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What would cause a paging system amplifier breaker to trip daily?

wega1985
wega1985 asked
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Last Modified: 2012-06-21
We have two Bogen C100 paging amplifiers in our wire closet with the phone system.  Recently, the unit designated for the shop speakers has been blowing the built-in breaker on the back of the unit.  Every few hours the receptionist lets me know that the shop isn't getting pages, and I reset the breaker.  The amps are both plugged into the "surge protection" side of an APC UPS.  

We have an old Executone phone system connected to the "aux 1" ports on both amps.  A few months ago, I reconfigured the amps into two zones so I could better adjust the volume and the load, and to get ready for zoning in our new VoIP system.  Until last week, it was working fine.  There are many options for the speaker voltage / resistance on the back of the amp, but I just maintained the same terminals that were setup some 15 years ago

I'm not sure if the incoming signal could trigger the breaker overload, the attached speakers (too many? short-circuited), or if the amplifier just needs to be replaced.  I'm looking for possible next steps in troubleshooting.  .  Thanks!
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Commented:
Thanks for the comprehensive response.  My first response is that yes, this unit is on the top of the stack, but the closet doesn't appear any warmer than usual.  I also noted that the unit is "buzzing" more loudly than the stable unit -- not sure if that is indicative of any problem.
It is a 70V configuration as you mention.  The speaker networks seem to be fairly even, 15-20 ceiling speakers on the office unit, 10-15 bull horn speakers on the shop unit.  As you mention, there is no notable sound detriment.
I will try swapping the units.

Author

Commented:
I also want to note, before the reconfiguration took place, our phone vendor installed a makeshift night ring into place due to limitations of our aging phone system.  It appears that he spliced the ringer/handsfree speaker of a spare phone into the input of the paging system, and setup a forwarded extension that rings over the PA after a certain amount of time.  My concern with this was that the ringer output may be overloading the circuit on top of the existing paging input.  I checked to make sure that the volume was turned all the way down on the ringer.
As the other amp is unaffected, and both were fine for quite some time following the setup, this also seems somewhat unlikely.
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Sorry, don't really have time to read through what everyone else has said, so if I'm repeating, I apologize.  When you reconfigured, you likely changed the ohm loading on the amps.  The original install would have been set up so that the speakers were strung in series and parallel to provide the proper ohm load for the amps.  If you changed the setup without knowing which were in series and which were in parallel, you may have inadvertently configured one amp to an extremely high ohm load, all in series, and one to an extremely low ohm load, all in parallel.  

I'd just about bet the one that's blowing is dealing with a very low ohm load, resulting in much greater output power demands.

Author

Commented:
That sounds like it might be the case.  I wasn't aware that the series/parallel factor played such a large role.  
The original configuration had all of the office speakers PLUS most of the shop horns on one C100 amp (very old, went bad).  The second C100 amp had only a newer, small portion of the rear shop (6 speakers, maybe).  It made sense to me to put all of the shop speakers on one, and all of the office speakers on the other, when the first amp went bad.  The first amp dying completely is what led to the reconfiguration at all.
At this point, the best option to me would be to buy a third amp, because I do not want the office and shop speakers on the same volume control.  It's either too loud in the office or too quiet in the shop under that configuration.
 

Author

Commented:
I just happen to have some of the loads:
Amp 1:  Tripping
Back shop (originally alone on now-failing amp):  78© @ 68w - 6 horns
Front shop (I added to now-failing amp):  190© @ 6W (I'm assuming per)
Amp 2:  No problems
Office:  750© @ 6W, and the label says AT-10 @ full (?)

Author

Commented:
Looks like EE didn't accept the symbols; those are ohms.

Author

Commented:
A go/no go test for the power supply would be to disconnect everything but the AC feed from the problem amplifier.  Energize it and see if the buzzing is still present - if it is, I would take it in for service.  Do this before/when you switch the amps, of course.
The buzzing was indeed present upon disconnecting everything except AC from the amplifier.
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Author

Commented:
Just wanted to follow up on this issue.  I swapped the two circuits and the problem disappeared.  Possibly the newer amp is more able to handle the larger load?  Either way, thanks for all of your in-depth responses.
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