here’s the situation:
i have a 120v/20a circuit in my shop that is wired with 12/3 and in each double gang box (10 total along about 25′ of one wall- some outlets on the wall, some on the front of the long countertop base) one dbl outlet is on the red, the other on the black, with shared neutral. it starts right next to the panel so it doesn’t wind all over the bldg before it gets to the business ends. this circuit has been in partial use for months. and since ‘electrician’ is not my regular job description, i am hyper-anal about connections, etc. lately, there has been only a Makita 7.2-14.4v battery charger on this circuit- in the 9th of 10 boxes.
well, i finally got around to finishing the front of the countertop supports and put the faceplates on those boxes, got done, swapped the 12v batteries in the driver and charger, took note of the red ‘charging’ light and forgot about it for a couple days. did some more work on other stuff, went to get a fresh batt and saw the light was off. checked the panel and the breaker had been tripped.
opened all the boxes, pulled the receptacles out, can’t find any sign of a short, bad or wrong connection, etc. highly unlikely that it’s a screw or nail in a cable somewhere because everything has been in use without problems since that work was finished (and i was pretty anal about avoiding that sort of thing, too).
suggestions? anybody ever heard of a batt charger causing an overload?
thanks,
mitch
Replies
Gardner-Bender makes circuit testers and they just plug into a receptical, with 2 yellow/orange LEDs and one red one. They have a diagram that shows correct, lifted ground or neutral and reversed hot/neutral.
Can you reset the breaker and get power thru the circuit without the charger plugged in? If so, does it arc and trip when you plug it in?
-- J.S.
yes- i forgot to mention that before. flip the breaker back on and everything appears perfectly normal.
just back from Lowe's with a more comprehensive Greenlee test unit. will report back soon. thanks.
m
okay, my brand spankin' new, (supposedly) trusty Greenlee GT-10 Polarity Cube shows every receptacle on the entire circuit to be in proper order (no missing grounds, misconnects, mix-ups, etc).
the DM-20 mini Digital Multimeter shows voltage on the red circuit, at the first outlet about 8' from the panel as the romex runs, at 120.2-120.5v and virtually no discernible loss at the far end, about 50-60' of cable and 9 receptacles, away. the black line consistently reads about .5-.7v higher(?), but also shows no drop over the length of the run.
now what should i test and how or with what? bad breaker?
thanks,
m
you try plugging the charger in a different outlet / circuit?
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., wer ist jetzt der Idiot ?
the charger is about 4 yrs old and has been in several different locations/circuits. never had any problem elsewhere, not to mention that it was on the headache circuit for some weeks before this happened, along with intermittent use of other tools such as a big shop vac, circ saw, lam trimmer, etc. the batteries also seem fine- no sign of overcharging.
also, no evidence of electrical glitches anywhere else in the bldg- i.e. two stereo receivers that haven't lost their radio station presets, etc. this is freaking me out because i have been working on and around this circuit recently but can find nothing i might have messed up, nor was anything unusual happening when it tripped. we haven't had any lightning storms or power outages that i'm aware of. everything tests normal.
m
you have not isolated the problem just yet...you should try to duplicate the conditions one more time to jog your memory for anything you may have forgotten .
......or perhaps someone had plugged something in while you were goneit sounds like your circuit is fine ..just don't drive yourself nuts with your DMM reading tenths of a volt.this circuit is not on an AFCi breaker is it?.
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., wer ist jetzt der Idiot ?
If I follow correctly this is multi-wire circuit. He was measuring leg 1 to neutral (red) and leg 2 to neutral (black) and noticed the difference in voltage.Has nothing to do with grounds.I have never really had that much of a need to measure the difference in the 2 legs, but I would suspect that .5-.7 volts is reasonable. Depents on how balanced all of the loads that are on the transformer.I to would suspect the charge first..
