# How can both wires be hot?



## zapagain (Oct 13, 2008)

I'M in my parents house trying to add on a switch to previously stand alone ceiling light with a pull switch on it. My dad had decided to take out the light after the roof/ceiling had leaked and left both wires just hanging there. Now i have to find the hot wire and the cold wire and both tested hot with 118v. Am i testing wrong or cam some one tell me what might be going on with this 100 plus yr old house.


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## EBFD6 (Aug 31, 2008)

I have been an electrician for quite awhile and have never seen a "cold wire", hot and cold are for plumbers, in electrical you have a hot and a neutral and maybe a ground wire.

There is not enough info in your post to determine how you are testing to get 118v on both wires. Do you have a ground wire that you are testing each wire to individually?

If so you should not be getting voltage on both wires in reference to ground. If you do not have a ground in the box, you can take an extension cord and plug it into a receptacle, if your receptacles are polarized, and wired correctly, then the long slot of the receptacle is neutral, and the short slot is the hot.

Using this extension cord with a known hot and neutral you should be able to test the wires in the ceiling against the cord and determine which wire is hot and which is neutral.


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## zapagain (Oct 13, 2008)

Well i have two wires coming out from the ceiling, neither are tagged as black and white. I tested both with a digital multimeter and touched one wire with the red and one with the black and then reversed and couldn't understand how both could be giving me a reading? I figured one would be positive and one neg and wouldn't get a reading if i reversed the test to find the charged wire. ( i guess Ive been working with electronics for to long, used to red pos. and black neg.)


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## jamiedolan (Sep 2, 2008)

EBFD6 said:


> There is not enough info in your post to determine how you are testing to get 118v on both wires. Do you have a ground wire that you are testing each wire to individually?


Please describe what wires are in your box or provide a photo.

Are you in the US? Could this have been a 240V fixture?

240V would be 2 hot wires and a neutral.

Question to others here: Is there any reason not to suggest that he puts his meter, 1 lead on each "hot" wire, and if it reads 240, then he really has 2 hots in the box? Any reason this would not be safe to advise or any reason it would give inaccurate results? (it can be hard to know what is safe to tell people they can do when you can't see what they are talking about)

Jamie


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## jamiedolan (Sep 2, 2008)

zapagain said:


> Well i have two wires coming out from the ceiling, neither are tagged as black and white. I tested both with a digital multimeter and touched one wire with the red and one with the black and then reversed and couldn't understand how both could be giving me a reading? I figured one would be positive and one neg and wouldn't get a reading if i reversed the test to find the charged wire. ( i guess Ive been working with electronics for to long, used to red pos. and black neg.)


What color are the wires?

This sounds like a normal 120V line. Polarity isn't really an issue here the way your thinking of it in small electronics. On most testers, when either probe is energized and the other probe is run back to ground or to neutral, it is going to give you a reading.

You can just turn off the power and hook up a light fixture. 

What kind of fixture are you planing on installing?

Jamie


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## zapagain (Oct 13, 2008)

Yes I'm in the U.S.. Do older houses usually not have a ground and two charged wires though? i thought all houses had a ground? I know the newer systems use a black, white, and a green wire( plain copper) with some using a red for a second circuit. So im assuming im testing wrong and should be doing it a different way?


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## zapagain (Oct 13, 2008)

well..... I have two wires coming out of the fixture and neither is labeled in any way as to there nature of being the traditional black and white or having a tag as to which is the charged line. I'm just trying to find the right wire to use to install my wall switch.


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## rgsgww (Jul 5, 2008)

Whats the reading across the red and black? red to white? black to white?


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## rgsgww (Jul 5, 2008)

zapagain said:


> Yes I'm in the U.S.. Do older houses usually not have a ground and two charged wires though? i thought all houses had a ground? I know the newer systems use a black, white, and a green wire( plain copper) with some using a red for a second circuit. So im assuming im testing wrong and should be doing it a different way?


Yes, older houses usually dont have a ground, except when your house is wired with "bx" which is armored cable, and when it has a "bonding wire" a copper or aluminum wire inside the armor.


