RCD doesnt trip on test.

[Templer]

Hi I have a 6 way split load board located in the shed and served by 10mm SWA. Anything on the unprotected side of the board tests and works fine. However this is not the same for the protected side. I can plug a radio in and the circuit does not trip, but if I use the lawn mower or a drill the RCD trips immediately. In addition, the RCD does not trip when the test button is pushed. I have swapped out the RCD too. Nothing trips on the house board when the RCD in shed trips. All connections are secure in CU. Any ideas where to go next?

 

[somersetsparks]

Ha s it ever worked or is it just something you have bodged in today?

 

[tony mc]

What tests on the protected side of the board have you done ?

 

[Marvo]

If the RCD is wired correctly plus there's power to it and it doesn't trip on the test button then replace it again, no if's or but's, it's faulty. The tripping under load could be a crossed/borrowed neutral or an insulation fault or it could also be a symptom of a faulty RCD.

Replace it then do global IR testing and recheck neutrals.

 

[somersetsparks]

Ha s it ever worked or is it just something you have bodged in today?

Sorry that sounded a bit mean, it sounds as if the neutrals are the wrong way around in the neutral bars.

 

[Templer]

Thanks for the reply (mean or not) . I didn't fit the board, we just moved in. The board looks like an off the shelf pre fitted one.

 

[Jabbajaws]

I have had this happen with the neutrals being crossed over to a different neutral bar. Id check that first and also treble check the wiring on all protected circuits but as Marvo says, if its wired correctly and the trip button doesnt activate then the RCD is faulty...

 

[Octopus]

Have you got 2 x fuseboards and 2 x RCD's in series?

 

[Templer]

Hi Jabbajaws. I have removed all circuits from the board and fitted a single socket and it still trips. I will check the neutrals. Would crossed neutrals cause the RCD not to trip on test?

 

[Templer]

Hi Murdoch, looking at it, the swa comes from a protected circuit on the main house cu. This runs 150' to the end of the garden into the 6 way. SWA is earthed at house CU.

 

[somersetsparks]

Hi Jabbajaws. I have removed all circuits from the board and fitted a single socket and it still trips. I will check the neutrals. Would crossed neutrals cause the RCD not to trip on test?

One Neutral should come from the bottom of the Main switch into the first neutral bar, then from that neutral bar into the top of the RCD, then from the bottom of the RCD into the second neutral bar.

 

[Templer]

One Neutral should come from the bottom of the Main switch into the first neutral bar, then from that neutral bar into the top of the RCD, then from the bottom of the RCD into the second neutral bar.

All neutrals are where they should be.

 

[Octopus]

What test kit do you have?

 

[MDJ]

Faulty Rcd? or your on LSD? lol

 

[Templer]

Just a Martindale MM39. I can get a meg next week if needed.

 

[Octopus]

Hi Murdoch, looking at it, the swa comes from a protected circuit on the main house cu. This runs 150' to the end of the garden into the 6 way. SWA is earthed at house CU.

So you do have 2 RCD's in series then.

Time to get my coat

 

[Templer]

So you do have 2 RCD's in series then.

Time to get my coat

So is that the problem?

 

[telectrix]

that's not the problem, but it's bad design as a fault on the sub-main circuits can cause the house RCD to trip, thus losing part of the house installation. i have had a similar fault caused by a N-E reversal in back of a socket outlet.

 

[Templer]

that's not the problem, but it's bad design as a fault on the sub-main circuits can cause the house RCD to trip, thus losing part of the house installation. i have had a similar fault caused by a N-E reversal in back of a socket outlet.

I can move the load to an unprotected side of the board.

 

[telectrix]

that would eliminate the series RCDs. i think you need to look more closely at the garage installation for a fault once you have determined that you have a good RCD.

 

[Templer]

that would eliminate the series RCDs. i think you need to look more closely at the garage installation for a fault once you have determined that you have a good RCD.

Tomorrow I will power up the garage CU from an extension and see if this removes the fault.

 

[somersetsparks]

Tomorrow I will power up the garage CU from an extension and see if this removes the fault.

I think you would be wasting your time doing that, as the garage rcd can't 'look back up the supply cable' for a fault.

