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I have measured high currents in the CPCs of four circuits as shown in the table below.
  • This is the case both with the circuits energised and isolated.
  • Removing the CPCs for these four circuits brings the current in the MET to DNO cut-out, back to genuine L+N measured leakage levels.
  • However with the CPCs connected, the current in the MET to cut-out increases significantly under load (4.1A with a 19A load, 5.6A with a 31A load) as opposed to 19mA and 22mA respectively with the four CPCs disconnected.
  • Ze is good.
Any ideas?

High Earth current flowing High CPC current tests 110819 - EletriciansForums.net
 
Did you test ze with main earth disconnected from earth bar?
I wonder if you have an earth fault from source and a fault is passing current to your pipework.
 
Did you test ze with main earth disconnected from earth bar?
Yes

I wonder if you have an earth fault from source and a fault is passing current to your pipework.
You mean an earth fault on the supplier's side?
It's certainly no coincidence the four circuits concerned are HVAC with continuity through the copper pipes.
 
What's the physical layout of this site?

Just wondering if you have cutout at one end of building, AC units are at the other end, outside on a concrete pad, and just over the fence from the AC units sits the substation?

Out of interest, what was the original symptom that caused you to measure these leakage currents in the first place?
 
If it's a TN-C-S with a fair amount of drop in the CNE, any load is likely to drive current through those CPCs as well as the MEB although the majority of it should go through the MEB. Is the MEB up to scratch, or might there be something substantial, in contact with the pipes and therefore the HVAC CPCs, that is not bonded as it should be?

I have to wonder, what first drew your attention to the EC current? PME supplies specify a large CSA for the MEB exactly because these circulating currents are more or less unavoidable, so having a few amps in the EC is not automatically indicative of a problem. However, if there is a high resistance anywhere it's on the DNO's side.

Post crossed with BE's, thinking along very similar lines...
 
What's the physical layout of this site?

Just wondering if you have cutout at one end of building, AC units are at the other end, outside on a concrete pad, and just over the fence from the AC units sits the substation?
It is a rural residential location (period barn conversion).
A single AC outdoor condenser connected to five room airflow units over four levels, the indoor units taking their 230V from the condenser.
The DNO head is to the front of the building, the AC condenser to the rear (circa 20m apart)
There is no substation close.

Out of interest, what was the original symptom that caused you to measure these leakage currents in the first place?
I noted them whilst investigating RCCB tripping on the standby generator.
 
Ah...the plot thickens! Is there a source electrode for the genny?
There will be - i have 8' of 5/8" rod on site, being buried on Tuesday, to satisfy 551.4.3.2.1. (the generator is not in standby use yet and won't be until this is done.)

Presumably it's a pole mount tx, and overhead supply to somewhere relatively close to the barn, final connection maybe underground to cutout if a recent conversion?
Exactly as you describe. The TN-S was jointed and PME'd underground 1m from the front of the property. The overhead supply is circa 30m away as the crow flies, there's probably closer to 45m of underground supply cable for the route it takes.
 
Bellendian said: Out of interest, what was the original symptom that caused you to measure these leakage currents in the first place?
I noted them whilst investigating RCCB tripping on the standby generator.

However, the CPC currents don't seem to be leakage and not necessarily related to any RCD tripping events as the insulation is good. It's just ordinary neutral current finding its way back to the transformer any way it can. One of the disadvantages of TN-C-S.
 
a bad/poor neutral somewhere,
forcing the neutral currents to find other return paths,
in this case the earth circuit.
check and double check all neutral and earth connecttions.
 
I happened upon this thread which may now be resolved. But in my research into equipotential bonding requirements I read in the reference that for TNC-S it must include HVAC too. See para 8.3 of attached file.

Does your installation physically bond the HVAC viz AC, Boiler, IH back to MET ( - in addition to gas and water at service entry) ?
 

Attachments

  • EART-01-002.pdf
    1.3 MB · Views: 2
Last edited by a moderator:
TonyMitchell: I have been playing about with some sums on your observations. Could you tell me please what Ze and Zs you measured or approximate figures?

Is the property near any others that might share the same gas and water pipes? Would you know if the service pipes are metal?

If the property has neighbours on the same transformer do you reckon they have TNS or TNCS?

When you say 'condenser' do you mean 'compressor'?

REgarding the 'condenser' does the home use an air space heat pump providing warmed air and warmed water as well as cooling as required?

A response before 8pm today would keep me amused while my wife and invited in-laws watch Britain's Got Talent - World Championships after we have eaten my home-made Devon pasties!

:)
 
I happened upon this thread which may now be resolved. But in my research into equipotential bonding requirements I read in the reference that for TNC-S it must include HVAC too. See para 8.3 of attached file.

Does your installation physically bond the HVAC viz AC, Boiler, IH back to MET ( - in addition to gas and water at service entry) ?
I've added the attachment to the post. We tend to find as posts get old, these links break, and it ruins the advice. We don't really have limits on attaching files so always try stick it in the post if you can matey. :)

I know your local devices might have restrictions. And you just might end up with dozens of unwanted files etc. So I don't mind adding them myself if I find them. Perhaps even report the post for me and I'll add it if that helps.

But looking back over the years, we have a lot of 'checkout this file here' posts and the file has long gone. :(
 
TonyMitchell: I have been playing about with some sums on your observations. Could you tell me please what Ze and Zs you measured or approximate figures?
Ze definitely 0.29Ω
Zs of Air Conditioning circuit (from memory) <0.55Ω

Is the property near any others that might share the same gas and water pipes?
The closest neighbouring property is circa 40 metres
No gas services in the hamlet
Water: there are plastic sections between the incomer and potential upstream sharing

Would you know if the service pipes are metal? If the property has neighbours on the same transformer do you reckon they have TNS or TNCS?
One neighbour is definitely on the same transformer and it's highly likely they are TN-S
I think the other neighbour is on a different transformer.

When you say 'condenser' do you mean 'compressor'? Regarding the 'condenser' does the home use an air space heat pump providing warmed air and warmed water as well as cooling as required?
It's a Daikin 4MXM80N2V1B used for room cooling.
A separate oil fired boiler is used for underfloor heating and hot water.

Source URL: High Earth current flowing - https://www.electriciansforums.net/threads/high-earth-current-flowing.176710/#post-1575700
A response before 8pm today would keep me amused while my wife and invited in-laws watch Britain's Got Talent - World Championships after we have eaten my home-made Devon pasties!
Thanks buddy :D
 

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