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## zapagain (Oct 13, 2008)

EBFD6 said:


> I have been an electrician for quite awhile and have never seen a "cold wire", hot and cold are for plumbers, in electrical you have a hot and a neutral and maybe a ground wire.
> 
> There is not enough info in your post to determine how you are testing to get 118v on both wires. Do you have a ground wire that you are testing each wire to individually?
> 
> ...


All i have is two wires comming out of the ceiling and neither has anything on them to lable them. So i don't know which is which. I tested them using a multimeter and then reversed the test and got the same reading at 118v. So what im i doing wrong to test for the charged wire and the ground. There isn't a green wire or a red wire just two black.


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## kbsparky (Sep 11, 2008)

Reversing the tester leads won't change the readings on AC circuits. One of your wires is "hot" and the other one is not. But the potential difference between them is 120 Volts (nominal - your reading of 118 is considered normal).

To determine which one of your wires is the actual "hot" one, you will have to measure to a different point, a known grounded point. 

Someone else here mentioned using a grounded extension cord to establish a point of reference to ground. Start with that, and report your findings.


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## InPhase277 (Feb 9, 2008)

Older homes are often not grounded outside of the service panel. But what you are asking is how both wires can be hot. They are not both hot. One is hot and one is the neutral, but reversing the meter leads won't tell the difference. There is a potential of 120 V between them, no matter how you measure it. Your meter can't tell unless you have a reference outside of the light box. An extension cord can be used to determine which is which, if the outlet the cord is plugged into is wired correctly.

The long slot on a properly wired receptacle is the neutral, so if you place one lead in the long slot, and test your wires, the wire that causes a reading of 120 is the hot. The other wire will read 0 or very near it.

P.S. KB beat me to it but... yeah


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## Speedy Petey (Feb 1, 2004)

Zap, you have to lose your DC thinking and try to comprehend AC.

Reversing the leads will NOT change your test at all. Just because you are getting a reading both ways does NOT mean both wires are "hot".

Listen to KB. :thumbsup:


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## zapagain (Oct 13, 2008)

we'll i'd like to thank all the electricians and other advice i got tonight and try it again tomorrow and i'll let every one know how things go. Thanks Alot.


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## Bubbagump (Apr 10, 2008)

Yeah, you are using the wrong tool for the job. One wire is the hot, the other neutral unless there is a major major problem. To determine which is which you need to use a voltage detector. The cheaper ones are just a neon light bulb in an insulated handle. You can usually get them for less than $10. They look sort of like screw drivers and light up when touched to a hot wire.

Example:

http://www.harborfreight.com/cpi/ctaf/displayitem.taf?Itemnumber=96125


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## tfb4me (Oct 9, 2008)

are the wires switched? If they are turn the switch off.Hook up the light and see what happens..Im almost 100% you have a non issue..Just old unmarked wire..It there a 3 way switch? Is there a junction box in the ceiling or just 2 wires sticking out of the plaster? Let us know


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## InPhase277 (Feb 9, 2008)

tfb4me said:


> are the wires switched? If they are turn the switch off.Hook up the light and see what happens..Im almost 100% you have a non issue..Just old unmarked wire..It there a 3 way switch? Is there a junction box in the ceiling or just 2 wires sticking out of the plaster? Let us know


Well, there's 100% chance that either way it's wired it will work. But there's a 50/50% chance that it will be wrong. The screw shell of the light cannot be hot... Even in Ontario:wink:.


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## tfb4me (Oct 9, 2008)

InPhase277 said:


> Well, there's 100% chance that either way it's wired it will work. But there's a 50/50% chance that it will be wrong. The screw shell of the light cannot be hot... Even in Ontario:wink:.


Correct me if im wrong..IF the light isint installed correctly it wont work and will trip the breaker? If it is will the light should now work?


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## InPhase277 (Feb 9, 2008)

tfb4me said:


> Correct me if im wrong..IF the light isint installed correctly it wont work and will trip the breaker? If it is will the light should now work?


That's the thing about AC wiring. If something is hooked up in reverse, it still works. In other words, the light bulb doesn't care which wire is hot and which is neutral. But if it is wired wrong the screw shell of the light socket will be hot and this is dangerous and against code.


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## tfb4me (Oct 9, 2008)

InPhase277 said:


> That's the thing about AC wiring. If something is hooked up in reverse, it still works. In other words, the light bulb doesn't care which wire is hot and which is neutral. But if it is wired wrong the screw shell of the light socket will be hot and this is dangerous and against code.


