ProSoundWeb Community

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: Mike Karseboom on July 01, 2014, 01:34:34 am

Title: Can Repeated Distro Trips Harm Audio Gear?
Post by: Mike Karseboom on July 01, 2014, 01:34:34 am
I was a subcontractor on a gig this weekend using  an undersized generator (Whisperwatt 25) and we had repeated losses of power for a variety of reasons.


First due to lack of timely delivery of the 6/4 feeder and spider box, we were running FOH, monitors, and backline off the two 20A convenience GFCI outlets.  Power was delivered through three 100 foot 12/3 SOOW cables.


The first problem seemed to be with the small (1.5 VA) APC UPS unit that was inline before the DR260 system processors and the FOH digital board.  Neither of those devices pulled much current so the UPS was in no way overloaded.  Yet that UPS would squeal with an alarm frequently which was sometimes followed by a shutdown of the UPS.  I am not sure what the alarm meant as it was a continuous squeal and historically the only alarm I have hear from it is the beeping sound it makes when mains power is not present and the battery is engaged.  After a couple of shutdowns that alarm noise became apparent and the battery backup was removed from the circuit.


Then it seemed there was just too much current draw for the GFCI outlets.  The breakers did not trip but the GFCI's did.  After three or four of those episodes the GFCI's seemed to be "fried" as they would no longer reset. 


Fortunately about this time the feeder cable and spider box arrived but unfortunately it was a pretty beat up spider box and only 3 of the GFCI outlets actually worked.  When they tried to runs some lights as well (old parr cans)  there were tripping issues that seemed to involve GFCI trips rather than breaker trips.


Anyway it goes on for a bit but the upshot is that the amps, processors, mixer, and powered monitors were subjected to numerous power resets.  I am wondering if that can be damaging to this equipment?
Title: Re: Can Repeated Distro Trips Harm Audio Gear?
Post by: Steve M Smith on July 01, 2014, 01:52:00 am
As far as the individual pieces of equipment are concerned, they are just being turned off and on as normal.  It makes no difference if it is via the equipment's on off switch or by the whole power going off and back on again.

Personally, I would just turn off the amps before putting the power back on.


Steve.
Title: Re: Can Repeated Distro Trips Harm Audio Gear?
Post by: jasonfinnigan on July 01, 2014, 01:58:23 am
I would get another generator rental company I think.

Anyway if the GFCIs kept triping it means somewhere there is a voltage leak on the neutral conductor. A GFCI outlet wants to see the same voltage it's that its sending out on the hot leg, coming back on the neutral leg. if its not it will trip as there is a loss which could be from someone getting shocked.
Title: Re: Can Repeated Distro Trips Harm Audio Gear?
Post by: Mike Sokol on July 01, 2014, 06:29:31 am
I would get another generator rental company I think.

Anyway if the GFCIs kept triping it means somewhere there is a voltage leak on the neutral conductor. A GFCI outlet wants to see the same voltage it's that its sending out on the hot leg, coming back on the neutral leg. if its not it will trip as there is a loss which could be from someone getting shocked.

Small correction, actually a "current leak" causes GFCIs to trip. Most likely there was a paralleled neutral and grounding conductor (secondary G-N bond). That splits the neutral return current, which now no longer balances with the outgoing line current. GFCIs don't work by sensing ground... they work by sensing a difference between line and neutral currents. Internally they have a current transformer wrapped around the line and neutral with a trigger circuit to trip the spring loaded contact. No ground wire on the GFCI is needed to make them trip.

Below is a graphic I made of the fault current flow that trips a GFCI. Note that the GFCI sensing circuit isn't connected to the EGC/ground at all. It's only looking for an imbalance between line and neutral, sort of like a balanced high voltage mic preamp input.
Title: Re: Can Repeated Distro Trips Harm Audio Gear?
Post by: Ray Aberle on July 01, 2014, 10:35:49 am
I would get another generator rental company I think.

This. Right. Here.

