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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: Steve Garris on October 29, 2017, 07:19:48 PM
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Only my second post on this Power forum and I don't know much about power, so bear with me.
Yesterday I did a show at a brewery taproom. My system is a small, active SRX speaker over sub per side, and 4 Yamaha DSR monitors. The board is a Mackie DL. While setting up, I ran my power strips around the stage coming from a dedicated GFI outlet. While I was turning boxes on, the GFI tripped. Next I split my stage power to another GFI box and all was good. Later as the bands were showing up and plugging in, the first GFI tripped, so I moved it to a 3rd location, then it tripped. As this point I was running out of options so I split the power to all 3 GFI outlets. This got me through the night, but one of them tripped during the break (thank goodness).
I was told by management that no one else has had this problem, and I advised them that neither had I. The venue also has a 220 GFI outlet at the stage area, and I believe the other sound providers have used that, but I'm not sure.
Any ideas or suggestions? The outlets tested good with my cheap receptacle tester (I know, I need better). I'm thinking about getting a distro box for myself, but I need to do some reading.
I've bookmarked TJ's page on stage power BTW, need some time to go over it.
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Only my second post on this Power forum and I don't know much about power, so bear with me.
Yesterday I did a show at a brewery taproom. My system is a small, active SRX speaker over sub per side, and 4 Yamaha DSR monitors. The board is a Mackie DL. While setting up, I ran my power strips around the stage coming from a dedicated GFI outlet. While I was turning boxes on, the GFI tripped. Next I split my stage power to another GFI box and all was good. Later as the bands were showing up and plugging in, the first GFI tripped, so I moved it to a 3rd location, then it tripped. As this point I was running out of options so I split the power to all 3 GFI outlets. This got me through the night, but one of them tripped during the break (thank goodness).
I was told by management that no one else has had this problem, and I advised them that neither had I. The venue also has a 220 GFI outlet at the stage area, and I believe the other sound providers have used that, but I'm not sure.
Any ideas or suggestions? The outlets tested good with my cheap receptacle tester (I know, I need better). I'm thinking about getting a distro box for myself, but I need to do some reading.
I've bookmarked TJ's page on stage power BTW, need some time to go over it.
You mentioned power strips. Most have surge suppressors (that don’t do much) but do leak some current. Perhaps your power strip is leaking just under the trip current and adding the band gear (which also may leak some) is what is getting you?
I opened up some of mine and snipped out anything that was not an outlet.
Sent from my iPad using Tapatalk Pro
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Only my second post on this Power forum and I don't know much about power, so bear with me.
Yesterday I did a show at a brewery taproom. My system is a small, active SRX speaker over sub per side, and 4 Yamaha DSR monitors. The board is a Mackie DL. While setting up, I ran my power strips around the stage coming from a dedicated GFI outlet. While I was turning boxes on, the GFI tripped. Next I split my stage power to another GFI box and all was good. Later as the bands were showing up and plugging in, the first GFI tripped, so I moved it to a 3rd location, then it tripped. As this point I was running out of options so I split the power to all 3 GFI outlets. This got me through the night, but one of them tripped during the break (thank goodness).
I was told by management that no one else has had this problem, and I advised them that neither had I. The venue also has a 220 GFI outlet at the stage area, and I believe the other sound providers have used that, but I'm not sure.
Any ideas or suggestions? The outlets tested good with my cheap receptacle tester (I know, I need better). I'm thinking about getting a distro box for myself, but I need to do some reading.
I've bookmarked TJ's page on stage power BTW, need some time to go over it.
Carefully read Rob's post.
He's spot on about both leaky power strips (the MOV components work by shorting the hot to ground) and the *cumulative* effect of leaky devices - guitar/bass amps, home made extension cords (many but not all, in my experience), etc. If the power strip leaks 2 or 3 mA, the GFCI is remains on; if a Fender Twin leaks 4 mA the GFCI stand on; if you plug the Twin into the power strip, the GFCI will trip.
Were all the outlets in the performance area on GFCI?
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If the power strip leaks 2 or 3 mA, the GFCI is remains on; if a Fender Twin leaks 4 mA the GFCI stand on; if you plug the Twin into the power strip, the GFCI will trip.
+1 A power strip can leak up to 3mA to ground and still be in UL compliance. So even two power strips plugged into the same GFCI receptacle can get to the trip threshold. And old tube amps with ageing power transformers or stinger caps can leak just as much. Also as noted, these leakage currents are additive, so tripping a GFCI with several backine amps and a few surge strips on it is almost a guarantee.
