100mA RCD tripping problem

[dx90]

An electrician came in a few months ago and installed a new CU. He has passed all the electrics and supplied the paperwork for this. I’ve had lots of tripping on the 100mA RCD side but no tripping on the 30mA RCD side. The system is TT. Once ever 3 days and on the odd action once a week, there’s no pattern to it.

The electrician says there’s nothing wrong with the wiring, he’s done all his tests and it’s all been passed.
He says that it must be an accumulation that’s causing it to trip but not enough to trip the 30mA RCD.

He said the main culprits were.

1. My mains powered alarm clock. (He couldn’t under stand how or why because it doesn’t have an earth wire).
Is this possible?

2. The two extension leads I use in the bedrooms. (They worked fine over my old house and never tripped the RCD).

3. The wall boiler that I have had checked by the gas board boiler electrician. (They said its passed)

4. The dishwasher might be at fault. I had it checked by another firm that I have it insured with no fault was found and it passed. (He spent a long time running through all the programs as he checked).

His advice was to get the boiler and dishwasher checked and to bin the alarm and extension leads and get new ones. That should help.

We can’t go away for any length of time because of this problem.

What do you think the problem can be and how can I solve this myself?

Many thanks

 

[Steve]

A time delayed RCD.

 

[dx90]

The CU is a Wylex and the RCD is an Wylex 80A 100mA WRM80/2. I have done a search for a equivalent timed delay and cannot find one.

How would this solve my problem?
I don't have the 30mA RCD trip at all.

Can you suggest anywhere that I can buy one?

 

[JohnD]

Let us know what circuits are on the non RCD side. Trippy faults can be hard to find but I'll put 5p on one of:
- Immersion heater
- Electric Oven
- CH boiler or pump if not on the 30mA RCD circuit.
- Outside lamp where rain is getting into the fitting or cable

You should have DP switches on each of these, so turn them all off except when you really need to use them, and see if this cures the tripping. An outside lamp would need to be disconnected inside the house.

If not, tell us what signs of mice or squirrels you have in your house, underfloor, or loft.

What circuit is your freezer on?

Keep a diary of weather days. Look for a pattern of cold (=heating on) or wet (=rain in circuits)

 

[BJS_Spark]

So you still haven't got to the root of the problem that you were posting about in June. Reading back I think for a start you need to identify how the CU is arranged.
It was asked back then if the 30mA circuits power off when the 100mA RCD is off to which you did not answer directly, but your replys indicate that they do not in which case the 30mA RCD is not fed from the 100mA and so the non-time delay RCD you have is correct.
Pictures as suggested before would be best but would have to be taken with the CU cover off so this may be outside your scope.
If the 100mA RCD is not feeding the 30mA RCD then it must be an individual circuit on the 100mA RCD and can be identified by a process of elimination.

The RCD reads 80A-100mA WRM80/2 and the other RCD 80A 30mA WRS80/2 on the 100mA is the cooker NSB40, lights NSB06 and combi boiler NSB16 and on the other 30mA is sockets up NSB16 and down NSB16, kitchen sockets NSB32, shower NSB40 all are Wylex.

So cooker lights or boiler?

 

[dx90]

BJS_Spark yes the same old problem. It went away for 3 weeks after the electrcian left the last time and then it started again.

Yes the 30mA circuits do power off when the 100mA RCD is off.

Once I figure out how to upload the pictures I will take some and put them up. I will try and do that today.
Do the pictures have to be resized to any particular size?


JohnD

The freezer is on the 30mA side pluged into the kitchen circuit.

There are 4 circuits on the 100mA side

1. Garage. I have had the Garage switched off for about 3 weeks from the 100mA side in the house with no effect.

2. Lights up and down stairs and door bell. I know the transformer for the bell is ok because at one point it was disconnected until we got a new one and it was still tripping then.

3. Wall combi boiler. Did have this all checked by an electrical boiler engineer/technician and he said there was no problem that he could find. He could be wrong.

4. Cooker. Defiantly not the cooker as we are on our 7th Hotpoint cooker as the rest had faults and in between this we where left without a cooker for 2 weeks. We still had tripping in that time.

Hope this helps.

 

[JohnD]

1. Garage. I have had the Garage switched off for about 3 weeks from the 100mA side in the house with no effect.

switched off is not enough. Switches and MCBs only cut the Phase conductor. you need to isolate Phase and Neutral. A DP switch will do this otherwise someone will have to disconnect both cores at the consumer unit. If you have to pay an electrician to do this for you, you could ask him to fit a DP switch on the cable which will allow you do do it yourself in future.

As for the cooker, a new one is less likely to have earth leakage, but it is necessary to isolate it with the DP switch.

