Testing a short run of wiring?
November 19, 2024 8:31 AM Subscribe
I have a 50ft run of THWN wiring that I want to check for continuity while it's still in an unpowered state; can I do this given the usual selection of batteries and a multimeter?
The wiring in question is THWN, 12 AWG, running to 2 GFCIs. I would prefer to test continuity without fully powering the circuit, as there is one connection (it's a T circuit) that uses specialist waterproof connectors that are difficult for me to physically test (once they're engaged it's hard to determine if you did it right without breaking them and starting over).
I am interested in doing this because, while I believe the electrician did a fine job, he was mildly dismissive of the need to test anything. Once it's all done it'll be an enormous pain in the ass if I find one of the branch circuits has failed at the junction, so even if HE is confident, I'm more of a "trust but verify" type of person and want to make absolutely fucking sure I've got continuity because god help me if I need to redo all this.
The wiring in question is THWN, 12 AWG, running to 2 GFCIs. I would prefer to test continuity without fully powering the circuit, as there is one connection (it's a T circuit) that uses specialist waterproof connectors that are difficult for me to physically test (once they're engaged it's hard to determine if you did it right without breaking them and starting over).
I am interested in doing this because, while I believe the electrician did a fine job, he was mildly dismissive of the need to test anything. Once it's all done it'll be an enormous pain in the ass if I find one of the branch circuits has failed at the junction, so even if HE is confident, I'm more of a "trust but verify" type of person and want to make absolutely fucking sure I've got continuity because god help me if I need to redo all this.
Response by poster: Just to interject: I didn't buy them, so I'm not sure of the exact brand, but basically they're a crimp-style connector filled with silicone oil. The crimp looked fairly difficult to execute (crimper with long arms, so lots of force). Each connection was crimped in more than one place (near the middle, presumably for the wires, and then again near the entrance, presumably to seal the silicone oil in?).
...I do know it was silicone oil because that was a point of irritation for the electrician; minor amounts escaped during install, which then made crimping a PITA due to the slipperiness.
The junction box is now sealed, but I could break it open if I have to (solvent-welded).
posted by aramaic at 8:53 AM on November 19
...I do know it was silicone oil because that was a point of irritation for the electrician; minor amounts escaped during install, which then made crimping a PITA due to the slipperiness.
The junction box is now sealed, but I could break it open if I have to (solvent-welded).
posted by aramaic at 8:53 AM on November 19
I'm a little confused about the constraints here. Is the source end of the run already connected to a breaker? Is there some reason you don't want to energize the circuit and use a load tester/outlet tester to measure the outlets?
If you're already tied into a breaker and are committed to MacGyvering a solution out of a multimeter and batteries then this is kind of a pain to do safely and/or without undoing the electrician's work at the panel. Outlet/load testers are cheap and readily available, or you could just plug literally anything into the outlets and see if it powers on.
If instead you're looking for evidence of dodgy splices that are okay but will fail under load, that's (a) harder to test but in theory possible if you don't mind tearing out the work at the panel and making a DIY impedance meter out of a battery and some resistors, along with a decent model of the wire and expected contact resistances but (b) pretty much the exact reason to use a licensed and insured electrician so it's not your problem (and if it was done correctly, if it fails it will fail safely and is then again the electrician's problem to repair).
posted by range at 9:03 AM on November 19 [2 favorites]
If you're already tied into a breaker and are committed to MacGyvering a solution out of a multimeter and batteries then this is kind of a pain to do safely and/or without undoing the electrician's work at the panel. Outlet/load testers are cheap and readily available, or you could just plug literally anything into the outlets and see if it powers on.
If instead you're looking for evidence of dodgy splices that are okay but will fail under load, that's (a) harder to test but in theory possible if you don't mind tearing out the work at the panel and making a DIY impedance meter out of a battery and some resistors, along with a decent model of the wire and expected contact resistances but (b) pretty much the exact reason to use a licensed and insured electrician so it's not your problem (and if it was done correctly, if it fails it will fail safely and is then again the electrician's problem to repair).
posted by range at 9:03 AM on November 19 [2 favorites]
Get a wire tracer / tone generator to check continuity.
That said, what kind of failures are you anticipating? A break in the wire? The connector not having been crimped properly?
A break in the wire would be extremely rare. And as for the connector not having been crimped properly.....code usually requires all junctions to always be physically accessible for that reason. If you're in a situation where you won't have access to repair a bad splice in the future, then maybe you should reconsider what you're doing?
posted by RonButNotStupid at 9:08 AM on November 19 [1 favorite]
That said, what kind of failures are you anticipating? A break in the wire? The connector not having been crimped properly?
