Very interesting. My electrician said that his modern unit could output up to 2000v, he didn't know at what amps. He performed a ground test with it. The unit was a yellow box about 5X10X12 inches with a 4 inch LCD screen on the top, but he was only here for 5 minutes, so I didn't get a good look.
It is only used for testing ground connections. That is its whole purpose put simply.....Those used on very high voltages, need to test with a higher voltage values, but the current flow in a properly made system is tiny, usually micro amps or less.....
There is a serious misunderstanding of how a Megger works and what it actually does (when correctly used!), at this time on Pedelec.
A megger measures insulation (for safety reasons) as a value of the number of Ohms between either one of the power wires (Phase & Neutral) and the ground wire or frame. With the minimum acceptable value being previously 1 MegOhm, when I last worked in high power.
It is not used to measure between the two power wires as many here seem to believe, as this is most often of a very low Ohm value anyway, would serve no useful purpose known to man, and might damage certain sensitive parts of the equipment.
SO REMEMBER,
NEVER MEASURE BETWEEN THE NEUTRAL AND PHASE WITH A MEGGER!
Also, if there is an insulation breakdown between the neutral and phase, a large current will flow and fuses and breakers will blow......exactly what they are designed to do.
Now it is possible that the frame of a unit may be connected to phase, via a high resistance path, not of a low enough resistance to blow fuses and or breakers, but still be dangerous to a user, as a current flowing say between both arms, or one leg and one arm, that exceeds 30ma., is likely to kill.
That is why there is a further type of breaker, that any sensible person has in his house electric system (I think that at least for any newly built houses it has been a requirement for many years in most countries), that monitors the current in the phase, and compares it to the current in the neutral, and depending upon its design and use, will remove the mains completely within a few milliseconds, if there is any tiny difference. You do still get a shock if you are the "bridge", slightly painful in my experience, but before your heart stops (for a normal healthy person), the power gets automatically removed.
These are so called
residual-current device (
RCD), or
residual-current circuit breaker (
RCCB) , and have been around for a great many years now. I installed my own first one in an old house I bought, in 1975. The house was built around 1450, so the title "Old" was fully earned!!
But I hope now that everyone now understands the basic usage of a megger far better, and that when correctly used, it will not damage any equipment that has been correctly designed for mains usage.
regards
Andy
