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Supposed the breaker is off but the left side is still hot (let's say breaker defective). Won't it work if you measure the terminal in the hot right and load left like in the following picture?

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Why won't it work (if it won't work)?

Original message:

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I'll connect two chair lugs to the screws in the above 125A main breaker feeder cooper. If I shut down the main breaker, how do I check both hot wires are gone without any neutral (we don't use neutral since all our equipments are 240v)? A defective breaker may only disable one of the hots. If I use a multimeter, where will I put the other lead on for each?

Samzun
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6 Answers6

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That's what a non-contact tester is for. You test with it before and make sure it is showing voltage and then flip the breaker and make sure it is clear. It should not be the only thing you do before working on potentially live wires/equipment, but it provides a very useful double-check.

manassehkatz-Moving 2 Codidact
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    I need another backup test in case the non-contract $5 tester fails. What if you put one lead of the multitester in one of the load and the other in the opposite line.. or what if you put in on the load and line of the same side.. would this damage the multimeter? – Samzun Nov 16 '18 at 06:22
  • also actually I bought one.. see https://imagizer.imageshack.com/v2/640x480q90/924/WDYx9T.jpg but I'm not sure if it can work if only one of the hot line is alive.. but there is also problem with sensitivity.. sometimes it can't pick up.. sometime it picks up even without touching it.. so I want another way to check using tested multimeter.. because one wrong move and it's early trip to heaven..lol.. – Samzun Nov 16 '18 at 06:44
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    Non-contact are the worst type of testers ever invented, get a 'contact-type' testlight instead that gives you higher accuracy (it's very uncommon for a contact-tester to read phantom voltage). – DDS Nov 16 '18 at 07:49
  • what do you mean by "contact-type' testlight? why light? Please give the right term so I can google it and purchase one because I want backup besides non-contact voltage tester. – Samzun Nov 16 '18 at 07:52
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    I mean object like this: you point the tip on a contact, touching the top and if light inside lights up it's a live conductor if stays off is either a ground, a PE or a non-energized phase: https://www.myelettro.it/wp-content/uploads/2018/04/CACCIAVITE-CERCAFASE-A-LAMA-65X3MM.jpg These suits your need because only need one wire to work. You can search them with the italian term "cercafase" (literally phase-finders) – DDS Nov 16 '18 at 07:54
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    *"what do you mean by "contact-type' testlight?"* -- see [When doing electrical work, what do I use to check wires are safe?](https://diy.stackexchange.com/a/90039/2815) – RedGrittyBrick Nov 16 '18 at 10:31
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    @DDS That tester operates by connecting the live wire through a neon bulb that is connected to your hand. You will never find this design in any rated or listed test equipment. The fact that you may have used one without harm is not support for their safety. – Dan D. Nov 16 '18 at 10:55
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    It's perfectly safe: less than 1mA runs trough the body, also the high-value resistor is made in a way that, in case of rupture, it breaks the tester instead of shorting preventing full voltage from running trough your body. This tester are widely available and CE and IMQ marked: it's perfectly safe. – DDS Nov 16 '18 at 14:27
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There are several ways to test to verify if the line(s) are dead, first non contact tester. Test the incoming line to verify the tester is working, then check both legs after the breaker , now verify the tester is still working on the hot side of the breaker if both legs show dead and both tests on the hot side showed good it is safe., Using a volt meter, verify the meter is working on the hot side, check leg 1 to ground, check leg 2 to ground, just to be crazy check leg 1 to leg 2. If all show dead verify the meter is still working.

Now you know how to properly test with both kinds of meters.

