RCD Tripping (split from Actic's thread)

[swinster]

Thanks for all the feedback, turns out the crabtree rccb was faulty, so it was swapped out for an 80 amp 30ms unit and this has resolved the problem.

Kev

I believe this to be the case with our system. this is the second RCCB we have gone through in about 8 years. Originally it tripped when the cooker was used so we replaced RCCB and no more problem. We eventually replaced the cooker as well and up until recently all had been working fine. Then the RCCB started tripping again (but not the MCB on the cooker circuit). Occasionally at first but now we can't put the cooker on for more than 5 mins.

Maybe there is a design fault with these RCCBs?

 

[JohnD]

much more likely you have the common problem of a cooker whose element starts to suffer earth leakage as it ages.

The MCB is irrelevant since it does not detect earth leakage.

Whu is your cooker on an RCD protected circuit?

 

[swinster]

Whu is your cooker on an RCD protected circuit?

I have no idea why this is so as I'm no electrician (although I have been reading the the usual practice is that the RCCB protects just the sockets). When the RCCB trips, we loose all power on all circuits - lights, sockets and cooker. The consumer unit was put in many years ago when my partner had grant work done on the house, before I was around. We have done nothing to the consumer unit other than to replace the original RCCB about 8/9 years ago.

Ut just seems odd that when we replaced the RCCB originally, all the problem went away. We continued to use the old cooker for another few years until we replaced it. The new cooker is now about 5/6 years old. Just so happen that we are moving the kitchen soon and will be replacing the cooker again.

 

[JohnD]

If your refit of the kitchen involves changing electrical circuits in there, you will need to have it done by a suitable qualified electrician (or pay to have it inspected and documented by Building Control which is usually more expensive) so you could ask him to move the cooker circuit to a non-RCD side and test it. This will be very easy unless the CU is full or it is not a split-load one. How many socket and shower circuits does it have?

If you can post a pic of the CU and the cables around it, it may spark some more ideas.

 

[swinster]

If your refit of the kitchen involves changing electrical circuits in there, you will need to have it done by a suitable qualified electrician (or pay to have it inspected and documented by Building Control which is usually more expensive) so you could ask him to move the cooker circuit to a non-RCD side and test it. This will be very easy unless the CU is full or it is not a split-load one. How many socket and shower circuits does it have?

If you can post a pic of the CU and the cables around it, it may spark some more ideas.

We are extending into the basement and the electrics have been done by a electrician to building regs. They have split the main feed and put another CU downstairs.

I will take some pictures and post them later.

 

[swinster]

OK, here are the requested picture - hope they are of use.

Crabtree CU Unit and associated wiring

• swinster
• 14 Apr 2008
• 2

Crabtree CU Unit and associated wiring 2

• swinster
• 14 Apr 2008
• 2

Crabtree Consumer Unit

• swinster
• 14 Apr 2008
• 3

 

[JohnD]

The way that has been installed is not ideal.

You do not seem to have any spare ways on your consumer unit, and it is not a split load one. I do not think you can get single-width RCBOs to put on the circuits needing them, It seems to be the sort with "tongues" that engage in a slotted busbar, though I can't see any part nos.

I can't see a main earth connection either from the supplier or an earth spike, which is worrying.

I suggest you ask your supplier if they can provide you with an earthing point; they can probably give you PME for £50-£100 or possibly free. Also consider replacing your existing CU with a more modern one, with more space and the ability to RCD protect your circuits wither by group, or individually. Ask around friends and neighbours for a recomended local electrician. Before engaging one, ask if he is a member of a self-certifdication scheme; which one, and ask to see evidence.

 

[swinster]

swinster, welcome to the forums.

Please familiarise yourself with forum rules
//www.diynot.com/forums/viewtopic.php?t=19448
and see no. 6

Apologies. didn't mean to hijack but thought this would be a simple query that related the the initial thread query to which all others might benefit.

 

[swinster]

The way that has been installed is not ideal.