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A leak or just an additional neutral-ground connection somewhere.
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A leak or just an additional neutral-ground connection somewhere.
Another thing that will trip a GFCI instantly is swapped neutral/ground wiring. This happens more often than you might think even in new construction.
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You mentioned power strips. Most have surge suppressors (that don’t do much) but do leak some current. Perhaps your power strip is leaking just under the trip current and adding the band gear (which also may leak some) is what is getting you?
I opened up some of mine and snipped out anything that was not an outlet.
Sent from my iPad using Tapatalk Pro
+1
I've told this story before, not only do cheap power strip have leaky protection (?) devices, but if you plug into a mains power drop with an open safety ground (like most of my house), the power strip leakage can energize the chassis grounds of all the equipment plugged into that same power strip.
Generally harmless low single digit mA leakage, but enough to feel if sensitive, and measure if you look for it.
JR
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Carefully read Rob's post.
He's spot on about both leaky power strips (the MOV components work by shorting the hot to ground) and the *cumulative* effect of leaky devices - guitar/bass amps, home made extension cords (many but not all, in my experience), etc. If the power strip leaks 2 or 3 mA, the GFCI is remains on; if a Fender Twin leaks 4 mA the GFCI stand on; if you plug the Twin into the power strip, the GFCI will trip.
Were all the outlets in the performance area on GFCI?
Yes, all 3 were GFI - a newer looking installation.
Can I measure this with a meter?
I've use the same 5 power strips at every gig for the past 4 years without problems. I do a summer concert series and run them from (1) 20 amp GFI outlet - supplying power for the PA, some lights and backline, all from one receptacle. Two of my strips are the metal Furman boxes, and 3 are some nice, black strips that have a long heavy gauge power cable. I would suspect these could be a possibility.
At this venue, the fist GFI tripped before the band arrived. The backline did consist of some very old looking tube amps though.
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Yes, all 3 were GFI - a newer looking installation.
Can I measure this with a meter?
I've use the same 5 power strips at every gig for the past 4 years without problems. I do a summer concert series and run them from (1) 20 amp GFI outlet - supplying power for the PA, some lights and backline, all from one receptacle. Two of my strips are the metal Furman boxes, and 3 are some nice, black strips that have a long heavy gauge power cable. I would suspect these could be a possibility.
At this venue, the fist GFI tripped before the band arrived. The backline did consist of some very old looking tube amps though.
I would be tempted to just clip out the protection devices inside all the cheap power strips. I removed them from mine that were causing measurable leakage.
In principle you could open up the ground circuit and put a VOM mA in series with the ground lead of an empty power strip. These leakage currents will be additive, so several together could easily trip a GFCI. Of course be careful making measurements around mains power.
JR
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When you say things were being plugged in, does this include bass amps and keyboards being plugged into the PA?
This may be an opportunity for a poor man's distro. I do a couple outdoor venues each year where I have to run from GFCI Edisons. Run things back to my PMD and never had any trip issues. I even have separate GFCIs on my backline stringer so there are two in series with various tube amps plugged into them. Still no issues.
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When you say things were being plugged in, does this include bass amps and keyboards being plugged into the PA?
This may be an opportunity for a poor man's distro. I do a couple outdoor venues each year where I have to run from GFCI Edisons. Run things back to my PMD and never had any trip issues. I even have separate GFCIs on my backline stringer so there are two in series with various tube amps plugged into them. Still no issues.
The first time I tripped it the bands had not arrived yet. I tripped the others while bands were setting up, plugging in to my power strips.
I'm also thinking about the "poor mans distro" idea. Just not sure how to do it but I'm assuming I can find the info online.
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You mentioned power strips. Most have surge suppressors (that don’t do much) but do leak some current. Perhaps your power strip is leaking just under the trip current and adding the band gear (which also may leak some) is what is getting you?
I opened up some of mine and snipped out anything that was not an outlet.
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I'm going to plug them all in at my house and see if I can recreate the problem. Thanks!
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Power conditioners can also dump the noise currents into the Safety Ground. Some audio components have leakage currents to their chassis, which is connected to the Safety Ground.
All these noise and leakage currents can add up and trip a GFCI.