Same with the boiler. It should have a switched FCU in the wall next to it, you need to turn off here. Water leaks in pumps or boilers can change according to whether they are hot or cold, running or not running, but are very common causes of RCD trips.

Earth Leakages are most common on "watery" appliances like kettles and washing machines.

If the fault was on the lighting, it might be e.g a water leak dripping onto something under the bathroom floor; or a nail through a cable.

I note that you have no immersion heater or electric shower.

If you are willing to spend more money, you could have the remaining circuits protected by RCBOs, which would almost certainly limit any nuisance tripping to a single circuit, which minimises the inconvenience and shows you where the fault is coming from. I think Wylex ones are about £40 each. In this case you would no longer need a 100mA RCD.

 

[dx90]

I do have a electric shower, but it is diconected from the mains.

Here are some photos as requested.

http://i226.photobucket.com/albums/dd39/dx90_photos/2007_0907CU_UNIT0053.jpg

http://i226.photobucket.com/albums/dd39/dx90_photos/2007_0907CU_UNIT0049.jpg

http://i226.photobucket.com/albums/dd39/dx90_photos/2007_0907CU_UNIT0048.jpg

http://i226.photobucket.com/albums/dd39/dx90_photos/2007_0907CU_UNIT0047.jpg

http://i226.photobucket.com/albums/dd39/dx90_photos/2007_0907CU_UNIT0044.jpg

http://i226.photobucket.com/albums/dd39/dx90_photos/2007_0907CU_UNIT0043.jpg

http://i226.photobucket.com/albums/dd39/dx90_photos/2007_0907CU_UNIT0042.jpg

http://i226.photobucket.com/albums/dd39/dx90_photos/2007_0907CU_UNIT0037.jpg

http://i226.photobucket.com/albums/dd39/dx90_photos/2007_0907CU_UNIT0036.jpg

http://i226.photobucket.com/albums/dd39/dx90_photos/2007_0907CU_UNIT0035.jpg

http://i226.photobucket.com/albums/dd39/dx90_photos/2007_0907CU_UNIT0034.jpg

So you’re saying that even though I have had some of the appliances checked it would still be a good idea to disconnect them one by one from the mains?

Only trouble is with a family 3 days to a week is a long time to keep any appliance off for.

If it is an accumulation from several items on different circuits then doing the above won't solve the problem.
But I will try one by one and hope its just one that’s causing the trip.

The bathroom is direct above the CU unit. I will have a good look for any leaks.

 

[plugwash]

From the pictures it looks like the RCDs are chained, that is the 100ma one feeds the 30ma one, it also looks like the RCD is not a time delay one.

It should be possible to reconfigure the CU so there is a seperate main switch and the RCDs do not feed each other. Basically you need to cut down the bussbar on the non-rcd side, slide the stuff on that side over two positions, fit a new isolator, move the incoming power to the new isolator and then connect both RCDs inputs to the output of the new isolator.

Unfortunately isolating the incoming power to do that will probablly require pulling the service fuse so I would suggest getting a pro in to do it.

 

[dx90]

If all the power was off in the house viea the RCD's and then the service fuse was pulled. Would that be safe enough as there shouldn't be any power draw on the service fuse?

 

[davy_owen_88]

You are not allowed to pull the service fuse yourself. Contact your DNO and request an isolator. It won't cost you much.

 

[plugwash]

If all the power was off in the house viea the RCD's and then the service fuse was pulled. Would that be safe enough as there shouldn't be any power draw on the service fuse?

You aren't supposed to do it and you have to be carefull if you do but provided the fuse carrier is in good condition, there is no significant current flowing and you take care not to touch any metal parts it should be as safe as pulling any other fuse live.

I wonder how many people actually followed the switch off before handling fuses text printed on the old wylex boxes, my guess is not very many.

 

[Taylortwocities]

Not many, Plug, including me. The last time I did it a careless housholder had left a longish tail of fuse wire hanging out of the screw at the end of the fuse.
The end of the fusewire was tucked under the end of the fuse and I didnt see it as I grabbed the fuse to pull it out
Since that day i have always respected the warning notice.

 

[securespark]

Yes, that main RCD is NOT TD, so the fault (which I was originally thinking must have been on the 100mA side as it was the 100mA that was tripping) could be anywhere.

It would be interesting to see the paperwork: why has he fitted a non TD unit - there is no compliance with the regs with this set-up.

Ring the guy & get him back - this needs altering so as to comply.

 

[Richard1]

I had the same problem with a wylex board on a TT system 2 weeks ago,
Wylex advised that the 100ma TD RCD had to be fitted in a separate enclosure and could not be exchanged for the main switch as shown in your photos.