Earth leakage and EICR's

[cprfenom]

I have an installation that has an inherent earth leakage of about 15mA. The issue I have is that when I go to do an RCD test it trips due to the the additional current created by my MFT.

Question is, if this was an EICR what would you code it as and why? My take on this is that 15mA is still within safe limits and that its my machine that is taking it over the threshold, and that the costs to hunt out the leakage wont be always beneficial to my customer.

Kind regards,

Chris

 

[Engineer54]

So what's causing this inherent 15mA of leakage would be a good place to start??

You should actually be testing the RCD device at it's load terminals with the load conductors disconnected. You are testing the RCD device not the circuit, ....that should have been thoroughly tested prior to RCD testing...

 

[Marvo]

The CPC of a circuit is functional as well as protective, not all earth currents are fault currents. As above, test the functionality of the RCD with no loads connected, if the standing leakage is causing nuisance tripping then it will need to be established if it's a fault current or not and either fix it or redesign to accommodate it.

 

[cprfenom]

With the load disconnected my test shows 25mA-30mA and with load connected 15mA. So strictly under normal use it is doing its functioning all be it at lower than 30mA, but around 20mA.

The reason I ask is that strictly its works, but its the MFT is causing it to trip before I can do the test. Hence the question that on an EICR is this really a C2 or still a C3 with the need to investigate further.

 

[cprfenom]

I guess my concern is that its only tripping because the test Im doing at the circuit end is pushing it above 30mA, but the rcd is within the window that its not faulty.

 

[Octopus]

You should actually be testing the RCD device at it's load terminals with the load conductors disconnected. You are testing the RCD device not the circuit, ....that should have been thoroughly tested prior to RCD testing...

OP - read this again.

 

[davesparks]

I guess my concern is that its only tripping because the test Im doing at the circuit end is pushing it above 30mA, but the rcd is within the window that its not faulty.

You are testing it incorrectly, it should be tested at the outgoing terminals of the RCD with all loads disconnected

 

[David M]

You are testing it incorrectly, it should be tested at the outgoing terminals of the RCD with all loads disconnected

Yes, and then he should determine what is causing the leakage as a separate issue

 

[Marvo]

With the load disconnected my test shows 25mA-30mA...

So the RCD is operating fine.

The reason I ask is that strictly its works, but its the MFT is causing it to trip before I can do the test. Hence the question that on an EICR is this really a C2 or still a C3 with the need to investigate further.

I'm confused, why would you code it if it's working perfectly?

 

[Kamikaze]

I’ve got a feeling he’s talking about taking earth loop readings on the “No trip” setting but it’s still tripping the RCD?

 

[cprfenom]

I’ve got a feeling he’s talking about taking earth loop readings on the “No trip” setting but it’s still tripping the RCD?

Yes. That's what I was trying to say. Sorry I didn't explain myself

 

[Sintra]

All loads should still be isolated whilst doing a Zs so you should have no leakage.

 

[Kamikaze]

Yes. That's what I was trying to say. Sorry I didn't explain myself

Christ almighty! You RCD lunatic. Wars have started over less than that. :angel_smile:

 

[richy3333]

With the load disconnected my test shows 25mA-30mA and with load connected 15mA. So strictly under normal use it is doing its functioning all be it at lower than 30mA, but around 20mA.

The reason I ask is that strictly its works, but its the MFT is causing it to trip before I can do the test. Hence the question that on an EICR is this really a C2 or still a C3 with the need to investigate further.

Your dilemma was answered in post 2?

ok, no it wasn't, because what you meant isn't what was asked!

Are you saying you can't Zs test on one circuit or all circuits? I feel more info is needed to help, but...

Calculate your Zs readings. Put a note in the EICR that the Zs readings were calculated because of the tripping. Were the R1+R2 and IR readings all OK?You then need to discuss the issue with the client. What you then do, or not do will depend upon your terms of reference/engagement from the customer for the EICR.

test the RCD as per post 2.

Given the the question and the above captioned comment do you feel competent to do this work mate?

 

[Octopus]

With the load disconnected my test shows 25mA-30mA and with load connected 15mA. So strictly under normal use it is doing its functioning all be it at lower than 30mA, but around 20mA.

The reason I ask is that strictly its works, but its the MFT is causing it to trip before I can do the test. Hence the question that on an EICR is this really a C2 or still a C3 with the need to investigate further.

On the basis of what you have written here, did you turn off the other MCB's connected to the same RCD?

What ever the outcome of the tests, I would write a comment about the existing earth leakage on the report - whether it merits a C3 is another question.