RCD's tripping

[gselectrical]

Evening all.

Had a call out earlier to a caravan park. The RCD's on various hookups trip during heavy rain. Checked enclosures, they are reasonably new, no moisture etc. They are all fed via a 16mm 3 core SWA. Main DB MET is connected to an earth rod (TT) which is in good condition. Tested a few hookups. All RCD tests fine. 112 ohms was the highest reading.

The site has had a new 3 phase supply installed recently and they believe the RCD's have only being tripping since then.

If anyone can point me in the right direction on this one it would be much appreciated.

Cheers

 

[Zeespark]

What milliampage are the new RCD's GS?

AndyGuinness

 

[a1spark]

From what you describe ,i would say it looks like Supply related problems.....a call to the DNO may produce some help .

 

[matt.leung]

y do u think it is a supply related problem... could be a low insulation resistance fault ???

 

[gselectrical]

y do u think it is a supply related problem... could be a low insulation resistance fault ???

All tests fine. It was all upgraded 2 years ago.

Cheers

 

[sparkytim]

Thunderstorms ? or just rain ?

Transient voltage disturbance on supply often takes out RCDs.

 

[Sidewinder]

A few things to get the grey cells going...

Are the hook ups on the same ph?

Are they physically adjacent?

Are they off the same DB?

What is the upstream protective device?

Are they on seperate CPD's?

What else is fed localy from that ph/db/CPD?

Did all trips go instantaneously?

Did they cacade?

Was it during a thunderstorm?

How often does it happen?

How many times has it happened?

Do all the RCD's trip times test OK on the affected devices it seems yes, but at what time value?

What is the trip current for each of the affected devices?

What is the standing leakage on each RCD?

Are they all the same make/batch?

If you trip one with your meter on test do any of the others go out?

Can you simulate a high earth fault current to see if that causes a cascade trip?

Have they added any additional kit to the DB recently?

Drainage pump on VSD?

HF lighting?

Could it be harmonic effects?

It could be mains disturbance and 1001 other things try working through these ideas and we can formulate a plan...

"I love it when a plan comes together!"...

 

[gselectrical]

--------------------------------------------------------------------------------

A few things to get the grey cells going...

Are the hook ups on the same ph? No

Are they physically adjacent?No

Are they off the same DB?Yes

What is the upstream protective device?60898 B40

Are they on seperate CPD's?Yes

What else is fed localy from that ph/db/CPD?other hookups that dont seem to trip

Did all trips go instantaneously?I believe so

Did they cacade? ?

Was it during a thunderstorm? It was when it was raining heavily so it could have been during a storm

How often does it happen?only when it rains heavily

How many times has it happened?3 times

Do all the RCD's trip times test OK on the affected devices it seems yes, but at what time value? Yes 26.7mS @ I, 6.5mS @ 5I

What is the trip current for each of the affected devices?16A 30mA DP RCBO

What is the standing leakage on each RCD?How can I measure this? Dont believe it exceeds 10mA

Are they all the same make/batch?No

If you trip one with your meter on test do any of the others go out?No

Can you simulate a high earth fault current to see if that causes a cascade trip?No

Have they added any additional kit to the DB recently?No

Drainage pump on VSD?

HF lighting?

Could it be harmonic effects?

It could be mains disturbance and 1001 other things try working through these ideas and we can formulate a plan...

"I love it when a plan comes together!"...

Thanks for the help

 

[matt.leung]

try doing a ramp test to see how sensitive the rcd is.....

 

[Sidewinder]

GS,

My typo, I meant do they fail in cascade manner, that is one fails then the others go in "sympathy"? I missed the s out of cascade!

Are they trye DP RCBO's? many are single pole solid N.

What make are they?

When I asked the trip current, I meant did you do a ramp test to measure the actual tripping current.

You can measure the standing leakage with an earth leakage clamp meter invaluable for these sorts of fault.

You answered no to my question:

Can you simulate a high earth fault current to see if that causes a cascade trip?

Do you mean you cannot simulate it, or that it does not happen?

They may not cascade they may go immediately.

Is there any upstream RCD protection?

 

[a1]

"I love it when a plan comes together!"...

You could use that as your "Signature" mate.

The supply in the pic below is the next one to us, that was wide open (Lock in locked position) when I arrived on oud Holiday last month.

There were tents all around it and children hanging around and nosing in it. Naturally, I didn't have a key, so I just closed it with a little persuation.

