Wires appear to be hot (tester), but do not spark

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Old 04-11-18, 11:26 AM
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Wires appear to be hot (tester), but do not spark

Can anyone tell me why a pen tester would beep hot for a wire, but the wires don't spark or appear to be hot? I'm remodeling a bathroom. Removed the electric baseboard heat and capped off the wires, temporarily. Then removed the thermostat on the wall. There are two 12-2 lines going in to the box where the thermostat was. Both lines are grounded to the box. The tester beeps hot for both lines coming in, however the wires do not spark at all. I can touch all wires together and nothing happens. I believe everything was working prior to unhooking, but now I'm skeptical. I've tested the tester and it works fine.
 
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Old 04-11-18, 11:51 AM
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Those testers are generally unreliable. Check it with a multimeter
 
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Old 04-11-18, 12:10 PM
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Haha, that's exactly what my buddy told me just prior to grabbing all the wires and touching them together to prove to me that they weren't hot. I was hoping for a different response (like a reason that this would/could occur).
 
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Old 04-11-18, 01:48 PM
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If you're "grabbing" 220 VAC lines and "touching them together" to see of they are hot you might want to check that your life insurance is up to date.

Get a multimeter.
 
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Old 04-11-18, 01:53 PM
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From the limited experience I have with things a "pen" style tester will pick up and show "hot" even if there are only a few volts bleeding through somewhere. I had a hard time tracking down an issue in this new house with a pen tester because I kept thinking a certain wire was "HOT" even when the breakers were off but when I finally went and got a Fluke meter it showed it had like 11 volts or something bleeding from somewhere that the pen tester was recognizing as voltage so it showed hot. I reworked that entire line anyway because the wires were old and frayed and the bleed went away but as far as the pen style testers .... I did not have much luck other than to tell me double check breakers and use a voltmeter or something before starting work.
 
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Old 04-11-18, 03:20 PM
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A non contact tester is only used for locating and indicating dangerous high voltage.

More then likely you have 120v there on the hot but have lost the neutral. In this incidence the tester will show power present. With your voltmeter.... check from hot to ground, hot to neutral and neutral to ground.

You should see 120v from black to white and black to ground.
You should not see anything from white to ground.
 
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Old 04-11-18, 05:54 PM
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Can anyone tell me why a pen tester would beep hot for a wire, but the wires don't spark or appear to be hot?
That is because if a wire running next to a wire with current flowing through will induce voltage to the wire. This is how transformers work. Non contact testers also work with same principle. It just detects voltage induced by a wire. If there is any AC current, it will pickup. Doesn't really test how high the voltage is.
If you check voltage on such a wire with a digital multi-meter, you will get some voltage usually around 2 digits. Some call it a phantom voltage. The voltage actually do exists, but just don't have enough current to do anything. The voltage will drop down to 0 or close to 0 if you touch the wire or put some load on to it.
Analog multi-meters cannot pickup such a voltage because it has too low of internal resistance (meaning it puts some load on the wire).
 
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