Ok, I know I have mentioned this befor but I am revisiting it because our HVAC guy insists. When the heat pump kicks on a loud vibrating noise for sometimes 2 seconds sounds off. I know with heat pumps it will have a big inrush current and if the conductor are in emt you will sometimes get vibration. I agree with the HVAC guy it is unusually load and long. He has replaced the compressor 2 times and will not do it again till I fix our electrical problem. I have checked voltage, ohmed out the wires, check the ground, and took a current reading. Everything seems to be fine. I don't know what else to check.
Vibrating conduit
- Thread starter JdoubleU
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A bit of a hassle, but load your circuit with simular load (motor load).....take your readings, and prove to him you are not at fault.........Im suprised he put in the second compressor with out finding the root of the problem.
Buck Parrish
Senior Member
- Location
- NC & IN
Put more straps on it. Make it tight so it will not vibrate.
- Location
- Windsor, CO NEC: 2017
- Occupation
- Hospital Master Electrician
This may be a screwy idea, but I'll throw it out there for consideration. What about squirting some expanding foam into the EMT every so often, you think that might quiet it up (providing proper size wires have already been installed)?
cadpoint
Senior Member
- Location
- Durham, NC
- Occupation
- Electrician - but not by NC Law.
Is it slapping condonductors or is the conduit itself doing this, is there any flex involved at the motors attachment.
Why is it conditional on the one run of EMT ? Can you describe the motor(s?) itself, and / or this layout, is there isolation pads under on this unit in question ?
Is it a direct drop to the motor then I'm with Buck more straps!
re-read the title - conduit...
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I would be hesitant on using foam simply because I don't know if it can damage the insulation.
Why not use duct seal instead?
byourdesky
Member
- Location
- vista,ca
Is this because the wires might possibly be undersized for the load or the distance they are travelling....ie-voltage drop?
My question is why is he loosing compressors? something else is going on Im wondering if the reverse valving process on the heatpump is functioning correctly. I agree conduit vibration would be a nuisance, but not the root.
The vibration has to be coming from the unit..and it sounds like the HVAC guy is blaming the electrician because he doesnt know what else to do.....:smile:
quogueelectric
Senior Member
- Location
- new york
It is probably the magnetic current from the inrush current to start the motor. Put an amprobe at the motor along with a voltmeter and record the voltage and amperage on startup then get back to us.
Isn't that part of every other trades' training?
Seems like it doesnt it....
If the voltages are correct under load, and there isnt a phasing problem, the root cause is in the unit........If the vibration is only two seconds, its definitely associated with starting current, or what's know in the vibration world as a "Critical RPM"....or heck maybe something is loose on the unit...
Regularkevin
Member
- Location
- Auburn, WA
Is he missing a screwdriver by chance?
Could you use a from-to connector and a little bit of flex near the compressor?
IMO, if you have it properly supported the conduit shouldn't be rattling around, right?
Could you use a from-to connector and a little bit of flex near the compressor?
IMO, if you have it properly supported the conduit shouldn't be rattling around, right?
MarkyMarkNC
Senior Member
- Location
- Raleigh NC
Has the HVAC guy changed out the entire compressor, or just the motor? I had this exact same problem one time, and it turned out there was something wrong with the motor starter in the unit. It caused the wires to rattle around in the conduit for a second or two. Same, scenario, the HVAC guy insisted it was an electrical problem. I don't remember what the amprobe reading was on it, but I remember it was spiking at 3 or 4 times normal at start-up. At the GC's request, we ended up re-pulling and up-sizing the wire, even though we were pretty certain our load and voltage drop calculations were correct. Only after that didn't solve the problem did the GC go back to the HVAC guy.
If you've ohmed out the wires and done a voltage drop calc, I would place money on it being an HVAC problem.
If you've ohmed out the wires and done a voltage drop calc, I would place money on it being an HVAC problem.
electricguy61
Senior Member
Is there "soft-start" installed (basically, a set of capacitors)? These can fail and provide real problems on start-up.
MarkyMarkNC
Senior Member
- Location
- Raleigh NC
Yep, that's exactly what they ended up figuring out in my case.
LarryFine
Master Electrician Electric Contractor Richmond VA
- Location
- Henrico County, VA
- Occupation
- Electrical Contractor
You might try temporarily running a separate supply cable, just to eliminate that.
Expansion foam wont hurt the conductors utility workers do it all the time rather then putting on weatherheads theyll use foam to close it off
76nemo
Senior Member
- Location
- Ogdensburg, NY
It's not been answered whether or not it's mechanical vibration, or vibration due the conductors inside the thinwall yet. Hard to draw any conclusion here
Jack Edwards
Member
- Location
- West Tennessee
Both Sparky and Mule are right on target. I started out with at combo Electrical/HVAC company and was cross trained for service calls. First you never run a non-flexible type conduit to a HVAC unit due to vibration and if the compressor is under that much load there must be an underlying problem usually a high head pressure which can be caused by the reversing valve and/or age of unit and/or over charging etc. Also usually is HVAC guy's responsibility to run the applicable flex from the disconnect (installed by the Electrician) to the unit around here. I was both at different times and I am not trying to stir up any rivalry as there are probably others that are on the forum as well.
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