RCD in consumer unit keeps popping, replaced with new one, still same issue

[roys]

You may find that even after you have switched off all the MCB's you still get the RCD tripping because there might be a neutral to Earth fault on one of the circuits. 

 

[AnthonyP]

Thanks Roy - would unplugging appliances as well as switching off MCBs help narrow things down? ie. if I swith off MCBs and also unplug everything from the sockets in the relevant rooms and the RCD is not tripped then can we say the issue is with a socket in that area?

 

[roys]

Un plugging what you can will certainaly eliminate items.

Switching off MCB's will also certainaly narrow things down a bit.

Trying to work out that when it trips is anything else happening, for example central timed to come on, small animal triggering PIR sensor for an outside light, fridge coming on. Electrical Items outside and items inside that have water in them are always a favourite. Of course it could be none of them.

Try and narrow it down you may get lucky otherwise just wait for the spark.

 

[Murdoch]

OP .......... when the spark comes, run through the elimination tests you have done, as it may help................ but don't be surprised when he/ she appears to be checking what you have said!

 

[Risteard]

Morning guys!

Over the weekend I noticed that the 80a RCD in my consumer unit kept tripping. The house doesn't have anything particularly power hungry - no air con, no DIY tools. It even trips in the  middle of the night sometimes (I know so because the house alarm has a little fit when it detects there is no longer any power and switches to the backup battery).

I am wondering what it might be? I replaced the RCD with a second hand one from eBay, seller has 100% feedback and stated it was tested. Is that my issues (I replaced a duff one with a duff one) or is there something else I should look for?

Here's the unit with the switch pointed out. I have a multimeter at the ready to test, just tell me what to target.





Thanks in advance!

Seriously?

I would have started with testing the RCD to see if it is operating correctly first. For this you will need an RCD tested that includes ramp test.

I don't agree that ramp testing is required to verify that an RCD operates correctly. The prescribed tests (half current; I delta n and 5 I delta n) prove this.

 

[Andy™]

I don't agree that ramp testing is required to verify that an RCD operates correctly. The prescribed tests (half current; I delta n and 5 I delta n) prove this.

prescribed tests are enough, however ramp can sometimes be useful for fault finding.

 

[Risteard]

prescribed tests are enough, however ramp can sometimes be useful for fault finding.

I don't disagree, but they certainly aren't needed to prove whether the RCD is operating correctly. What needs to be remembered is that a 30mA RCD can legitimately operate anywhere between 16mA and 30mA.

 

[Murdoch]

prescribed tests are enough, however ramp can sometimes be useful for fault finding.

I would say say the ramp test is a vital test when looking at random rcd tripping, 

as is use of an earth leakage clamp meter ....... but that’s just me ....

I don't disagree, but they certainly aren't needed to prove whether the RCD is operating correctly. What needs to be remembered is that a 30mA RCD can legitimately operate anywhere between 16mA and 30mA.

Yes .... but if it’s tripping at 16 mA and there is background leakage of, say 15 mA ......

 

[Risteard]

I would say say the ramp test is a vital test when looking at random rcd tripping, 

as is use of an earth leakage clamp meter ....... but that’s just me ....

Yes .... but if it’s tripping at 16 mA and there is background leakage of, say 15 mA ......

I think you're missing the point. I'm not denying that a ramp test could be useful as a fault finding tool - what I am stating is that it isn't of any use to determine whether an RCD is operating within its parameters or not. That is verified by normal RCD testing, which is precisely why the tests are what they are.

 

[Murdoch]

I think you're missing the point. I'm not denying that a ramp test could be useful as a fault finding tool - what I am stating is that it isn't of any use to determine whether an RCD is operating within its parameters or not. That is verified by normal RCD testing, which is precisely why the tests are what they are.

I disagree.

If an RCD has a low threshold, say under 10 mA, then it could be the cause of the tripping ............... if this is not tested , how can it be verified good or not?

 

[Risteard]

I disagree.

If an RCD has a low threshold, say under 10 mA, then it could be the cause of the tripping ............... if this is not tested , how can it be verified good or not?

The half-current test already proves that it doesn't.

