Can anyone tell me why I would get a 27 volt reading on a 120v circuit. I have a old home but some of the home has been re-wired. I am remodeling my bath room and removed old florescent lights. I tested the power at the connections and got a reading of 27v. I climbed in the attic and it looks like the wire is coming from a junction box with several other wires. It looks like the work was done by a pro. The upstairs has 2-20amp (connected together) circuits.
Probably because you're using a digital voltmeter, which is reading a very very low amperage induced current in the conductor you're testing. Try using an analog meter instead, and you'll probably see -zero- volts.
snipped-for-privacy@yahoo.com wrote in news:1161608374.490859.297690 @h48g2000cwc.googlegroups.com:
You are using a low impedance (resistance) meter (cheapo). It is not invisible to the circuit when you connect it. All meters have an internal resistance.
The lower the resistance of anything, the more current (amps) will flow through it. The more current that flows through it the higher the voltage drop across it.
The sum of the voltages in a loop with 120v source will be 120. How the
120 is divided among the components in the loop depends on the resistance of each device but it will always add up to 120.
I have a cheapo digital and an old high impediance analog meter. When I get a reading such as you did, I get out the analog. It always proves the cheapo wrong.
You have a few choices here:
a) Trust me (ill advised according to many). b) Get a high impedance digital or analog (needle type) meter. c) Get a cheap test lamp for 120. Compare brightness of lamp to an outlet working normally. d) Grab the alleged 27v wires. Do you get a tingle or jolt? (ill advised according to many)
Option d has the advantage of a free ekg if you survive. If you don't survive, as the Monty Python "Bring out your dead" skit went:
---------------------
[clang] Bring out your dead!
Customer Here's one.
Cart Master Ninepence.
Dead Person I'm not dead!
Cart Master What?
Customer Nothing. Here's your ninepence.
Dead Person I'm not dead!
Cart Master 'Ere. He says he's not dead!
Customer Yes, he is.
Dead Person I'm not!
Cart Master He isn't?
Customer Well, he will be soon. He's very ill.
Precisely backwards...a _high_ impedance meter can load a circuit and read "phantom" voltages. For such tests of household wiring circuits an inexpensive analog meter is probably more reliable than the digital.
To OP, need more. Were the lights functioning before and where/what are you measuring? Breaker on/off, at the switch or the feed.
What you're seeing at the upstairs junction box is probably simply a feed junction. Two circuits connected together is one circuit.
If you're actually measuring something that should be a true voltage, it implies a loose neutral or hot. If you're simply measuring the leads from the switch you just disconnected w/ the switch off, it is almost certain your _HIGH_ (not low) impedance digital meter is loading the circuit. Put a light bulb across the wires and measure again and it will undoubtedly be zero.
Nope, *you've* got it backwards: high impedance = high sensitivity. For a meter with an impedance in the megohm range, it's very easy to pick up stray, "phantom" voltage readings.
. Some replies are making this too complicated. Forget the volts and amps and impedance stuff.
Your question has been asked frequently here; it's sensible one but usually asked by someone without much electrical experience and training and almost always involves voltage read with one of those digital display meters.
Non technical reply:
Digital meters are so sensitive (even the cheapest ones) that they can pick up voltages induced into even dead/disconnected wires from adjacent working/activated wires.
In some circumstances they can pick up the faint voltages of the multitude of radio and wireless-device waves that surround us these days! Even if a wire is grounded at the far end it can still act as an antenna at many frequencies and thus pick up enough electrical energy to read 'something' on a meter. Depends on the location, radio field strengths the meter etc.
Heck; I have one meter sensitive enough that, if I touch the leads with my fingers it will pick up enough energy for a reading even if I'm standing in my basement. Hook it up to a spare coil of wire hung up and not connected to anything and one gets a higher reading again.
For house AC work a spare bulb screwed in a lamp socket with a couple of leads is often the best way to test whether a wire is permanently 'live' from the AC breaker/fuse panel, is (switch on/off) switched live, a neutral or a ground.
The mention of two 20 amp circuits 'connected together' is confusing. It also might be confusing/unsafe for anyone working on that/those circuits; my understanding is that once the breaker/fuse for a circuit is off/removed there should be no other power (from another connection circuit etc.) to anything on that circuit or in the same AC boxes. That's a little worrying and possibly not up to code? Possibly an insurance concern?
Maybe you mean two 'separate' 20 amp circuits; or is the breaker a 'double 20 amp' with the handles connected together so that both breakers will trip at same time?????????
my first thought is that you have your meter set at DC.
my second thought is that you are not using it correctly. one probe on black, the other to the ground, then the first probe on the white. (white should be zero, black 100-140V, unless i got em reversed in my head)
another thought is that you are measuring voltage on a dead line (to see if it is live before you work on it), and you are reading DC off of other devices on the circuit. or you are reading 27 millivolts and are picking up stray radio signals.
yet another thought is that you are reading oddball stuff off the ballast, which does not equal yer usual voltages, thats why the ballast is there. not sure though.
STILL yet another thought is your battery in your meter is dead.
does anyone notice I dont say any rubbish about meter loading? if the meter is designed to read line voltage, it was designed to work at the proper loads, maybe not perfect, but i'd point at the first few thoughts before I'd even think of loading.
lets try to keep the common sense handy people
hope the OP replies, I betting my money on dead battery
I have used this meter a lot over the years and it has always worked when checking circuits. It works on other circuits in my home however I tried as you suggested on a few different outlets. All but the line in question reads as follows. Black wire about 122. White wire .694. I am reading volts not mV and I do have my tester set to AC. The battery indicator is not showing low but I haven't changed it in a long time.
I usually place the terminals of a battery across my tongue. A sour taste implies the battery is good. Haven't tried that technique as a test for impedence. Maybe impudence.
I have used this meter a lot over the years and it has always worked when checking circuits. It works on other circuits in my home however I tried as you suggested on a few different outlets. All but the line in question reads as follows. Black wire about 122. White wire .694. I am reading volts not mV and I do have my tester set to AC. The battery indicator is not showing low but I haven't changed it in a long time.
The part where he said "a high impedance meter can load a circuit". I shoulda been more clear; a high-impedance meter reads phantom voltages because it loads the circuit *less*, not more.
Instead of "impedance", substitute "resistance" (which is essentially the same in this context) and then re-think the question: I'm assuming you know enough about basic electricity to work it out for yourself.
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