 

[somersetsparks]

Right I'm gonna suggest something that I may get screamed at for by some on here, I don't recommend doing it but as you have no test equip. It may be the only way to test (ish) an RCD. I would remove rcd from board, connect a flex with plug top on one end into the top L and N terminals and plug into working socket outlet in your house, then push test button, if it trips the rcd then you at least know it fuctions and its your wiring at fault.

 

[Templer]

I think you would be wasting your time doing that, as the garage rcd can't 'look back up the supply cable' for a fault.

I can run a temporary from the CU to the garage, that should work?

 

[somersetsparks]

I can run a temporary from the CU to the garage, that should work?

Would be a waste of time though mate as if there was a fault it would be after the RCD in question not on supply cable to garage

 

[Octopus]

Or get a sparky with a MFT to come and ramp test your RCD?

 

[Templer]

Or get a sparky with a MFT to come and ramp test your RCD?

Do you ever get out this way?

 

[Octopus]

Do you ever get out this way?

Rarely travel more than 10 miles from my front door!

 

[guest119]

Rarely travel more than 10 miles from my front door!

Have you got one of them electronic tags on yer ankle M?

 

[somersetsparks]

Have you got one of them electronic tags on yer ankle M?

Ahh it all makes sense now, that's how comes hes on here not at the pub! 7pm curfew!

 

[saveloy]

Check inside the garage board. I had a fault exactly the same as this last week. RCD would hold but wouldn't work on the test button. Tripped on Zs test.Wouldn,t trip on any RCD tests. Disconnected everything from RCD and it worked perfect. Tripped on test button and all trip times within limits. As soon as busbar and outgoing neutral reconnected fault re appeared. Turned out to be an earth nicked on neutral bar. Once that was sorted all was perfect. Not saying this is definitely your problem but worth a look.

 

[Templer]

Check inside the garage board. I had a fault exactly the same as this last week. RCD would hold but wouldn't work on the test button. Tripped on Zs test.Wouldn,t trip on any RCD tests. Disconnected everything from RCD and it worked perfect. Tripped on test button and all trip times within limits. As soon as busbar and outgoing neutral reconnected fault re appeared. Turned out to be an earth nicked on neutral bar. Once that was sorted all was perfect. Not saying this is definitely your problem but worth a look.

I am tempted to put in another board. This one is an Excel, but I don't want to do all that and the fault still exists. There are benefits to buying a property that has unfinished work, but there are also many issues!

 

[saveloy]

You really need a tester. I wouldn't bother with changing the board until you have tested the RCD to ensure that this is not faulty.

 

[markc123]

Board change could be and probably is pointless.

The test button on the RCD is purely to make sure the RCD is working properly, it's nothing to do with the installation. If it doesn't trip when you press the test button then replace it, if you put in another and it does the same replace it again - they are dodgey RCD's. What make is the RCD? (sorry if already mentioned, just cba to read the full thread) stick a hager RCD in, more money but you get what you pay for and that is quality.

Replace RCD for a fully functioning one, then global IR to see if there are any issues with the installation. Board change probably unnecessary.

 

[Templer]

You really need a tester. I wouldn't bother with changing the board until you have tested the RCD to ensure that this is not faulty.

Which would you recommend?

 

[Templer]

Board change could be and probably is pointless.

The test button on the RCD is purely to make sure the RCD is working properly, it's nothing to do with the installation. If it doesn't trip when you press the test button then replace it, if you put in another and it does the same replace it again - they are dodgey RCD's. What make is the RCD? (sorry if already mentioned, just cba to read the full thread) stick a hager RCD in, more money but you get what you pay for and that is quality.

Replace RCD for a fully functioning one, then global IR to see if there are any issues with the installation. Board change probably unnecessary.

Hi Mark, thanks for the reply. The RCD is the same as board, Excel.

 

[markc123]

If you've bought a replacement Excel RCD and it doesn't trip when you press the T button, send it back.

When im doing installations, unless the client is on a poor budget i always fit either hager or Mk - there is a reason why some RCD's are 10x the price of others, even though they do the exact same thing lol.

 

[Templer]

If you've bought a replacement Excel RCD and it doesn't trip when you press the T button, send it back.