If the rental company did the delivery for you, then they should have brought the feeder/box at the same time, set it all up, fired it up, and verified full operation of everything. (That's the nice thing about a governmental inspection; inspector is going to check things like GFCI - and, well, basic circuit operation.)

If you picked it up and did the drop yourself, the person doing the pickup should have grabbed the feeder/box. And when he did not, the rental company should have suggested that it go with it.

If you rented the gennie from one place and the cable/box from another, a reputable gennie rental place would also want to have you bring your cable and box to verify that it works acceptably with the generator. Common sense, I mean, that would have detected at LEAST the 3 non-functional circuits from the get-go.

Hopefully the festival promoter has learned their lesson about getting the right sized generator, and here's an opportunity to bring it to their attention, thus establishing yourself as -- well, maybe a bit more qualified to help them produce their event. You can easily just approach them with, "I can help with any questions you might have next year about power, generators, and grounding, so here's my card, and please feel free to call at any time." Who knows, they may already be considering a new event provider, and will notice you also run sound.

-Ray
Title: Re: Can Repeated Distro Trips Harm Audio Gear?
Post by: Mike Karseboom on July 01, 2014, 11:54:19 am
This. Right. Here.

If the rental company did the delivery for you, then they should have brought the feeder/box at the same time, set it all up, fired it up, and verified full operation of everything. (That's the nice thing about a governmental inspection; inspector is going to check things like GFCI - and, well, basic circuit operation.)

-Ray


This Whisperwatt 25 was purchased by the consortium of small time promoters that lease the outdoor venue and put on 3-4 shows a year.  It is out in the sticks and in a way it is pretty cool that they have purchased this high quality unit.  The generator is in good condition. 


The problem was the stage and lighting provider who also said he would bring the distro and feed cable for audio.  While he did construct a very good 30'wide  x 20' deep x 5' high  covered stage, everything was done late so instead of setting up sound gear at 5:00PM we started setting up at 1:00AM. By 3:30AM when we were ready to plug into the spiderbox we realized the feeder cable was going directly into his multi channel light dimmer box. 


It is a long and sad story spanning over two days of festival  where various partial and inadequate solutions were implemented.  Lots of temporary halts of performances and one act that just did not really get their set.  By the evening of the second night we finally had a stable situation with two separate feeder cables and a spider box just for audio.  Even then that spider box was iffy as only 3 of the GFCI outlets worked.  Also due to the small size of the generator and the fact that stage lighting was from parr cans, the  lights had to be run with just 1/4 of them in service and with no gels.  I was a sub to the main audio guy so it was really not my place to demand anything.  But the lame service provided by the stage contractor sure caused me to loose a lot of sleep and experience a lot of stress during the show. 


In the end it was mostly the promoters, performers and the folks involved with production that were feeling the pain.  The crowd was pretty laid back and seemed to enjoy the weekend without a second thought to the power drop outs.


Why is it always about the POWER??  It is the first thing I ask about when someone offers me a gig and I give detailed minimum requirements  for good results.  Regardless of the assurances  that everything is taken care of, it always ends up being about the POWER!
Title: Re: Can Repeated Distro Trips Harm Audio Gear?
Post by: Ray Aberle on July 01, 2014, 12:12:07 pm
This Whisperwatt 25 was purchased by the consortium of small time promoters that lease the outdoor venue and put on 3-4 shows a year.  It is out in the sticks and in a way it is pretty cool that they have purchased this high quality unit.  The generator is in good condition. 

The problem was the stage and lighting provider who also said he would bring the distro and feed cable for audio.  While he did construct a very good 30'wide  x 20' deep x 5' high  covered stage, everything was done late so instead of setting up sound gear at 5:00PM we started setting up at 1:00AM. By 3:30AM when we were ready to plug into the spiderbox we realized the feeder cable was going directly into his multi channel light dimmer box. 

