Low Resistance Meter

The problem is likely to be calibrating it (and ensuring that it stays accurate)

Not sure about that. Pieces of copper and other cables have known resistances based on length which could be used to give a reasonable calibration. Most of the measurements needed are comparisons between the resistances, not absolute measurements to lab-accuracy.

The difficulty is finding a way to measure a range of 0 - 2 ohms with divisions of 0.05 ohm without spending 100 GPB a week. I seem to remember something from school days about a Wheatstone Bridge, but it was over 45 years ago. :-)

R.

don't low resistance meters work with mains voltage on? Wheatstone bridges are low voltage and you cannot use them with a voltage in the circuit

Not sure exactly what part P requires now, but there's a lot of Meggers of various ages on Ebay.

They should all measure down to < 0.1 ohms.

or

john

Get a large milliameter and connect it in series with a pot (variable resistor) and a battery, arranged so that you can get fsd on the meter. Connect a couple of probes across the meter movement and hey presto. If, for example the probes are fully shorted you'll clearly get no indication on the meter. The lower the resistance between the probes the less indication. You'll have to calibrate it with known low resistances, but it works and is very cheap!

Look for an insulation tester - they often have a low ohms range. Such as this one (which is the one I used last year for mine). No formal calibration certificate, but for private use (and see other messages re calibration):

TLC sell an Earth Loop and PSC tester for 320 quid + vat. However, this is a modern device that can do this without damage to a RCD and download test results to a PC. If you bypass any RCDs, an older one will be perfectly satisfactory. These often come up on Ebay.

To test insulation you need a different beast, commonly known as a Megger. These tend to be cheaper. TLC cost 89 quid. Again, common on Ebay.

Dave....the earth loop/PSC tester doesn't generally do the low resistance measurements in the way the OP needs...the TLC 'megger' does, as I mentioned in a previous post. I'm not sure if the OP was wanting to do the earth loop tests (although he probably should).

I think I paid 140 quid on ebay for a Robin earth loop/PSC tester, and I got the TLC insulation/resistance tester to complement it.

I want to do sufficient tests to ensure that the wiring is both safe and legal (I'm not stupid enough to imagine that the lawmakers got it right and the two are the same ;-). I plan to do some changes to the wiring myself, mainly tidying up 30 years of additions, and then have the whole lot tested professionally - but for cost reasons I don't want it to fail! (Hence: 320 is too much, but 100 is OK)

I've rewired houses completely before, but Part P didn't exist then.

Also my system is PME, so the earthing is pretty important for safety too.

Looking on E-bay, I see a Bridge Megger currently 39 quid, which looks ideal.

R.

Think it does.

It's not too clear from the description.

Ah - if you've got one then it must be so. ;-)

I bought a LT5 Megger Loop Tester and a Megger BM221 off Ebay - both with up to date calibration certificates. Completely OTT for DIY, though.

Although I've got the right gear and use it, I've never found a problem with my own work. So I'd say if you take care you'll be ok. Of course this won't necessarily be the case with your original pro installation.

I've found plenty of those with faults. ;-(

I'm not being picky, but it might help someone else! My Robin came off eBay though.