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Help with IR test & bonding query


avinalarf

Question

Testing a ring and get 289ohms for line-earth and 222ohms for neutral-earth.

But when I try testing for line-line or line-neutral my Fluke 1652 won't do anything :( . Any suggestions? Could I be doing something wrong?

A PME installation and at the main fuse (is this what you guys also refer to as "cut-out"?) there are 3 earth cables coming from it, but only 1 of them at the CU. Does this mean that one goes to water and the other to gas? Would this at all explain why I'm getting 201ohms when I do a continuity test from the CU to the gas?

TBH, I'm not 100% sure how to check the bonding with this sort of set up. Some guidance would be greatly appreciated.

Nat

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Okay.........er Nat:

1. If you`re doing IR tests, your readings should be in the Mohms range, not ohms.

2. For the fluke, no matter which cables OF THE INSTALLATION you`re testing, you ONLY use the phase and earth leads (as signified by the two dots in the top centre of the display..?)

3. For testing the earth continuity, run a long lead out from the CU. Connect to EITHER earth OR phase connections of meter. Suppose you use earth.

Then connect red test lead from meter to MET in CU, effectively creating a loop with your long lead. On low ohms (knob pointing straight up, third position from left), press and hold "zero" to short out the resistance of your leads.

Note that you do not zero test leads on insulation testing.

Now unclip the red lead from the CU, and go to the gas / water bonds.

Disconnect the cable from the clamp, and clip your red lead to that. Press "Test". The result should be something like "0.06" (dependant on length / size of conductor).

I don`t quite know what you were trying to test with the insulation. If it were a socket circuit, and you`ve used the test lead with a plug on, then the best thing is to remove the 4mm plugs from the back of the meter, and connect the plugs coloured for the test you want to do into the RED and GREEN sockets only. i.e.

RED plug-RED socket & GREEN plug-GREEN socket = phase/earth insulation test.

BLUE plug-RED socket & GREEN plug-GREEN socket = neutral/earth test

RED plug-RED socket & BLUE plug -GREEN socket = phase/neutral test

Got it???

KME

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Thanks for all your help guys. Earth clamp was loose and pipe was very green underneath! Scrubbed it so it looked like copper again and fitted new earth clamp.

Got a reading of 0.16 megohms. Is this still a bit high? Would changing cable to 10mm make any difference?

Got 0.03 on water.

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If you can see cable I would test that do an R2. If you have a high reading then as you say there may be a break in cable. If its a good reading it may be that clamp is loose or corroded.

Batty

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Thanks for all your help guys. Earth clamp was loose and pipe was very green underneath! Scrubbed it so it looked like copper again and fitted new earth clamp.

Got a reading of 0.16 megohms. Is this still a bit high? Would changing cable to 10mm make any difference?

Got 0.03 on water.

I do hope 0.16 is ohms NOT megohms!!!:_|:_|

Assuming they are both ohms....

you can check your expected values using the resistance tables in OSG page 166.

so if you are getting reading 0.03ohms for 6mm copper,

then from the table 1m of 6m is 3.08miliohms

(0.03/3.08) x 1000 = 9.7.. suggesting your water bond is round 10m long?

and

0.16ohms of 6mm copper..

(0.16/3.08) x 1000 = 51.9.. suggesting your 'gas?' bond is approx 52m long?

would either of these figures match up with the size of the installation and the likely cable routes? e.g. ups & downs as well as horizontal distances?

IF your one reading IS 0.16MEGohms..

that would give you

(160,000ohm / 3.08) x 1000 = something like 519000 x 100m drums of 6mm!!!:o:_|

:^O:^O:^O:^O:^O

HTH:x

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Update on previous week's job...

Called EDF [yesterday] and, surprisingly, they booked an engineer for this morning Applaud Smiley.

Great guy who was a fountain of knowledge and informed me that the installation was one of the early PMEs and that's how the earths were installed.

Anyway Ze checked out ok, but the reason for the high reading when checking continuity to gas bonding was due to the fact that there was no link between the neutral and the earth bars at the CU, which was necessary :|.