It is a long and sad story spanning over two days of festival  where various partial and inadequate solutions were implemented.  Lots of temporary halts of performances and one act that just did not really get their set.  By the evening of the second night we finally had a stable situation with two separate feeder cables and a spider box just for audio.  Even then that spider box was iffy as only 3 of the GFCI outlets worked.  Also due to the small size of the generator and the fact that stage lighting was from parr cans, the  lights had to be run with just 1/4 of them in service and with no gels.  I was a sub to the main audio guy so it was really not my place to demand anything.  But the lame service provided by the stage contractor sure caused me to loose a lot of sleep and experience a lot of stress during the show. 

In the end it was mostly the promoters, performers and the folks involved with production that were feeling the pain.  The crowd was pretty laid back and seemed to enjoy the weekend without a second thought to the power drop outs.

Why is it always about the POWER??  It is the first thing I ask about when someone offers me a gig and I give detailed minimum requirements  for good results.  Regardless of the assurances  that everything is taken care of, it always ends up being about the POWER!

I hope that you were paid well for your hellish hours! I mean I worked my guys like crazy this past weekend, but when they're getting $800-$900 for a couple three days of work, they remain upbeat. :)

I think the lesson here is for the audio guy who hired you to purchase his own 6/4 (or even 4/4; opinions vary, but the NEC (I seem to recall) specs that 6/4 is good for only up to 45a/conductor?) and a spider box. That would be an investment of-- well, a full 100' roll at Homo Depot is like $450. Connectors can be readily found online (http://www.bestmaterials.com/SearchResult.aspx?CategoryID=879) for under $60 total. A used spider box for $500 or less-- so maybe a grand and he can be assured that feeder and distro will be solid in the future?

Sounds like a cheap insurance policy to me! :)

-Ray
Title: Re: Can Repeated Distro Trips Harm Audio Gear?
Post by: jasonfinnigan on July 01, 2014, 01:59:45 pm

This Whisperwatt 25 was purchased by the consortium of small time promoters that lease the outdoor venue and put on 3-4 shows a year.  It is out in the sticks and in a way it is pretty cool that they have purchased this high quality unit.  The generator is in good condition. 

IMO Owning a generator is not the best way. Renting usually comes out ahead even if you are doing an event every week needing it hauling, and maintenance are very expensive for generators, on the other hand renting is cheap around $100-$150 for a 30Kw + Generator. 3-4 times a year really probally means the generator isn't being run enough, they need to be run once a month in my opinion to keep the coils good. they also need a lot of up keep & maintenance.
Title: Re: Can Repeated Distro Trips Harm Audio Gear?
Post by: g'bye, Dick Rees on July 01, 2014, 02:11:34 pm
3-4 times a year really probally means the generator isn't being run enough, they need to be run once a month in my opinion to keep the coils good. they also need a lot of up keep & maintenance.

I call BS.
Title: Re: Can Repeated Distro Trips Harm Audio Gear?
Post by: jasonfinnigan on July 01, 2014, 02:20:29 pm
I call BS.
You might call it BS but generators can lose their magnetivity and will not properly generate power.
Title: Re: Can Repeated Distro Trips Harm Audio Gear?
Post by: frank kayser on July 01, 2014, 02:55:57 pm
... 3-4 times a year really probally means the generator isn't being run enough, they need to be run once a month in my opinion to keep the coils good. they also need a lot of up keep & maintenance.


I don't know about keeping the "coils" good - I'm not sure permanent magnets are part of a current "generator" design. 


But most engines don't really like to sit - condensation in the oil and fuel, battery maintenance, seals dry out, belts, hoses. 


FWIW...
Title: Re: Can Repeated Distro Trips Harm Audio Gear?
Post by: Ray Aberle on July 01, 2014, 02:57:55 pm
You might call it BS but generators can lose their magnetivity and will properly generate power.

And this statement is confuddling, soooo...

Either way, everyone will have a different POV as to owning versus renting. As Tim Mc would say, Excess Capacity Is Infinitely Expensive.

