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Soft question here. I grew up in Ireland where phase testers (see picture) were used to check liveness of domestic wiring. They were also convenient for checking the ignition in a car.

I never see them used in the USA.

Why not? Grounding issues?

Clarification: I appreciate the answers, but I am not looking for product suggestions or comments regarding safety unless they pertain to the prevalence question.

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copper.hat
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  • I seem to remember seeing them. But, its been a long time since I lived there. Maybe they aren't common anymore. Or, maybe they are but you just couldn't find one. – JRE May 08 '18 at 06:40
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    I think you are referring to devices that detect the "hot side" of the plug. If so, I have several and I'm in the US. Plus, I have some that aren't metal at the end, but just plastic. And they work fine for checking ignition, just as well. I also have full plugs that check for hot, neutral, and ground all at once. As well as a line tracer that works by inserting a high frequency into the line and using a receiver to trace or identify the wire vs a panel relay/fuse. They are here, I think. Maybe there are fewer DIY people here, as a %? – jonk May 08 '18 at 06:48
  • I personally would not put my life into the hands of a puny little resistor... – PlasmaHH May 08 '18 at 09:20
  • @PlasmaHH: I would suspect that puny resistors are part of your life in many ways. – copper.hat May 08 '18 at 14:51
  • @jonk: I should not have written 'never' above, I should have written 'rarely'. – copper.hat May 08 '18 at 21:08
  • @copper.hat Sure. In any case, the US is pretty litiginous, too. So while I used to find those screwdriver types more often years ago, they've probably been mostly removed from the shelves because of the concerns of lawyers here. But yes, "never" is an extreme word. ;) – jonk May 08 '18 at 21:11

2 Answers2

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Those are the most dangerous tools you can get.
They rely on you completing the circuit to light up the neon light by touching the metal on the cap of the screwdriver.

Inside:

schematic

simulate this circuit – Schematic created using CircuitLab

There are a lot of dangerous conditions it cannot see:
- You are not grounded, but the line is live.
- The voltage is not high enough to light the neon light. Which is probably why they aren't common in 120V regions.
- The resistor or lamp is damaged and shorted or open.
- Floating potentials (behind isolation transformer).

If you insist in using an contactless detector, buy an active one. Fluke VoltAlert for example. But read the manual and know the limits of your equipment.

But the best way is to use a meter with a low resistance mode. Like the Fluke T90, to make sure what you measure is correct, and not a "ghost voltage".

Jeroen3
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    It's not a filament, it is a miniature neon (orange) lamp. https://en.wikipedia.org/wiki/Neon_lamp – Grabul May 08 '18 at 07:41
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    Carbon composition resistors fail open, so that isn't a direct danger. You always check that it lights to indicate power on, then flip the breaker and check that it is now off. Also, your meter won't tell you when a wire is hot compared to the ground you are standing on. That is (to me) a much larger danger than anything you've mentioned. Just because a wire is coded as neutral or ground doesn't mean that it really is. – JRE May 08 '18 at 07:42
  • Having recently installed a lamp in appartment where the color code said there were two neutrals and no hot, I prefer to know what is hot relative to the ground under my feet. – JRE May 08 '18 at 07:45
  • I would probably put them at #3 after my chainsaw, and any tool that Minnie is wielding – Henry Crun May 08 '18 at 09:36
  • I think your first comment is a bit alarmist and I am not quite sure what danger you are referring to. When working with open wiring one needs a little care in the first place. Neons used in phase testers have a typical breakdown of 80-90 V, so it seems unlikely to be a 120/240 issue. Phase testers have a ballast resistor that limits current. I am not sure what you mean by using a meter in 'low resistance mode'. The last thing I want when measuring voltage in a domestic setting is low resistance! – copper.hat May 08 '18 at 14:49
  • @copper.hat The danger is not you getting shocked while using the detector. The danger is not detecting a live wire. – Jeroen3 May 08 '18 at 19:12
  • @Jeroen3: Any means of detection are prone to failure. – copper.hat May 08 '18 at 19:20
  • @copper.hat: There are a variety of things "low" resistance might mean. Many volt meters have a resistance of 10M or more. Compared to that, a meter with a resistance of 330K would have a "low" resistance even though it would let through less than 1mA on a 240V line. – supercat May 08 '18 at 20:00
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In the USA there are little plastic boxes with 3 LED's as a ground and power test. It has 3 prongs so all modes are tested. Along with a ground and neutral test some better ones have a GFCI test.

These have all but taken the place of a simple "poke" tester which required more skill and careful use.

This is one of many available just from Home Depot:

enter image description here

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    Which does jack for you when installing a lamp, since lamps aren't on outlets. – JRE May 08 '18 at 07:45
  • I have a Fluke 77 DVM for device testing. And a LCR meter. And an oscilloscope. Granted that not much of the population knows how to use these. I have seen the 'poke' probes at Home Depot as well, I just don't want to buy one. –  May 08 '18 at 07:49
  • Thanks for the suggestion, but I am not sure how it relates to the question. – copper.hat May 08 '18 at 14:45