When im doing installations, unless the client is on a poor budget i always fit either hager or Mk - there is a reason why some RCD's are 10x the price of others, even though they do the exact same thing lol.

Will a hager or MK fit into an Excel board?

 

[markc123]

Will a hager or MK fit into an Excel board?

Hager are pretty good at being universal, however i wouldn't like to advise mate - never used Excel.

Do you have a specialist wholesaler near you that could advise you?

 

[Templer]

Hager are pretty good at being universal, however i wouldn't like to advise mate - never used Excel.

Do you have a specialist wholesaler near you that could advise you?

I will pop in tomorrow and ask the question. I think the time has come to invest in a tester

 

[FAA Greenie]

Templar - have a think about what happens when you press that test button.

I suspect you have a N-E fault. Your radio probably doesn't even draw 30mA so wouldn't trip it anyway.

Try testing the T button on the RCD with ALL the MCBs tripped and circuit neutrals disconnected - I bet it works.


If you have a short N-E in one of the circuits this board supplies, the test current generated when you press the button will be divided through the actual fault path, and also the artificial one provided by the test button. The odds are that the device will not trip because the required trip current will not met.

Worth trying.....

 

[Templer]

Templar - have a think about what happens when you press that test button.

I suspect you have a N-E fault. Your radio probably doesn't even draw 30mA so wouldn't trip it anyway.

Try testing the T button on the RCD with ALL the MCBs tripped - I bet it works.


If you have a short N-E in one of the circuits this board supplies, the test current generated when you press the button will be divided through the actual fault path, and also the artificial one provided by the test button. The odds are that the device will not trip because the required trip current will not met.

Worth trying.....

Interesting... I have removed all circuits from the board and it still does not trip on test.

 

[FAA Greenie]

Sorry buddy, I edited the post after I read it through again, did you disconnect final circuit neutrals too?

 

[Templer]

Sorry buddy, I edited the post after I read it through again, did you disconnect final circuit neutrals too?

Hi board has no circuits on it apart from a single socket on a lead and the RCD does not trip on test but trips as soon as load is placed on it. Could I have a N-E fault on the SWA? If so, would it not trip the RCD in the house CU which feeds it?

 

[FAA Greenie]

Hmmmmnnnn

See, if you also have the RCD in the main board supplying, you are still dividing the test current between two RCDs. It's a difficult one.

You really need to be able to IR test.

Do you have an unprotected way on the main board to connect the external board to?

 

[Templer]

Hmmmmnnnn

See, if you also have the RCD in the main board supplying, you are still dividing the test current between two RCDs. It's a difficult one.

You really need to be able to IR test.

Do you have an unprotected way on the main board to connect the external board to?

Hi, I do, but I would have to move the SWA as it is at the opposite end of the board. What if I took to RCD out of the garage board. Would the RCD in the house CU (it is an exclusive one for this circuit) be sufficient?

 

[FAA Greenie]

Not only sufficient, but preferable. The RCD on the main board would protect the whole installation from the SWA to the final circuits.

Don't forget that when you remove the RCD you need to do full testing and notify the work though, you will be changing the characteristics of the circuit.

Also, removing the RCD is not going to cure the fault you probably have somewhere.........

 

[Templer]

Not only sufficient, but preferable. The RCD on the main board would protect the whole installation from the SWA to the final circuits.

Don't forget that when you remove the RCD you need to do full testing and notify the work though, you will be changing the characteristics of the circuit.
Also, removing the RCD is not going to cure the fault you probably have somewhere.........

Thanks for the advice. If the fault was anywhere other than the RCD in the garage board, would the RCD in the house CU not have tripped when a load was placed on the side of the garage unit that was not protected?

 

[Templer]

Morning, I have this morning removed the RCD in the garage CU. The board is now served by SWA via 40A MCB protected by 63a RCD. Reconnected the ring and nothing trips when load applied (drill) at either end of circuit. The RCD in the board was 80a, will the 63a on the house cu be sufficient? Also, would you change the 40a MCB or leave it as is? Thanks again to all those that offered their advice. This is a great forum

 

[Thomas123]

What tests on the protected side of the board have you done ?

The "switch the mcb on and if it holds it works" test