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Author Topic: AC Circuit Load Tester?  (Read 13625 times)

John Roberts {JR}

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Re: AC Circuit Load Tester?
« Reply #30 on: December 24, 2013, 10:35:50 am »

I suspect that the NCVT works by using the user as a reference, which under normal circumstances should act like a ground of sorts.
I think if you were isolated and touching a hot chassis with one hand and used an NCVT with the other it wouldn't light up.

If I'm correct, then putting an NCVT into any device would require a known good ground for it to be useful, otherwise it isn't any better than a neon bulb.

I could be wrong..

Jason
While I haven't designed one yet, and probably won't, I did think it through.

Indeed all voltage is relative. My hypothetical "smart" outlet strip would presumably have some products plugged into it. With none of those products energized, their mains cords should all be pretty quiet. Using a high impedance voltage detector to measure for voltage between outlet ground and all the mains plugs (H+N+G) we should be able to identify a hot outlet ground lead. About the only scenario that would create a false OK is if one or more of the unpowered mains cords had a hot voltage present too.

This scenario is extremely unlikely, but possible, I guess.  For extra insurance I could poll between the multiple product mains cords plugged in separately. It seems even less likely that "all" mains leads would also have hot grounds too. So if significant voltage is detected between outlet ground and "any" one mains cord ground that outlet ground is disconnected, and the red LED starts flashing. If the outlet ground is hot and the product ground is ALREADY hot I didn't make the situation worse by connecting them, and the GFCI should still disconnect power if it detects leakage.

So I believe it could be done, but like many of my ideas, the world is not likely to beat a path to my door to buy one, well many just one to Jason to prove it works.  8)

JR
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Jonathan Johnson

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Re: AC Circuit Load Tester?
« Reply #31 on: December 25, 2013, 11:02:25 pm »

Interestingly enough the Australian plug is actually a US plug that got borrowed in (I think) the 1920's but then faded into obscurity in the US.

The NCVT certainly lights up when it comes near a live Australian outlet.  Sometimes the ground pin side of the outlet produces a lesser response, but can sometimes produce a significant response especially when the wire in the wall leads downwards towards the floor.


Yes, Lyle, I believe you are correct. For many years, 240V heaters on a 15A (or was it 20A?) circuit in the United States used this plug configuration.

The version now accepted for this application is a NEMA 6-20 (compatible with NEMA 6-15) and is shown below.
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Jonathan Johnson

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Re: AC Circuit Load Tester?
« Reply #32 on: December 25, 2013, 11:12:46 pm »

...The key I missed was testers can't detect fault when both neutral AND ground are hot - they can detect -OR- just fine.

Even with my new toy (euphemism) I will continue to test with the non-contact tester as described in addition to the Extech. 

Trust no one, test, and think like an electrician.

The only way to truly test for a hot or floating ground (RPBG) is to meter between the grounding contact and the ground. That is, meter to a trusted reference ground, which could be the framing of a metal building, metal water pipes (that have a conductive path to the earth), or a ground rod driven into the earth.

Always test the tester. Before metering a circuit and declaring it dead, did you test the meter on a known live circuit? If not, you don't know that it's dead. (Sometimes I test the tester both before and after.)

When I'm identifying which circuit breaker controls a particular light, receptacle, or other point of use, I have a helper watch a test light. When I flip off a breaker and the helper says the light's out, that's not enough... I flip the breaker back on, verify that the light comes on, then off again. Don't want to fall into a trap of simultaneous failure.
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ProSoundWeb Community

Re: AC Circuit Load Tester?
« Reply #32 on: December 25, 2013, 11:12:46 pm »


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