The Megger is DMC305e is a better specification than the DiLOG DL6518E (or the even cheaper TEK775 that looks identical) but also costs more, so you need to ask yourself if it is money well spent?
Generally for most electricians work (leaving aside R&D labs, etc, where anything is possible) you would be looking at two uses:
- Current consumption (clamp on only L, or only N)
- Earth leakage (clamp on both L & N to see residue)
For current consumption you are probably worried about if a load is close to (or above) the MCB or switch rating so probably you would be looking at 1-100A in a domestic situation and normally you would want to be able to see a bit above the expected range, so going to 200A is a reasonable upper limit here.
For earth leakage you are going to see RCD that are mostly rated at 30mA, a few incomer that are 100mA, and a few special area that are 10mA. So when testing at the cables to the appliance or RCD/RCBO you would want to measure down to 1mA with decent accuracy.
Most digital meters have a combination of % and digits as the "accuracy" so in my DiLOG meter's case it says the lowest range is 200mA, resolution 0.1mA, and accuracy 2.5% + 8 digit. So for very low currents it is possibly 0.8mA out, but for something like 10mA it would be 10 * 2.5% + 0.8 = +/-1.1mA max error. That is still adequate to check if a circuit is close to the trip threshold for practical RCD cases.
Some boast lower settings so you can measure appliance leakage at low levels, as if doing a PAT test, but that is an unusual approach as if you are needing to do PAT testing it is far better to get a proper tester for that role, such as this sort of thing:
The Battery powered Seaward Primetest 100 PAT Tester is a quick and easy to use PAT tester. The Primetest 100 gives readings as well as PASS & FAIL readouts, ideal for the novice user.
www.test-meter.co.uk
