Power Noise

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bphgravity

Senior Member
Location
Florida
I was recently in a large gymnasium that has 6 rows of 1500-watt high bay fixtures. There are 8 fixtures in each row. There are three lighting contactors relaying 2 rows each.

Upon shutting down each of the three circuits, a very large and thunderous clicking noise with a low frequency hum followed as each set of lights turned off. Click-boom, Click-boom, Click-boom.

I have noticed this same noise at ball fields and during widespread power outages. My assumption has been two things. First, I assummed it was the noise of the contacts opening and resonating through the empty building, however this is not the case. I then assumed that it is actually the sound of silence that is made clear upon all noises being removed. For example, have you ever been alseep and wake just as the power goes out during a storm? Silsence is somehow very loud.

Any theories on where the noise is comming from? Does electricity create sound? :confused:
 

hurk27

Senior Member
Re: Power Noise

It would seem that if those contactors are anywhere close to this gym then you would hear them as a 125 amp rated lighting contactor will make a loud clap sound when turning on or off. The other noise you might be hearing is the hum or buzzing of the HID type fixtures as ballast almost always make noise. now going back to other noise is since the NEC requires wiring in this type of structure to be installed in a metal conduit, There will be noise from the magnetic field around these wires. Ever have a motor start up when you were close to the conduit feeding it and heard the hum in the conduit? with each set of lights being switched by one contactor the load on that contactor is around 100+ amps and thats not even figuring in the aux. load of the ballast so there might be as high as 130 amps on each of these contactors that would produce quit a magnetic field in the conduit. So HID fixtures are not a good choice if noise will be a problem.

[ May 02, 2004, 12:18 AM: Message edited by: hurk27 ]
 

hbiss

EC, Westchester, New York NEC: 2014
Location
Hawthorne, New York NEC: 2014
Occupation
EC
Re: Power Noise

It's possible that there were mechanically held contactors and you were hearing the coils energize and the contacts drop out. I will assume here that you were just a casual bystander and happened to notice this. I would say that without further investigation, like where are the contactors located as well as operating them and actually listening to where the sounds are coming from, any theories would be pure speculation.

-Hal
 
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