Announcement Announcement Module
Collapse
No announcement yet.
Can I test a neutral wire? Page Title Module
Move Remove Collapse
X
Conversation Detail Module
Collapse
  • Filter
  • Time
  • Show
Clear All
new posts

  • Can I test a neutral wire?

    I just replaced a wired in smoke detector. The old one didn't work anymore... or did it?

    The old one had no battery backup and looked pretty old. Even if it wasn't garbage, it probably needed replacing.

    The new one has a battery backup so I'm happy to have it.

    The problem is that now that it's all hooked up, the green LED that indicates it's getting A/C power isn't on. I used my tester to check that the black wire is hot, and it is. I'm wondering now what can cause a break in the current.

    My electrical experience is mostly based on 12V DC in cars, so I'm sure that most of what I know probably doesn't apply here.

    With DC, so long as you've got a hot wire and a ground, you'll get a complete circuit.

    I'm not so sure with A/C. I believe the neutral wire also needs to go somewhere of value, right? So if it's disconnected somewhere, even though the hot wire is hot, I will not get a complete circuit, right?

    Is there some way to test this?

  • #2
    Re: Can I test a neutral wire?

    I just hooked the old one up to a working power source and it's LED comes on and the test button works, so now I'm sure there's a break in the circuit somewhere.

    So now what?

    Comment


    • #3
      Re: Can I test a neutral wire?

      WW

      This requires that you be careful. Do you have a multi meter around? That is one that can read resistance in Ohms? If you do, shut off power to that circuit at the breaker panel - fuse box and be sure it is in fact off. Then measure the resistance from ground (green or bare copper wire) to the neutral (white). It should be less than 10 Ohms. Back at the point of service entrance (main fuse or breaker box) neutral and ground are bonded together, but that's the only place they should be. If you measure from ground to neutral out where your smoke detector is, and you get more than 10 Ohms, start checking connections on that circuit. Remember to do this only after you are sure the power to that circuit is OFF. You can also try using a flashlight style continuity tester in place of the meter. You should see the bulb light up some. It may not be bright but it should light up.

      Finally, try connecting up a test socket with a low Wattage (15 or 25 Watt) light bulb in it to the black and white wires and have someone turn power back on. It should light up to full brightness.

      Remember to always practice SAFETY and also have another adult around in case help is needed quickly.
      Last edited by Woussko; 02-11-2007, 07:00 PM.

      Comment


      • #4
        Re: Can I test a neutral wire?

        Hard wired smoke detectors should be on their own circuit. If you do not have power at this one your break is likely at the next one up the line at the wire nut used to connect the white wires together.

        Comment


        • #5
          Re: Can I test a neutral wire?

          This is the only one in the house that's hard wired.

          There's a conversation elsewhere about these things where I was wondering how hard it would be to interconnect them if the house isn't already wired to do so.

          When I get a moment, I'll use Woussko's method to confirm that the neutral wire is disconnected somewhere. Then I'm going to check the outlets in an adjascent room where I replaced the old ones with newer Decora style outlets to see if maybe there's a wire I missed or something.

          Comment


          • #6
            Re: Can I test a neutral wire?

            WB brings up a good point. You would need additional wiring to make up a new special circuit. Personally I use battery power only smoke detectors and make sure they are good and loud. Hint: Install several in areas that are prone to a fire and be sure in sleeping areas to have more than one. Also be sure to have several CO detectors as well. A little $ for protection is a good investment. For what it's worth I keep a small ABC fire extinguisher in the hallway near bedrooms, in kitchen but away from stove and in workshop. I also have one in my garage near the walk-in door. That one has more than paid for itself when a neighbor's lawnmower caught in fire last summer. I'm glad I was home and saw it. It's not a bad idea to have an 8 pounder sledge hammer handy in case you have to bash your way out in an emergency. The last thing anyone needs is to have a fire and be trapped inside. Maybe in time I'll go wild and install EXIT signs. I do have small automatic emergency lights for both stairways and the main hall. My area has lots of power failures. I think of them as good cheap life insurance. Yes, I went a bit wild, but am glad for it.

            Comment


            • #7
              Re: Can I test a neutral wire?

              I think someone also mentioned that there are wireless detectors available that trigger all the others when one goes off, eliminates the need to run 3-wire.