Ed Beal
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  • I have no ground. That was why i was asking if i can test between hot #1 and load #2, then hot #2 and load #1? – Samzun Nov 21 '18 at 20:36
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    No ground or neutral in the panel? Wow that would not be a safe setup. But a non contact voltage detector will still work. A high impedance volt meter will show a voltage in most cases but to be absolutely sure with a volt meter you would need a ground reference. – Ed Beal Nov 21 '18 at 22:39
  • As Harper noted, we mostly don't have neutral in our country because we only use 240v equivalent to black and red or 2-pole in the US. I need to know why it won't work where you measure between hot #1 and load #2, then hot #2 and load #1? The reason is that if breaker #1 is still on even when it is turn off, then hot#2 and load#1 would register a voltage even when the breaker is off. – Samzun Nov 21 '18 at 22:41
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    With no ground reference you cannot be 100% sure. I have quite a few 240 only panels here in the US for only 240v loads (no neutral) but in every case there is an equipment ground wire bonding the case to a driven rod/ pipe or ufer ground (ufer is a grounding system where the rebar in the foundation is connected to the panel with number 4 wire in residential wiring). If you want to be sure a grounding rod driven at least 8' into earth connected by a #6 copper wire to the panel would improve the safety of your system. If your load setup faults to ground without a bonding method the frame is hot – Ed Beal Nov 21 '18 at 22:50
  • please see edited main post above so you can see illustration of what I meant. Why won't it work? – Samzun Nov 21 '18 at 23:26
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    There is no ground potential as I said in an earlier comment a high impedance volt meter may provide a reading, you can try this by sticking a meter probe in an outlet and the other end in the air you will probably get a reading but it won't be accurate because there is no ground potential at this point. I just pulled one of the cheapest meters I use out and on voltage stuck 1 lead in the hot side of an outlet it reads 29v. – Ed Beal Nov 22 '18 at 00:34
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    if I hold it in my hand it goes up to 63v if I touch a grounded surface with my other hand 113v. In no case was my meter properly grounded when I properly tested hot to ground it is 124v so all the other readings were wrong because of no true ground path. – Ed Beal Nov 22 '18 at 00:35
  • You mean your multimeter has 3 leads (with one connected to ground)? Here is picture of my multimeter.. https://imageshack.com/a/img923/6850/zncxRb.jpg To measure voltage, we plug the 2 leads into the COM and V on the right sides. Where to plug the 3 leads? – Samzun Nov 22 '18 at 00:45
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    No 2 leads I have answered your questions many times you have no business or skills to do the simple things you are asking after asking you to up vote some of the many questions you have asked you still only ask more questions that are ignorant or stupid in my opinion so I will now start down voting everything because you do not have any skills or information to help this site including a simple up vote of questions you have asked you used in another 1, 2 or 3 posts. – Ed Beal Nov 22 '18 at 02:43
  • But I have upvoted the above question 3 hours ago when you first mentioned it. Ah, you meant the comment can be upvoted too. I just know it now. I'll upvote them now. – Samzun Nov 22 '18 at 02:45
  • When you mentioned the upvote thing 3 hours ago. I upvoted them. But I didn't know you were also referring to upvote comments which I wasn't aware. So I'll upvote the comments now. – Samzun Nov 22 '18 at 02:51
  • What I don't get in the above questions is if we measured the hot black and hot red leads.. it is accurate even without ground. Remember our country ignored the neutral and ground. Yet we can easily measured the voltage.. so I don't get why it must be grounded before the multimeter can test the 2-pole as 240v which we always do. – Samzun Nov 22 '18 at 02:54
  • Because when I first joined.. I couldn't up vote... beginners at stack exchange can't up vote.. it's only now that I'm aware I can up vote already... and I just upvoted the answers by Ed and others (3 hours ago). And I don't know comments should be upvoted too (I upvote comments now). – Samzun Nov 22 '18 at 03:01
  • No you can always up vote a question you asked you consistently challange at least 3 professionals on this site , with nothing other than time wasting questions I and others have spent a lot of time trying to help so i finally decided to let others know. – Ed Beal Nov 22 '18 at 03:05
  • When I tried to upvote last week. I couldn't because the system said I don't have sufficient reputation to up vote.. that was why I didn't do it. But now I will because I can already. – Samzun Nov 22 '18 at 03:06
  • When I tried to upvote last week. I couldn't because new users need to have certain reputations first before they can upvote. Try asking the system owner. I'm sorry. Can't you forgive me and give me one more chance? – Samzun Nov 22 '18 at 03:11
  • I will upvote everthing now and if you see i didn't, then i will leave voluntarily. I'm really sorry. – Samzun Nov 22 '18 at 03:12
  • Anyway. I got what you mean now.That I must measure the voltage to ground. To ensure there is grounded reference. Well. In my country. 99.99% don't have neutral nor grounded at home. We are using USA power system when they conquered us half a century ago. And I'm trying to use US equipments (2-pole) in my power system that even local electrical engineers are ignorant.. So please really forgive me for my questions. I'll just spend one more week week and that's it. Please understand me. We never have neutral nor ground any appliances, and Harper knows.. that is why I'm using GFCI 2-pole from US – Samzun Nov 22 '18 at 03:23
  • I have upvoted every single answer the past hour and will do so until all have been upvoted. please see this link .https://imageshack.com/a/img924/8579/7PtzSY.jpg . it will explain everything. When I first participated here in physics or electrical exchange.. I always got this message "Thanks for the Feedback, votes cast by those with less than 15 reputation are recorded. But do not change the publicly displayed post score". So you see.. I wanted the check to be displayed publicly. So I waited.. and seemed to forget all about it until you reminded me it's called upvote and stuff. Sorry. Thanks – Samzun Nov 22 '18 at 03:55
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You can check against PE (if present) or metal water pipe because almost all distribution systems are referenced to earth.

