how do i test for earth ?

[andy-10]

I've just moved into a new flat. I want to test that the water pipes and central heating pipes have been earthed properly.

Can I use a multimeter to do this ? How exactly can that be done ?

 

[blacksheep]

I would of thought that a basic test is to test continuity (ie. near zero ohms on the multi) between the pipes and a nearby earth point (ie. an earth prong on a socket). But saying that I know it is possible to get a low-ohm reading on a wire when its nearly broken or wouldnt stand up to any sort of load (like what is required to trip a fuse etc.). Plus im NOT an electrician only someone with some knowledge (more electronics) so dont take what I said as any definite answer!!
I have some broken bonding under my bath, easy enough for me to cleanup the pipe and fix the earth clamp (not sure what you sparks/elecs call it) but still not a definite test which needs doing in my house at some point!

Im still wondering if anyone is going to say anything about this in another thread I have going..

 

[sparkybird]

To prove main equipotential bonding is in place you need to get a reading of 0.05 Omhs or less between the pipes and the main earthing terminal. You can do this using your multimeter and a length of conductor as a wander lead. Don't forget to zero out the leads and conductor. You need to also check the gas pipe.

SB

 

[plugwash]

most multimeters are not going to give you meaningfull readings for values that low, they also don't tend to have a zeroing facility. To test this kind of thing properly you really need a proper low ohms meter.

 

[blacksheep]

I got a nice analogue meter with zeroing control. Does this mean that there is not 'load' test if you see what I mean?

 

[RF Lighting]

You would still need to find the ends of the cable.

It is possible to get a 'satisfactory' reading despide the main earth being drastically undersized, or even non existant (if parallel paths exist)

 

[JohnD]

when you say "test" I presume you mean you have already inspected, and see 10mm G&Y connected to the MET, and clamped onto the incoming metallic services at the proper place?

If not, you should install such cables rather than waste your time testing.

 

[Spark123]

You should use a low resistance ohm meter with a no load voltage 4-24V DC and a closed circuit current of not less than 200mA:
The wander lead method:
Isolate the supply.
Connect the wander lead across the meter and either note the resistance or zero the meter.
Connect one end of the wander lead to the MET
Disconnect the Main Equipotential Bonding conductor under test at the pipework etc.
Measure the resistance between the MEB conductor and the wander lead.
Deduct the resistance of the lead from the result unless you zeroed it with the lead.
Ensure you reconnect the Main Equipotential Bonding conductor before you re-energize the supply.

 

[blacksheep]

I havent done any testing of the earth yet but I presume you mean the OP although everything here he will find useful. My lack-of bonding is here

Underbath earth bonding
http://www.zen44027.zen.co.uk/DSCN0650.JPG
http://www.zen44027.zen.co.uk/DSCN0653.JPG

Ok what exactly (dont want to assume) is MET and MEB (I admit to have not tryed to look around board and find out)

 

[Spark123]

MET is Main Earthing Terminal.
MEB is Main Equipotential Bonding (and me being too lazy to type it in full)

 

[bengasman]

You can use a multi meter to check if it is really no good but you need a earth fault tester to be sure that it is okay. And you need to know how to do the test. This is one of those tests that a lot of people do slightly wrong.
One good reason to leave it to a pro, during the testing the earth is disconnected and therefore the entire house is at risk if it is not reconnected correctly.

 

[andy-10]

thanks for all your help ;
much appreciated.

andy

 

[blacksheep]

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