Shower trips the fuse on the consumer unit

[Llarius]

At the beginning of the year we had our bathroom completely refitted and along with that installed a new Mira Sport Max air boost shower. As it is 10.8kW rated, we needed to upgrade all the cabling etc and that was done.

Everything has been mostly fine, but it has recently started tripping out on the consumer unit. At first this was just when the washing machine was on, or if the unit was on for longer than 30 minutes (EDIT: or so it seems, I guess this is when I've shaved in the shower and taken longer than usual. My wife is probably downstairs using the kettle, TV turned on, computers plugged in etc - perhaps increasing the load on the system?). For the first time today, it tripped it without anything else on, bar normal appliances on standby etc - twice. Once within about 15 minutes of the shower being on, and then 5 minutes or less after being reset.

I've had a look at our consumer unit and noticed a couple of things:

1) I'm sure in the manual, it says there should be a 45A as the recommended MCB size. If I've understood that correctly, I can see that the label on ours says 40A - see picture below. I cannot pull it out to check what is actually fitted as you can see in the picture it seems to be wedged in... (labelled below it as Shower)
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2) I also noticed that there is a warning on the consumer unit that says the total load should not exceed 100A "For all circuits total load not to exceed 100 A" (see picture above at bottom right corner). From totalling everything on the top of the fuses, I can see that the total across all of them does exceed this (see pics below). Sockets 30A, Sockets 30 A, Shower 40A (should be 45A), Water Heater (20A), Lights 5A, Lights 5A.

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Is this likely to be a simple case of upgrading the consumer unit to one that can cope with the load?

 

[ericmark]

The MCB's must be quite old to be type 2. Today they are rated B, C, or D not 1, 2, 3, and 4. In theory one MCB will not affect another but they have two bits inside a magnetic and thermal and the latter can result in one MCB warming up the next one to it. Coupled with age this may cause them to fail premature.

However before going too far into that you have all but lights supplied from one RCD rated at 63A which is more of a worry with overload than the maximum ratting for whole box one because of maximum current rating and two because of the cumulative earth leakage from all circuits.

I am not domestic and I don't know what is available but I would be looking to see if RCBO's can be fitted to that box and move some of the circuits from the single RCD.

I am sure you will get more advice if you wait but in mean time please confirm it is the MCB tripping not the RCD?

 

[Llarius]

Please can you tell me the difference between the two?

 

[PrenticeBoyofDerry]

There could be a number of reasons for the RCD tripping out, based on what you have said.
It is not uncommon for an RCD to randomly trip once in a while, then once reset the problem does not then reoccur.

The main isolator rating at 100A nor the main fuse, if also rated at 100A, is not a concern (regarding your loads), as using diversity and the chances of every circuit and breaker being on maximum load for a long enough period to damage isolator and take main fuse out is very unlikely, and this would not be the reasoning behind your issue.

RCD trip when earth leakage is detected above the range of it's rating, normally 30mA in domestic installtions (you will find most equipment will have a degree of earth leakage)

The things that cause RCD to trip regularly are faulty equipment, and possible loose connections.
So it often come down to a process of elimination.
Common equipment that cause RCD trips are appliance that have heating elements in them.
The RCD has a 63A load rating in which you have two circuits at 30A and a shower circuit at 40A plus heating circuit at 20A loaded on to it, that could be an issue.
But it seems you are saying the trip occurs without or very little load.
If the trips are regular, remove all plugged in appliance and replace one by one, trying to use a process of elimination.
Also at this time with shower circuit isolated and proved dead, remove cover of shower and check for loose connection and water ingress, also check the shower isolator for loose connections.
You quite rightly have pointed out that the 40A protective device is under rated for the load of the shower and should indeed be either 45A or 50A device. Do you know the size cable that was installed and if the cable runs through thermal insulation, conduit or trunking?

 

[Llarius]

Sorry I should say it's not the main switch that trips but the shower specific one. I presume that is clearer. Apologies for confusion.

 

[PrenticeBoyofDerry]

Sorry I should say it's not the main switch that trips but the shower specific one. I presume that is clearer. Apologies for confusion.