Well, this was all new to me, but I did as he suggested and hey presto, reading comes right down to 0.16 Mohms, which, even though I thought it was still a bit high, he said was fine.

I think I've convinced the client that she REALLY should upgrade her CU, so obviously, I'll upgrade earths whilst I'm at it.

Thank you all for your valued input.

Nat

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Okay.........er Nat:

1. If you`re doing IR tests, your readings should be in the Mohms range, not ohms.

Hi KME, thanks for taking the time to answer. Yes, I know that - just didn't add the M to the icon Blushing

2. For the fluke, no matter which cables OF THE INSTALLATION you`re testing, you ONLY use the phase and earth leads (as signified by the two dots in the top centre of the display..?)

Yep, ok with that also.

3. For testing the earth continuity, run a long lead out from the CU. Connect to EITHER earth OR phase connections of meter. Suppose you use earth.

Then connect red test lead from meter to MET in CU, effectively creating a loop with your long lead. On low ohms (knob pointing straight up, third position from left), press and hold "zero" to short out the resistance of your leads.

Note that you do not zero test leads on insulation testing.

I was using a long bit of cable and it was 0.05, so was just going to subtract that from the reading to gas.

Now unclip the red lead from the CU, and go to the gas / water bonds.

Disconnect the cable from the clamp, and clip your red lead to that. Press "Test". The result should be something like "0.06" (dependant on length / size of conductor).

Ok, this is where you're confusing me! We were taught to disconnect gas/water earth from MET (to avoid parallel paths), connect PE lead (green) to disconnected earth and just press the probe of the (red) test lead onto the pipe as close to the bonding clamp as possible, but not on it! We were definitely not told to undo the earth clamp.

I don`t quite know what you were trying to test with the insulation. If it were a socket circuit, and you`ve used the test lead with a plug on, then the best thing is to remove the 4mm plugs from the back of the meter, and connect the plugs coloured for the test you want to do into the RED and GREEN sockets only. i.e.

RED plug-RED socket & GREEN plug-GREEN socket = phase/earth insulation test.

BLUE plug-RED socket & GREEN plug-GREEN socket = neutral/earth test

RED plug-RED socket & BLUE plug -GREEN socket = phase/neutral test

Got it???

KME

I WAS trying to do an IR test on a ring. I had pulled the cables at the CU and was testing that way (how I was taught). Just couldn't understand why my tester counted up to over 500V when testing from earth to line or neutral, but only going up to 1 when testing between line and neutral. Hope that makes sense.

Was my assumption about the earth cables from the main fuse correct?

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The reason I said about using the plug is that, esp. in the little wylex boards, removing & correctly identifying the ends of the ring can be a pain. If, on the other hand, you open a socket on the ring without spurs (2 cables), you can easily see what is what. :)

I've had to go to a job in Berkshire (make-up job!) so I've not been able to get on the forum much :(...

I did manage to locate the RM quite easily - fortunately. Sounds dumb, but I didn't realise you could test for IR anywhere in the ring Blushing. Doesn't the fact that the neutral and cpc conductors are still connected at the CU matter then???

If your fluke is only reading 1V test on insulation, there is a load / leak which is dragging the voltage down; i.e. if the washing machine was still coneected & switched on, the fluke would "try" ( & fail dismally) to power it. The insulation test, albeit at high holtage, has minimal current behind it, meaning the slightest leakage will drop the voltage at the tester.

So how come the tester still counts up to over 500Mohms when carrying out the cpc - line/neutral test:|

Do a trial ins. test on your calibration check thingy, and you`ll see the voltage doesn`t get up to the same figure as open circuit.

Will do when I get home on Saturday.

If you`ve only got 1V, try using either low ohms scale, or a multimeter if you have one, to measure the resistance between phase & neutral. Something as small as a neon built into a socket will do it (make sure that socket is off), or a spur to something that hasn`t been isolated.

Test at 250V first - you won`t damage anything then. Once you find & remove the load, go back up to 500V test.

Any better?

KME

I do have a multimeter and since reading a previous thread on the forum, I always test at 250V first [just in case...] ;)

Won't return to this job until next week, so I'll let you know.