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A-holes. Hey every group has to have one. And I have been elected to be the one. I should make that my tagline.
yes, this is an outbuilding, but it has its own 200A service straight from the pole.
yes, this a multi-wire or double receptacle w/ shared neutral circuit. i did that so i can use two pieces of equipment- for example, a big shop vac and sander- without overloading or plugging one of them in across the room. btw- i also used white and grey outlets side by side as a visual reminder ('red with white on the right, black with grey on the left' to keep track as i worked). they look pretty slick with the stainless steel faceplates (and no, no sign of arcing to the faceplates, either). also, there are 5 such circuits in the bldg- along with some 220Vs for bigger eqpt & dedicated HVAC, and two 15A lighting loops- and none have ever caused any concern.
yes, it's a pretty nice shop- or at least is slowly but surely getting to be.
no, no AFCI or GFCI (probably should according to strict code, but doesn't. when the inspector checked original panel install he said GFCIs weren't necessary in the adjacent, then more finished, room, so i didn't use them in this room either.)
how could i test the charger? it seems to still work ok.
thanks again, all y'all.
m
also, nobody else used anything else on that circuit or in that room. DW hardly sets foot in there- maybe to dump the trash from the small shop into the bigger barrel in the big shop, but rarely even that.
m
sounds like a nice shop..especially the different colored receps..nifty idea.. I said earlier, try to duplicate the conditions using a different circuit to see if your charger is the culprit. other than that I'm just making a WAGgood luck, enjoy your shop.....
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., wer ist jetzt der Idiot ?
i just called the local Makita expert, which in this area actually means something- Louis Williams & Sons of Hendersonville, NC, quite possibly the biggest Makita dealer on the planet - and he said it's highly unlikely the charger is the problem if it still seems to be working okay. he said they draw barely half an amp or so. he suspected a weak or bad breaker. hmmm...
m
You could open the case of the charger but it's probably a small transformer with a circuit board inside. I have a 7.2V Makita that quit and it looks like there's nothing wrong so from that standpoint, you can unplug yours and put an ohmmeter on the plug. If it shows a dead short, that could indicate a source of the problem. You should see some resistance if you're checking the primary. Look for the secondary leads and check for continuity to the primary- there shouldn't be any direct connection. You could also unsolder the power cord from the transformer and check that independent of the transformer. If you see close to 0 ohms, it's too low. You may be able to call the manufacturer and ask what you should read, too. If it was left ON for too long, the transformer could be cooked.
"I cut this piece four times and it's still too short."
i would be more suspicious of the charger, but as far as i can tell, it still works just fine. also, this unit has routinely been left plugged in for weeks or even months at a time, sometimes with the same batt in it for several weeks. never any problem.
could you elaborate or be more specific about checking continuity, primary & secondary leads, etc? my fancy new meter apparently has some capabilities in that area.
i have bravely decided to recreate the circumstances, so we'll see if anything happens in the next few days- my insurance is paid up.
the mystery continues....
m
The primary is basically where the current flows into the transformer and the secondary is where it flows out and goes to the other circuit(s). I don't know if you know how a transformer works but there is a set of windings that are close to/would inside of at least one other set. The ratio of the primary windings (where the current comes in) to the secondary windings has everything to do with what voltage comes out. Any time current flows in a conductor, a magnetic field is created and if the field varies or the conductor is moved relative to an inductor or wire, the varying field induces a current to flow. It could still be in the charger but who knows? Sunspots?
"I cut this piece four times and it's still too short."
At this point, I'd reach for the clip-around ammeter. To check things that plug in, like the charger, make up a little test cord, like an extension cord, only with individual conductors, so you can clip the meter around the hot by itself, and likewise the neutral and ground. Compare what you get with the nameplate amps. Also, back in the panel, check the hots with everything unplugged/turned off.
-- J.S.
yeah, that's what I been thinking.
the charger maybe has some kind of intermittemt thing.
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., wer ist jetzt der Idiot ?
Is this an outbuilding and is there a sub-panel? The grounds may not be at the same potential and that could explain the voltage on the ground. If there's no separate ground conductor running from the sub-panel to the main one, the two aren't bonded and any resistance in the ground and/or neutral will make up the difference anyplace it can.
"I cut this piece four times and it's still too short."