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Sound Reinforcement - Forums for Live Sound Professionals - Your Displayed Name Must Be Your Real Full Name To Post In The Live Sound Forums => AC Power and Grounding => Topic started by: Jim Klas on August 24, 2022, 03:32:00 AM
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Hello,
This is a basic question, I have not seen any other similar topics here so far - but if anyone has some direction on the issue I'm having I would be greatly appreciative.
Bottom line is that I find my power stringer system occasionally trips GFCIs on distro boxes, particularly when we're in a tent or something like that, for example with generator delivered power.
I have been using a number of Whirlwind's PowerLink stringer boxes, the PL1-420 units - for bands and I really like them. I especially like that they are connectable with PowerCon and that means the cable can be disconnected from the box at the end of the night, and that packs up easier. There are certain drawbacks to PowerCon which I am aware of, for example they cannot be plugged in under load. This is always observed during setup.
The PowerCon cables I use to interconnect the stringers were made for me by a local electrician with 12/3 SOOW and I generally connect the stringers to edison outlet sources at the venue, they have heavy duty Leviton Edison plugs on the end, I do not have any NEMA twist lock or other type of AC source connector yet.
The PowerLink boxes are UL listed, they do say they are not rated for outdoor use but I do use them in, for example a large tent when there is a raised stage, good protection from weather and they are never on the ground. With regards to the occasional GFCI trips, I was wondering if this could be a fault in my PowerCon cables. I have checked them all, nothing is ever in any wet situation, and as far as I can tell checking with an ohmmeter and an AC outlet tester indicates all cables are 100% correct.
I apologize if this is basic question. My intent is to try to provide safest possible power outputs for musicians onstage.
Thank you in advance, Jim
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Are they tripping with equipment plugged in, or just the stringers? Is it the same distro each time? The same GFCI? They sometimes go bad.
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I don't presume to know where Whirlwind sources the receptacles they use for their boxes-I know that a few years back I grabbed some cheap receptacles from a big box store that ended up being installed downstream on a GFCI circuit in a detached garage. I started getting nuisance trips-finding no problems, I replaced the receptacles with a spec grade receptacle (probably Leviton) and the problem went away. Might be something to try-maybe just enough damp outdoors to create an issue-the tent would be similar in environment to a detached garage.
If it's equipment, there are other threads on here where people smarter than I discuss the fact that UL allows a certain amount of leakage from wallwart supplies-I think 1-2 milliamps. Given that a GFCI trips around 8-10 milliamps, a couple of power supplies running on the edge could be a problem as well. My numbers may be off by a digit or two, but they are close.
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Are they tripping with equipment plugged in, or just the stringers? Is it the same distro each time? The same GFCI? They sometimes go bad.
Thank you for reply - My experience has been that in one of the venues where this happened it was not the same distro unit each time that caused the trip and the last time it happened to me, it seemed like that particular GFCI was tripping with the same equipment plugged in until I unplugged the equipment and plugged a different distro into that outlet, and then it would trip again. So at least until now, I haven't been able to nail down a specific piece of gear. In some cases I had no equipment plugged into a particular distro and the outlet tripped.
I did have one instance where I believe it was just a bad GFCI outlet.
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I don't presume to know where Whirlwind sources the receptacles they use for their boxes-I know that a few years back I grabbed some cheap receptacles from a big box store that ended up being installed downstream on a GFCI circuit in a detached garage. I started getting nuisance trips-finding no problems, I replaced the receptacles with a spec grade receptacle (probably Leviton) and the problem went away. Might be something to try-maybe just enough damp outdoors to create an issue-the tent would be similar in environment to a detached garage.
If it's equipment, there are other threads on here where people smarter than I discuss the fact that UL allows a certain amount of leakage from wallwart supplies-I think 1-2 milliamps. Given that a GFCI trips around 8-10 milliamps, a couple of power supplies running on the edge could be a problem as well. My numbers may be off by a digit or two, but they are close.
Thank you for the reply. The outlets used on the PL-1-420 are made by Hubbell. I believe they are excellent quality - I see that type of receptacle used in hospitals as they are manufactured in different colors. To be honest though, I am not sure if the problem is the outlet box itself, I would be more inclined to believe it's the cables that I had built for me, or like you said maybe just damp enough that a problem occurs.
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Hi Jim,
I have a bunch of the PL1-420 and haven't any issues with GFCIs. I have found them to be excellent quality. Maybe go through each one with a circuit tester?
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With regards to the occasional GFCI trips, I was wondering if this could be a fault in my PowerCon cables. I have checked them all, nothing is ever in any wet situation, and as far as I can tell checking with an ohmmeter and an AC outlet tester indicates all cables are 100% correct.
Normally cables are pretty foolproof, but in the case of PowerCons there is one significant difference that your electrician may not have taken into account. In a normal twistlock or "edison" plug, the receptacle is the mirror image of the plug. This is convenient, because the lay of the wires inside the jacket on one end is the mirror image of the other, but this is not the case for PowerCon plugs. NAC3FCA (blue) and NAC3FCB (grey) connectors have the same pin arrangement, so if you just connect the black wire to the "L" terminal and the others wherever they most easily fit, you'll wind up swapping neutral and ground in each cable. The kicker is that your AC plug tester can't tell the difference, and will tell you its OK, but the GFCI knows the current is returning on the ground instead of neutral and will trip.
It's a bit difficult to get ohmmeter probes in the end of the PowerCons to check for continuity, so an easy workaround is to just chain all your PowerLink boxes together with the PowerCon cables. Don't plug it into an AC supply, and don't plug anything else into it. You should be able to measure continuity (very low ohms) between the chassis of any of the PowerLink boxes and any other box. If there is a swap happening, there will only be continuity between every second box in the string.
In the days before the "pin 1 problem" was addressed, this would be a recipe for copious amounts of hum in a PA system. I assume you haven't had any trouble with that, so at least the gear is working properly. :)
Or maybe it's something else totally different. :(
GTD
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Normally cables are pretty foolproof, but in the case of PowerCons there is one significant difference that your electrician may not have taken into account. In a normal twistlock or "edison" plug, the receptacle is the mirror image of the plug. This is convenient, because the lay of the wires inside the jacket on one end is the mirror image of the other, but this is not the case for PowerCon plugs. NAC3FCA (blue) and NAC3FCB (grey) connectors have the same pin arrangement, so if you just connect the black wire to the "L" terminal and the others wherever they most easily fit, you'll wind up swapping neutral and ground in each cable. The kicker is that your AC plug tester can't tell the difference, and will tell you its OK, but the GFCI knows the current is returning on the ground instead of neutral and will trip.
It's a bit difficult to get ohmmeter probes in the end of the PowerCons to check for continuity, so an easy workaround is to just chain all your PowerLink boxes together with the PowerCon cables. Don't plug it into an AC supply, and don't plug anything else into it. You should be able to measure continuity (very low ohms) between the chassis of any of the PowerLink boxes and any other box. If there is a swap happening, there will only be continuity between every second box in the string.
In the days before the "pin 1 problem" was addressed, this would be a recipe for copious amounts of hum in a PA system. I assume you haven't had any trouble with that, so at least the gear is working properly. :)
Or maybe it's something else totally different. :(
GTD
Interesting and good to know about Powercon's. Going to have to look over my cable testers and make sure they will test the Powercon stuff.