2 light switches in single box getting odd voltage readings?

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Old 12-07-14, 02:33 PM
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2 light switches in single box getting odd voltage readings?

Hello!

I have a single box with 2 switches that control 2 separate lights. The switches are regular on/off single poles with 2 terminals and green ground. Each have independent wires to the top terminals. The bottom terminals are fed by the same wire which is split before the switches, so it's the hot I would assume? There is no ground wire to the switches. I'm not sure if there is one to the metal box. But most of the house is not grounded to begin with. Old 2 prong receptacles and all.

Ok, when I put the meter on the 2 terminals of the first switch, the voltage continuously cycles like this...112v, 105, 99, 92, 88, 106, 112, 106, 98, 91, 88, 106, 112v etc etc. Never higher than 112v and never lower than 88v.

On the second switch I only get a reading of 25v across the terminals. But it does not fluctuate like the first switch.

Is this normal? Or what could be causing this?

PS> I also checked another multi-switch I have that's on the same circuit but with 3 switches. Same basic 2 pole switches, wired the same except there's a jumper from one switch to the next on the bottom terminals instead of a split feed. I get the same fluctuation on the first switch, the same 25v at the second, and nothing on the 3rd. Though the 3rd switch has never worked and I don't know what it even controls because so.
 
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Old 12-07-14, 02:39 PM
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There is usually no useful information to be gained by measuring across a switch. Why are you doing it.
 
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Old 12-07-14, 05:49 PM
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I bought a new outside wall light with GFCI that is controlled by the first switch, but I also bought new switches because the one that was in there (first switch) had an occasional audible buzz when turned on. I just felt like checking it with the meter before killing the power to change the switches, and got a seemingly strange result. Same result after new switches as well.

I also checked the receptacles on the same circuit and get a steady 122v on all of them. Then on another single switch on the same circuit, it also has the same fluctuating voltage as the other two.
 
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Old 12-07-14, 05:59 PM
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If you are using a digital multimeter not analog that could be part of your problem. Your 25v is likely a false reading reading caused by induced voltage if you have a digital meter.

When a switch is on the reading should be about ). With the switch off it will depend on the impedance of the load since you are in effect creating a series circuit
 
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Old 12-07-14, 06:20 PM
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Yes, digital meter and they get 0V when turned on. Would I be able to actually measure the true voltage at the light fixture or the wires behind it with the switch on? I understand now I have no ground at the switch to get a true reading, just a hot and the
continuation wires to the light.
 
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Old 12-07-14, 08:35 PM
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You don't need a ground to check for circuit voltage. The measurement is made between the black hot wire and the white neutral wire.
 
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Old 12-08-14, 10:25 AM
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What I meant by ground, is because there is no common/neutral available at the switch, I would otherwise need a ground to check the incoming voltage of the hot at the switch. Maybe I'm wrong.

Either way...if I check the voltage at the light fixture off the hot and common with the switch on, I should then get a proper voltage reading and can disregard the funky stuff at the switch? Correct?
 
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Old 12-10-14, 09:57 AM
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Throw away all the data and readings you got by measuring across two screw terminals of a switch.

If there is no neutral in the switch box then you can measure between any one switch terminal and the ground wire. This reading is usually useful but typically needs a pinch of extra intuition or a grain of salt.

Yet another thing you can do is stretch a long wire from the main panel ground/neutral bus bar up the stairs and to the place you are working. This will be a reliable point to measure voltage with.

Because metal parts may be tarnished a little, it is not unusual for the meter reading to bounce. You can make it settle down more quickly by pressing the meter probe on the wire or contact being tested quite hard and back and forth as if to try to scratch the terminal.
 
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