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Author Topic: Can Repeated Distro Trips Harm Audio Gear?  (Read 6671 times)

Mike Karseboom

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Re: Can Repeated Distro Trips Harm Audio Gear?
« Reply #20 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) 
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jasonfinnigan

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Re: Can Repeated Distro Trips Harm Audio Gear?
« Reply #21 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.
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Tim McCulloch

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Re: Can Repeated Distro Trips Harm Audio Gear?
« Reply #22 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.
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Mike Karseboom

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Re: Can Repeated Distro Trips Harm Audio Gear?
« Reply #23 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?



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--Mike
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Jeff Robinson

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Re: Can Repeated Distro Trips Harm Audio Gear?
« Reply #24 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
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Tim McCulloch

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Re: Can Repeated Distro Trips Harm Audio Gear?
« Reply #25 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....
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Kevin Graf

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Re: Can Repeated Distro Trips Harm Audio Gear?
« Reply #26 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.
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Steve M Smith

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Re: Can Repeated Distro Trips Harm Audio Gear?
« Reply #27 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.
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Re: Can Repeated Distro Trips Harm Audio Gear?
« Reply #27 on: July 09, 2014, 05:01:18 pm »


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