Cooker tripping RCD unit

[weelnut]

I have a current fault of a cooker that trips my RCD. The trip may not come immediately on turning the cooker supply on but it will normally trip after a given amount of time. For example the trip may occur when I turn the oven on or after a few minutes with no action or change occurring (no load change). Another example was when the cooker was on for 59 minutes and I went to take a shower. As soon as I switched the electrical shower on the trip occurred.

This RCD unit is on all of the house supply (separate breakers obviously) and none of the circuits are split. I have recently installed new electrical circuits in the kitchen but the cooker circuit was only modified (change of position). I cannot work out if...

1. The cooker is faulty (has been in the garage not used for 3 years).

2. The wiring is faulty or there is another faulty circuit somewhere.

3. The RCD trip device is faulty (i.e. over sensitive).

The RCD has some history of nuisance tripping and previously with the original electric cooker it used to trip if sometimes if both ovens were used or if the cooker was not used for a week or so (like returning from holiday).

I could bypass the RCD but I would lose all protection for all circuits.

I hesitate in bypassing a safety device.

Are RCDs suitable for cookers?

 

[JohnD]

no

It is usually inadvisable to have the whole house on a single RCD. this is because

(1) A fault on any one circuit will cut power to all the others

(2) the danger of having all the lights go out unexpectedly can be very great, for example if you are lifting a child out of the bath, running downstairs, carrying a cooking pan of boiling water, carrying a heavy object; up a ladder...

(3) Minor leakages (which, individually are not dangerous or significant) on multiple circuits and multiple appliances may add up to enough to trip the RCD.

What sort of earth does your electrical installation have? Are you in a rural area with an overhead supply? What is the sensitivity of your RCD, and is it time-delayed?

Do you know he reason why the whole house is on a single RCD?

Incidentally, electric cookers are prone to earth leakages, especially as they age. They are not required to be on an RCD, as they are nor portable, and are unlikely to be used out of doors. The earth leakage will not be dangerous if they are properly earthed. It is usually better not to have them on an RCD as they often cause nuisance tripping.

Other appliances prone to earth leakages are principally "watery" appliances such as kettles, immersion heaters, washing machines, tea urns, central heating boilers and their pumps.

there are various other ways of arranging things. To help us suggest:

Do you know the make and model of your consumer unit?

Can you post some pics showing the CU, suppliers fuse and meter, incoming cable, main earths, and the various connections between them all?

 

[weelnut]

The rcd is a 2 pole 63A, 30ma unit feeding a 100A mcb board.

I am not in a rural area as such but we are on the end of a vulnerable network. Lightning and power cuts have taken out the RCD in the past.

I do not know why one RCD is protecting the whole house but I just had a look and two cables come from the meter (assume live and neutral) but a third smaller cable comes from the ground (garage floor) straight into the board (not into the RCD). i am not sure if that is relevant?

30ma seems mighty small earth leakage when you consider two PCs, cooker, immersion heater, 2 fridges, freezer, 2 ring mains, installed outside sockets, 3 TVs, electric shower, etc...

The RCD is a Proteus unit (last test in 2003) 63/2/30.

I can take some pictures tomorrow and post on here.

Thanks

andy

 

[JohnD]

you are right, 30mA for the whole house is unreasonably sensitive and not a good design.

I would have hoped to see the following large green & Yellow sheathed earth wires:

One from the incoming cable or suppliers fuse, to the CU

One from the CU to the incoming water main

One from the CU to the incoming gas main (or oil pipe, if you have it)

You might also have one to an Earth Spike, in which case there should be an inspection hatch over the top of the spike (usually about 6 inches square) with lettering to identify it.

Can you see any of these? If present, they should all be accessible for inspection. It is also useful to know if the incoming supply cable appears to be shiny PVC, or tarry cloth, or rubber, or wrapped in steel bandage-like armour.


p.s. see if your CU and components are the same as on about page 29 of this cat. part no's are shown.
http://www.proteusswitchgear.co.uk/downloads/proteus_switchgear_cat2005.pdf

 

[weelnut]

Ok

there are two cables coming from the meter (fuse) presumably live and nuetral.

There is a smaller cable coing from the garage floor and has been joined with a choc block and extended to the CU.

there is alos an earth cable the other side of the wall diasappearing into the ground (earth bonding with water or gas pipe?).

I have taken some photos as you requested but i did tonight so it was dark. They have not come out too wel so I will take som more ehen it is light.

The CU looks like proteus as well as the RCD unit. The RCD unit has a stciker on it stating it was tested in 2003. The consumer unit has a stciker on it stating it was checked in 2001.

ok I dont know how to post pictures!