Thank you

:x

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What about if you cut the earths coming out of the main cut out...

fit your own earth block..

then re terminate the earths back into your new earth block....

you can also then do a few continuity test to identify where each earth wire goes... Gas / water etc..?

thats what I would probably do:):|

Note...

If you do go ahead and cut & re terminate the earths..

kill the rest of the installation while you are doing it as there will be NO earth protection to any of the circuits while you have them open circuit.!:);):D

SL - if I were to do what you suggest, would I be obliged to upgrade the cables to 10mm as they're only 6mm at the moment :o Also, would it be ok just to cut them off and leave the bits hanging? My guess is "not", but I don't know how to get in to this box.

Anyway, I'm returning to the job next week, so I'll take a closer look.

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Earth cables from the cut-out , well there is supposed to be only one, the main earth cable, (usually 16mm) to the C/U or main earth bar. However I can only guess that the other two are indeed the bonding cables , is the board an old Wylex with the pathetically short earth bar with the tiny terminal holes ??

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Continuity... high reading...

Assume IT IS correct!

e.g. the earth is open circuit! or very bad joint somewhere?

Is there any paint or corrosion visible on the pipe by where you are testing?

Have you got a CalCard "checkbox" very useful to verify your meter is working in these situations?:|;)

Any paint or corrosion around the earth clamp?

:|

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I do hope 0.16 is ohms NOT megohms!!!:_|:_|

Assuming they are both ohms....

you can check your expected values using the resistance tables in OSG page 166.

so if you are getting reading 0.03ohms for 6mm copper,

then from the table 1m of 6m is 3.08miliohms

(0.03/3.08) x 1000 = 9.7.. suggesting your water bond is round 10m long?

and

0.16ohms of 6mm copper..

(0.16/3.08) x 1000 = 51.9.. suggesting your 'gas?' bond is approx 52m long?

would either of these figures match up with the size of the installation and the likely cable routes? e.g. ups & downs as well as horizontal distances?

IF your one reading IS 0.16MEGohms..

that would give you

(160,000ohm / 3.08) x 1000 = something like 519000 x 100m drums of 6mm!!!:o:_|

:^O:^O:^O:^O:^O

HTH:x

Its a mansion.

ROTFWL

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Hi Deke

Earth cable to CU is defo not 16mm! Yes it's a horrible old Wylex. Don't know what to do regards checking continuity to gas & water 'cos I can't open main fuse to get to earth cables there...

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what you could do is go to the end of the service pipe (box) find a nearest live to use and do a loop impedance measurement , it's not strictly good practice but it will give you a indication if the bonding/earthing is working????

oh and make sure no customers are near any metalwork:)

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Hi Deke

Earth cable to CU is defo not 16mm! Yes it's a horrible old Wylex. Don't know what to do regards checking continuity to gas & water 'cos I can't open main fuse to get to earth cables there...

Nat just check between main earth bar in consumer unit and the services.

Batty

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I do hope 0.16 is ohms NOT megohms!!!:_|:_|

Assuming they are both ohms....

ROTFWL

Sorry about that typo Blushing. Yes, SL, it's ohms

you can check your expected values using the resistance tables in OSG page 166.

so if you are getting reading 0.03ohms for 6mm copper,

then from the table 1m of 6m is 3.08miliohms

(0.03/3.08) x 1000 = 9.7.. suggesting your water bond is round 10m long?

and

0.16ohms of 6mm copper..

(0.16/3.08) x 1000 = 51.9.. suggesting your 'gas?' bond is approx 52m long?

would either of these figures match up with the size of the installation and the likely cable routes? e.g. ups & downs as well as horizontal distances?

HTH:x

That does help - I really need to make better use of my OSG.

The water one seems realistic, but 52m for the gas :o??? Forgive my ignorance, but isn't the earth clamp closest to the meter supposed to be the first one on the chain or am I missing the point a bit here?

Could they have run the earth cable from the MET to various points within the house and then to the one that's nearest to the gas meter - bearing in mind, it's not actually that close!

