3 LED circuit tester shows good when switch ON, but bad when OFF
#1
07-25-12, 11:37 PM
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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?
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?
#2
07-26-12, 08:54 AM
Why would it show Hot/Grd Reversed with the switch off?
Everything works perfectly when switch is on, so should I worry?
#3
07-26-12, 10:02 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
07-26-12, 10:12 AM
Is there another way to test?
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.
#5
07-26-12, 10:14 AM
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.
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 01:32 PM.
Yeah!
Funny echo in here...
#7
07-26-12, 02:29 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
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
07-26-12, 02:49 PM
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
07-26-12, 02:57 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
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
07-26-12, 03:13 PM
With switch OFF
hot / neut about 10 volts
hot / grd same, about 10
neut / grd same, about 10
hot / neut about 10 volts
hot / grd same, about 10
neut / grd same, about 10
Glad you tested again, though. Furd's question was on point.
#11
07-26-12, 03:24 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.
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.