AHH HA! Id be wrong then..Sorry to mislead.I have ran into this before.Perhaps I should check to see if all is still good..I to have an old home built in 1897.Im going to get out the extention chord tonight and test to see if im good to go or not...


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## Bubbagump (Apr 10, 2008)

YOu may want someone to do this for you. If you are this sketchy on DC versus AC, you are liable to get yourself in some trouble. Touch a terminal of a car battery versus touch the hot of an AC circuit are very different animals. Whatever you do, don't work that circuit hot. Kill the breaker.


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## BeastinBlack (Oct 19, 2008)

Ok guys, who's going to be the one that instructs on how to backfeed this light, if he wants it on a switch?
Otherwise the new fixture is going to have to have a chain/switch on it as well.


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## jamiedolan (Sep 2, 2008)

BeastinBlack said:


> Ok guys, who's going to be the one that instructs on how to backfeed this light, if he wants it on a switch?
> Otherwise the new fixture is going to have to have a chain/switch on it as well.


He really needs someone local that can help him learn a few more things about electrical work. When someone doesn't even have a grasp of the basics and they have never done any ac work, it just doesn't feel safe to explain much anything beyond how to wire in a fixture. Even then, I have seen so many people that make very poor connections that are unsafe, just because they don't know any better. 

When I get a chance, I am going to take some photos of good connections with wires twisted for nuts and wires looped on screws so people can see what good connections look like.

Jamie


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## rgsgww (Jul 5, 2008)

Well, if you feel like pulling new wire then you can add a switch.
You cannot modify ungrounded circuits.:no: Have to pull new wire, if it is bx, you have to have a bonding strip to use it as a ground.


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## Dumbasker (Jul 12, 2020)

I have the same problem and none of the answers are helpful, obviously the reason someone posts a question is because he is looking for an answer that would help with his issue. Telling him to go and learn the trade isn't the answer. If you are not going to be helpful you can skip the question and move on to another one where you can provide some help. 
I am installing a new light fixture, it is an older home, both wires are the same colour and no ground wire. Can you tell me if there is a way to tell which one I should twist the black wire on to? If yes, can you give step by by step instructions?


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## Dumbasker (Jul 12, 2020)

Also would like to add that my non-touch tester lights up when I touch it on either wire.


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## rjniles (Feb 5, 2007)

I'll be non helpful. Jumping on a 12 year old thread and adding a bunch of snark does not make a lot of friends.

Sent from my Moto E (4) Plus using Tapatalk


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## surferdude2 (Nov 21, 2019)

Dumbasker... If you have half-sense and one eye you'll be able to read the entire thread and see that the answer was given with plenty of regard to the skill level of the OP and concern for his safety.

Use the same method he was advised to use and you'll get it sorted out easy enough.

You may also notice that he didn't report back to say thanks or to ask for more information. That happens often and we don't squawk about it. We mostly just hope the their absence doesn't mean that some inexperienced newbie didn't misunderstand the advice and get electrocuted.

Read the thread, help yourself like a good DIY'er and stay safe.


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## Oso954 (Jun 23, 2012)

> Also would like to add that my non-touch tester lights up when I touch it on either wire.


You are most likely getting a false alarm on one wire due to capacitive coupling. That's why I use a non-contact tester primarily as a safety check. 

If you want to test or diagnose things (particularly when it's not a completely terminated circuit) use a multi-meter.


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## Datawise (Mar 14, 2017)

The answer was in one of the very first responses, get a tester and an extension cord. Test and mark the wires. The NCVT is a useless tool...

Make sure your extension cord is connected to a properly wired and grounded receptacle other wise it will be of no help either.

Cheers
John


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## MTN REMODEL LLC (Sep 11, 2010)

zapagain said:


> Well i have two wires coming out from the ceiling, neither are tagged as black and white. I tested both with a digital multimeter and touched one wire with the red and one with the black and then reversed and couldn't understand how both could be giving me a reading? I figured one would be positive and one neg and wouldn't get a reading if i reversed the test to find the charged wire. ( i guess Ive been working with electronics for to long, used to red pos. and black neg.)


You have alternateing current in your home...you're thinking DC.

(EDIT: Did not realize this was old and already responded to thread.)


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