But, the promoters have already purchased it, so discussing whether that's a good idea or not is futile. The decision was already made. So let's help Mike be a better resource for the people who hired him, and not question the wisdom of buying a generator! As long as it works reliably... And Mike always meters his power before connecting his gear to it. :)

-Ray
Title: Re: Can Repeated Distro Trips Harm Audio Gear?
Post by: Mike Sokol on July 01, 2014, 03:55:51 pm
You might call it BS but generators can lose their magnetivity and will not properly generate power.

I think I know the answer to this, but can someone please reference re-flashing a generator? I don't think it's a big deal to do at all, and is generatlly only needed if the generator was disassembled or sat inoperative for a decade. But maybe I'm wrong.

However, gas engines need to have their fuel system drained for extended storage, and having a shutoff valve on the carb is an easy way to burn off the excess fuel at the end of every gig. That's what I do with my lawn-mower and house genny, and it works great. I throw in some Sta-Bil fuel additive if it won't be run for more than a month, burn-off the fuel out of the carb if I won't be running it the next day, and call it done. Or am I making this too simple? 
Title: Re: Can Repeated Distro Trips Harm Audio Gear?
Post by: frank kayser on July 02, 2014, 07:20:57 pm

However, gas engines need to have their fuel system drained for extended storage, and having a shutoff valve on the carb is an easy way to burn off the excess fuel at the end of every gig. That's what I do with my lawn-mower and house genny, and it works great. I throw in some Sta-Bil fuel additive if it won't be run for more than a month, burn-off the fuel out of the carb if I won't be running it the next day, and call it done. Or am I making this too simple?
I can reference only what multiple sources (oil distributor, motorcycle shop, riders) that when putting a motorcycle away for the winter, fuel should be drained, and run out (tank should be able to evaporate any condensation that will form) oil should be changed to get rid of any acids and other combustion byproducts from the oil, and battery put on a battery tender.  Taking it out of storage, oil should be changed AGAIN, as condensation during the winter months will have formed in the crankcase and contaminated the oil.  Fresh fuel, check running gear and fire it up.


I don't do that.  I don't buy into the oil change every 3K miles - owners manual doesn't require that.  Oil gets changed with tire changes (between 8K and 12K miles) fuel gets Stabil if it will sit more than a week (methanol in the fuel evaporates/breaks down very quickly), and try to park it with nearly a full fuel tank (my tank is plastic so condensation is less of an issue).  Same with the lawn mower (though the lube system on the engine is more primitive, and the tires that never wear out)


Seals will dry out when an engine is not used, and rust can form (in extreme cases seizing the engine) especially if exhaust or intake are subject to water penetration.  Hoses, belts, and other rubber parts will deteriorate at about the same rate whether the engine has been
run or not. 


Diesels are particularly sensitive to water in the fuel - diesel injectors / mechanical injector pumps operate at extreme pressures, and need ultra-tight tolerances to build that type of pressure.  What appears to be minor pitting in the surfaces result in non-operational or poorly operating injectors.  Watch for condensation, and service the fuel/water separator religiously.


Don't forget belts.  Our very big quasi-government business had an entire COOP (Continuity of Operations) drill ruined as the generator for the main management/IT site threw a belt in the first 10 minutes of the drill.  No com.  No computers. 


frank 

Title: Re: Can Repeated Distro Trips Harm Audio Gear?
Post by: Steve M Smith on July 03, 2014, 02:44:00 am
Taking it out of storage, oil should be changed AGAIN, as condensation during the winter months will have formed in the crankcase and contaminated the oil.

If it's sitting in a garage and its temperature is matching the ambient temperature in the garage, there will be no condensation.


Steve.
Title: Re: Can Repeated Distro Trips Harm Audio Gear?
Post by: Steve Alves on July 03, 2014, 09:58:14 am
The first problem seemed to be with the small (1.5 VA) APC UPS unit that was inline before the DR260 system processors and the FOH digital board.  Neither of those devices pulled much current so the UPS was in no way overloaded.  Yet that UPS would squeal with an alarm frequently which was sometimes followed by a shutdown of the UPS.  I am not sure what the alarm meant as it was a continuous squeal and historically the only alarm I have hear from it is the beeping sound it makes when mains power is not present and the battery is engaged.  After a couple of shutdowns that alarm noise became apparent and the battery backup was removed from the circuit.

