AC circuit

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Tracy Scott

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Littleton,CO
I am having a problem with an air conditioner circuit. When it starts up, the conductors in EMT are making a buzz for a split second and this is a concern to the homeowner. I think it has to do with the initial surge of current (117 LRA) in the metal conduit. How can this buzz be eliminated?
 
Tracy Scott said:
I am having a problem with an air conditioner circuit. When it starts up, the conductors in EMT are making a buzz for a split second and this is a concern to the homeowner. I think it has to do with the initial surge of current (117 LRA) in the metal conduit. How can this buzz be eliminated?
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did you use individual conductors? I've seen it before. the ac shouldn't pull the full 117 lra. if it is pulling high amps look into having the installer put a kick start type device on it to lower the start up amps.
 
That would be my first thought also. A soft-start on the A/C .
 
Tracy Scott said:
I am having a problem with an air conditioner circuit. When it starts up, the conductors in EMT are making a buzz for a split second and this is a concern to the homeowner. I think it has to do with the initial surge of current (117 LRA) in the metal conduit. How can this buzz be eliminated?
Click to expand...

I think that it is not the metal conduit itself that is causing the problem but the magnetic forces between the individual conductors inside the conduit.
The current is making the wires attract or repel each other strongly at a 120Hz rate, and they are then probably vibrating against the walls of the conduit.
If you tightly twisted the wires before pulling them it might help. Or fill the conduit with some sort of goop.

As a practical matter, the two alternatives that come to mind are:
1. larger sized and therefore more rigid wires.
2. A soft start device as mentioned earlier.
 
Start Gear

Start Gear

What has been referred to as soft start on HVAC applications is really " Hard Start Gear."
You generally have 2 choices.
A PTC device, which has to be wired in a particular way and not with a single pole contactor...
OR
Factory specified hard start components which will consist of a potential relay and a start capacitor.
They must be sized exactly for the compressor motor or the start windings will be damaged.
PTCs need a minimum off time of about 5 min. to recycle. This has to be accounted for with T-stat control logic or sometimes an added time delay.
Carrier has made a reliable PTC start assist for many years that comes standard on some higher end units.
The instant inrush current on some intermediate generation scroll compressors can get your attention, especially on 5 ton systems as it can be over 200A without start assist.
 
Or ... and this is what I would do ......... nothing, absoulutly nothing. :D

I would tell the HO that is is nothing to be concerned about.
 
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