Earth Sparkin (not ur usual......)

[Ipswich Sparky]

Testing an installation - RCD's not testing properly (can get a good test occasionally.?)- Newish Megger recently calibrated
just tested RCD's at home and all good

All MCB's off, RCD's off, main switch off and main fuse removed, no alternative supplies

can get a good tingle off of the earth - disconnected earth bonding to water (no gas or oil etc) and main earth bond no voltage on consumer unit earth bar measured

PME installation - overhead supply - old uninsulated neutral style (N-L 243v , L-E 243v)

ALL circuits test perfectly IR, R1R2, ZE, ZS etc (supply 0.16 ohm Ze same as main bond approx 450mm long)

Can get a goodly spark to the earth bar in the consumer unit from either.... - have a video of this - showing exactly above
cannot measure a voltage across either and earth in the consumer unit common but they spark

Realise there will be earth potential on water pipework etc

Any ideas ?

 

[Strima]

Correct polarity?

 

[Lucien Nunes]

It sounds like the circulating currents that are common in PME, with some current from other installations returning to the transformer via your bonding and the earthed services. It's not necessarily a problem, seeing as you are not getting a significant voltage discrepancy or high Ze that would indicate a broken PEN. It might be an indication of why PME specifies a larger minimum size of MEB conductor, and why the gas meter people put a cable across the meter pipework before removing or fitting a meter, to avoid exactly that spark.

I don't think it is necessarily related to the RCD behaviour.

 

[moose]

Is there any Battery connections in any fittings. Supply cable DNO? check that

 

[Ipswich Sparky]

Correct polarity?

Yep

 

[Ipswich Sparky]

Is there any Battery connections in any fittings. Supply cable DNO? check that

Hi
Nothing whatsoever connected with a battery- property also empty , timer for immersion mechanical etc

 

[moose]

What voltage you getting off dare i say it incomming CPC when not connected. be carefull.

 

[Ipswich Sparky]

It sounds like the circulating currents that are common in PME, with some current from other installations returning to the transformer via your bonding and the earthed services. It's not necessarily a problem, seeing as you are not getting a significant voltage discrepancy or high Ze that would indicate a broken PEN. It might be an indication of why PME specifies a larger minimum size of MEB conductor, and why the gas meter people put a cable across the meter pipework before removing or fitting a meter, to avoid exactly that spark.

I don't think it is necessarily related to the RCD behaviour.

Hi
Thanks for that
Surely any circulating currents would effect the rcd operation - I can get a good test on both rcd's sporadically -was there almost three hours and tested rcd's randomly many times over that period - 50% success , often two or three tests on the trot good..
Surely this cannot be acceptable ?
Would the DNO be able to check / sort ?
Thanks

 

[Ipswich Sparky]

What voltage you getting off dare i say it incomming CPC when not connected. be carefull.

No voltage - tested several times over a period of three hours...

 

[moose]

The problem could be inside the property. from anything. Take them all out find which CPC is the issue there. one random cpc doing something.

 

[Ipswich Sparky]

The problem could be inside the property. from anything. Take them all out find which CPC is the issue there. one random cpc doing something.

All PC test well all Ir tests good

 

[pc1966]

Surely any circulating currents would effect the rcd operation -

No, as the RCD measures the imbalance between L & N, is it not looking at any CPC current that might be circulating (assuming it is an RCD and not an ancient VOELCB).

Now if you have an N-E fault it could be a different situation, as you might have some anti-phase current in the N making the trip threshold for the RCD test higher than usual, etc. But you should always (and apparently already have) have checked the global IR (overall L+N to E) situation first before wondering about potential RCD issues.

 

[pc1966]

Do you have access to a similar model to do a simple swap and check to see if it is just a dodgy RCD?

 

[Ipswich Sparky]

No, as the RCD measures the imbalance between L & N, is it not looking at any CPC current that might be circulating (assuming it is an RCD and not an ancient VOELCB).

Now if you have an N-E fault it could be a different situation, as you might have some anti-phase current in the N making the trip threshold for the RCD test higher than usual, etc. But you should always (and apparently already have) have checked the global IR (overall L+N to E) situation first before wondering about potential RCD issues.

Surely if you have circulating currents on a pme system when a second earth via water pipes etc is introduced this would affect the rcd ?

 

[Ipswich Sparky]

Do you have access to a similar model to do a simple swap and check to see if it is just a dodgy RCD?

Have done with both - no change

 

[Ipswich Sparky]

Surely if you have circulating currents on a pme system when a second earth via water pipes etc is introduced this would affect the rcd ?

Surely the circulating current is a closed loop until the secondary earth via water pipes is connected ?

 

[pc1966]

Surely if you have circulating currents on a pme system when a second earth via water pipes etc is introduced this would affect the rcd ?

The CPC/earth is not passing through the RCD, it looks only at the final circuts' L&N which ought not to have connected to the CPC in any way.

If you have a high circulating current in the PME to earth bonds it might change the L-N volts slightly but it is not going to have any significant impact on the RCD behaviour.

As you have done a swap and it seems not to be the RCD, and the IR is fine so there should not be any oddities due to a N-E fault, you should look to see if there is any odd loads on the circuits that might be causing some stray current.

Do you have a clamp ammeter that can measure down to mA to see what sort of imbalance is currently happening?

Another possibility is there is a faulty load causing a DC fault that might blind a 'type AC' RCD, but again that sort of thing ought to show up on the IR tests. Though maybe try the IR test with both polarities in case you just happen to have tested a diode fault the wrong way for any significant leakage.