Electrical Issue In The Shop

[Joe Wood]

Folks, I've been a general contractor since 1985 but have stayed away from any Elect. work, so I know almost zero about it.


I have a bunch of circuits in the shop, but one, with lights on it, starts flickering, then it goes off for 5+ minutes, then it comes on again. The breaker isn't tripping. Someone said it could be caused by something plugged in?


Before I call an electrician, is there any qizmo I can plug in to one of those outlets, that will log these outages and help me diagnose where the problem is?

[Bill George]

Lights and outlets should not be on the same circuit breaker but my guess is a loose connection or a bad light switch.

[roger wiegand]

There might be, but that sounds like something pretty funky, which could include a possibly arcing bad connection (eg a fire hazard). I'd get the electrician sooner rather than later. I might choose to check all the boxes, devices, and outlets on the circuit for loose connections (starting with the wire into the breaker in the box if the whole circuit is coming an going-- you might just swap the breaker to be sure) or any signs of failure before calling a pro, but I'm pretty comfortable with wiring.

I'd shut the circuit off at the breaker when leaving the building until you have it diagnosed.

Just this morning I had in intermittent fault that turned out to be a loose terminal screw in a plug. (a cord I acquired from someone else and didn't check before using, lesson re-learned for the Nth time. )

[Dave Zellers]

I agree with RW. One of the issues in woodshops can be wood dust accumulating inside ele boxes. I'd get to the bottom of this ASAP.

[Joe Wood]

wow yeah this could be serious. So is there a tool I can use to diagnose what / where the problem is? Or at least narrow it down?

This pic shows what happened to me last year, and is why I'm doubly concerned about messing with electrical!

[Paul F Franklin]

Well you spend a couple of hundred (or much more!) on a voltage/current data logger (like this: https://www.triplett.com/products/tr...#inline-button) and it probably won't tell you anything you don't know, that the power intermittently goes on and off. It *might* help you narrow down where the issue is by using it sequentially at multiple points on the circuit, but you could do that by plugging a lamp or radio into each receptacle and observing whether or not it goes on and off. So in this case, I'm with the others...if you don't want to kill the circuit and check all the connections, call a sparky pronto.

[Maurice Mcmurry]

I would start by checking the screw that attaches the branch wire to the circuit breaker for tightness, and the screw where the neutral connects in the breaker box. Then follow the circuit through all of the connections and devices along its path, checking screws and wire nuts for tightness. An outlet or switch with a loose screw will sometimes get warm or hot. You could check all of the devices along the circuit with an infra red thermometer. I have found loose screws and faulty back-wired (poked in) duplex receptacles causing this sort of problem on several occasions. For some reason I find a loose neutral more often than a loose hot.

[Joe Wood]

Thanks guys you're some great help!

[Jim Becker]

Yea, loose connection and you do want to trace it because it can cause sparking and well, you know...not nice things potentially. So check the connections at the breaker, on the switch(s) and at the fixtures. If you don't find anything loose and are still getting the flickering, call in an electrician to diagnose further.

[Bill Dufour]

After checking in the sub panel I would ,unplug everything except a light or radio on the last outlet. It is possible a light or device is failing and drawing too much power.
If the problem is still there unplug and move closer to the panel.
My guess is the outlets are daisy chained not pigtailed. Either way a loose connection in a box. Remove outlet from the box with something plugged into it. turn the breaker back on and wiggle the outlet around and see if anything moves or flickers.
If the breaker is zinsco or federal pacific I suspect breaker is failing. My main panel sounded like frying eggs from time to time.
Bill D

[John K Jordan]

This is good advice. Over the years I’e fixed several intermittent electrical problems for others and in houses I bought that were due to insufficient tightening, especially in wire ends twisted into a wire nut. Sufficient current in even a slightly insufficient connection can cause heating which can further degrade the connection. If I find where someone jammed too many wires into a wire nut I would either get a larger wire nut or split the bundle into two smaller connections joined with a short jumper. The worst case is where someone tried to fit too many conductors and connections in a box that is too small - difficult to do it right and a nasty job to inspect and fix.

Joe, before twisting any wire nut on several wire ends I always use pliers and tightly twist the bare wire ends (clockwise) to make a solid mechanical connection before twisting on the wire nut. After applying a wire nut (or tightening a suspected wire nut) I like to tug on each wire in the bundle to see if everything’s secure.

Note that some older installations may use connectors that are not as effective as the better quality connectors you can find today. For wire nuts I use the type with an internal coiled spring that cuts into and really grips solid wires.

Another thing, some lighting fixtures invite sloppy connections where they use (and even supply) a small plastic wire nut to connect a thin stranded wire to a 14ga solid wire. There are better and safer connectors. I always shop for connectors at a commercial electrical supplier that caters to electricians - only at HD when in a pinch (like on a weekend). The commercial supplier has good quality and the guys I deal with know their stuff.

