Poor loop impedence in factory

daludo

Hi all
After installing an extra socket today in a factory we did a loop impedence test,result was >2000 ohms and the corresponding 20 amp rcbo tripped out. We presumed this means no earth present at the socket. However using a lead we got a resistance reading when attaching it from socket earth to main earth block in fuse board(.22 ohms).So is there a weak earth present? Is it a neutralising link issue? What would you test next?

TheBully

Where did u install the new socket? Did you loop if from existing or is it straight From board? If looped did u check previous socket?

ptogher14

With that type of reading it's something very obvious, even a mistake. Even with a broken earth you'd be expecting a high reading through metal work, parallel paths etc. That reading is suggesting an open circuit. Is it something as simple as wrong leads. Was the meter set live to earth or live to neutral? Did you try any other circuits?

2011

+1

daludo

ptogher14 wrote: »

With that type of reading it's something very obvious, even a mistake. Even with a broken earth you'd be expecting a high reading through metal work, parallel paths etc. That reading is suggesting an open circuit. Is it something as simple as wrong leads. Was the meter set live to earth or live to neutral? Did you try any other circuits?

We looped from existing socket. Fluke 1662 tester. We checked other sockets in d factory and they were fine.just used plug top,settings were left the same all the time.however when we did switch to L-N on the test there was a reading and the rcbo didn't trip

ptogher14

Was it an end of line socket you looped from? Did you test the socket you looped from?

daludo

ptogher14 wrote: »

Was it an end of line socket you looped from? Did you test the socket you looped from?

Same reading from other socket, not end of line

ptogher14

I would start by identifying all the sockets on the circuit and test each one. See if you can narrow down the problem. Or dead test and prove each conductor.

If you're testing I'm sure you're aware of regulations regarding spurring off circuits

daludo

ptogher14 wrote: »

I would start by identifying all the sockets on the circuit and test each one. See if you can narrow down the problem. Or dead test and prove each conductor.

If you're testing I'm sure you're aware of regulations regarding spurring off circuits

Hard to test every socket when it trips out the rcbo each time,office staff will not be impressed :-(

ptogher14

Harder to explain when someone or something gets harmed. I would prioritise safety over convienence of office workers.

Without insulting you are you aware of the importance of fault loop impedance

ptogher14

If this socket is feeding office workers, by any chance is it fed by a UPS? That's a different scenario

daludo

ptogher14 wrote: »

If this socket is feeding office workers, by any chance is it fed by a UPS? That's a different scenario

No ups involved.

Tuco88

Why not measure the L+E voltage at each point you may find a floating earth. I'd say you have even proven that by the wander lead.

Did you test the rcbo also?

I used to be like that too, feck the staff if they can't understand it.. a good belt from a pc they will be houling at you. I would give them a time x o clock power down for 20 mins or come in early.

Gashmuncher

The basic questions you are asking suggest you are not competent to carry out electrical work in the first place. Are you carrying out the loop test in the low current mode. It is normal that a high current loop test will trip an RCD or RCBO. Your circuit should not be put into service unless the correct loop value is achieved. Have a look at Annex 63B in the wiring rules ET 101. You should not have added a new socket in the first place unless you had the correct loop value at the socket you are looping off. Do you realise that it is critical that the earth loop reading is below the required limit in order to generate enough fault current to take out the protective device in the required time. Get a proper electrician to check out your work before you kill some innocent person.

PS. .22 ohm is a completely normal reading for resistance of a protective conductor and is equivalent to the resistance of 30 meters of 2.5 MM. cable. This is not a "weak" Earth as you suggest further highlighting your lack of competence.

daludo

Gashmuncher wrote: »

The basic questions you are asking suggest you are not competent to carry out electrical work in the first place. Are you carrying out the loop test in the low current mode. It is normal that a high current loop test will trip an RCD or RCBO. Your circuit should not be put into service unless the correct loop value is achieved. Have a look at Annex 63B in the wiring rules ET 101. You should not have added a new socket in the first place unless you had the correct loop value at the socket you are looping off. Do you realise that it is critical that the earth loop reading is below the required limit in order to generate enough fault current to take out the protective device in the required time. Get a proper electrician to check out your work before you kill some innocent person.

PS. .22 ohm is a completely normal reading for resistance of a protective conductor and is equivalent to the resistance of 30 meters of 2.5 MM. cable. This is not a "weak" Earth as you suggest further highlighting your lack of competence.

Thanks to all of you who contributed positively to this thread,I'll take your comments on board.On a personal note I'd love to meet this ars##### above in person. Thanks again to the rest of you for your positive advice.I'll pm some of you again. Over and out.ðŸ‘

Bruthal

Gashmuncher wrote: »

PS. .22 ohm is a completely normal reading for resistance of a protective conductor and is equivalent to the resistance of 30 meters of 2.5 MM. cable. This is not a "weak" Earth as you suggest further highlighting your lack of competence.

That reading was a resistance test with a long lead. The weak earth thing was in reference to the poor impedance result I would think.

A circuit with a perfect protective conductor can still return a poor loop test result.

Tuco88

Gashmuncher wrote: »

The basic questions you are asking suggest you are not competent to carry out electrical work in the first place. Are you carrying out the loop test in the low current mode. It is normal that a high current loop test will trip an RCD or RCBO. Your circuit should not be put into service unless the correct loop value is achieved. Have a look at Annex 63B in the wiring rules ET 101. You should not have added a new socket in the first place unless you had the correct loop value at the socket you are looping off. Do you realise that it is critical that the earth loop reading is below the required limit in order to generate enough fault current to take out the protective device in the required time. Get a proper electrician to check out your work before you kill some innocent person.

