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3 LED circuit tester shows good when switch ON, but bad when OFF

3 LED circuit tester shows good when switch ON, but bad when OFF

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  #1  
Old 07-26-12, 12:37 AM
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3 LED circuit tester shows good when switch ON, but bad when OFF

20 years in this house with no electrical problems. Curious, I tried a small 3 prong circuit tester with two yellow lights and one red. All the wall outlets test perfect: two yellow lights. On garage and basement outlets that have a switch beside them to power the outlet, they test good--two yellow lights--but only with that switch ON. With the switch OFF, there is one yellow and red light, and the code says, "Hot/Grd Reversed".

But this cannot be accurate because a volt meter shows zero on all three plug holes with the switch off. Switch on, all tests are normal. 115 V on smaller slot, zero on larger slot and ground.

Why would it show Hot/Grd Reversed with the switch off?

Everything works perfectly when switch is on, so should I worry?
 
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  #2  
Old 07-26-12, 09:54 AM
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Why would it show Hot/Grd Reversed with the switch off?
An anomaly in the tester? It should show "open hot," I would think, but there may be some reason it doesn't.

Everything works perfectly when switch is on, so should I worry?
Not about the receptacles. You might worry about the tester.
 
  #3  
Old 07-26-12, 11:02 AM
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That was my first thought, so I bought another tester. Exact same results. Is there another way to test?
 
  #4  
Old 07-26-12, 11:12 AM
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Is there another way to test?
Yes. I thought you already did that:
a volt meter shows zero on all three plug holes with the switch off. Switch on, all tests are normal. 115 V on smaller slot, zero on larger slot and ground.
If you stuck the two probes of an analog meter in the hot (smaller) and neutral (larger) slots of each receptacle and watched voltage appear and disappear as you toggled the switch; and did the same with the hot and ground slots; and checked the neutral and ground slots just to verify that no reading appeared regardless of the switch position, then there's not much else to test. That's pretty much it.
 
  #5  
Old 07-26-12, 11:14 AM
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A multimeter* is the better way to check. Measure voltage Between:
White>Black ~120 volts 10%
White>Ground ~0-5 volts
Black>Ground ~120 volts 10%

*If you are buy in a new multimeter a cheap analog is the better buy because the low impedance will tend to cancel out false readings caused by induced voltages. An expensive brand name digital multimeter is okay but the cheap ones may give false readings due to induced voltages.

Dang, Nash types faster.
 

Last edited by ray2047; 07-26-12 at 02:32 PM.
  #6  
Old 07-26-12, 01:30 PM
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Dang, Nash types faster.
Yeah!

Funny echo in here...
 

Last edited by Nashkat1; 07-26-12 at 03:39 PM.
  #7  
Old 07-26-12, 03:29 PM
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Many thanks all.
The VOM tests fine, so I will take this off my worry list.
I don't know why the LED testers both show a problem, and my 'flashing squealer' tester also shows AC current with switch off. But the VOM shows nada.

And the reason this whole thing surfaced was another problem with a ceiling light fixture. That is what made me curious about outlets. I didn't want to mix two Q's, so will post that one separately.
t
 
  #8  
Old 07-26-12, 03:49 PM
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Hot/ground reversal often means the neutral is missing. In your case I suspect the neutral is being switched and that is also the reason why the "squealer" works when the switch is turned off. If your multimeter is reading the correct voltages with the switch on then try all wire combinations with the switch off. I'll bet you get 120 volts between hot and equipment ground but not between hot and neutral.
 
  #9  
Old 07-26-12, 03:57 PM
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Just about the time I figured this was done, I read your post and decided to test again.
With switch ON
hot / neut 115 VAC
hot / grd 115
neut / grd 0

With switch OFF
hot / neut about 10 volts
hot / grd same, about 10
neut / grd same, about 10

Curiouser and curiouser
 
  #10  
Old 07-26-12, 04:13 PM
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With switch OFF
hot / neut about 10 volts
hot / grd same, about 10
neut / grd same, about 10
Sounds like induced voltage. Enough to set off your non-contact tester and maybe confuse your plug-in tester.

Glad you tested again, though. Furd's question was on point.
 
  #11  
Old 07-26-12, 04:24 PM
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Many thanks. This condition exists in two basement outlets and two in the garage. I thought is was rather clever of the previous owner to have a 'master' switch to kill all the outlets. I don't worry about leaving something turned on in the garage or basement.

It's been this way for about 20 years, so I will assume this 'induced voltage' is reasonably safe?
After 20 years? I never leave them on, 95% of the time they are off with this mystery induced voltage.
 
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