RCD tripping

[Bozwell99]

I know RCDs are covered frequently on this forum, but I've not seen anything else here that describes the type of problem I am having.

In my garage I have a double socket to which a Freezer and Tumble Dryer are plugged in, 2 florescent tubes, and 4 x security lights outside. All of these are connected to the house via a single cable.

The problem we have started to get is that recently when the Tumble Dryer is being used the RCD in the CU trips. I have done a bit of troubleshooting and it appears that the Dryer works fine until the main light in the Garage is switched off (the 2x fluorescents). As long as the lights are kept on it seems to mostly work happily.

However occasionally the RCD trips when the dryer is running and the light isn't switched off, although I suspect it happens when another switch in the house is turned off, or one of the security lights is activated.

I have also noticed that the RCD sometimes trips when the electric fan oven is running (but not the tumble dryer), but that has happened only a handful of times in the last 5 years we have lived in this house and only once since owning the dryer (which is just over a year old).

I noticed the light switch crackled a bit when I switched it so I checked and found that the wires were lose. As I had the switch off anyway I replaced it with a new one.

So then I thought that the dryer might have an earth fault, but if that was the case then why does it mostly work when the garage light is left on?

It's also crossed my mind that the RCD might just be sensitive, but replacements seem hard to come by (or expensive) for my Memera 2000 box. I've seen some used ones on eBay for a few quid but I've no way of knowing if they're any good either, but I might try one anyway.

Anyone have any ideas to what is causing my symptoms? I've included a pic of my CU if that helps at all. If there is any more info you need let me know.

Memera 2000

• Bozwell99
• 24 Jan 2010
• 1

Memera 2000

 

[Lectrician]

People always jump to the conclusion that it is the RCD at fault. It rarely is.

You need someone who owns an insulation resistance tester and who is capable of using it correctly to locate a fault.

You likely have a low insulation resistance somewhere on the RCD side of the board, more than likely a N to E fault of some impedance.

I would start by disconnecting the LIVE and NEUTRAL of your outside lights to begin with if you are going to try and fault find this yourself.

 

[BS3036]

My eyes not being what they used to be... Which of those breakers is controlling the garage?

 

[sparkwright]

Have you a separate consumer unit in the garage? If so send a photo.

 

[ericmark]

If you have a neutral earth rather than line earth fault tripping is very dependent on current draw.
If nothing is being used with a TN-C-S supply even a direct short between neutral and earth may not trip a RCD.
As current is drawn the different parts of neutral system start to have a voltage differential to earth system.
So if the toaster for example has a neutral earth fault even when not being used it could cause the RCD to trip when the kettle is used.
Tumble Dryer will also use a lot of current so that is also likely to do the same. Any discharge lighting will likely have some power factor correction built in and this could account for it not tripping when lights are switched on.

So two ways to cure. One is to test all the items for earth neutral faults which is likely best option.

Second is to split the circuits so each has its own RCD protection which will mean. A) If it does trip you only lose that circuit. B) because any small leakage is shared between a number of RCD's it does not add up to enough to trip RCD. However not sure if your consumer unit will take RBCO's and it would cost far more than getting fault fixed.

I have two RCD's protecting my house and have had for nearly 20 years and in resent years they have tripped out more often as the amount of IT gear has increased which has filters each which adds a little earth leakage. I would say one or other trips about once a month maybe a little less but I accept this as normal.

There are two meters to find the faults. The insulation resistance meter needs expert use but can be used to test everything. It is not just an ohm meter as it uses 500v to do tests.

The second is a PAT tester this will test items by just plugging them in and switching them on and uses two methods. One same as insulation tester the other by measuring ma leakage to earth.

Both are expensive and both are likely to be owned by most electricians. Maybe you can get items checked where you work? But in mean time get in habit of unplugging items not in use. Then if they do have an earth neutral fault they will not be causing tripping when something else is used.

 

[Bozwell99]

Thank you everyone for your replies so far.

Lectrician: I have now disconnected everything except the double socket and lights from the garage circuit. Problem still apparent.

BS3036: Whoever installed this box did a bad job of labelling the breakers. The garage id connected to the 2nd from the left. It shares this with the upstairs ringmain.

sparkwright: I knew I forgot to mention something. There is an old box in the garage with 3 breakers in it. 1 x 5A and 2x 15A. The lighting is attached to the 5A, and the sockets are attached to the first of the 15A. The 2nd 15A breaker is now unused. It did have several transformers attached to it to power outdoor lights (via a 4-way switch), but as none of them work any longer I completely removed those connections from the box. I did take a picture but it didn't come out too clearly. I can try and get one again later if it helps.

ericmark: Thanks for your input. I will probably need a pro to put your suggestions into practice.




Today, as well as disconnecting everything that was unneeded, and testing without the outdoor lights attached I did another test. I attached the Dryer to a socket in the kitchen (on a different MCB protected by the same RCD) with an extension lead and when I switched off the garage light, the RCD tripped again.