              Comment


              • #8
                Re: Can I test a neutral wire?

                There are such. Companies that install alarm systems are using them now. They have a little 5 year lithium battery inside and a blinking light to show when the battery is good and when to replace it. Some have an additional 9 Volt alkaline batery that is for safety where if the main battery gets low it beeps every few minutes and the blinking light flashes fast. The battery also lets the alarm work if the power is off. The whole alarm system normally has a rechargable battery inside the main control unit. Every few years that gets replaced. I think for all the PITA of it, why not just get several regular battery powered smoke detectors? If someone can't hear when one is BLASTING away I doubt that person would hear them all going off. They do make some with flashing strobes on them too. Hardwired ones that is.

                Maybe WW can contact the technical department of a local alarm systems company. I bet he would love to get info on them. Also, check good electrical supply houses.

                Comment


                • #9
                  Re: Can I test a neutral wire?

                  be sure to check votage with the meter first. in case someone has run a mutiwire branch circuit for you. (I hate MWBC's)

                  Comment


                  • #10
                    Re: Can I test a neutral wire?

                    Woussko: I think the real value of the interconnected ones isn't the extra noise of them all going off at once but, rather, the fact that you may not hear the one in the basement going off if you're sound asleep upstairs. If they're interconnected, the one upstairs will go off as well so you can wake up before smoke makes its way up 2 floors.

                    I've also got an extinguisher in the kitchen, one outside the furnace room, and one in the garage. I bought them after that little incident with a torch I mentioned in the plumbing forum.

                    Comment


                    • #11
                      Re: Can I test a neutral wire?

                      WW True about if the one in the basement was blasting and you were upstairs. Good for you getting some fire extinguishers. Let's hope you don't end up needing one of them. By the way every year or so, take them to a fire extinguisher service place to be checked. At the very least, check the pressure gauge, pull pin and invert it with an ear on the cylinder about once a month. You need to be able to hear the powder inside falling. If it doesn't try tapping (not too hard) the bottom with a rubber mallet a few times, stand uprite and after an hour or so, tip it over next to your ear and listen again. If you don't hear the powder fall, time to take it in for service. A fire extinguisher that won't work is worse than not having one. By the way if any of you burn wood, please keep several 5 gallon pails of water handy. You won't put a big hot fire, but you might buy some time if you catch a problem early.

                      Time I take a vacation from this thread. I PLPLPLPL and ARRRROOOOOOO way too much.

                      Comment


                      • #12
                        Re: Can I test a neutral wire?

                        Originally posted by Woussko View Post
                        Time I take a vacation from this thread. I PLPLPLPL and ARRRROOOOOOO way too much.
                        There's nothing wrong with throwing in your 2 cents when it comes to safety. If you hadn't just posted that, I'd have never thought to turn over the extinguishers to ensure the powder was loose. I'd have just looked at the pressure gauge now and then to ensure it's still charged.

                        You're like a living, breathing, PSA.

                        Comment


                        • #13
                          Re: Can I test a neutral wire?

                          smoke detectors are supposed to be wired into a circuit you would miss right away if it failed, like the power for the hall light.
                          Also, they make a 120 volt S/D that is radio interconnected, so you can put in other 120 volt units without running 3-wire or if you have more units than the basic detector will operate.
                          [your open neutral is probably at a nearby wirenut or at a receptacle terminal - anything else not working?]
                          Licensed Philadelphia electrician
                          Philadelphia emergency lighting certification

                          Comment


                          • #14
                            Re: Can I test a neutral wire?

                            Well... I've checked where I thought the issue was and had no luck.

                            Now I think I'll just ignore it until it's not so cold up there and I've got the ladder back from my father-in-law to get up into the attic and just see where the wires go.

                            There's some haphazard looking wiring up there so it wouldn't surprise me if whoever did that just cut the wire somewhere to use for something else.

                            In the meantime, I'm disconnecting the A/C lead from the detector so I don't have a hot wire just dangling loose somewhere that I can't see it.

                            Comment


                            • #15
                              Re: Can I test a neutral wire?

                              You may want to just kill the breaker for that circuit, if the neutral came loose the hot may not be far behind and can arc if there is a heavy load downstream. Best to be safe until you are sure what the problem is

                              Comment

                              Working...
                              X