Caused by the power going in not being clean and the UPS having to repeatedly switch to battery. Could have been caused by the same problem that was tripping the GFCI's or just voltage sag.
Title: Re: Can Repeated Distro Trips Harm Audio Gear?
Post by: Tim McCulloch on July 03, 2014, 10:42:27 am
I was a subcontractor on a gig this weekend using  an undersized generator (Whisperwatt 25) and we had repeated losses of power for a variety of reasons.


First due to lack of timely delivery of the 6/4 feeder and spider box, we were running FOH, monitors, and backline off the two 20A convenience GFCI outlets.  Power was delivered through three 100 foot 12/3 SOOW cables.


The first problem seemed to be with the small (1.5 VA) APC UPS unit that was inline before the DR260 system processors and the FOH digital board.  Neither of those devices pulled much current so the UPS was in no way overloaded.  Yet that UPS would squeal with an alarm frequently which was sometimes followed by a shutdown of the UPS.  I am not sure what the alarm meant as it was a continuous squeal and historically the only alarm I have hear from it is the beeping sound it makes when mains power is not present and the battery is engaged.  After a couple of shutdowns that alarm noise became apparent and the battery backup was removed from the circuit.


Then it seemed there was just too much current draw for the GFCI outlets.  The breakers did not trip but the GFCI's did.  After three or four of those episodes the GFCI's seemed to be "fried" as they would no longer reset. 

Mike, if the GFCI were tripping there was an actual or perceived current leakage...  A GFCI will not trip due to over-current.  WILL.  NOT.  TRIP.  You had a bad device (maybe the MOVs in the surge-only side of the UPS) or cord somewhere.  On another site I have a blog post about a gig where the generator provider had to work on the sound genny and we had to fly the PA using power from the lighting genny.  The lighting guys were using the courtesy outlets to set DMX addresses and it didn't occur to me to meter the voltage.  Our 1 ton hoists are 120v single phase, so I took power from the same outlet the lighting guys had used.  Stage left went up without a problem, but stage right kept tripping the GFCI.  My boss was there and metered power, was convinced that the 150v he found was the problem (the lighting guys never metered, we found out).  I set the voltage back to 120v but the GFCI kept tripping.  Eventually the hoist stopped working, we got the fork lift to take the PA down and replaced the hoist.  The replacement worked flawlessly.  Upon inspection we determined that the failed hoist had a 1 strand hot wire short to the motor housing (the strain relief wasn't preventing twisting).  The GFCI was, in fact, doing its job correctly.  It would have been possible to energize the entire Apex mobile stage (like a Stageline) via the hoist chain.

NEVER simply assume that a GFCI is defective (although it might be), and never assume they trip due to load - they don't.

Quote
Fortunately about this time the feeder cable and spider box arrived but unfortunately it was a pretty beat up spider box and only 3 of the GFCI outlets actually worked.  When they tried to runs some lights as well (old parr cans)  there were tripping issues that seemed to involve GFCI trips rather than breaker trips.

Again, I'd assert that there was actual current leakage.  Old PAR cans?  Yeah, we find all kinds of dodgy stuff that comes from not keeping up on maintenance.

Quote
Anyway it goes on for a bit but the upshot is that the amps, processors, mixer, and powered monitors were subjected to numerous power resets.  I am wondering if that can be damaging to this equipment?

No.
Title: Re: Can Repeated Distro Trips Harm Audio Gear?
Post by: Mike Sokol on July 03, 2014, 12:09:38 pm
Mike, if the GFCI were tripping there was an actual ground fault.  A GFCI will not trip due to over-current.  WILL.  NOT.  TRIP. 

