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[Sir Tigger KC]

I had a new boiler fitted in a rental property 12 months ago by British Gas under one of the free boiler schemes. 

The British Gas engineer has been today to service it and told my tenant that "The earth is over 100 and should be below"   I've now got a worried tenant. 

It seems strange to me that it was fine 12 months ago but now there is a problem.  Have regs changed recently?    Or is it a case of the British Gas guy being over zealous? 

I'm not an electrickery wizard, but I guess that the 100 he refers to is 100ohms resistance and maybe a good clean of all the earth straps and connectors might do the trick? 

TIA 

[Marks DTM Calib]

100 ohms is stupidly high, what was he measuring between?

Any work recently e.g. new gas meter/supply pipe?

[Sir Tigger KC]

I don't know how he measured it as I wasn't there and the only work that has been done was fitting the new boiler and radiators last year. 

What do you mean by stupidly high?  As in I have a real problem or a British Gas made up problem? 

It's strange that all was OK 12 months ago when the work was done. 

[Marks DTM Calib]

Do you have the test certificate from the install?

I would expect it to be well below 100miliohms

The only earth bonding would generally be at the gas pipe within a short distance of the meter (hence the question regarding new meter/supply pipe), at the cold water supply pipe within a short distance of the stop cock and then usually some cross bonding of heating pipes.

The original installation certificate should state the measured value as was.

Nothing has changed with respect to these regs for a few years (in fact the latest IET regs simplified the earthing requirements)

[Marks DTM Calib]

Oh......there not engineers.......far from it, barely can be classed as fitters..... (standard rant lol)

[Sir Tigger KC]

Oh......there not engineers.......far from it, barely can be classed as fitters..... (standard rant lol)

That's why I'm suspicious!  I'm guessing that he plugged a device into a socket and it gave him a green/amber/red light or something along those lines! 

Ah so it's 100milliohms, the message I got was 'over 100' so I assumed it was 100 ohms. Like said, not an electrickery wizard!   

[Marks DTM Calib]

Key thing is, what was it when installed......

[Sir Tigger KC]

Key thing is, what was it when installed......

Yes I'll have to check that.  Thanks. 

[Marks DTM Calib]

Other thing to do is inspect the earth bonding points.

Thing is he cant measure the 'earth' (without big long spikes banged into suitable ground), only the resistance between the bit he puts the probe onto and the bit he puts the other probe onto. 

[Rods2]

How was the earth resistance being measured?

If from the boiler to a main earthing point then I would expect milliohms, where it needs to be under 1ohm, but if measuring to the ground then it will vary depending upon the ground conditions.

Have a read of this thread to get the picture:

http://www.theiet.org/forums/forum/messageview.cfm?catid=205&threadid=52356

This is a very good guide for measuring earth resistance.

http://www.wiley.com/legacy/wileychi/eca_wiringregulations/supp/Appendix_12.pdf

You can get 4 wire milliohm meters on ebay for about £60, but do you need to go to these lengths?

It was useful looking these up as I got to rewire the mother-in-laws house in Ukraine this summer, which is a standard ex-Soviet live and neutral system with 2 pin plugs and sockets and I will be adding an earth rod and converting to a three wire, three pin system, like the rest of mainland Europe. Aluminium cored cable is also common over there where it is cheaper!

[Sir Tigger KC]

Thanks for that Rods. 

I don't know how the guy measured the earth resistance as I wasn't there, but I can't imagine he did a thorough test as he was only there to service the boiler. 

Scanning through your links I get the impression that 2 electricians could get 2 different readings depending on how they tested it and whether the ground is sodden or dry. 

All the paperwork for the boiler is at the property so I'll go round later in the week for a lookysee.  Thanks for the replies! 

[zirk]

Not sure how they check Boilers for Earth, but on a Gas Mater Earth strap they push a Spike in the Ground at the nearest point, then do comparison checks with whats already fitted or installed.

Wouldn't surprise me, if the last visit, was miss read somehow, we had a random visit last year from a Safety Engineer (outside contractor), who said we have a series leak in the concrete buried pipework feeding our gas, and with that switch the Gas off and filed a report, within 12 hours we had a team of guys from National Grid turn up, who measured it, quietly said, nothing wrong with it, but the paperwork says Blah, Blah, and with that, then spent the next 3 days digging the Street Feed, Garden and re plumbed the pipework work around the outside of the House.