Print

Please login or register.
1 Hour 1 Day 1 Week 1 Month Forever
Login with username, password and session length

[Ray Aberle]

It is not clear where the GFCIs are located?  If neutrals are shared/parallel/connected to each other or to ground anywhere after the GFCIs you will have trouble with tripping.  Basically, the hot wire from the GFCI and the neutral from that GFCI must be connected to the same loads and ONLY to those loads.  If that is the case, then as Tom said you may have leakage in equipment, but I would think that should show up at other locations (unless there is a possibility of getting moisture in your equipment overnight here and never anywhere else?)

FWIW, newer GFCIs are "supposed" to reset only if they are working right-not knowing the age it would be hard to tell if this is the case.

I think we are talking about a standard Spider Box, with 6-20A circuits broken out from a 50A/220V connection, wherein there is GFCI protection on each circuit, all handled within the Spider Box itself.

-Ray

[Stephen Swaffer]

In that case, I would suspect "creative" wiring in the spider box, or bad GFCIs.

If it were me, I might be tempted to "borrow" their connector for my own distro, take a pic and be ready for next year?  But I am an electrician so my doing so wouldn't raise many questions. 

Thinking out loud-could a poor connection/intermittent neutral in the feeder cause GFCIs to trip? (Essentially putting loads in series across the 2 hots-not good either!) Might pay to check the voltage on each hot to neutral at spider box and at receptacle.

[Eric_Muller]

I think we are talking about a standard Spider Box, with 6-20A circuits broken out from a 50A/220V connection, wherein there is GFCI protection on each circuit, all handled within the Spider Box itself.

-Ray

Yes, GFCIs are in the spider box.

I did ask for clarification on the voltage when I received the original (confusing) information. However, I never got an answer, even after visiting the site office and being told I would be contacted.

My rack distro takes 2 inputs from standard wall receptacles and breaks out into multiple receptacles. it is a centralized, 2 x 20 amp power strip. Nothing fancy, all my speakers are powered so I use combo cables and this rack distro allows me to patch everything from the front.  I have been using it for 3 years now.

When I need one circuit (small bar gigs) I just jumper circuit 1 into input 2 and all receptacles are powered.

When I need 2 circuits, I source 2 circuits from the venue and use both inputs.

When I need more power, I source 2 circuits for the rack distro and use it for monitors, backline and mixrack. Then I source more circuits for main speaker power connection.

I provide mainly for smaller shows. 99% of the time I get my power from a standard wall receptacle and I only need 1 or 2 circuits.

-Eric

[Mike Sokol]

GFCIs can potentially go bad, it is also possible that you have something leaky in your rig that you aren't aware of.  What happens when you measure continuity (devices unplugged of course) from ground to neutral of male plug end of each of your loads - i.e. unplug the cord from the distro and probe hot to ground on the male plug?  the resistance is less than 40K ohms, that means you have 3ma of leakage current.  If the number is somewhat higher but you plug several power strips into the same circuit, the leakage is cumulative.

Actually, there's a better and really easy way to test for ground leakage currents. As I'm sure you know, a clamp-amp meter needs to be connected around a single wire to measure AC current. So if it's clamped around both the neutral and hot the currents will null-out since they're going in opposite directions. However, if the current is leaking somewhere else (to an amplifier on another circuit or whatever), there will no longer be a perfect null, and a clamp-meter around the entire power cord WILL read the leakage currents, even while there's  many amperes of normal Hot-to-Neutral current at the same time. Of course, once your external leakage currents get over 5mA you'll be a GFCI trip. This test shows you the external leakage currents to earth or another circuit. If you want to know the actual leakage current of a stand-alone piece of gear, you need to make a simple split out cable and clamp around either the ground wire by itself, or the hot and neutral wires, ignoring the ground wire. Either way will give you a direct readout of hot-to-chassis leakage.

This is a pretty good way to measure hot-to-chassis leakage currents in old tube guitar amps and such, which often have insulation failure in aged power transformers. Of course, the UL ratings for leakage currents with "grounded" gear is 3.5 mA max, and "ungrounded" gear is 0.75 mA, so don't expect zero leakage. Basically, anything hooked to a power line leaks a bit. If you want to have some real fun, plug your smartphone into a wall-wart charger and measure the voltage on the metal body of the phone in reference to earth ground. You'll probably read around 1/2 line potential (60 volts or so). 

[Tim McCulloch]

Eric, thanks for the picture.

There are a couple of explanations, the first is a common neutral bus bar (shouldn't be case here, Six2 knows better); another is neutral grounded inside the box (ditto); the final one is leakage in the Edison to PowerCon cables.  I've seen shop-built cables trip GFCIs due to less than ideal assembly practices.... 

You can test for the first 2 by using your ohm meter to check for open or short between the neutral slots of the red and black circuits.  The neutral should be the taller slot, typically in the 9 o'clock position.  You should find this to be an open.  A short indicates that somehow the neutrals from both inlets are tied together.  Test for ground bonding by checking for short/open between the neutral and ground pin for both Black and Red circuits.  These, too, should test as open circuits.

That takes us back to the cords you're powering the distro with.

[TJ (Tom) Cornish]

Actually, there's a better and really easy way to test for ground leakage currents. As I'm sure you know, a clamp-amp meter needs to be connected around a single wire to measure AC current. So if it's clamped around both the neutral and hot the currents will null-out since they're going in opposite directions. However, if the current is leaking somewhere else (to an amplifier on another circuit or whatever), there will no longer be a perfect null, and a clamp-meter around the entire power cord WILL read the leakage currents, even while there's  many amperes of normal Hot-to-Neutral current at the same time. Of course, once your external leakage currents get over 5mA you'll be a GFCI trip. This test shows you the external leakage currents to earth or another circuit. If you want to know the actual leakage current of a stand-alone piece of gear, you need to make a simple split out cable and clamp around either the ground wire by itself, or the hot and neutral wires, ignoring the ground wire. Either way will give you a direct readout of hot-to-chassis leakage.

