measuring an single appliance's earth leakage current?

Author: Daisy

May. 06, 2024

measuring an single appliance's earth leakage current?

To clarify what I personally meant about disconnecting the CPC/earth,
DO NOT

Check now disconnect
ANY
of the
FIXED
wiring, unless you are a qualified electrician. As well as the safety implications, there are issues around insurance, and if it's rented accommodation, you'll be in breach of your tenancy agreement.

What I meant is this: if the plug on the equipment is a rewireable type, remove the plug and in conjunction with a Safeblock or Quicktest, connect a DMM in series with the earth. It should not be necessary to state, but I will anyway:
DO NOT
do any of this while connected at the wall outlet. Once you have everything connected as it should be, only then plug the Safeblock in.

If the equipment has a moulded plug and you don't want to cut it off, you'll have to make an adapter, such as a trailing socket with the plug removed that can be connected to a Safeblock.

If you wanted something you could keep and use in the future without a Safeblock, you could make something like this:

Plug on a flex to a
PLASTIC
adaptable box, stuffing gland into the box. Inside the box, break out the conductors and wire them individually in flex out of the box and back in, making a small loop. Use stuffing glands. Then connect to a flex out through a stuffer to a trailing socket. With this, you can measure with a clamp the individual currents on each conductor, and all the exposed wiring is double insulated, so is reasonably safe.
DO NOT
use a metal adaptable box, it will effectively become a shorted transformer winding.
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How to measure leakage current?

How to measure leakage current? I have an AC powered device, and a customer asks for exact leakage current.

Of your device? I believe you are referring to current to ground that should be on the neutral. If you want to find how much current is leaking to ground in a device, electrically isolate it and measure current to ground through a known path.

Current that can trigger a leakage current circuit breaker, so it's obviously something flowing through Y capacitors to the ground wire.

Hmm in retrospect there may have been something wrong with that first sentence and maybe it was supposed to be part of this one. Anyway I think you're talking about an AC GFCI circuit breaker. Most GFCI devices work by passing both live and neutral wire through an induction loop. If all of the current flowing out on the line wire flows back on the neutral, the magnetic fields will cancel out and no current flows in the induction loop. If any of the current flows to ground instead, it won't return through the loop on the neutral and a portion of the magnetic field won't cancel out, causing a current to flow in the sense loop and breaking the circuit. This article goes into detail about what's legally defined as a class A, C, D, E device and why trip level requirements are what they are.

The question is, what is usually measured and what actually matters? Peak to peak? RMS? Pulse width?

The circuit I'm aware of mentioned above is basically measuring the absolute value of the total lost current, meaning both that it is measuring quantity and that it measures current regardless of direction of flow. The legal requirements for NEC specifications are clearly based on both current and exposure time, but because faster is always better in this case it matters more that it measures up to the minimums set by the government and performance may be significantly better in reality.

At any rate, Class A GFCIs must trip at 5mA and class B GFCIs at 20 mA, class B GFCIs are for old underwater fixtures in swimming pools where leakage current exceeds 5 mA and can cause nuisance tripping.

Want more information on leakage current test equipment? Feel free to contact us.

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