 

[Murdoch]

The half-current test already proves that it doesn't.

not convinced ............. I will keep on doing this test when investigating RCD tripping.

 

[Sharpend]

Surely if you are fault finding then as many tests as possible will eliminate or locate a potential source of the problem? 

 

[Risteard]

Surely if you are fault finding then as many tests as possible will eliminate or locate a potential source of the problem? 

I already said it has merit when fault finding but the proper sequence proves that the RCD is operating within its parameters. So other than fault finding it offers no benefit. 

not convinced ............. I will keep on doing this test when investigating RCD tripping.

A 15mA test proves it's not tripping at 10mA. How are you unconvinced of that incontrovertible fact? 

 

[Doc Hudson]

Morning folks. I have been a recommended a good electrician but he is only able to come and see me next Thursday.

While I am waiting I would like to do more fault finding, because the issue is that as soon as the RCD trips, the house alarm goes ballistic because it thinks somebody is trying to bypass it. It went off once at 3am and today at 7am....I apologised to the neighbours by they were not happy (understandably).

Why not fix your house alarm while you are waiting for someone competent to arrive to test your electrical fault?  A correctly working alarm system will not start sounding due to a power failure. It sounds to me as though you need a new back up battery fitted inside the alarm panel. Typically the common batteries have a manufactures recommended lifespan of around 5 or 6 years. And they will keep the alarm system running all good and quiet during a power failure due to RCD issues or external suppliers power cut.

Doc H.

 

[Doc Hudson]

Went to bed last night and before doing so, I switched off the 4 x MCBs to the right of the RCD:

1. Electric shower (we never use this, it does work, but we just don't use it)

2. Sockets first floor (on the image it is on, ignore, at the time of going to bed it was down / off)

3. Lights

4. Wall lights

So only the Ring Circuit 1st Floor and Ring Circuit Ground Floor was on. And at 7am, the RCD tripped.

My plan is to repeat the above experiment again, but this time, in addition to having the 4 x MCBs to the right of the RCD in the off position, I shall disconnect anything plugged into the mains ion the 1st floor.

I am wondering if a lose wire is touching the back box or earth? We had some screwless sockets installed about 7 months ago, perhaps that is the cause?

Without disconnecting the neutral legs of the circuits you aren't proving much. Any one of those 6 circuits could supply current through a neutral - earth fault to any part of the installation that is connected to the common earth and neutral terminations at the fuse box. This problem needs correct test gear to start eliminating circuits out of the equation.

Doc H.

 

[Doc Hudson]

I don't agree that ramp testing is required to verify that an RCD operates correctly. The prescribed tests (half current; I delta n and 5 I delta n) prove this.

You are quite correct to just verify the RCD complies with BS7671 requirements you do not need a ramp test. But I am guessing that both the current RCD and the one that was taken out are both working correctly and doing exactly what they were designed to do; Remove the power due to a detected fault. Once that has been established I tend to want to know just how sensitive the RCD is and what sort probable causes I am looking for. Which cannot really be done by just switching some circuits off and waiting to see what happens.

Doc H.  

 

[Andy™]

I disagree.

If an RCD has a low threshold, say under 10 mA, then it could be the cause of the tripping ............... if this is not tested , how can it be verified good or not?

itll trip in the 1/2 test when it shouldnt. therefore its faulty

 

[Murdoch]

itll trip in the 1/2 test when it shouldnt. therefore its faulty

Fair point but I wouldn't be fault finding RCD tripping with out doing a ramp test and using my earth leakage clamp meter ........................................ cumulative leakage is a nuisance in its own right............

 

[AnthonyP]

Little update - went to bed with the shower, first floor sockets, lights and wall lights MCBs all in the down position and all plugs taken out of their respective sockets - result? Still trips the RCD.

Next step was to try and see if perhaps it is one of the MCBs to the left of the RCD: ring circuit ground and first floor. 

I noticed that when the ring circuit ground floor MCB was down and everything was unplugged, there were no issues and the RCD didn't trip. However, and not always, but sometimes when I would flick that particular MCB up (we keep our bins and recycling in the garage, which has an electric door and this operates on that circuit), the RCD would immediately trip....does that tell us anything new or useful?