The meter's on the outside wall of the garage. Pipe runs through garage wall, up in a corner, along the width at ceiling height, then above some panelling in an external walk-through between the house and the garage. Earth clamp is here, which is about 7/8m from the meter itself, but only about 3m from MET, which is why I'm assuming it was placed here instead of where the pipe entered the garage :|.

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Hi Deke

Earth cable to CU is defo not 16mm! Yes it's a horrible old Wylex. Don't know what to do regards checking continuity to gas & water 'cos I can't open main fuse to get to earth cables there...

What about if you cut the earths coming out of the main cut out...

fit your own earth block..

then re terminate the earths back into your new earth block....

you can also then do a few continuity test to identify where each earth wire goes... Gas / water etc..?

thats what I would probably do:):|

Note...

If you do go ahead and cut & re terminate the earths..

kill the rest of the installation while you are doing it as there will be NO earth protection to any of the circuits while you have them open circuit.!:);):D

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AH.

I didn`t say undo the clamp; just disconnect the cable from it. Doesn`t matter which end you disconnect from (although, on reflection, removal at CU end may help to differentiate which bond is which :) )

The reason I said about using the plug is that, esp. in the little wylex boards, removing & correctly identifying the ends of the ring can be a pain. If, on the other hand, you open a socket on the ring without spurs (2 cables), you can easily see what is what. :)

If your fluke is only reading 1V test on insulation, there is a load / leak which is dragging the voltage down; i.e. if the washing machine was still coneected & switched on, the fluke would "try" ( & fail dismally) to power it. The insulation test, albeit at high holtage, has minimal current behind it, meaning the slightest leakage will drop the voltage at the tester. Do a trial ins. test on your calibration check thingy, and you`ll see the voltage doesn`t get up to the same figure as open circuit.

If you`ve only got 1V, try using either low ohms scale, or a multimeter if you have one, to measure the resistance between phase & neutral. Something as small as a neon built into a socket will do it (make sure that socket is off), or a spur to something that hasn`t been isolated.

Test at 250V first - you won`t damage anything then. Once you find & remove the load, go back up to 500V test.

Any better?

KME

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Sorry guys, but I've had to backtrack...Blushing

I have removed that link between neutral & earth at CU under Elecsa's advice. They stated that the EDF chap (as nice as he was) was totally wrong advising me do that - tut, tut :o

One handy thing he did do though, was to break out the covering of the earth bar at the cut out, so I could access it. This enabled me to identify all 3 earth cables which were coming from it.

Anyway, Ze at CU was 0.19 Mohms (fine for TNC-S).

Problem is that when doing continuity check on bonds for gas and water, I'm getter over 1500 Mohms :_|

Any explanations please?

Confused.Nat

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Not meaning any disrespect Nat, but have you got the settings on your tester set properly? very easy to get them wrong unless you purposely check each time.

AndyGuiness Drink

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None taken Andy. Fluke was definitely on continuity setting. Did test three times! Have spoken to an ex electrician and now tutor who thinks the bonding cables are broken somewhere.

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Thats very possible. Can you do long lead method? as you can get an idea of where the break is by dividing reading by resistivity tables in the back of the OSG to see how far the break is.

AndyGuiness Drink

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Thats very possible. Can you do long lead method? as you can get an idea of where the break is by dividing reading by resistivity tables in the back of the OSG to see how far the break is.

AndyGuiness Drink

Ok, now you're talking above me :(

How would I do that?

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Nat are you testing on the bonding clamp or at a pipe. If you are testing at a pipe it maybe that it has plastic in it so there is break in the bond.

Batty

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Hi Batty

I was taught to always test at the pipe as near to clamp as possible, but not on it. The system is fairly dated - client has said that she's going to get a new boiler, so unsure about plastic piping.

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Hi Batty

I was taught to always test at the pipe as near to clamp as possible, but not on it. The system is fairly dated - client has said that she's going to get a new boiler, so unsure about plastic piping.

Can you actually see the cable though if you are getting high readings like that I would think there is plastic pipe in the system.

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