DDS
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Between the line and the load on the breaker. You want to test if the breaker disconnects both of its load terminals from its line terminals.

Dan D.
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  • How do you test this using a multimeter? If I put the lead between the same side (line and load), would the multimeter be destroyed? Imagine putting it in series between two wires. So I guess one must put one lead in an output on right side.. and put one lead on input on left side? – Samzun Nov 16 '18 at 11:04
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    @samzun, with the meter in voltage mode, you can put it on two points with a voltage between them without destroying the meter. Yes, current flows through the meter, but the impedance of the meter in voltage mode is high enough that it can handle it. In current mode, you would likely blow the fuse in the meter. – batsplatsterson Nov 16 '18 at 15:48
  • I mean can you measure the red arrows in this picture? https://imagizer.imageshack.com/v2/1024x768q90/924/CJJDGQ.jpg and then the other sides? Can it check if one of the load side is still on? – Samzun Nov 17 '18 at 10:50
  • Exactly where are you proposing to measure? (It isn't clear to me, and it seems to the OP as well.) – Daniel Griscom Nov 17 '18 at 14:49
  • measure the left load side.. measure the right line side... if the left load side is live.. it can show voltage.. isn't it.. and also the other way around.. see the above picture with arrows again where the multimeter or voltage leads will be put – Samzun Nov 17 '18 at 14:53
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I can't say for sure since I am unfamiliar with the electrical service in the OP's location. I believe at the utility transformer it's the same as the common US system, 240V line to line with a grounded center tap, so 120V line to ground at the transformer. However there is no service neutral / grounded conductor, not sure if there's a grounding electrode system, and no equipment grounding system. I believe the line to ground voltage in the house would be less than 120V due to ground resistance.

Most non contact voltage testers depend on a ground path through the person holding the tester. They may be less reliable with a system with no grounded conductor on the service / GES / EGS.

I'd definitely recommend that the OP back up the NCVT with readings from a solenoid tester or other voltage tester / meter. I'd check line to line and line to ground on both sides of the main breaker before and after opening the breaker. If any reading is other than expected, it's a show stopper.

There are a lot of other things you need to know to work safely in the panel, I am just addressing the OP's question about testing.

batsplatsterson
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  • My panel is high up the wall and I have to step on top of the kitchen plastic countertop 1 meter above floor yet I am getting a reading of the panel in the non-contact voltage tester.. I'm not even standing on the floor.. how come it can form capactive coupling? – Samzun Nov 16 '18 at 12:58
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    @samzun - it doesn't need much of a ground path. If you don't mind - could you suspend yourself from the ground in a helicopter drone and see if it works and report back. I am curious. – batsplatsterson Nov 16 '18 at 13:52
  • I just read about capactive coupling today after curious about how non-contact voltage tester works. Of course if one floats in air from suspending in helicopter drone.. it should work too because as you said.. it doesn't need much of a ground path. I wonder if the technology can be used to detect people in building, etc. – Samzun Nov 16 '18 at 14:41
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    It really depends on the voltage detector. Almost all of them use the "hall effect" the hall affect is a change in solid state sensor that is caused by the electric fields when there is voltage on the wire. With residential wiring or low voltage wiring according to the NEC there is no capacitive coupling it is actually inductive coupling the lines of force crossing a conductor induce a voltage. This is how transformers work. The more wire in parallel the higher the potential, vary number of turns in primary and secondary and you can make step up or step down transformers all from inductance – Ed Beal Nov 21 '18 at 19:27
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Just test line to line. First test the load side with the breaker closed and record that voltage, i.e. 240V. Then open the breaker and test it again, if both sides are open, it would read zero. Anything other than zero means there is a problem and if it reads less than the prior reading, it means there is eather a cross connected circuit somewhere from another source, or one pole of that breaker is not opening, but it is reading through a load somewhere.

JRaef
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  • I was asking what if one hot is still live while only the other hot is cut (let's say the breaker is defective and only disconnect one of the 2 hots). – Samzun Nov 16 '18 at 22:33