You do not seem to have any spare ways on your consumer unit, and it is not a split load one. I do not think you can get single-width RCBOs to put on the circuits needing them, It seems to be the sort with "tongues" that engage in a slotted busbar, though I can't see any part nos.

I can't see a main earth connection either from the supplier or an earth spike, which is worrying.

I suggest you ask your supplier if they can provide you with an earthing point; they can probably give you PME for £50-£100 or possibly free. Also consider replacing your existing CU with a more modern one, with more space and the ability to RCD protect your circuits wither by group, or individually. Ask around friends and neighbours for a recomended local electrician. Before engaging one, ask if he is a member of a self-certifdication scheme; which one, and ask to see evidence.

Thanks for this. One question - What is PME?

How should it have been done so I can understand (in a limited fashion) what I should expect. The second CU downstairs which was installed last year doesn't look that much different from this one, however the one you see in the picture has got to be over 10 years old.

 

[JohnD]

PME is Protective Multiple earthing (also known as TNC-S). It is a method of the electricity supplier providing a good-quality earth. they do it by earthing the neutral conductor at frequent intervals, so that the Neutral is effectively earthed, and they provide an earth terminal from this at the service Head where they put the main fuse. It is now the most common way of providing an earth to domestic properties. They even do it in houses with an overhead supply now.

If the supplier can't provide PME they might be able to provide an earth from the cable sheath. IMO these are not as reliable since you often see cable armour rusted and sheaths damaged. The supplier is not obliged to provide an earth to an existing installation without one; but they often will.

You can request it by sending a letter to the address on your electricity bill. The work will actually be done by a different company, but your letter will get passed on. If you phone you may speak to someone who has no idea what to do.

modern consumer units are often Split Load, where some circuits are grouped together and protected by an RCD, and the others are either not protected by an RCD at all, or are protected by a different RCD.

The idea is that a fault on one circuit will not cut power to all the other circuits in the event of an earth fault.

An even better method is to use RCBOs (which have a separate RCD combined with each MCB, so that each circuit is individually protected). this is however more expensive. It can cost about £25 more per circuit.

 

[swinster]

Thanks for this very complete answer. I will be writing the supplier shortly.

It's strange but the second CU unit downstairs looks very similar (almost exactly the same) as the one in the pictures, and was fitted by a different electritian well over 10 years later (in fact just last year). The numbers on the MCB's (B06, B16 and B32) and RCCB (380/030) are the same as the one pictured and if you trip the RCCB, all circuits donwstairs will be affected - not just the points.

 

[JohnD]

Crabtree Starbreaker MCBs usually have a part no on the front, such as 61/B32. The older ones begin 610. I was puzzled because yours look like the 61 range, but I don't see the part no.

Crabtree Starbreaker is still made and is a good brand. But your old one seems to have no space in it to add an RCD. I'm a great believer in fitting excessively large CUs so you have plenty of space for future changes or additions. The initial cost is not much higher as you are only paying for some fresh air and a slightly bigger box. My house has a 22-way

 

[swinster]

Crabtree Starbreaker MCBs usually have a part no on the front, such as 61/B32. The older ones begin 610. I was puzzled because yours look like the 61 range, but I don't see the part no.

Crabtree Starbreaker is still made and is a good brand. But your old one seems to have no space in it to add an RCD. I'm a great believer in fitting excessively large CUs so you have plenty of space for future changes or additions. The initial cost is not much higher as you are only paying for some fresh air and a slightly bigger box. My house has a 22-way

Ah, the benefit of knowing what you are doing! In the same way, I am an IT networking guy and will over specify network ports and cabling. Of course, i simply relied on the electrician to fit the best for what was needed. I really have no clue as to whether the CU is correct or well specified - as long as the lights go on! Now I'm experiencing problems I then delve a little deeper and start to find that there are better ways of doing something.

 

[bongos]

I'm not sure but it looks like there may be an earth cable. There seems to be a short length of G&Y at the top of the pic which runs from the CU then goes behind the wooden board and re-appears at the bottom of the pic again from behind the wooden board.

If this is the case and assuming it joins the sheath of your main cable then you have at least got a TN-S earth supply.