Yes that is understood, When you had the shower installed did the installer pass over documentation of the installation with cable size and RCD tests?
It is not impossible for the RCD to also start to fail!

 

[ban-all-sheds]

I can see that the label on ours says 40A - see picture below. I cannot pull it out to check what is actually fitted as you can see in the picture it seems to be wedged in... (labelled below it as Shower)

What's actually fitted is a 40A - there's nothing to see or check, it's not a fuse.

And they don't pull out.

 

[Llarius]

No documentation passed over at all.

Not sure of the cable size or what it runs through as I'm not near it now. It is quite significantly larger than what was there previously - and added a good chunk to the cost of our bathroom installation - just checked the invoice and that doesn't give me any clues, apart from the cost at £170 - no/little mark up they said.

Apparently the breaker is new too according to the invoice.

It's a grey cable (looks like this, but different size I guess: http://www.wickes.co.uk/25mm2-twin-and-earth-cable-6242yh/invt/156254/) that is easily over 10mm wide, and as far as running I can see it runs from the consumer unit to under the floor boards in our box room, and then under the hallyway floorboards, and was then chased into the bathroom walls under the tiling.

 

[ban-all-sheds]

Yes that is understood, When you had the shower installed did the installer pass over documentation of the installation with cable size and RCD tests?
It is not impossible for the RCD to also start to fail!

It's not the RCD which is tripping.

It's a 40A MCB supplying a 45A load.

At the beginning of the year we had our bathroom completely refitted and along with that installed a new Mira Sport Max air boost shower. As it is 10.8kW rated, we needed to upgrade all the cabling etc and that was done.

Whoever installed the shower was incompetent, dangerous, and, if they gave you an EIC, a fraudulant liar.

 

[Llarius]

I can see that the label on ours says 40A - see picture below. I cannot pull it out to check what is actually fitted as you can see in the picture it seems to be wedged in... (labelled below it as Shower)

What's actually fitted is a 40A - there's nothing to see or check, it's not a fuse.

And they don't pull out.

Ok. Thanks. Wasn't sure - since it looked like it was wedged in, it looked like it should come out, if you get what I mean!

 

[Llarius]

Yes that is understood, When you had the shower installed did the installer pass over documentation of the installation with cable size and RCD tests?
It is not impossible for the RCD to also start to fail!

It's not the RCD which is tripping.

It's a 40A MCB supplying a 45A load.

At the beginning of the year we had our bathroom completely refitted and along with that installed a new Mira Sport Max air boost shower. As it is 10.8kW rated, we needed to upgrade all the cabling etc and that was done.

Whoever installed the shower was incompetent, dangerous, and, if they gave you an EIC, a fraudulant liar.

EIC?

Thank you for contributing and helping, but please notice I'm not an electrician, and would really appreciate spelling out the acronyms. It will help me when I'm speaking to an electrician who comes to check it all out - not the same one as who installed it...

 

[Llarius]

So, I assume that we need to get the 40A changed to a 45A?

Am I also right in understanding that we ought to try to split the two circuits into 3 (however this is done)? Splitting out the 2 x sockets, shower and heater one?

 

[ericmark]

That 40A MCB is NOT new. Not sure of date but it was around 1990 when we changed from 1, 2, 3, and 4 to B, C, and D MCB ratting may have been earlier. So swapping the 40A type 2 for a 40A type B will likely cure the problem.

Also the MCB does not seem to be fitted square and I have in the past had problems where the plastic of the MCB is warped by strain on cables and it trips at the wrong current.

I am not up to date maybe one of the others can say if MCB's are still made for that board. It may be it's an obsolete board and the installer has had to buy old stock from some where to fit the board.

 

[PrenticeBoyofDerry]

It's not the RCD which is tripping.

It's a 40A MCB supplying a 45A load.

I may have misunderstood, there was a mention of things tripping out around the house.
Can I please have this confirmed, is it the 40A device only that trips causing power-loss to shower or is it the RCD that trips causing power-loss to shower, sockets and heater?

 

[ericmark]

I found this http://www.proteusswitchgear.co.uk/product_details.asp?product=1330 which states it is obsolete so likely they had to buy old or second hand so not their fault they have clearly tried to keep down costs for you.