opinion please, about power circuit rating?

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yapweiliang
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2018/11/03 10:10:04 (permalink)

opinion please, about power circuit rating?

Hi - I'm hoping this is not too off topic.
 
I'm trying to troubleshoot why a circuit breaker keeps going off in relation to the equipment in the audio rack at church.  I have narrowed it down to a power amplifier (Behringer EP2500).  This works fine, but sometimes when power on, this trips the circuit breaker.  It is also noticeable there is a very tiny subtle flicker in the room light when the amp is powered on.
 
This is a new building, but some of the equipment from old building including this power amplifier was re-used, and this power amplifier has never had issues in the previous building, and it still works fine provided it didn't trip the circuit breaker.  And although it is quite a hefty amp, we do not generally drive it to its limits - normally it is operating at a fraction of its potential.
 
The circuit breaker (an RCD) is rated at 16A, and the RCD rating is 30mA.
 
My question is - should I suspect this power amplifier is nearing the end of its life span and replace it, or, should the supply to an "AV room" be rated at greater than 16A?  (for reference it also supplies a few other amplifiers, hearing loop amp, mixer, computer, video projector, network stuff, etc // but no high power stuff e.g. no spot lights)
 
EDIT: PS : in the UK, therefore 230V mains supply
 
Many thanks,
Wei Liang
 
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    fireberd
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    Re: opinion please, about power circuit rating? 2018/11/03 13:16:17 (permalink)
    The initial "surge" current when the amp is powered on is what is causing this.  I would suspect the amp should be repaired or replaced.  It should not exhibit that amount of surge at power on and definitely should not cause lights to blink.  Many devices will have a surge current when first powered on but it is not enough to be of concern.  

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    #2
    Wayfarer
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    Re: opinion please, about power circuit rating? 2018/11/03 16:50:54 (permalink)
    Musical electronic gear won't generally draw a whole lot of power. Tube amps are probably the worst, but they still are light load devices compared to something like a space heater, iron, microwave etc. (Anything that heats.) Could be that there's a branch running from the same circuit to another room in the building where someone has something plugged in that's a power drain. Maybe a nursery with a space heater? An outlet in a kitchen area etc. In that case you would not only need a more powerful circuit breaker but thicker Romex as well.
     
    Bill
    #3
    yapweiliang
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    Re: opinion please, about power circuit rating? 2018/11/03 17:11:02 (permalink)
    Thanks for your thoughts, Fireberd and Wayfarer; as far as I am aware there is no other high-current equipment on this line.  The next-highest rated equipment is an NX1000 Amp (150W @ 1/8 power according to manufacturer, therefore 1200W at full power), and then next is a 500W video projector.  The EP2500 power rating is 2600W.
     
    If the assumption is made that the EP2500 is not faulty, but does have a high in-rush current, one suggestion had been to change to a Type C breaker (keeping the same 16A rating).  (It is a Type B breaker installed). 
     
    We'll try to get the EP2500 checked out anyway, as I'm not sure that such equipment should draw such a large current at start up - enough to trip a 16A breaker!
     
    Thanks,
    Wei Liang
    #4
    mettelus
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    Re: opinion please, about power circuit rating? 2018/11/03 17:22:08 (permalink)
    Look up "inductive kick" or "inductive kickback." This is most prevalent in motors, where the start current is typically 5-7 times running current due to pole slippage on start, but the principle applies to any circuit with an inductive load. The "power on" spike is normal, and usually mitigated via a power supply rated for the spike and unloading the circuit prior to start (volumes down, no physical load on a motor, etc.). E.g., a 5-amp inductive motor can draw up to 35-amps if started under load.

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    Wayfarer
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    Re: opinion please, about power circuit rating? 2018/11/03 17:56:16 (permalink)
    If there's nothing wrong with the amp and it works well in other rooms (take it out and try it elsewhere), then you know there's something else that's drawing too much current for that circuit. If that's the case, what may be the easiest fix is just to run a new circuit from the power box specifically for that amplifier. I say easy, but of course that depends on the layout of the facility and ceiling / wall access. Chances are the breaker box is in the basement, and if it has a drop-down ceiling, that will give you fairly easy access to run a cable. The power box will almost assuredly have some empty slots for a new breaker.
     
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    Leadfoot
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    Re: opinion please, about power circuit rating? 2018/11/03 18:45:31 (permalink)
    I've had faulty breakers in the past also. Just a thought.
    #7
    tlw
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    Re: opinion please, about power circuit rating? 2018/11/04 00:52:13 (permalink)
    The amp might be starting to have issues with it's capacitors, so getting it checked over is a good idea - it's a good idea to have them looked over once in a while anyway, because if they're going to fail without warning it's always at the worst possible time. A simple portable appliance check is unlikely to show up that kind of problem because it tests different things.
     
    Having said that, some breakers are much more sensitive than others....
     
    RCDs are capable of mis-reading what's happening and tripping. For example, a good rule of thumb is to never test an RCD that's plugged into a circuit that has it's own RCD breaker because testing the first one will almost certainly trip the second.  So it's not impossible for the breaker to be at fault or simply not the right one for the job.
     
    A 2600W amp running "flat out" at UK voltage is going to draw around 11 Amps if it is 100% efficient, and no amp is anywhere near that so it will draw quite a lot more. I've a Behringer 2KW amp that uses 13A fuses and we always have to be careful what's on the same mains strip when connecting to domestic-type 13A sockets even though the amp rarely gets run near full power. Basically we'd expect the amp+a small mixer and a processor or two to be about it before hitting the 13A limit.
     