BTW, I’ve done a lot of wiring but I’m not an electrician (except in central Mexico). If not very familiar and comfortable with installing, testing, tracing, and fixing electrical wiring it might be best to hire a pro. If not done right you could loose more than your shop…

As for your question, as someone mentioned monitoring equipment can be expensive. I sometimes uss my storage oscilloscope that can be set to trigger and start recording on a specific voltage event. However I don’t think much would be gained in the case of an entire flickering lighting circuit. A poor connection upstream from the first flickering fixture seems likely, If there were a bunch of junction boxes and switches it might help narrow the search but I’d probably just go with the box-by-box inspection. Note there shouldn’t be any general purpose receptacles on a lighting circuit unless they are only for plugging in fixtures that come with an attached cord and plug. I sometimes wire such switched receptacles for task lighting.

Hey, I NEVER use the quick back wired “poked in” connections on the back of receptacles. For me, it’s form a loop and tighten the screw.

I would start by checking the screw that attaches the branch wire to the circuit breaker for tightness, and the screw where the neutral connects in the breaker box. Then follow the circuit through all of the connections and devices along its path, checking screws and wire nuts for tightness. An outlet or switch with a loose screw will sometimes get warm or hot. You could check all of the devices along the circuit with an infra red thermometer. I have found loose screws and faulty back-wired (poked in) duplex receptacles causing this sort of problem on several occasions. For some reason I find a loose neutral more often than a loose hot.

[Andrew More]

Find a way to divide the problem in half, like in the middle of the circuit disconnect it, and then see if the remaining half of the circuit still has a problem. If it does, divide in half again, if it does not, check the half you disconnected. You'll quickly find the problem in this manner no matter how large the circuit.

[Thomas McCurnin]

1. Shut Down Panel That Services Shop.

2. Snap Out Breakers That Service The Faulty Circuit. Some commercial breakers are screwed in. Check breaker by (a) insuring that hot and neutrals are being clamped on raw copper and not the insulation, you should be able to see about a 16th inch of copper on the outside of the breaker if you electrician was good, thats what our inspector likes to see; and (2) give the wires a tug and insure they are indeed clamped down tightly; and (3) slip a screw driver into the back of the breaker to insure those two screws are tight, but don't strip them out.

3. Check The Switch Box. Open up the switch box for the faulty circuit and check all connections. Green/Ground should be attached to the switch and the box (if metal) and to the incoming Green/Ground which goes back to the panel and downstream to other devices. White should be tied together and again attached to the incoming White/Neutral back to the panel and to other devices. Hot/Black (sometimes red) should attach to the gold screw of the switch and again to the incoming Black/Hot back to the panel or to other devices. Switching is only done on hots, not neutrals. Check the same way. Give the wires a tug and hopefully the wire nut has seated well and nothing moves. Give the wire to the switch a tug and again, nothing should move. Give the wire nut and switch screws a gentle tightening, nothing should move.

If everything is AOK, then the problem is a bad breaker (not tripping), a bad switch, or a loose connection down stream. Time for Plan B.

To check Plan B, the box has got to be hot (or use a continuity meter). I would check them hot by carefully spreading the wires and connections out like opening a present and go to work with a simple wobbler electrical tester, which wobbles when current is present. But this involves some basic knowledge of electricity and being very careful. You might want to pass on Plan B if you don't feel comfortable. But the general idea is to check the incoming hots and neutrals for current (should be hot and the tester will wobble. And when the switch is turned on put the tester on the White/Neutral and the Gold Screw of the switch one at a time. You should get a wobble on both of the screws in the switch when turned on but when the switch is turned off, only one of the Gold Screws, the incoming hot.

If you are particularly paranoid about electricity, with the panel off and the switch box open, I have attached the wobbler or another type of test to bare wire with alligator clips, then flip the breaker on so I'm not sticking my hands in a hot box. And go back and forth, as this will take a lot of time. Gotta be careful that the alligator clips only touch the wire or screw in question and nothing else or you'll get some arcing and the breaker will probably flip. But at least your hands are not in the box. I work on live boxes all the time, but would understand why some folks are uncomfortable doing so. Sometimes there is no other way except to work on hot circuits. There are special gloves for this purpose by the way.

[Ken Fitzgerald]

Joe, I have used equipment to monitor and log both AC voltages and DC voltages. Other than tell you when something happened, they won't fix or help you find your problem.

I am with the others here that suggest checking all connections on the circuit that is presenting problems. A loose connection is the most common cause of your symptoms and a loose connection can cause fires.

Always shut the electrical circuit down at the panel when troubleshooting this. I worked on radar for 8 years in the US Navy. I worked on high voltage power supplies used to generate x-rays in CT scanners and x-ray machines. As suggested about twist on connectors, screws holding wires on switches, on outlets etc. Check every connection for tightness.

Like John, I always form a loop and screw a wire to a device, switch or outlet. Those push-in-the-hole devices don't give me much satisfaction.

I have seen loose RF connections on the RF transmitter used in MR scanners burn and destroy a high-power RF cable.

With power turned off at the panel, find the loose connection!

[Jim Koepke]

For me, it’s form a loop and tighten the screw.

One thing about this is many nonelectrical people do not know the wire should go around the screw clockwise. This tends to pull the wire into the screw post. Going counter clockwise can push the wire out.

I remember when transistor radios were small one could often find a loose connection by tuning between stations and placing the radio near the junction boxes one at a time. The arcing from a loose connection would cause more noise on the radio the closer it got to the source.

jtk