Tim, the rest of your explanation is spot-on, but your above statement is a bit misleading. I've done this experiment a bunch of times on my lab bench to get my head wrapped around GFCI tripping mechanisms. If you double-bond the neutral and ground wires together at both ends of the branch circuit, keeping the GFCI within that loop, then the neutral return current will be split between the ground AND neutral wires. Since a GFCI is looking for the same amount of current on the neutral and line wires, it will then trip with most any small load. So it's not only a hot-to-ground fault that will cause a GFCI to trip, but also a neutral-to-ground fault.  But yes, you are correct that a GFCI receptacle is NOT an over-current device, though a GFCI panel mounted circuit breaker certainly is. 

One thing that I've found that if the GFCI won't reset at all with no appliance/tool plugged into it, then the GFCI is likely at fault. If it holds with no appliance/tool plugged in but trips when the appliance/tool is plugged in, then it's likely there a hot-to-chassis/ground fault. However, if it holds with no appliance/tool plugged in, holds with the tool  plugged in but not turned on, but then trips when the appliance/tool is turned on and presents any kind of load to the circuit, then it's possible there could be a neutral-to-ground fault somewhere. Of course, your mileage will vary, but this is at least a starting point for GFCI troubleshooting which can be a real PITA at times.

Interesting stuff, isn't it?  ;D
Title: Re: Can Repeated Distro Trips Harm Audio Gear?
Post by: Tim McCulloch on July 03, 2014, 12:30:08 pm
Tim, the rest of your explanation is spot-on, but your above statement is a bit misleading. I've done this experiment a bunch of times on my lab bench to get my head wrapped around GFCI tripping mechanisms. If you double-bond the neutral and ground wires together at both ends of the branch circuit, keeping the GFCI within that loop, then the neutral return current will be split between the ground AND neutral wires. Since a GFCI is looking for the same amount of current on the neutral and line wires, it will then trip with most any small load. So it's not only a hot-to-ground fault that will cause a GFCI to trip, but also a neutral-to-ground fault.  But yes, you are correct that a GFCI receptacle is NOT an over-current device, though a GFCI panel mounted circuit breaker certainly is. 

One thing that I've found that if the GFCI won't reset at all with no appliance/tool plugged into it, then the GFCI is likely at fault. If it holds with no appliance/tool plugged in but trips when the appliance/tool is plugged in, then it's likely there a hot-to-chassis/ground fault. However, if it holds with no appliance/tool plugged in, holds with the tool  plugged in but not turned on, but then trips when the appliance/tool is turned on and presents any kind of load to the circuit, then it's possible there could be a neutral-to-ground fault somewhere. Of course, your mileage will vary, but this is at least a starting point for GFCI troubleshooting which can be a real PITA at times.

Interesting stuff, isn't it?  ;D

Fixed it to read "...actual or perceived current leakage."
Title: Re: Can Repeated Distro Trips Harm Audio Gear?
Post by: Mike Sokol on July 03, 2014, 12:42:45 pm
Fixed it to read "...actual or perceived current leakage."

Perfect.... I hate to pick nits sometimes, but this stuff is tricky.

Mike
Title: Re: Can Repeated Distro Trips Harm Audio Gear?
Post by: Mike Karseboom on July 03, 2014, 05:09:34 pm
Thank you Tim - I did have some residual questions about the events as they relate to GFCI outlets.


What I got from your comment is that a GFCI will NOT trip due to over current.  OK, what about an over voltage - like 128V?  I think the generator voltage adjuster was cranked up to max and I was measuring 125V at the end of 100' of 12/3 with not much load.






One thing that I've found that if the GFCI won't reset at all with no appliance/tool plugged into it, then the GFCI is likely at fault. If it holds with no appliance/tool plugged in but trips when the appliance/tool is plugged in, then it's likely there a hot-to-chassis/ground fault. However, if it holds with no appliance/tool plugged in, holds with the tool  plugged in but not turned on, but then trips when the appliance/tool is turned on and presents any kind of load to the circuit, then it's possible there could be a neutral-to-ground fault somewhere. Of course, your mileage will vary, but this is at least a starting point for GFCI troubleshooting which can be a real PITA at times.