A break in the wire would be extremely rare. And as for the connector not having been crimped properly.....code usually requires all junctions to always be physically accessible for that reason. If you're in a situation where you won't have access to repair a bad splice in the future, then maybe you should reconsider what you're doing?
posted by RonButNotStupid at 9:08 AM on November 19 [1 favorite]
If I'm reading your setup right, verifying continuity is likely not to get you where to want to go, since if the wires in the connectors are touching even a little bit, you may not see a difference.
range has this right, since you used a professional you have a "throat to choke" if there's an issue.
posted by Dr. Twist at 10:12 AM on November 19 [1 favorite]
range has this right, since you used a professional you have a "throat to choke" if there's an issue.
posted by Dr. Twist at 10:12 AM on November 19 [1 favorite]
To test basic continuity of a new wire run you can go to one end and connect two of the wires together (after double checking that they are NOT HOT). Once connected at one end you can use the continuity function on the multimeter to check if these two wires carry the signal down to the temporary connection and back. Typical there is going to be at least 3 wires - so this process is much faster with a partner to make the different connections. Just be very careful checking the lines are not hot.
In the future ask about getting a voltage drop test part of any new electrical work like this - some jurisdictions inspect for this and my expectation is no more than 3-5% loss without explanation. A voltage drop test should include both the hot and neutral sides, which means that it also includes a continuity check in the process of testing any resistance in the line. This test would insure that the crimping is working as expected (at the time it was tested - it's not a perfect test for all problems/situations). A large voltage drop can have many causes, not just bad crimping, and this issue can directly damage electrical devices like computers and it can even cause fires.
I also recommend getting a basic GFCI tester tool, which aren't very expensive, and very handy in your situation and as part of annual maintance. GFCI's get old and become unreliable and I prefer checking manually than waiting for an accident.
posted by zenon at 10:29 AM on November 19 [1 favorite]
In the future ask about getting a voltage drop test part of any new electrical work like this - some jurisdictions inspect for this and my expectation is no more than 3-5% loss without explanation. A voltage drop test should include both the hot and neutral sides, which means that it also includes a continuity check in the process of testing any resistance in the line. This test would insure that the crimping is working as expected (at the time it was tested - it's not a perfect test for all problems/situations). A large voltage drop can have many causes, not just bad crimping, and this issue can directly damage electrical devices like computers and it can even cause fires.
I also recommend getting a basic GFCI tester tool, which aren't very expensive, and very handy in your situation and as part of annual maintance. GFCI's get old and become unreliable and I prefer checking manually than waiting for an accident.
posted by zenon at 10:29 AM on November 19 [1 favorite]
my cheap klein multimeter can check continuity. You just connect the probes to each end of the run you want to check and it will either beep or not. But I agree, continuity alone doesn't tell you how safe a splice is. If you're worried about a loose connection, the main hazard would be arcing. In that case you can get an AFCI deadfront (or receptacle if you prefer, or even replace the breaker with an AFCI breaker) and put it upstream of the splice in question. If the connection is loose, it will eventually cause arcing, and the circuit will trip before it gets dangerous.
I am more concerned about your statement that the junction box is welded closed. That's definitely not OK -- splices need to be accessible. Are you sure that's the situation? The interior of the junction box is not accessible except destructively?
posted by dbx at 10:30 AM on November 19 [1 favorite]
I am more concerned about your statement that the junction box is welded closed. That's definitely not OK -- splices need to be accessible. Are you sure that's the situation? The interior of the junction box is not accessible except destructively?
posted by dbx at 10:30 AM on November 19 [1 favorite]
I've seen stranger situations on things like for rooftop air handling units. In my experience this is to provide a separation of concerns - the electrician running the power is responsible right up to the point of service and then the equipment installer is responsible for crimping the 'hard' connection. The work can be completed on separate schedules. Code wise the sealed box is purely for installation and is likely listed under Receptacles for Plugs and Attachment Plugs (RTRT) and is not your standard 'service junction'.
Resin filled straight joints are very much a thing - here is one from 3m, which is not 'user serviceable', and as noted, the resin is the worst. And so very permanent. There are lots of these types of things - and probably many that I haven't seen - I can imagine solar installation likely requires all sorts of sealed permanent high voltage connections.
posted by zenon at 11:06 AM on November 19
Resin filled straight joints are very much a thing - here is one from 3m, which is not 'user serviceable', and as noted, the resin is the worst. And so very permanent. There are lots of these types of things - and probably many that I haven't seen - I can imagine solar installation likely requires all sorts of sealed permanent high voltage connections.
posted by zenon at 11:06 AM on November 19
Response by poster: I was not entirely clear -- I am seeking to double-check the work of an electrician without him being aware of that ("difficult" clients tend to have a hard time getting work done around here), and also without spending four weeks and $500 to get another electrician in for what I hope will be ten minutes of fiddling with a meter.
...thank you everyone for your comments thus far!
posted by aramaic at 11:12 AM on November 20
...thank you everyone for your comments thus far!
posted by aramaic at 11:12 AM on November 20
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Could you provide a link to these connectors?
posted by RonButNotStupid at 8:46 AM on November 19