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high voltage

woodbutcher

woodbutcher

Well-known Member
I plugged in my Northstar electric power washer to wash my riding mower before I stored it. The 2 hp. motor would click and try to turn over, but never make a full revolution. When it tried to start, the lights in the storage building became extra bright, and then blew out. I had just had the motor off for a start switch problem, so I took it back to the shop. They checked it out and found nothing wrong. They said it could be caused by low-voltage. So, I got out my Handy-Andy multi-meter and did some checking. I took a reading on an outlet in the house, and it showed 120 volts. The house has its own meter. Then I went to my shop where the service drop comes down to a panel with its own ground rod. The outlets in the shop read 120 volts. UF cable runs underground to my tractor shed to feed a subpanel that has its own ground rod. Outlets in the tractor shed showed 134.5 volts. From this subpanel, triplex is run overhead 150 ft. to a subpanel in a storage building where there is no ground rod. Outlets in the storage building show 134.5 volts. I've used the power washer on outlets in the tractor shed and the storage building in the past without any problem. What could be causing these high readings now?
Butch
 
if you have 120v at the main panel and your remote sub panel is showing higher voltage, i would take a look at the neutral. could be a bad connection.
 
This would be a common result when the neutral feeding the shop (or tractor shed) has a bad connection or is disconnected. When you plug a motor or other high Amperage electric load into an outlet, the Voltage on that half of the 120 VAC goes low and the Voltage on the other half goes high (high enough to blow out lights)( the 240 VAC from the transformer stays at 240 VAC if the two hot wires are OK).
Check your neutral connections starting at the shop. You should use the Volt meter to check both sides of the 120 VAC. Plug in a good load (heater or hair dryer) and check both sides of the 120 VAC. Neither side should drop or rise much. It is possible that the neutral in the underground cable has opened up. Do the same test at the tractor shed.

Mark -- recently retired EE.
 

yes.. bad neutral... and your circuits are moving up and down in voltage based on which side has the most load, drops and the other side goes up in voltage. Not a good scenario. My neighbor and I share the same transformer. His neutral went out and it unbalanced the load at the power pole enough for me to see some imbalance on my side... minor,,, but a huge imbalance on his side. I converted his shop from 220 back to 110, using one of the hot legs to become a neutral to get him back into service. He is happy now and I dont see my side getting weird on me. His tv quit working till he turn on a spot light on the other side, then it worked fine.. Yes it was pretty weird. One of my servers kept rebooting was what started me looking and measuring. I traced it to the power meter, called the power company and they kept blaming my side... SO.. after some head scratching, and suspecting the transformer, I went over to my neighbors and found he was really out of bounds...
 
Be careful!

Open neutral can cause some strange things to happen. Even if there is a ground rod, the ground can feed back hot!
 
An outbuilding that is fed with 3 wire triplex or UF should have neutral and ground bonded together at panel. The ground rod that is in very dry ground or bad connection may not be effective for safety if your neutral goes open.
 
You are basically creating a short from one leg of the 240 to the bad neutral, which creates a voltage of up to 240 V on the other leg to the bad neutral.

Be careful and do not run anything until this is corrected.
 
Years ago I worked in an appliance shop, and a man came in and bought a new motor for his electric clothes dryer. He said the old one was running slow. He came back the next day and said new motor was running slow. Remember, the dryer is 220, but the motor only runs on 110. The dryer was in a laundry room that had been added to the house with the wiring in a metal conduit running about 45 feet on the outside. Voltage at dryer outlet was good, till I turned dryer on, then one side only red 60 volts to ground, but still 220 across the hot sides. This was many years ago when most dryers only had 3 wire plugs with the neutral and grounds tied together. Whoever ran the wiring did not run a neutral, but used the conduit for the neutral. All was well till the metal box where the wiring left the house became rusty and the neutral had a bad connection.
 
Thanks to all for the replies. I plan to trip the disconnect at the main panel before I check all my lugs and makeups.
Butch
 
At our huge naval industrial facility the fist thing I had our electricians check when we experienced high voltage on one leg of a 120/240 single phase three wire service WAS FOR A BAD NEUTRAL CONNECTION

If you have the old 3 wire service to remote subpanels for 120/240 you need to bond to all readily available "Grounding Electrodes"

John T Retired Electrical Power Distribution Design Engineer
 
Lights got both phases at once on backfeed due to lost neutral. Very bad condition. I can draw it but I can't explain it with a drawing.
 
I would think you would blow out all the lights on the opposite phase when the motor tried to start.
 
I opened the disconnect box below the panel in the shop where the UF cable goes underground to the tractor shed. It is in conduit from the box to 24" below ground. All three conductors are insulated. I noticed that the lip of the conduit is blackened where the neutral/ground conductor goes into the conduit, and the insulation on that conductor is bubbled like it had melted, but no bare metal was showing. I recall now that I had to replace the cable that comes into the ground bar from the ground rod about a year ago due to a lightning strike to the weatherhead on this meterbase. When it burned through the grounding cable, it could have sent enough juice through the neutral buss bar to melt the neutral through also. I'm thinking about abandoning that neutral conductor and going overhead with a single bare conductor to the subpanel in the tractor shed. Is there anything wrong with that idea? I'll probably abandon the ground rod at the subpanel, also.
Thanks for all your suggestions that helped me know where to look.
Butch
 
No you can not run a single wire overhead . Probably about ten different violations of code. Clean and megger the neutral.
 
NOOOOOOOOOOOOOO don't run a single separate Neutral

NOOOOOOOOOOOOOO don't abandon the ground at the sub panel

YESSSSSSSSSSS repair the bad Neutral

When in doubt about electrical safety CONSULT THE NEC and professional electricians and local authority and don't bet the farm or risk your life or a fire based on what Billy Bob or Bubba or your brother in law has to say lol

John T Retired Electrical Power Distribution Design Engineer
 
a meggar tests insulation resistance. an inexpensive meggar will run you a couple hundred bucks. a good one around a grand. see if you can find an electrician that has one. i doubt if you can rent one
 
Blistering of insulation indicates a lot of heat, it may have been caused by lightning, or poor connection. The conductor could be compromised at any point if it got direct hit by lightning. I do not know if it is aluminum or copper, but aluminum conductors will turn into an aluminum oxide powder if exposed to water due to failed insulation. You might end up replacing the whole segment, but best to hire an electrician to diagnose, they will have the proper equipment

What is the amp rating of the upstream breaker and gauge of wire; if smaller might just replace whole line yourself.
 
Water over the dam. But PVC conduit is rather inexpensive, Once a ditch is dug why not leave a hole before filling the ditch in/install some conduit ? Sure makes it rather easy to fix a problem later. Even maybe go with oversized conduit. Maybe tomorrow one may find that they need more power.

Dusty
 
(quoted from post at 18:31:56 10/12/17) Water over the dam. But PVC conduit is rather inexpensive, Once a ditch is dug why not leave a hole before filling the ditch in/install some conduit ? Sure makes it rather easy to fix a problem later. Even maybe go with oversized conduit. Maybe tomorrow one may find that they need more power.

Dusty
Click to expand...
Or fiber optics. Or something. Good idea.
 
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