RCBO question

[goosemonster]

I'm having a problem with my electric shower that I hope is caused by the RCBO.

Shower works for a few minutes then all power cuts out, including power to the pull switch.

Thing is the actual switch on the RCBO hasn't tripped.

But when I turn off the RCBO for a few minutes, then turn it back on again the pwer returns to the shower.

So is the RCBO faulty or are they designed to trip without the actual physical switch moving to the off position?

Also - it's a 40A 30mA switch for a 10.8kW shower. Is there any disadvantage going with a 40mA switch?

 

[Taylortwocities]

I'm having a problem with my electric shower that I hope is caused by the RCBO.

Shower works for a few minutes then all power cuts out, including power to the pull switch.

Ooh lets do some simple maths.

10,800 watts at 230volts = 47amps

Your RCBO is 40amp. Can you spot the problem yet

Also - it's a 40A 30mA switch for a 10.8kW shower. Is there any disadvantage going with a 40mA switch?

OK, you go and buy a 40mA RCBO. Do let me know where you find one.

I think you need some competent help, on site.

 

[goosemonster]

Thanks for the quick response. Reading between the sarcasm you seem to be suggesting the RCBO should be 47A and you can’t get a 40Ma version.

So assuming someone will be kind enough to respond to the ‘is the RCBO faulty’ element of my post and also assuming the RCBO need replaced, then I should be looking for a 47A 30mA switch?

Can you get 47A switches?

 

[Spark123]

No, 47A isn't a standard size, nor is an RCBO just a switch .
Problem is that you are overloading the RCBO and probably the isolator and the cables.
Best get an electrician in to check it all out.

 

[bernardgreen]

The amp rating is the current that will cause the RCBO to operate after a short delay. This turns off the power due to possible overload of the cable. Overloaded cables can start a fire.

The mA ( milliamp ) rating is the difference in current between Live and Neutral that will cause immediate operation of the RCBO. This turns off the power due to current leaking from the circuit wires to earth, in a shower that could be through a person's body. Current through the body can kill or cause injury.

The RCBO is crucial to the safety of people in the shower and the prevention of fire.

DO NOT MEDDLE WITH IT.

As the shower is too powerful for the RCBO fitted get an electrician to check the wiring is the right size for the shower and can safely carry the 40 amps the RCBO will allow to flow to the shower.

Who fitted the shower ?

 

[sparkwright]

How long have you had the shower, has it recently been fitted to replace a less powerful one?

There is a very good chance the existing cable may be too small for the shower, so you need to check this all out.

Send pictures if possible.

 

[goosemonster]

The shower was fitted about 3 years ago as part of a complete bathroom re-fit. The contractor claimed to have all relevent qualifications and a member of the IEE. Although I have my doubts.
The shower has a seperate CU and is wired with 10mm cables.

This is the 2nd time I've had an issue with the CU for the shower.

First time, about a year ago, a loose conection casued it to overheat and fused the neutal and earth wires. This blew the main fuse into the house.

A different electrician then fitted the new CU I have at the minute, with the 40A 30mA RCBO.

Now this one is paying up and according to the shower manual it should have been 45A.

So rather than, once again, blindly trusting the so-called electricians in my area I would like to do a bit of research before calling one out.

As stated in my OP, the RCBO cuts the power without the physical switch moving to the off position. I'm hoping this indicates a faulty RCBO as this will be a lot cheaper to replace than the £220 a new shower will cost.

Thanks for all the replies so far.

 

[Taylortwocities]

If the RCBO truly switches off without the lever moving then there is a problem.
BUT
How do you know that the RCBO is turning itself off?
Maybe something else in the circuit (like a bad connection) fails after a short amount of time on full load. This would give the appearance of the RCBO disconnecting.
Has anyone done ANY even basic tests using even basic test equipment?

You have a number of things that need checking. With respect, your responses so far indicate that you don not have enough knowledge to do these checks yourself.

You need a qualified electrician to get this sorted.

Pay money, shower with confidence!
(Could be NICEIC's next marketing strapline!)

 

[EFLImpudence]

Could it be the shower itself which is 'cutting out'?

 

[riveralt]

First time, about a year ago, a loose conection casued it to overheat and fused the neutal and earth wires. This blew the main fuse into the house.

A different electrician then fitted the new CU I have at the minute, with the 40A 30mA RCBO.

Have a look at the Electrical Installation Certificate and give us the readings for the RCD figures.

As stated in my OP, the RCBO cuts the power without the physical switch moving to the off position. I'm hoping this indicates a faulty RCBO as this will be a lot cheaper to replace than the £220 a new shower will cost.
Thanks for all the replies so far.

If the RCBO is not in the off position then how do you know that it is causing the problem. While they do go wrong occasionally it is rare.
Have you tested the RCBO recently with the test button - this should cause the RCBO to trip - if not then you will need to it checked out by an electrician. If it does trip then it is likely that the fault lies elsewhere.
Are you sure that the shower is not switching itself off due to lack of water pressure?

 

[goosemonster]

Thanks for all your replies.

Based on the fact that I should have a 45A fuse, plus the posibility that the RCBO may be faulty due to the lever not moving, I'll go ahead and arrange to have this replaced with a 45A unit.

Thanks again.

 

[RF Lighting]

Is 45A more than 47A these days?

 

[goosemonster]

Is 45A more than 47A these days?

45A is stated in the shower instruction manual. Would 50A be better?

 

[riveralt]

Thanks for all your replies.

Based on the fact that I should have a 45A fuse, plus the posibility that the RCBO may be faulty due to the lever not moving, I'll go ahead and arrange to have this replaced with a 45A unit.

Thanks again.

Is this a Mira shower?

If it is then, like many other shower manufacturers, they up the anti on the power of the shower - Using 10.8kw on the outside of the packaging but in the installation guide quoting 10.8kw @240 and 9.9kw @ 230v which of course both work out to 45Amps or less.
If the manufacturers instructions say 45A MCB then I would go for that.

 

[ban-all-sheds]

I would like to do a bit of research.

• //www.diynot.com/wiki/electrics:mcbtocable
  
  
• http://www.tlc-direct.co.uk/Book/4.3.1.htm
  
  
• http://www.tlc-direct.co.uk/Book/4.3.11.htm
  
  
• http://www.tlc-direct.co.uk/Book/5.3.1.htm
  
  
• http://web.archive.org/web/20080213151445/http://www.kevinboone.com/cableselection_web.pdf
  
  
• http://www.tlc-direct.co.uk/Technical/Charts/VoltageDrop.html