I'm beginning to think that the problem lies with the Dryer itself, but I'm reluctant to go out and get a new one only to find I get the same problem. When I get a chance I will take a look inside the dryer to see if there is any sign of water inside the unit. It wouldn't surprise me to find condensation accumulating as it is pretty cold in the garage at this time of year.

 

[BS3036]

I've been thinking along the lines that the garage neutral is connected to the neutral bar on the 'not protected by rcd' side. A photo inside the cu may help, but I don't want to encourage you to provide one if you're not going to do it safely. It would definately involve switching the main switch on the cu first.

 

[Lectrician]

I've been thinking along the lines that the garage neutral is connected to the neutral bar on the 'not protected by rcd' side. A photo inside the cu may help, but I don't want to encourage you to provide one if you're not going to do it safely. It would definately involve switching the main switch on the cu first.

Not if the drier is connected to the kitchen via an extension....

You need a sparky with an insulation tester, the knowledge to use one effectively, and the patience to spend an hour or two locating the fault. It will not cost the earth (at most sparks rates), and will determine the cause for you.

Can you live without a dryer for a while? See if your problems vanish?

I have now disconnected everything except the double socket and lights from the garage circuit. Problem still apparent.

You isolated the neutrals too??

 

[BS3036]

Not if the drier is connected to the kitchen via an extension....

and when I switched off the garage light, the RCD tripped again.

 

[Lectrician]

Not if the drier is connected to the kitchen via an extension....

and when I switched off the garage light, the RCD tripped again.

Ok, I missed a little there, but if the light operates perfectly well when lit, I can't see how the garage can have a 'crossed' neutral.

 

[BS3036]

Yes, I know, but it's simple to check, so has to be worth eliminating.

 

[ericmark]

Very likely dryer high lighting problem rather than being problem I would not replace it until tested as likely it will not help.

 

[Bozwell99]

You isolated the neutrals too??

Yes as far as easily possible. In other words all I had left were lengths of straight cable with nothing connected to the other end. All cables are exposed, and I can see they are in good condition.

You need a sparky with an insulation tester, the knowledge to use one effectively, and the patience to spend an hour or two locating the fault. It will not cost the earth (at most sparks rates), and will determine the cause for you.

Can you live without a dryer for a while? See if your problems vanish?

I think I might have access to an insulation tester, but not a person to operate it. How difficult are they to use for the intelligent amateur? Would it at least be relatively simple to use to test the Dryer?

For the last few weeks the problem has only occurred when the Dryer is in use. So still leaning towards that being the culprit, or is it possible that it takes the load of the Dryer in use to trigger another fault?

I've been thinking along the lines that the garage neutral is connected to the neutral bar on the 'not protected by rcd' side. A photo inside the cu may help, but I don't want to encourage you to provide one if you're not going to do it safely. It would definately involve switching the main switch on the cu first.

Do you mean the main CU in the house? Or the one in the garage. If the latter see below as I managed to get some better pics. You can't see all that much of the inside shot, but I had a good poke around and everything looks well connected.

Untitled

• Bozwell99
• 25 Jan 2010
• 1

Untitled

• Bozwell99
• 25 Jan 2010
• 1

Untitled

• Bozwell99
• 25 Jan 2010
• 1

 

[ericmark]

I think I might have access to an insulation tester, but not a person to operate it. How difficult are they to use for the intelligent amateur? Would it at least be relatively simple to use to test the Dryer?

Some tests are easy and some are complex.
Clipping on to neutral and earth pins and pressing button on every 13A plug may find the faulty item(Switched on of course). However as you start on house then it gets more complex.

You are looking at better than 1M ohm. Some items you can damage if they have filters and hard to be sure if anything you have would be damaged.

However unplugging items should also help in working out what is faulty.

With main switch off and everything unplugged you should have better than 1M ohm between earth and neutral and between earth and live. So first test not bad. But once that is completed I would not like to take someone through the tests even if on phone so in real terms unlikely you will find fault your self.

Sometimes one just has to admit better to get some one in to test it all.

Problem with a tumble dryer is most have some timer so to check often it needs some dismantling.

Try to explain to some one how to ride a bike. OK we all know it's easy but try putting into words. The same problem trying to explain testing. For me I find it easy but to explain to some one else that's different.

 

[BS3036]

Not if the drier is connected to the kitchen via an extension....

and when I switched off the garage light, the RCD tripped again.

Ok, I missed a little there, but if the light operates perfectly well when lit, I can't see how the garage can have a 'crossed' neutral.

Having slept on it, you're right.

I think the drier has a high leakage, which is not enough to trip the RCD on its own, and the leakage is being pushed over the edge by for example a faulty choke on the garage light. When switched off, the high voltage generated in the choke is leaking to earth. I think that's what Eric was saying here:

Very likely dryer high lighting problem rather than being problem I would not replace it until tested as likely it will not help.