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Old 03-13-2015, 02:29 PM   #1
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Non-Contact Voltage Detectors

Before you type "they don't work," please read a bit further.

Recently, an RV Inspector told me that "THEY" don't work because when a group of inspectors got together at an RV park their detectors went off on a rig they were inspecting, but when they did a hot skin test with a multimeter there was no voltage present on the skin of the rv.

Actually, the detector was working.

BUT, such detectors don't actually detect Voltage. In fact, they were so named for marketing purposes. They really are electromagnetic field detectors or capacitive coupling detectors. Savvy electricians use them primarily as safety devices, not diagnostic tools, AND SO SHOULD YOU to check your rv every time you enter it or your friends rv.

The electricians use professional models at their work sites
"to detect the radiated electrical field (V/m) present in energized conductors."

So lets start over...

Why did the NCVT's give a positive reading for the inspectors but no voltage was present? That is because other situations provide readings as well.

But what what can the detector detect? In the case of the ungrounded metal enclosure (rv) the voltage sensor won't tell you if the enclosure is just "hot" from the capacitive coupled (stray) voltage, or if it is hot from contact with a live wire (like frayed insulation) i.e. really danger hot.

The difference is life and death.

So, be happy with a warning that something is alerting it and then do the hot skin test to see if you have a dangerous condition.

So another way to say it is the detector will also read ghost voltages that are high enough to set off the detector, but have virtually no current to harm you.

Detectors don't work on DC voltage.

A Greenlee is sensitive down to 5 VAC and a Milwakee down to 50 VAC. Since 30VAC will kill you, be happy with a very sensitive Greenlee providing too many indications, rather than too few.

Detectors do work, but you need to understand what they do and what they don't do, and how sensitive a one you need for your intended purpose.

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Old 03-13-2015, 02:38 PM   #2
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Here is a great video to go along with the post above.

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Old 03-13-2015, 02:49 PM   #3
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I have one in the coach and a second in the home kitchen catch all drawer.
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Old 03-13-2015, 04:25 PM   #4
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I'm quite happy using my Beckman RMS meter. Besides, it makes me look as if I actually know what I'm doing.
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Old 03-13-2015, 04:41 PM   #5
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I bought one a while back, but have not used it yet. One question for the electricity gurus. If you touch the probe to the side metal case of shore power box should it not go off, or will it go off even if all is good. I am always a little nervous opening the shore power box when it's a little damp outside. I usually tap the box with my hand before gripping the cover on it, just incase.
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Old 03-13-2015, 05:43 PM   #6
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With all due respect he set my bullshit detector off more than he passed good information. It's loaded with scare mongering. OTOH I do recommend owning and using a non contact probe for the simple task of telling if there is power present that warrants a proper meter check. They avoid the "I thought it was off" issue. ;-)
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Old 03-13-2015, 05:57 PM   #7
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If the box is properly grounded I would not expect a field on the outside of the box. OTOH when you get near the connector you may get an indication that there is power present. There is a bit of fudge factor depending on whether the breaker is on or off, how close it is to the plug, and how sensitive the probe is. The breaker will normally have power to it so the indication should always be there. Ideally with the breaker off there will not be an indication at the socket. OTOH as long as the closed box was not alerting I would plug in with the breaker off and then flip it on without concern. It is worth turning breakers off to avoid arc damage to your plug.

FWIW I would also encourage folks to use their probe in a few known situations. That way one finds out what to expect in real case unknown conditions.
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Old 03-13-2015, 06:21 PM   #8
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I am not going to enter this discussion save to say the alert is a good thing even if it is false..>Cause it makes you LOOK with more accurate tools.
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Old 03-13-2015, 07:00 PM   #9
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Originally Posted by wa8yxm View Post
I am not going to enter this discussion save to say the alert is a good thing even if it is false..>Cause it makes you LOOK with more accurate tools.
I agree. However, I will comment on my experience. I had a hot skin situation on my recent 5th wheel. When I noticed it, I didn't know the severity of the situation. I had a phone conversation with Mike Sokol and realized how serious the "tingle" actually was. Whe I bought a NCVT, it lit up from about 18" away from any metal part of the RV. The dealer had screwed up a repair on the 1st of 2 ATS's that fried. Needless to say, I replaced the 2nd one myself, which led to the discovery of poorly landed wire connections.

The NCVT may give false positives, but they certainly react when there actually is a problem.
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Old 03-13-2015, 07:31 PM   #10
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If a person has a digital volt meter you can check for a hot skin quite easily. Just grasp one probe in your fingers and touch the other one to the skin. You WILL NOT even feel anything, but the meter will show you voltage if present.
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Old 03-13-2015, 08:26 PM   #11
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Nothermark thanks for the reply.

BTW, I had to look up all these acronym to figure out WT% everyone was talking about in this thread. FWIW I learned something today. LOL
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Old 03-13-2015, 08:40 PM   #12
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I appreciated the general insult from nothermark, despite his inability to point out something specific that is bad information. Apparently, that kind of reply is acceptable under the forum rules.

So, I'm formally requesting all my comments in this thread be deleted and in future I will refrain from wasting my time by attempting to give something back to this forum.
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Old 03-14-2015, 07:08 AM   #13
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I stay simple because it did not seem worth a detailed technical discussion. 30 Volts is not an issue for normal people under normal conditions. Any competent mechanic can make a safe extension cord while I have seen faulty molded factory made one's. Running the voltage up and down was circus. There is no source of 30 VAC in most camping vehicles in a situation that would power up the chassis. The fiberglass panels are not conductive so one has to get to the frame. Those were the top hits.

If you look I have already made the recommendation people buy and use non contact sensors. They save lives. What I objected to was the "smoke a joint and you will be a heroine addict for the rest of your short miserable life" approach in the movie. The devices are simple technology that require some understanding of what they measure. In this case the presence of a changing magnetic field. If one approaches them with the attitude that if the light indicates a problem then check it out or get some one who can they are doing their job. That is all they do. By the way that is also why they do not alert on fact that the chassis is hot in DC terms. ;-)
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Old 03-14-2015, 10:05 AM   #14
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2nd request: please remove all my posts from this thread.

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