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

 

[cprfenom]

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.

Tested without any loads, tested with all mcb's off I got 25mA at the rcd, which is an up front rcd before and consumer unit. If I test at the circuit end where I got my highest R1+R2 on a no trip setting then the RCD was still tripping when i try to measure Zs or do an RCD test at the same point. Now I know that it's earth leakage that's causing the issue and the rcd itself is fine. I've no issue calculating Zs, but I don't like the fact I cant do my tests at the point of highest R1+R2 without tripping it.

 

[richy3333]

Tested without any loads, tested with all mcb's off I got 25mA at the rcd, which is an up front rcd before and consumer unit. If I test at the circuit end where I got my highest R1+R2 on a no trip setting then the RCD was still tripping when i try to measure Zs or do an RCD test at the same point. Now I know that it's earth leakage that's causing the issue and the rcd itself is fine. I've no issue calculating Zs, but I don't like the fact I cant do my tests at the point of highest R1+R2 without tripping it.

So this is one circuit you are dealing with?
What are the circuit details - what does it do, what are your test values? Cont, IR, Zs Ze/Zdb
You say all loads off, are they also unplugged/disconnected?

 

[HandySparks]

Tested without any loads, tested with all mcb's off I got 25mA at the rcd, which is an up front rcd before and consumer unit. If I test at the circuit end where I got my highest R1+R2 on a no trip setting then the RCD was still tripping when i try to measure Zs or do an RCD test at the same point. Now I know that it's earth leakage that's causing the issue and the rcd itself is fine. I've no issue calculating Zs, but I don't like the fact I cant do my tests at the point of highest R1+R2 without tripping it.

It would help us to understand the problem if you stated exactly what the 'load' is that's causing this high leakage to earth and why you can't isolate or disconnect the load in order to take a Zs measurement at the downstream end of the circuit.

 

[davesparks]

Tested without any loads, tested with all mcb's off I got 25mA at the rcd, which is an up front rcd before and consumer unit. If I test at the circuit end where I got my highest R1+R2 on a no trip setting then the RCD was still tripping when i try to measure Zs or do an RCD test at the same point. Now I know that it's earth leakage that's causing the issue and the rcd itself is fine. I've no issue calculating Zs, but I don't like the fact I cant do my tests at the point of highest R1+R2 without tripping it.

Are you saying that with all MCBs off you had a 25mA earth leakage? Or do you mean a ramp test tripped the RCD at 25mA?
You are doing the RCD test incorrectly, this should be carried out at the RCD, not at the end of the circuit.
Did you have all loads disconnected when you carried out the Zs test? You could always use the alternative Zs test method.

 

[Sintra]

Tested without any loads, tested with all mcb's off I got 25mA at the rcd, which is an up front rcd before and consumer unit. If I test at the circuit end where I got my highest R1+R2 on a no trip setting then the RCD was still tripping when i try to measure Zs or do an RCD test at the same point. Now I know that it's earth leakage that's causing the issue and the rcd itself is fine. I've no issue calculating Zs, but I don't like the fact I cant do my tests at the point of highest R1+R2 without tripping it.

There is an alternative method of testing Zs that does not require your instruement to be on a "no trip" setting.

Edit. Notice this has been mentioned above.

 

[cprfenom]

Just want to than you for your advice.

It is clear that I really cant explain myself, and that isn't helping you to aid me.

Personally I have never seen an RCD trip on a no trip before when it hasn't been a faulty RCD. I also understand that my terminology is not great, and that must be frustrating.

The circuits I was testing normally have several computers, florescent tube fittings and 12v transformers on it. When testing the circuits, they were all disconnected and all readings were fine. I then reconnected and moved on to an under floor heating circuit, disconnected the load side of the FCU and tried to do the Zs test at this point the RCD tripped. If I turned off all MCB's it still tripped, if I removed all the nuetrals for the circuits Im not testing, the readings are good.

The original point for the EICR is that it by design has 15mA leakage and was strictly asking if this was a c3 with further investigation, or should I just leave it as is.

If this is still confusing, then I will not waste anymore of your time, but thank you for not being nasty about it.

 

[Engineer54]

Just want to than you for your advice.

It is clear that I really cant explain myself, and that isn't helping you to aid me.

Personally I have never seen an RCD trip on a no trip before when it hasn't been a faulty RCD. I also understand that my terminology is not great, and that must be frustrating.

The circuits I was testing normally have several computers, florescent tube fittings and 12v transformers on it. When testing the circuits, they were all disconnected and all readings were fine. I then reconnected and moved on to an under floor heating circuit, disconnected the load side of the FCU and tried to do the Zs test at this point the RCD tripped. If I turned off all MCB's it still tripped, if I removed all the nuetrals for the circuits Im not testing, the readings are good.

The original point for the EICR is that it by design has 15mA leakage and was strictly asking if this was a c3 with further investigation, or should I just leave it as is.

If this is still confusing, then I will not waste anymore of your time, but thank you for not being nasty about it.

If you have a 15mA background leakage, i'll ask if high integrity earthing has been applied to these circuits?? Many here would say that circuits supplying primarily IT/computer loads shouldn't be provided with RCD protection, but that's open for discussion....

 

[cprfenom]

If you have a 15mA background leakage, i'll ask if high integrity earthing has been applied to these circuits?? Many here would say that circuits supplying primarily IT/computer loads shouldn't be provided with RCD protection, but that's open for discussion....

High integrity earthing has been applied. Oddly enough the two RFC that supplied the computers were mixed up and missing one leg at the start.

 

[telectrix]

you could bridge the RCD to get your Zs readings on high current. don't forget to remove the bridging links immediately after, though.

 

[Engineer54]

Well if high integrity earthing has been applied, why are you questioning the 15mA inherent leakage?? If RCD has also been provided then as stated early on, test the RCD at it's disconnected load terminals!! You only need to test the RCD device itself, ''NOT'' the circuit or circuits that it is protecting. Never test an RCD downstream on the circuit wiring when conducting official results that will form part of a test report. Fine for fault finding and the like, but not for testing the permissible operational parameters of an RCD device!!