    As for the room supply's capacity, the best/only way to find out what's going on is to hook up a meter that reads the total amps passing through it at a point where all the power will be going through the meter. Or if that isn't possible read what each set of gear connected to each mains socket is drawing then add the readings to get the total drain. You'll need to allow some headroom as well. If the room lights are wired into the same circuit as the mains sockets then they'll need to be taken into account as well.
     
    Finally, don't assume that because the wiring is new it is installed correctly. I've come across stages with brand new professionally installed ducted wiring complete with all the necessary paperwork that when checked with a socket tester turned out to have no earth or have live and neutral reversed. One venue had both faults. Some years ago my wife investigated an industrial accident involving a 415V three-phase supply in a newly built industrial unit. How the accident happened should not have been possible, but that wasn't much comfort to the friends and relatives of the deceased. A specialist electrical inspector traced the problem to a simple "wires crossed" error in the distribution circuit. Installing building wiring is not exciting or entertaining, and like the rest off us electricians sometimes slip up. Mistakes can happen.
     

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    #8
    sock monkey
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    Re: opinion please, about power circuit rating? 2018/11/04 19:03:25 (permalink)
    (for reference it also supplies a few other amplifiers, hearing loop amp, 
    The next-highest rated equipment is an NX1000 Amp (150W @ 1/8 power according to manufacturer, therefore 1200W at full power), and then next is a 500W video projector.  The EP2500 power rating is 2600W.
     
    Those ratings are all OUTPUT power. If you look on the back, usually near the AC power cord it might tell you what the power consumption is. It will be more like 200 Watts if it's a classA/B type amp. Class D amps use a lot less power and why they are so popular now. 
    My rule of thumb is no more than 3 Power amps on a standard 15 AMP circuit. But that said, a power amp running subs will draw a lot more than a amp just running some small low level speakers. And that projector! thats like having 2 power amps maxed out. So they certainly did not plan for a AV room properly. You should have at least 2 x20 AMP outlets just for the power amps  

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    yapweiliang
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    Re: opinion please, about power circuit rating? 2018/11/04 20:53:30 (permalink)
    Dear all, thank you very much for your thoughts and suggestions.  The ratings I quoted are what the manufacturers give in the instruction manuals for power consumption (not power output).  The EP2500 would give about 450W into 8 ohm x 2 channels, but power consumption quoted as 2600W (and I think that is when it is used in bridge mode to deliver 2400W into 4 ohm load).  It comes with its own 8 amp breaker.
     
    The projector has to give an image on the wall nearly 10 metres away, so I'm not too surprised it is quoted as a 500W.  A halogen flood light would be 500 - 1000 W in comparison.
     
    I've summed all the equipment power consumption quoted by manufacturers for all that I am aware is running from that circuit, and if all are at maximum, then it is well in excess of the 16A.  Although when running at normal use it will be comfortably below 16A, but there may be unexpected loads, or, power-on surges, etc which therefore require more capacity.
     
    So I think we need to consider these options:
     
    1) increasing the rating of the breaker to a 20 or 32 Amp (assuming the internal wiring is appropriate)
     
    2) change the type of breaker from type B to type C - to allow a bigger initial surge;  check that the existing breaker is not faulty
     
    3) check +/- replace/repair the EP2500
     
    4) check that there are no other appliances outside this room that happen to share the same circuit
     
    I think I have enough information to proceed, so, again, thank you very much to everyone for their advice.
     
    Wei Liang
     
     
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    rabeach
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    Re: opinion please, about power circuit rating? 2018/11/08 10:13:32 (permalink)
    The RCD is also possibly tripping due to earth leakage, a difference in the current in the active and the neutral (greater than 30mA in this case) this can occur due to a fault in the circuit or with the equipment.
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    rabeach
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    Re: opinion please, about power circuit rating? 2018/11/10 14:59:31 (permalink)
    yapweiliang
    Dear all, thank you very much for your thoughts and suggestions.  The ratings I quoted are what the manufacturers give in the instruction manuals for power consumption (not power output).  The EP2500 would give about 450W into 8 ohm x 2 channels, but power consumption quoted as 2600W (and I think that is when it is used in bridge mode to deliver 2400W into 4 ohm load).  It comes with its own 8 amp breaker.
     
    The projector has to give an image on the wall nearly 10 metres away, so I'm not too surprised it is quoted as a 500W.  A halogen flood light would be 500 - 1000 W in comparison.
     
    I've summed all the equipment power consumption quoted by manufacturers for all that I am aware is running from that circuit, and if all are at maximum, then it is well in excess of the 16A.  Although when running at normal use it will be comfortably below 16A, but there may be unexpected loads, or, power-on surges, etc which therefore require more capacity.
     
    So I think we need to consider these options:
     
    1) increasing the rating of the breaker to a 20 or 32 Amp (assuming the internal wiring is appropriate)
     
    2) change the type of breaker from type B to type C - to allow a bigger initial surge;  check that the existing breaker is not faulty
     
    3) check +/- replace/repair the EP2500
     
    4) check that there are no other appliances outside this room that happen to share the same circuit
     
    I think I have enough information to proceed, so, again, thank you very much to everyone for their advice.
     
    Wei Liang
     
     


    I would not recommend 1) increasing the breaker size without increasing the conductors current carrying capacity is a code violation and very dangerous. 2) it does not appear that you have any inductive appliances therefore I question where an inrush current would come from.
     
    Lights dimming could be a ground fault probably in the equipment but since you mentioned that this is new construction it could be a circuit fault. I would rule out the equipment first. Although it is pure speculation I'm betting the equipment has a fault within the equipment's circuitry.


    #12
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