Gomez Addams said:

The electrician measured the rod resistance at 534 ohms.

How did he do that?

Gomez Addams said:

The electrician measured the rod resistance at 534 ohms.

How did he do that?

Good question. He wouldn't engage with me at all when I questioned his report. I did it with a Megger CM500, a long wire and a ground probe. Measured a least 15M from the rod in more than one place.

Today I called by to speak to my tenants about something else. I asked about the electrician, who I have never met, he was referred to me by a letting agent. My tenant told me he said he could only half the checks because "he didn't have the right equipment with him". She didn't know what he meant, which is fair enough, why should she? She asked him if the house was safe and he told her yes. I am wondering if he had any idea of what he was doing at all.

The instructions for your meter state that the temporary electrode should be 20 - 30m away, so that may account for some of the discrepancy, plus of course you're not measuring the supply side, maybe another 20 ohms? 

Personally I always loop test if the supply is connected as it's far less faffing about.

It does sound like he's inexperienced when it comes to TT, or perhaps EICRs in general.  I would have coded as C3, with no expectation that any improvement would ever be sanctioned by the client. 

I know of at least one DNO that insist on less than 200 ohms for new installations and they can, and have, issued demands for improvement within a 3 month time frame.

You sound like you are competent, so why not put in another rod (or 2) and move on knowing that your paying tenants are safe?  

I fully intend to check after the weekend if there is an issue with the connections to the rod, and if not pop a second rod in. I have four houses on TT in a radius of less then 100m. 3 are fine this ones not. I really don't think the ground conditions are going to be significantly different in such a small area.

I'm not disputing that the value is high and lower would be better. I am disputing the C2 and the "potentially dangerous" that comes with it.

As an aside. My own house is one of the 4 on TT. When my kids were little they said they could feel a tingle when the were washing their hands. We are on a plastic water supply. I felt nothing, but I measured everything and found nothing untoward. Eventually, I felt it too when I had a cut finger. It wasn't off the taps or the steel drainer, it was in the running water. I suspect they could feel it because they didn't have hands like leather. I got rid of it with 20m of copper under my front garden. The touch voltage was about 30V to start with, It was about 3V when I was done. Insulation measurements were all good. I was never sure where leakage came from. I suspect it was any or all of fluorescent tube fittings, fridge freezers or switching power supplies.

The comparison with the neighbouring properties is the killer information actually.

- while others "400-500Ω is around 5x to 10x higher than I'd get for a simple 4' rod sunk into half decent soil around here "

I have worked in a (dry sandy) place where we sunk two sets of 8 foot rods in parallel about one rod length apart, and still only  just got down to about 200 ohms, varying a bit with method of measurement (I think 340-370 or so per single rod). Equally, a few years ago now I did some electricals at the Essex Scout Jamboree, and in the ever damp Essex clay we saw 80-100 ohms off half length rods (2ft) adequate results from container gensets dropped on their skids even with no electrodes, and  single figure ohms from a metal framed marquee.  So what is OK really varies with location.

Mike