Some more questions.


1)  If I plug my 2 amp racks  and mixer into a known good GFCI outlet at the shop using the  same extension cords as I used at the gig, and the GFCI does not trip, then does than mean it is likely that there is not a ground fault in those amp racks, mixer, and cords?


2) This is what happened with the generator convenience outlets:  If a GFCI outlet works OK for a while and then gradually gets more load put on it and then it begins tripping, what does that mean.  This was a situation where load was added, such as more draw from the amps as the bigger bands came on and had more channels in play and we turned the volume up.


3) If that same outlet, after tripping several times,  then refuses to reset at all, what does that mean?  I know the next question is whether anything was plugged in and I was not the one that could not get them to reset so I don't know.  Maybe this question cannot be answered without more info.


4)  At one point things were somewhat stable with audio only running off 3 of GFCI outlets on the beat up spider box.  When pressing the reset button to reset one of the other GFCI outlets that would not previously reset, at least one of the other "good" outlets tripped and took out the sound again.  It could have been coincidence but it popped precisely when I pressed the reset on the other GFCI outlet.   That was a red faced situation for me and I got really gun shy of touching anything  that was not broke at that point.   How does messing with one of the GFCI outlets somehow trip the others on a spider box?


 


2) 
Title: Re: Can Repeated Distro Trips Harm Audio Gear?
Post by: jasonfinnigan on July 03, 2014, 06:59:32 pm

2) This is what happened with the generator convenience outlets:  If a GFCI outlet works OK for a while and then gradually gets more load put on it and then it begins tripping, what does that mean.  This was a situation where load was added, such as more draw from the amps as the bigger bands came on and had more channels in play and we turned the volume up.

Sounds like when it started drawing more current the netrual conductor for some reason be it a problem in the amp or the cabling some where is having trouble carrying the same current back and is having loss. You can get GFCIs with different tolerances I believe.
Title: Re: Can Repeated Distro Trips Harm Audio Gear?
Post by: Tim McCulloch on July 04, 2014, 03:23:37 am
Thank you Tim - I did have some residual questions about the events as they relate to GFCI outlets.


What I got from your comment is that a GFCI will NOT trip due to over current.  OK, what about an over voltage - like 128V?  I think the generator voltage adjuster was cranked up to max and I was measuring 125V at the end of 100' of 12/3 with not much load.

If you read my little story included in the post, you'll see that the genset was originally at 150v.  The lampies were using it to set DMX addresses; what I failed to consider was the universal PSUs in the LED fixtures.  I should have metered the power even though they were successfully using it, but our stage left chain hoist motor ran fine and the GFCI did not trip.

We encounter a lot of GFCIs but seldom use them as very little we own/use will directly plug into an Edison outlet (our amps racks for example).  When we do small powered speaker gigs we end up on a spider box (shore power or genset), and so far even relatively new boxes seem to have at least 1 bad GFCI.  Most of what we've found to trip GFCIs are shop-built extension cords and cords with compromised outer jackets.  I can't remember when we've had molded cordsets with intact jackets trip a GFCI (modern equipment attached to those cords).

While it's clear you had some bad GFCIs I'm almost certain you have equipment or cords that are being detected as bad by working GFCIs.
Title: Re: Can Repeated Distro Trips Harm Audio Gear?
Post by: Mike Karseboom on July 05, 2014, 09:35:58 am

While it's clear you had some bad GFCIs I'm almost certain you have equipment or cords that are being detected as bad by working GFCIs.


Ugh!  That is my fear and I guess I need to test all of them.  I did go through them all over the winter and inspect/tighten cord ends.