 

[JohnD]

posting pictures

//www.diynot.com/forums/viewforum.php?f=6

 

[weelnut]

http://i222.photobucket.com/albums/dd92/crundall/rcd003.jpg

http://i222.photobucket.com/albums/dd92/crundall/rcd005.jpg

http://i222.photobucket.com/albums/dd92/crundall/rcd004.jpg

 

[JohnD]

thanks

can you do one of the meter, and the service head (where the suppliers cable comes in, and has a black or grey plastic or iron box on it, with the tails to the meter coming out, and a large fuseholder

Does the supply come in from an overhead pole, or underground?

In http://i222.photobucket.com/albums/dd92/crundall/rcd004.jpg there is a thinner cable under the RCD, can you see if it has been joined or is it original? under the paint it might be sheathed in green and Yellow (grrrrr!)

An RCD does not have an earth, but there may have been a much older device here before, that did need to be earthed. look if there are screwholes or other marks on the wall at this point where there may have been something else.

ta

 

[weelnut]

Sorry for the delay...

The cable you refer to is an earth cable and is joined by a connector block as the first photo shows. This does go to the CU through a white trunking.

There is another earth that I can trace to the outside of the garage which then comes through the garage floor into the CU with the live and neutral (the smaller of the three incoming cables to the CU in the picture...

http://i222.photobucket.com/albums/dd92/crundall/IMAG0547.jpg
http://i222.photobucket.com/albums/dd92/crundall/rcd003.jpg

I have taken a photo of the meter cupboard and fuse as you requested. This is mounted on the outside of the garage near the earth cable (the one that goes into the ground).

http://i222.photobucket.com/albums/dd92/crundall/IMAG0548.jpg

I took yet another photo of the RCD unit with the earth cable 'pulled out' showing the connection (as previously discussed above).

I don't know whether this is sufficient information for you to tell whether this is why the RCD unit is protecting the whole board?

Regards

Andy

 

[JohnD]

there is no suppliers earth. This is unusual and not very good, but explains why the whole installation is on an RCD, though a 100mA one would be better and less prone to nuisance tripping. You have probably got an earth spike under the path, but it might not be satisfactory.

Contact your electricity supplier and ask for a supplier's earthing point to be provided. If you don't get a good response by phone, write a very short letter requesting it. They can't so easily fob off a letter, and will have to track it until it reaches someone who knows what do do.

They may charge you £60 to £100 but it will be money well spent. If you are lucky they will do it free. Don't mention cost in your letter.

You will have to provide a 16mm G&Y earth wire into the meter box for them to connect to, with the other end connected to your consumer unit earth bar, and the gas and water supplies must be main-bonded to the same terminal using 10mm G&Y.

 

[nozspark]

I would say that your supply is TT and as such all circuits must be RCD protected. What look to have happened in your case is that the RCD was fitted some time after the CU, this would make it comply with the regs but it is the cheap way of doing it. It also makes it a bit inconvenient when the RCD trips.

A better way of doing this would to either get a PME conversion and a split load CU with the socket circuits and shower on the RCD side, or get a split load CU with a 100A 100mA (TD) RCD main switch for the lights and oven and a 80A 30mA RCD for the socket/shower circuits. This is quite a big job to do so I would advocate getting someone in. It is also Part P notifyable so get someone who is a member of a scam provider..

 

[weelnut]

Thanks for your quick response guys...

If i get a suppliers earth how will this solve my RCD tripping problem?

The inference you suggest is that the RCD is required for the whole installation because I have not got a proper earth? Is this correct?

In this case (if the above is correct) I could not install a split CU with only half on RCD (sockets, etc)?

Is there anything I can do to solve the problem downstream (i.e. cooker and other circuits) or is it inevitable in this sort of case this problem tripping is going to be experienced sooner or later?

Is it an option to change out the 30ma RCD for a 100ma?

Wife is keen to solve problem so she can use the cooker (isolated at present) but I obviously want to get to root cause rather than addressing the symptoms of the problem!

 

[JohnD]

yes, if you get a "proper" earth you will not have to have an RCD on your whole installation. So your cooker will nort be on an RCD so will not trip it.

It is however advisable to have RCD protection on sockets and shower.

Your existing 30mA RCD could be changed to a 100mA Time delayed one, but this would probably cost more and might not cure the nuisance tripping. The best solution is to get the main earth done.

 

[weelnut]

Ok I will contact my supplier who is British gas (so I guess i will have to pay) Seeboard are the LEC.

I could retro fit a 100ma RCD (i.e. swap out the 30ma unit) but I would have to remove the supplier fuse to do this.

Am I allowed to do that?

 

[Steve]

No your not allowed to pull the fuse. Only seeboard are.

And 100mA isnt enough protection for your sockets.