PS. .22 ohm is a completely normal reading for resistance of a protective conductor and is equivalent to the resistance of 30 meters of 2.5 MM. cable. This is not a "weak" Earth as you suggest further highlighting your lack of competence.

No need for the personal insults to be fair point was made clear enough, A few people that post in the Electrical forum are as helpful as a shovel of sand imo. At the end of the day all they want is helpful input.

Gashmuncher

Bruthal wrote: »

That reading was a resistance test with a long lead. The weak earth thing was in reference to the poor impedance result I would think.

A circuit with a perfect protective conductor can still return a poor loop test result.

The resistance of the long lead (wander lead) should be discounted by nulling or zeroing the meter with the wander lead in the circuit. This in effect cancels out the lead resistance and gives a correct reading for the true resistance of the protective conductor (including parallel paths). I have assumed that the original poster did the test correctly thereby getting a perfectly normal reading for the protective conductor. Most electricians who carry out tests do not know how to correctly Zero their own test equipment leading to incorrect resistance of protective conductors being recorded.

There is no room for incompetence in electrical testing. Any electrician who needs to post on this tread asking how to carrying it electrical tests should not be carrying out electrical work in the first place.
The purpose of this tread is to give advise for general electrical work, not to tell an incompetent electrician how to deal with a loop impedance reading that does not comply with the wiring rules. If an electrician has to post on boards to find the answer to that, he should not be doing the work in the first place.

Bruthal

Gashmuncher wrote: »

The resistance of the long lead (wander lead) should be discounted by nulling or zeroing the meter with the wander lead in the circuit. This in effect cancels out the lead resistance and gives a correct reading for the true resistance of the protective conductor (including parallel paths). I have assumed that the original poster did the test correctly thereby getting a perfectly normal reading for the protective conductor. Most electricians who carry out tests do not know how to correctly Zero their own test equipment leading to incorrect resistance of protective conductors being recorded.

Thanks, didnt realise that:pac:

There is no room for incompetence in electrical testing. Any electrician who needs to post on this tread asking how to carrying it electrical tests should not be carrying out electrical work in the first place.

I dont know many who know everything about electrical testing

The purpose of this tread is to give advise for general electrical work

Is it?

not to tell an incompetent electrician how to deal with a loop impedance reading that does not comply with the wiring rules. If an electrician has to post on boards to find the answer to that, he should not be doing the work in the first place.

You said a "weak earth" is not the cause of the problem. Why not tell the lesser mortals what the cause is then?

Gashmuncher

"You said a "weak earth" is not the cause of the problem"


Where did I say that ????

What I did say is that the reading of .22ohm is a perfectly normal reading and not a weak earth.
I suspect the cause of the high loop reading is that the incorrect high current setting of the Fluke meter thereby tripping the RCBO any displaying 2000 (which is out of range reading on a Fluke meter)
If the meter is set at the correct low current range the RCBO won't trip. I have also seen lots of mistakes being made by mixing up the neutral and earth leads on the fluke lead with the 13amp plug top. The fact remains that the original poster should have verified that the correct loop value was present at the first socket before he looped another soctet off it.

ptogher14

Gashmuncher wrote: »

"You said a "weak earth" is not the cause of the problem"


Where did I say that ????

What I did say is that the reading of .22ohm is a perfectly normal reading and not a weak earth.
I suspect the cause of the high loop reading is that the incorrect high current setting of the Fluke meter thereby tripping the RCBO any displaying 2000 (which is out of range reading on a Fluke meter)
If the meter is set at the correct low current range the RCBO won't trip. I have also seen lots of mistakes being made by mixing up the neutral and earth leads on the fluke lead with the 13amp plug top. The fact remains that the original poster should have verified that the correct loop value was present at the first socket before he looped another soctet off it.

Out of memory the fluke meter doesn't have a no trip function for Z loop. I stand to be corrected though

Bruthal

Gashmuncher wrote: »

Where did I say that ????

Slight hint of it there...

Gashmuncher wrote: »

This is not a "weak" Earth as you suggest further highlighting your lack of competence.

The fact remains that the original poster should have verified that the correct loop value was present at the first socket before he looped another socket off it.

Should he? And then what?

It probably is simply the tester tripping the RCD. Perhaps assistance rather than bordering on abusing would be indicative of a better electrical crafts person.

Gashmuncher

ptogher14 wrote: »

Out of memory the fluke meter doesn't have a no trip function for Z loop. I stand to be corrected though

Have a look at the photo at this link

https://www.google.ie/search?q=fluke+multifunction+tester&rlz=1C9BKJA_enIE681IE681&hl=en-GB&prmd=ivsn&source=lnms&tbm=isch&sa=X&ved=0ahUKEwikgpqJr97SAhUXM8AKHbsUBVMQ_AUIBygB&biw=1024&bih=653&dpr=2#imgrc=TyxvDStYIYUr_M:

All multi function Fluke meters have "No Trip" (low current) and "trip" (high current) loop functions.

ptogher14

I stand corrected

Gashmuncher

[QUOTE=Bruthal;102945235


Should he? And then what?

[/QUOTE]

He should not have added further sockets until he had determined and repaired the cause of the incorrect loop reading. This would have ensured that the reading at the new added in socket could also be correct. This would be normal electrical good practice when adding to existing circuits.

Tuco88

Even testing with the high current setting if I remember you still get some sort of reading or error for the power loss.

I take its dado sockets no steel conduit in sight?