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HPWC installation question - humming noise coming from conduit. Is this normal?

New Tesla owner here. I recently had a HPWC installed in my garage.
Concern is a subtle humming noise from conduit while charging at 48 amps.
Is this normal??

Details: Dedicated 60 AMP circuit running from my panel approx 100 feet to attached garage.
3 Wires (l1, l2, ground) are #6 copper and run approx 60 feet across the inside of my house (finished basement ceiling). That is the source of the noise. When the charging is stopped the noise stops, too.
Conduit then turns out my home at the back, turns around side of house, and runs 40 feet in outside conduit to garage access point.
Charging works fine, approx 44 mph at 48 amps as expected.
Electrician has already been back to change the brakes, check all connections, and has no ideas how to silence the sound.

Is the humming / vibrating / reverberating / harmonic tone to be expected from the interior conduit?
Should I be worried? Is there a common fix?


Thanks!
 

eprosenx

Active Member
May 30, 2018
2,076
2,542
Beaverton, OR
New Tesla owner here. I recently had a HPWC installed in my garage.
Concern is a subtle humming noise from conduit while charging at 48 amps.
Is this normal??

Details: Dedicated 60 AMP circuit running from my panel approx 100 feet to attached garage.
3 Wires (l1, l2, ground) are #6 copper and run approx 60 feet across the inside of my house (finished basement ceiling). That is the source of the noise. When the charging is stopped the noise stops, too.
Conduit then turns out my home at the back, turns around side of house, and runs 40 feet in outside conduit to garage access point.
Charging works fine, approx 44 mph at 48 amps as expected.
Electrician has already been back to change the brakes, check all connections, and has no ideas how to silence the sound.

Is the humming / vibrating / reverberating / harmonic tone to be expected from the interior conduit?
Should I be worried? Is there a common fix?


Thanks!

So 60 cycle hum is common in electrical systems. It is caused by electromagnetic fields generated by the AC current. I normally see it in transformers though. Not common in conduit as far as I know (though I am not an expert) - I have seen one other post in the forums about this same issue.

I would make sure the conduit was solidly grounded back to the main panel (to drain any inductive current) and that all the couplers between conduit sections were tight (to make sure the ground is continuous). I would also make sure the conduit was physically strapped down tightly in many locations to keep it from moving.

Note that my math is that voltage drop is 1.77% for 100 feet of 6awg at 48 amps of load. So I have no issue with 6awg (instead of 4 awg) in this application. Also, voltage drop requirements are only a recommendation in the code, not a requirement. Note that Tesla's will only draw a fixed amount of current regardless of voltage so it is not like a motor or anything that might draw more than its rated amps if the voltage drops.

If your conduit is 3/4in you could upgrade it to 4awg. While I don't think this is necessary for safety, I would not be surprised if it would solve the issue. The wire would be heavier and fill more of the conduit and it would run at a lower percentage of its capacity so it might not vibrate. I personally would not want to go to this expense until I had exhausted all other options, but I am not sure what else to try!
 
Thanks for making the point about the voltage drop not being a significant factor - very interesting. While the conduit is 3/4", the electrician thought it would be a tight fit. Safety is my primary concern in this case and I appreciate your thoughts that that is not an alarming situation.

The electrician did confirm the ground wire connection to the conduit. The noisy stretch runs through a finished basement ceiling and so I can not strap anything down or be certain of any breaks in the conduit. Is there a way to know that the conduit is well grounded from the outside? or at the wall connector?

Appreciate any thoughts or suggestions!
Seems like there should be an obvious fix for this if everybody is using the same circuit / wires but nobody else has the same sounds & vibrations.

Thank you
 

eprosenx

Active Member
May 30, 2018
2,076
2,542
Beaverton, OR
Thanks for making the point about the voltage drop not being a significant factor - very interesting. While the conduit is 3/4", the electrician thought it would be a tight fit. Safety is my primary concern in this case and I appreciate your thoughts that that is not an alarming situation.

The electrician did confirm the ground wire connection to the conduit. The noisy stretch runs through a finished basement ceiling and so I can not strap anything down or be certain of any breaks in the conduit. Is there a way to know that the conduit is well grounded from the outside? or at the wall connector?

Appreciate any thoughts or suggestions!
Seems like there should be an obvious fix for this if everybody is using the same circuit / wires but nobody else has the same sounds & vibrations.

Thank you

Ah, so the conduit runs behind a wall where you can not inspect it? So maybe it was not strapped down well?

I have heard that in the super long run when transformers are making noise they can wear through their insulation on the wires due to the vibrations, but I suspect in your use case that could take an exceedingly long time (and the grounded conduit should cause the breaker to quickly clear the fault if that happened).

So I am not sure how to test the quality of the ground connection. At a basic level, at the Wall Connector you could measure voltage from each hot to the conduit and to the ground wire to see if the conduit was at least grounded at a basic level. But that needs might not tell you if it could carry sufficient current to blow a breaker during a fault condition. There may be ways to measure the resistance or use a “meggar” to check it, but I don’t know.

So my math shows that two #4’s and a #8 ground could fit in a 3/4in conduit. (I know this as I toyed with upgrading mine at one point since that way if a friend brought over a Model S or X I could charge it a little faster).

F99BC4CE-E197-478D-B5E0-B3E6580D165D.png


I am curious what your solution ends up being!

I would not be surprised if pulling off sheeteock and strapping the conduit down more fixed it.
 
Very interesting and insightful. Probably will leave well enough alone for now. Simplest fix in my case would be to abandon the interior conduit and have the electrician come back out to run exterior conduit ~60 ft to the electrical service. While it may not silence the sound, it would be outside and so we would never hear it.
Thanks again for your comments and contributions.
 

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