The guy in the tent said it hasn't worked since he was there (RCD Triiped). Explained that the conductors were still Live, hence me shutting it.

Apparently - tripped all the time.

At the end of the week, just before we come home, new arrivals arrived at the camp site, complained in the office that the leccy didn't work - Guy came up on his golf cart, and just switched the RCD back on.

 

[Sidewinder]

Just like that...

That pic is appaling Admin!

Was that local? Is it the site KME is pricing up on?

I don't think that complied with the 16th as far as the location goes. IIRC each "socket/supply" must be on its own RCD.

If that was me I'd have issued an EDN there & then! (I'd probably be sad enough to have my pad with me!) :coat

 

[a1]

It's a well known Caravan (Static & Tourers) and Camping Site in Swansea, Mate.

It is an old one.

Lol at your Pad with you.

I don't know which site he is pricing up mate. :C Maybe he could PM me?

 

[gselectrical]

GS,

My typo, I meant do they fail in cascade manner, that is one fails then the others go in "sympathy"? I missed the s out of cascade! Not too sure, i dont think the owner could distinguish between them tripping in symphany or all together

Are they trye DP RCBO's? many are single pole solid N. Believe they are DP

What make are they? some square D (6ka) and some proteus (3ka)

When I asked the trip current, I meant did you do a ramp test to measure the actual tripping current. 23-28mA

You can measure the standing leakage with an earth leakage clamp meter invaluable for these sorts of fault. on order

You answered no to my question:

Can you simulate a high earth fault current to see if that causes a cascade trip? With an RCD tester? (500mA)

Do you mean you cannot simulate it, or that it does not happen?

They may not cascade they may go immediately.

Is there any upstream RCD protection? Don't believe there is. Hookups fed from B40 breakers. That board is fed from 160A 60947-2 MCCB (TP)

Cheers

 

[Sidewinder]

I'm almost certain that the SqD are Single Pole Solid Neutral, SPSN.

BTW which leakage clamp did you go for?

I was thinking about something a bit more than that simulated dead short or very near for the fault current check.

I guess both makes of RCBO are tripping?

IF the SqD is one of these: SQOR116B03, it is only single pole with a solid neutral.

Thus, you could have an N fault causing "confusion" downstream from one of the rcbo's close to the system origin causing the others to trip?

I just re read a few posts and the mains has been upgraded recently, how recently and is it definite that the tripping has only arisen since then?

What is the main incomer?

Almost certainly TN-C-S with PME, but how it is presented & labelled is another thing.

How far away is the local sub do you know?

Do all the hook ups share the same rod?

Try swapping 2 rcbo's one that trips & one that does not to see if the fault transfers?

The rcbo's are only rated at a certain number of trips before they should be replaced, it is possible that they have reached the end of their natural life?

Is it the RC or the O side that is going? Difficult to tell I know. One disadvantage of RCBO's.

Could you put a temp RCD & MCB in place to test?

 

[gselectrical]

I'm almost certain that the SqD are Single Pole Solid Neutral, SPSN.

BTW which leakage clamp did you go for? Went for the Metrel TEK 633

I was thinking about something a bit more than that simulated dead short or very near for the fault current check.

I guess both makes of RCBO are tripping?Yes, they are

IF the SqD is one of these: SQOR116B03, it is only single pole with a solid neutral. Sorry, made a mistake. The Square D device is an RCD with OC protection provided by an MCB, I have added an image of an RCBO below, this is similar to the others

Thus, you could have an N fault causing "confusion" downstream from one of the rcbo's close to the system origin causing the others to trip?Good point

I just re read a few posts and the mains has been upgraded recently, how recently and is it definite that the tripping has only arisen since then? ?Within the last 2 years. Deffinatly since then, however some other electrical work has been carried out at around the same time. (new hookups etc)

What is the main incomerAlmost certainly TN-C-S with PME, but how it is presented & labelled is another thing. Yes TN-C-S

How far away is the local sub do you know?Not sure, fed from overhead lines

Do all the hook ups share the same rod?They do. This is located next to the main I-line board

Try swapping 2 rcbo's one that trips & one that does not to see if the fault transfers?Would it be worth concidering replacing all the RCBO's that have tripped? (6 in total)

The rcbo's are only rated at a certain number of trips before they should be replaced, it is possible that they have reached the end of their natural life?

(Only 2 years old)

Is it the RC or the O side that is going? Difficult to tell I know. One disadvantage of RCBO's. I can only assume its the RC side as the Square D RCD went aswell

Could you put a temp RCD & MCB in place to test?