This is a pretty good way to measure hot-to-chassis leakage currents in old tube guitar amps and such, which often have insulation failure in aged power transformers. Of course, the UL ratings for leakage currents with "grounded" gear is 3.5 mA max, and "ungrounded" gear is 0.75 mA, so don't expect zero leakage. Basically, anything hooked to a power line leaks a bit. If you want to have some real fun, plug your smartphone into a wall-wart charger and measure the voltage on the metal body of the phone in reference to earth ground. You'll probably read around 1/2 line potential (60 volts or so).

What kind of clamp meter do you have that can read down to 3mA?  Mine is pretty dubious for less than 1/4 amp or so.  When leakage is to the ground pin (and not through the environment), it is still in the cord, which is still in the jaws of the clamp, and should still cancel.  What am I missing?

[Mike Sokol]

What kind of clamp meter do you have that can read down to 3mA?  Mine is pretty dubious for less than 1/4 amp or so.  When leakage is to the ground pin (and not through the environment), it is still in the cord, which is still in the jaws of the clamp, and should still cancel.  What am I missing?

Here's a pic of the Fluke meter I use for bench testing of gear leakage which measures down to 1/10 of an mA. It's a bit expensive for field work, but I also a few less expensive clamp testers that go down to 1 mA resolution. I'll look in my field kit later today and let you know the brands/models.

Also, note that I was talking about external current flow (not through the ground wire in the extension cord) being measured with the clamp meter around the entire extension cord. I also noted that if you wanted to find internal current flow (back through the power cord's EGC) you'll need to split out the EGC wire for the measurement as pictured. Maybe that wasn't clear in my previous post, but it should be obvious once you think about it a bit.

And this same idea is what allows you to put a clamp meter around the outside of an XLR mic cable to measure ground loop current flow. Since the ground loop current is only in the shield and loops back through the external grounding system, you don't need to split out the shield from the twisted pair. Just clamp the meter around the mic cable for a direct measurement. If you need more resolution, looping the mic cable through the clamp jaws a few times acts as a resolution multiplier. So 5 loops is 1/5th of the read current, and 10 loops is actually 1/10th of the read current. For example, if you loop a wire 10 times through the amp jaws and your meter now reads 10 mA, there's actually 1 mA of current flow in the test wire.   

The reason for all this testing is to identify exactly what fault currents in the field are going where, which can give you a handle on hum current paths and how they act. I've built all sorts of current injecting demonstrations which is what allows me to experiment with hum testing on my test bench at will. I don't know all of it yet, but it's making me a much better field troubleshooter.

[TJ (Tom) Cornish]

Here's a pic of the Fluke meter I use for bench testing of gear leakage which measures down to 1/10 of an mA. It's a bit expensive for field work, but I also a few less expensive clamp testers that go down to 1 mA resolution. I'll look in my field kit later today and let you know the brands/models.

Also, note that I was talking about external current flow (not through the ground wire in the extension cord) being measured with the clamp meter around the entire extension cord. I also noted that if you wanted to find internal current flow (back through the power cord's EGC) you'll need to split out the EGC wire for the measurement as pictured. Maybe that wasn't clear in my previous post, but it should be obvious once you think about it a bit.

And this same idea is what allows you to put a clamp meter around the outside of an XLR mic cable to measure ground loop current flow. Since the ground loop current is only in the shield and loops back through the external grounding system, you don't need to split out the shield from the twisted pair. Just clamp the meter around the mic cable for a direct measurement. If you need more resolution, looping the mic cable through the clamp jaws a few times acts as a resolution multiplier. So 5 loops is 1/5th of the read current, and 10 loops is actually 1/10th of the read current. For example, if you loop a wire 10 times through the amp jaws and your meter now reads 10 mA, there's actually 1 mA of current flow in the test wire.   

The reason for all this testing is to identify exactly what fault currents in the field are going where, which can give you a handle on hum current paths and how they act. I've built all sorts of current injecting demonstrations which is what allows me to experiment with hum testing on my test bench at will. I don't know all of it yet, but it's making me a much better field troubleshooter.

While that is really interesting and certainly gives more data, I'm not sure all of this is easier than just measuring hot -> ground impedance to find leakage that will trip a GFCI.  It may not give you directional flow, but should by process of elimination indicate gear that is leaking - weak MOVs, transformer problems, etc.

[Mike Sokol]

Update: Here's a pic of the Fluke 322 clamp-meter I use which has 10 mA resolution. As noted above, you can loop the test cable through the clamp jaws a few times to increase the resolution.

[Mike Sokol]

While that is really interesting and certainly gives more data, I'm not sure all of this is easier than just measuring hot -> ground impedance to find leakage that will trip a GFCI.  It may not give you directional flow, but should by process of elimination indicate gear that is leaking - weak MOVs, transformer problems, etc.

I think both test methods have validity. I like to measure actual leakage currents in the field so I can duplicate them on the bench. That's because I need to know the actual amperage/voltage values as well as which way the current it going. In that way I can correlate any theoretical models with empirical data and know if I'm on the right track. Your method is quick and dirty (which can be good under pressure), and while my method takes more gear and setup time, it yields more data (which is sometimes more confusing).

[ProSoundWeb Community]