Proving Unit? Does anyone use one?

[fixbear]

Scott, you are getting down to the nitty gritty. And exactly why a use Fluke meters. Temperature meters are of course easily tested with Ice and water. Ohm meters by zero reference and 100 ohm, 1000 ohm and 10,000 ohm 1% resistors. But voltage and current are hard to find economical true references in the field. Interesting if you’ve found something for us on this.

[techtownmayor]

This is the unit I bought for myself. Outputs 240V AC and DC.

https://www.fluke.com/en-us/product/electrical-testing/basic-testers/prv240-proving-unit

Pricey unit since it doesn’t do much, and probably only a matter of time till we see cheap knockoffs.

Megger also make a nice version:

https://amzn.to/3x4WiJr

Amazon now lists bundles with meters and the proving unit. From what I’ve heard from UK based electricians, they are required by law to use a proving unit to test their equipment before they test any residential or commercial systems that now require regular inspections. This EICR test sounds very comprehensive, down to earth tests on every single outlet. Sounds like something the US could use as I’ve seen some truly disgraceful wiring. These new UK regulations also explain why Megger was one of the first to market with such a nice little proving unit.

[olivero]

I generally don’t check a known source as a dedicated “motion” but generally when I troubleshoot, I’m testing for voltages and if I find none anywhere, I’ll go to like the L1 main landing and find voltage there which confirms the meter works.

Never gave it much thought, in most cases it’s obvious if something’s powered as there’s lights and such on boards, or VFD screens light up or what have you.

For strictly wiring and landing wires, I’ll generally verify with a meter before touching it and not just assume I got the right breaker.

Which again can be verified easily with any outlet.

[chanlui]

I know of the proofing unit from Fluke but I don’t use one. When shutting down a piece of equipment to work on I would measure the voltage before shutdown so that I know the meter is working and then check the voltage again after shutting down the machine.

The proofing unit I think is a useful tool and perhaps I will use them in the future.

[Juan2099]

Proving units are a valuable addition to electrical safe work practice. Ensuring that your meter is functioning is crucial to preventing injury/incident. Remember to always check your leads as well.

[nafets47]

As stated earlier, I could understand their use (proving units) but I honestly have no need for them. I dont have anything that requires voltage to be exactly XYZ. Its mostly is it getting power? or is it getting approx XYZ.

[fixbear]

I think the idea here is to prove that your meter and leads are working before we declare the machine is no longer live to be able to commence repair/maintenance work. Most of us know how to find a live circuit safely to test before lock-out. If not, you don’t belong working on it. Basically someone screwed up and upper safety auditors had to close out with corrective actions. Looks good on paper type of thing. Is it cost effective and practical? Time will tell. But carrying another instrument that has to have batteries?

[chanlui]

The proofing unit isn’t sufficient to check for the meter accuracy. It means to check for functionality and it’s a safety related item like FixBear said.

[Tech2]

Another older thread I know but I only just found the site and I’m catching up 🙂. I carry a proving unit but often when out on site fault finding on equipment I just use a known live source before and after testing. The proving unit gets used when working on mains circuits, distribution boards etc, along with a dedicated 2 pole test probe used to prove a circuit is dead before working on it.