Maybe it would be best to replace them all?

Cheers for the help Sidewinder

 

[Sidewinder]

Proteus don't now list a 3kA RCBO, 4.5 or 6.

Their single module devices are SPSN as SqD, as are most to be honest, MK included.

IF they are 2 module then they are probably DP.

That looks like an RCD mind, not an RCBO, can quite make out the schematic properly.

I think you may struggle with the TEK633, the jaws are very small.

Ok for single circuits, but you'd struggle to clamp an incomer, let us know, how about a review on it once you have used it a bit?

I'm not going to enter into debates wrt PME & TN-C-S, but ESQCR demand that CNE/PEN supples are PME end of.

Thus, you may have an earth rod on the incoming network near your rod, could this be causing circulating currents due to a DNO fault?

Look around at the local poles, you should see the earth coming down the side of the pole, it may be capped, and the rod is probably buried a few inches.

So the SqD supplies are a single RCD & MCB in series per hook up?

This is the 26th/17th requirement as I understand it.

The proteus ones are DP RCBO's yes?

The SqD MCB had not tripped? Thus we can rule out overcurrent faults.

Is the TN-C-S adequately seperated to TT, or is "your" rod just acting as another PME rod on the DNO network?

 

[gselectrical]

Proteus don't now list a 3kA RCBO, 4.5 or 6.Thats my mistake then, it must be a different make. But I know that its a 2 module RCBO

Their single module devices are SPSN as SqD, as are most to be honest, MK included.

IF they are 2 module then they are probably DP. 2 module

That looks like an RCD mind, not an RCBO, can quite make out the schematic properly.

I think you may struggle with the TEK633, the jaws are very small.Great! Should have done more research

Ok for single circuits, but you'd struggle to clamp an incomer, let us know, how about a review on it once you have used it a bit?Will do

I'm not going to enter into debates wrt PME & TN-C-S, but ESQCR demand that CNE/PEN supples are PME end of.

Thus, you may have an earth rod on the incoming network near your rod, could this be causing circulating currents due to a DNO fault? Good point. Relocate rod?

Look around at the local poles, you should see the earth coming down the side of the pole, it may be capped, and the rod is probably buried a few inches.

So the SqD supplies are a single RCD & MCB in series per hook up?Yes this is the setup of the Square D Device that has tripped in the past

This is the 26th/17th requirement as I understand it.

The proteus ones are DP RCBO's yes? 2 module so I assume DP

The SqD MCB had not tripped? Thus we can rule out overcurrent faults. Yes we can rule out OC faults

Is the TN-C-S adequately seperated to TT, or is "your" rod just acting as another PME rod on the DNO network? I believe it to be aduqualtly seperated. It is connected the the main Iline MET via 35mm earth

Cheers

 

[Sidewinder]

Is the TN-C-S adequately seperated to TT, or is "your" rod just acting as another PME rod on the DNO network? I believe it to be aduqualtly seperated. It is connected the the main Iline MET via 35mm earth

Cheers

Can you please clarify this?

As I understand your comment the TT rod at the ILine is connected to the board, via a 35mm sq. earthing conductor. ILines are metal aren't they?

Is this board tied back to the premises MET?

If so then your rod is acting as another PME on the DNO side as well as a TT rod, but your earth readings sound high for this to be the situation.

The earthing should be isolated at the ILine and connected at the other end of the sub main to offer correct disconnection at the sub main origin.

Perhaps it may be just as well to rod the individual distribution points?

You'd need to check the requirements in the brb.

Also it may be just as well to put together all the comments & Q&A's then draw up a diagram of the system and start making notes as to what is happening where and the various parameters etc. so that you can start to build a picture of the install etc.

 

[gselectrical]

Can you please clarify this?

As I understand your comment the TT rod at the ILine is connected to the board, via a 35mm sq. earthing conductor. ILines are metal aren't they?

Is this board tied back to the premises MET?No

If so then your rod is acting as another PME on the DNO side as well as a TT rod, but your earth readings sound high for this to be the situation.I didn't word it very well. The Iline is not tied back to the premises MET

The earthing should be isolated at the ILine and connected at the other end of the sub main to offer correct disconnection at the sub main origin.

Perhaps it may be just as well to rod the individual distribution points?

You'd need to check the requirements in the brb.

Also it may be just as well to put together all the comments & Q&A's then draw up a diagram of the system and start making notes as to what is happening where and the various parameters etc. so that you can start to build a picture of the install etc. Will do