore connections, I'll upload a picture tonight.

There was a bit of melting in the 45amp pullcord connection at the live from the source but other than that nothing.

How far back did you cut the cable before re-fitting it?

Not that far, infact I just trimmed the ends to display unblackened copper.

Do you think it might just be the MCB was old and had fried ?

Unlikely, as it's only got an 8.5kW shower on it.

That's what I thought.

I'm hoping it is as I'm getting married next week and it's 1 less thing I could do with not having to worry about.

Get an electrician.

My mates a sparky but sods law he's away until next Wednesday, a day before the future in laws arrive...

 

[RADabz]

Stupid question maybe but would a change in water pressure cause this, the water seemed to be coming out twice as fast as before and that was even when it was running hot.

The shower does work for about 5mins and then the MCB trips off you see.

Also it works fine if I put it on economy which seems to pull through less water (more like what I remember it running at) ?

Oh and the power indicator comes on on the shower which I've never noticed before.

 

[flameport]

Water pressure will have no effect.

The shower works on 'economy' mode because this uses half of the power.

Electric showers are just heating elements in a box.
The eco/full switch just selects one or both of the elements.
The rotary knob controls the flow of water.
That's it. Doesn't matter if the shower costs £50 or £500, they all work in the same way.

On half power, you will need to have a lower flow rate to get the same temperature. Same thing occurs in the winter - the incoming water is colder, so to get the same temperature output, the flow must be reduced compared to summer use.

Replacing the MCB may resolve the problem, however it is likely that the contacts where the MCB plugs into the board have been overheated and damaged, or perhaps the wires connected to the board are loose/damaged.

The real solution is to replace the shower fusebox completely.

 

[RADabz]

Here's the pictures of it.

So you think it may be the wires under the box, only issue with that is the bottom is live with no way of switching it off, if the new mcb doesn't work the I'll remove the cover and have a look, if there's sign of damage I'll get my friendly sparky to fix.

Untitled

• RADabz
• 22 Jul 2010
• 1

The overheating MCB

Untitled

• RADabz
• 22 Jul 2010
• 1

Main fusebox (MK)

Untitled

• RADabz
• 22 Jul 2010
• 2

How it all looks overall.

[/img]

 

[flameport]

Definitely have that old fusebox for the shower replaced.

It has no RCD, is probably damaged internally from the overheating, and isn't connected to the supply properly either.
There is plenty of space to get a new one in, even if the shower cable needs to be shortened to remove any damaged ends.

 

[RADabz]

I'm happy with that, what should I replace it with ?

I take it a combined RCD and mcb unit ?

Any recommendations ?

 

[LoveRocket]

Something like this should do the job, fitted with a D.P. RCBO.

If your mate's a spark, get him to bring his clamp meter around and check how much current that shower is actually drawing... Something's maybe not quite right here.

 

[RADabz]

Excuse me being stupid but that just looks like a big on/off switch to me.

I take it I have to fit the protection afterwards ?