kwired
Electron manager
- Location
- NE Nebraska
- Occupation
- EC
May not be as common for small conductors, say 6 or 8 AWG and smaller, larger conductors are more available in triplexed or quadplexed assemblies AFAIK than they once were.
Warm conduit and vibrating/ humming wires
- Thread starter Tudmutt
- Start date
- Status
MNSparky
Senior Member
- Location
- Minneapolis, MN
- Occupation
- Electrical Contractor - 2023 NEC
Hi all, I have a similar issue that is stumping me. It's in a house so residential 120/240v single phase service. There is a 100amp service disconnect that is fed from the meter with EMT that ultimately feeds a 100amp subpanel in the house on the opposite end from the service. The feeder is all 1" EMT that goes up the side of the house, through the attic, and down an 2nd floor interior master bedroom into the first floor mud room where the subpanel is mounted. The subpanel feed various lighting and receptacle circuits along with an EV charger and an electric dryer. We installed the EV charger recently. There is also a 200amp main panel that is in the basement below the meter. That is piped in EMT that goes into the ground outside.
The issue is whenever a larger load is turned on the feeder hums (sounds just like a transformer). The homeowner didn't notice it until the EV charger got put in. He said he charges at night so he heard a humming coming from his bedroom wall in the middle of the night. It seems like the wires are vibrating. The EV charger is wired in conduit in the garage and it's especially noticeable in there when charging as those wires are vibrating too. The humming gets louder as we turn the charger up to higher amp draws, max is 48amps. The dryer also causes the feeder to hum but not as much as the amp draw is less. It does not cause the EV charger conduit to hum when the EV charger is off.
Here's what I've done:
- Voltages at all 3 points (service, sub, EV charger) are all good with or without load. 48amp load causes phase voltages to drop from 123 to 120 to ground which should be fine.
- There is no current on the neutral when the EV charger is running. I have 48amps on each phase and 0 on the neutral. Neutral currents seem to be normal, just the unbalanced
- Voltages from phases to the feeder pipe are the same on each end which tells me the pipe is continuously bonded together
- POCO has been out and found nothing wrong with the supply. This issue does not occur in the 200amp main panel in the basement.
- We have cycled the main breaker and disconnect, no change.
- Replaced the EV charger with a different one, no change.
- Clamp on meter around the feeder pipe shows 0amps
Things I noticed are wrong but haven't corrected:
- no GEC at the 100amp disconnect, bonding bushing on the incoming pipe but no wire. The disco enclosure has minimal resistance to a piece of EMT outside that comes from the 200amp basement panel so I believe there is a ground path (all conduit) the the 200amp panel where the water pipe GEC is landed.
- Service disconnects not grouped
- I was unable to find any ground rods
Every reading I took was good, nothing even remotely odd. Any thoughts why the conduits hum?
The issue is whenever a larger load is turned on the feeder hums (sounds just like a transformer). The homeowner didn't notice it until the EV charger got put in. He said he charges at night so he heard a humming coming from his bedroom wall in the middle of the night. It seems like the wires are vibrating. The EV charger is wired in conduit in the garage and it's especially noticeable in there when charging as those wires are vibrating too. The humming gets louder as we turn the charger up to higher amp draws, max is 48amps. The dryer also causes the feeder to hum but not as much as the amp draw is less. It does not cause the EV charger conduit to hum when the EV charger is off.
Here's what I've done:
- Voltages at all 3 points (service, sub, EV charger) are all good with or without load. 48amp load causes phase voltages to drop from 123 to 120 to ground which should be fine.
- There is no current on the neutral when the EV charger is running. I have 48amps on each phase and 0 on the neutral. Neutral currents seem to be normal, just the unbalanced
- Voltages from phases to the feeder pipe are the same on each end which tells me the pipe is continuously bonded together
- POCO has been out and found nothing wrong with the supply. This issue does not occur in the 200amp main panel in the basement.
- We have cycled the main breaker and disconnect, no change.
- Replaced the EV charger with a different one, no change.
- Clamp on meter around the feeder pipe shows 0amps
Things I noticed are wrong but haven't corrected:
- no GEC at the 100amp disconnect, bonding bushing on the incoming pipe but no wire. The disco enclosure has minimal resistance to a piece of EMT outside that comes from the 200amp basement panel so I believe there is a ground path (all conduit) the the 200amp panel where the water pipe GEC is landed.
- Service disconnects not grouped
- I was unable to find any ground rods
Every reading I took was good, nothing even remotely odd. Any thoughts why the conduits hum?
Attachments
ptonsparky
Tom
- Occupation
- EC - retired
Large loads will cause wires to vibrate and may be especially noticed while everything else is quiet in the house.
4x4dually
Senior Member
- Location
- Stillwater, OK
- Occupation
- Electrical Engineer/ Ex-Electrician
It will stop if you just fill the conduits full of expanding foam. 
Joking of course.
Joking of course.
ptonsparky
Tom
- Occupation
- EC - retired
Using a cable vs the conduit would help.
MNSparky
Senior Member
- Location
- Minneapolis, MN
- Occupation
- Electrical Contractor - 2023 NEC
So this is fairly normal? I'm not sure how I've made it through my career without knowing this...
ptonsparky
Tom
- Occupation
- EC - retired
Normal enough that if you crossed your 't's and dotted your 'i's, I wouldn't worry much. That doesn't help with your customers complaint of hearing it though.
It won't be an easy fix now.
- Status