Help with IR test & bonding query

[avinalarf]

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.

 

[batty]

Hi BattyI 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.

 

[avinalarf]

I can see the cable. I'll try and look for some plastic. Does that mean the plastic could be anywhere within the house then?

 

[batty]

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

 

[SPECIAL LOCATION]

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?

:|

 

[avinalarf]

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.

 

[SPECIAL LOCATION]

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

HTH:x

 

[batty]

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

HTH:x

Its a mansion.

ROTFWL

 

[avinalarf]

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 ??? 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 :| .