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Keep in mind that all GFCI's are not created equal. In the last 3-4 years there have been significant changes in the requirements they need to meet. Then, too, standards (as is the case with any code including the NEC) are a minimum-the don't guarantee a quality product. I guess I could never bring myself to take the cheapest route when it came to a safety device-especially in a mass market/big box scenario.
The main take away form my point is this-you may not be able to duplicate it at home becasue you may have a different brand/vintage GFCI-and the problem could be (and sounds like it is) right on the ragged edge of working. Ohms law stil applies- and one location running at 114 volts and the other at 124 volts could cause a very small difference. You really don't have control over that or the GFCI's installed in a venue. The best policy would be to eliminate as many potential leakage paths as possible.
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The best policy would be to eliminate as many potential leakage paths as possible.
You can measure the ground leakage on any piece of gear by measuring how much current is flowing through the ground wire of the power plug. However, affordable clamp-on meters typically only measure down to 10 mA which is WAY above the 6mA threshold. One solution is to strip open about 2 feet of a grounded extension cord and wrap the green ground wire 10 times around the clamp jaw. That will create a 10X current multiplier, effectively allowing your $50 clamp meter to read down to 1mA resolution like a $500 meter. I would say that anything leaking more than 1 or 2 mA to the EGC ground wire should be more closely examined.
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What are some of the affordable clamp-on meter models that measure down to 10 mA?
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What are some of the affordable clamp-on meter models that measure down to 10 mA?
You need to measure <10mA. The current multiplier Mike discusses is the affordable solution if you need a clamp meter solution. If you can put a conventional meter in line with the EGC wire most any quality multimeter (think Fluke 177) will work.
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You need to measure <10mA. The current multiplier Mike discusses is the affordable solution if you need a clamp meter solution. If you can put a conventional meter in line with the EGC wire most any quality multimeter (think Fluke 177) will work.
That is correct. All you need to do is make a short extension cord with the green-ground wire interrupted and terminated into banana plugs or whatever is needed to plug into your meter. Or you can just use the meter's alligator clips if you like. Here's the resolution that a Fluke 117 will measure on the 6-amp and 10-amp current inputs. You'll see that it has 1mA of resolution on the normal 6-amp input which is fuse protected. That means you shouldn't blow up your meter if the piece of gear you're checking develops a line-to-chassis short during the test.
You should probably put a sticker on each piece of gear with the mA current leakage you measure. Most modern gear should be way below 1mA, but the old/vintage stuff could easily be leaking a few mA and still be otherwise operational. Interestingly, Crown states in the engineering specs that their modern iTech amplifiers can leak up to 3mA to ground and still pass QC-Inspection. Remember that ground leakage currents are additive, so it would only take a few leaky stage amplifiers on a single backline GFCI to hit the 6mA threshold and trip.
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Some of the modern digital amps can have RF filters on mains power cord to keep emissions below acceptable limits. These filters can register as low level leakage between mains and safety ground.
JR
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That is correct. All you need to do is make a short extension cord with the green-ground wire interrupted and terminated into banana plugs or whatever is needed to plug into your meter. Or you can just use the meter's alligator clips if you like. Here's the resolution that a Fluke 117 will measure on the 6-amp and 10-amp current inputs. You'll see that it has 1mA of resolution on the normal 6-amp input which is fuse protected. That means you shouldn't blow up your meter if the piece of gear you're checking develops a line-to-chassis short during the test.
I'll point out that this may not be an accurate test. If there is leakage, and the equipment is interconnected with other equipment or if the chassis is grounded by other means (such as being in contact with structural steel), then some of the leakage current may find a path to ground other than through the equipment grounding conductor.
For an accurate test, disconnect any audio leads from the equipment and insulate the device from incidental grounding.
(Leakage is a common source of "ground loop hum.")
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I'll point out that this may not be an accurate test. If there is leakage, and the equipment is interconnected with other equipment or if the chassis is grounded by other means (such as being in contact with structural steel), then some of the leakage current may find a path to ground other than through the equipment grounding conductor.
For an accurate test, disconnect any audio leads from the equipment and insulate the device from incidental grounding.
(Leakage is a common source of "ground loop hum.")
I believe this is what Mike implied.
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I believe this is what Mike implied.
Yes, do this on the bench disconnected from all other gear. That's the only way to get an accurate reading. Another aspect of this to consider is that some brand GFCI's may be more sensitive to high-frequency ground leakage from switching power supplies. A standard meter won't be able to measure those high-frequency currents, but any good o'scope measuring across a series resistor should be able to discover that sort of leakage.