I have about 1/2 shop made (me) SOOW cords with good quality cord ends and 1/2 commercial SJT cords with molded ends.  In general I dislike the molded SJT  cords because the cord ends sometimes exhibit poor tolerances, they are stiff unless it is very hot out, they are typically a garish color, the jacket does not seem that rugged, and when they do get a nick or something they are not supposed to be repaired.  I have been gradually replacing them with nice thick, black, rubbery, supple, durable home made ones.  Don't tell me I am going the wrong direction?



Title: Re: Can Repeated Distro Trips Harm Audio Gear?
Post by: Jeff Robinson on July 09, 2014, 09:29:55 am
I was a subcontractor on a gig this weekend using  an undersized generator (Whisperwatt 25) and we had repeated losses of power for a variety of reasons.


First due to lack of timely delivery of the 6/4 feeder and spider box, we were running FOH, monitors, and backline off the two 20A convenience GFCI outlets.  Power was delivered through three 100 foot 12/3 SOOW cables.


The first problem seemed to be with the small (1.5 VA) APC UPS unit that was inline before the DR260 system processors and the FOH digital board.  Neither of those devices pulled much current so the UPS was in no way overloaded.  Yet that UPS would squeal with an alarm frequently which was sometimes followed by a shutdown of the UPS.  I am not sure what the alarm meant as it was a continuous squeal and historically the only alarm I have hear from it is the beeping sound it makes when mains power is not present and the battery is engaged.  After a couple of shutdowns that alarm noise became apparent and the battery backup was removed from the circuit.


Then it seemed there was just too much current draw for the GFCI outlets.  The breakers did not trip but the GFCI's did.  After three or four of those episodes the GFCI's seemed to be "fried" as they would no longer reset. 


Fortunately about this time the feeder cable and spider box arrived but unfortunately it was a pretty beat up spider box and only 3 of the GFCI outlets actually worked.  When they tried to runs some lights as well (old parr cans)  there were tripping issues that seemed to involve GFCI trips rather than breaker trips.


Anyway it goes on for a bit but the upshot is that the amps, processors, mixer, and powered monitors were subjected to numerous power resets.  I am wondering if that can be damaging to this equipment?

Just to be contrary, I'll relate a story from the early 80's.

I got a call around 7PM from a friend asking me to bring an amplifier because his BGW died from the janitor flipping breakers to turn off the overhead lights in Southwest High School. When he heard the music stop he immediately turned the last breaker back on and fried the amp (let out the magic smoke).

While turning stuff off will not kill it, turning it on too soon (after an interruption) might. More modern gear may have more protective circuits, but the old school heavy iron BGW700 (IIRC) didn't. I think it's protection was an SCR across the power supply caps called a bridging crowbar.

Just to excite the peanut gallery, the amp I brought was a Flame Linear 400. It was a DJ gig by Disco Dukes of Kansas City, mirror ball and everything!

My 2 cents worth,

Jeff Robinson
Title: Re: Can Repeated Distro Trips Harm Audio Gear?
Post by: Tim McCulloch on July 09, 2014, 10:37:04 am
Disco Dukes?  You're showing our age, Jeff... but I remember when Union Station was actually used by railroad passengers....
Title: Re: Can Repeated Distro Trips Harm Audio Gear?
Post by: Kevin Graf on July 09, 2014, 02:26:47 pm
Lots of big power amps have soft start circuits to protect the bridge rectifier from capacitor charging over-current at start-up. But some of these soft start circuits can get confused with repeated on/off cycles.  Designing a soft start circuit is trickery than it would first appear.
Title: Re: Can Repeated Distro Trips Harm Audio Gear?
Post by: Steve M Smith on July 09, 2014, 05:01:18 pm
Lots of big power amps have soft start circuits to protect the bridge rectifier from capacitor charging over-current at start-up. But some of these soft start circuits can get confused with repeated on/off cycles.  Designing a soft start circuit is trickery than it would first appear.

At start up, the capacitors are discharged and have the potential for high current draw as they charge.  However, a brief off then on shouldn't cause any problems as they will be charged so the current needed to get them back to full charge would be minimal (depending on the time it was off and the current draw from the supply).


Steve.