208v on a single conductor

[Toasted922]

Hey guys, so I have an odd issue. I have 208v single phase feeding a pole vac at a car wash. I was called out to get the vac up and running again. The feed comes through a 2” underground pvc conduit along with 5 other vac feeds and 1 lighting circuit shared between the 5 lights atop each vac. The first pull point after exiting the building is a handhole adjacent the pole vacs. In the handhole each leg reads normal for this circuit, 120v to ground with each leg and 208v between each leg, black and red. From there it dumps into a 3/4” pvc conduit exiting the handhole and goes directly to the inaccessible base of the pole vac and then up to a bell box for a service switch. After taking the switch apart to eliminate any kind of backfeed from the motor and/or the wiring the maintenance guys did, I tested at the pole vac to find 0 volts on the black and somehow 208 volts on the red conductor. The service to the building is 3 phase, 277/480v with a transformer inside giving us the 208 three phase. No bastard leg and the service is newly installed, hardly a year old. How is that possible to get 208v on a single conductor with no bastard leg and nothing else hooked up to the circuit to backfeed or interfere? The 3/4” pvc is filled to the brim with water as the maintenance fellas forgot to cap the vac pole, so theres ice given its been 20°F. My assessment was rip out the vac, pull new wires, put the vac back gingerly without damaging the conductors.

 

[tom baker]

Is this 120/208 three phase or 120/240 high leg delta? The high leg will have a bastard phase but the 120/208 will not. A 208 vacuum will have a 2 pole breaker if a 120/208 system

 

[Toasted922]

Is this 120/208 three phase or 120/240 high leg delta? The high leg will have a bastard phase but the 120/208 will not. A 208 vacuum will have a 2 pole breaker if a 120/208 system

This is a typical 120/208v single phase circuit, no bastard leg. I checked the breaker first once I got the 208 on the single conductor. Everything checks out up to the handhole. After that I’m not sure how it’s happening. I verified its the correct wires using a circuit tracer first by opening and closing the breaker and voltage checked out. Then a toner when it was dead.

 

[hillbilly1]

Betting XO is not bonded (Neutral floating), and there is a fault to ground on one of the phases. Happens way more than it should.

 

[ptonsparky]

Betting XO is not bonded (Neutral floating), and there is a fault to ground on one of the phases. Happens way more than it should.

Sounds right, even though I'v never come across it myself/

 

[LarryFine]

What are you measuring each line against? I'm guessing the local conduit, which may actually be energized by the line you're reading zero volts against.

If I'm correct, it's lucky nobody has gotten shocked yet.

Why no breaker tripping? My first guess is poor bonding between the incoming and outgoing conduits in the hand-hole, if they're even metal, or a broken EGC.

Carefully check the voltage between the building's grounding system and the load-end's EGC with a long wire or an extension cord.

 

[hillbilly1]

Sounds right, even though I'v never come across it myself/

I have, multiple Home Depot’s, Best Buy’s, Montgomery Wards, K Marts. Most common are transformers feeding computer panels. They take isolated grounds to a new level! LOL!

 

[hillbilly1]

After re-reading the op’s post, it is probably what Larry said, Egc is broken, and one leg is faulted.

 

[ptonsparky]

After re-reading the op’s post, it is probably what Larry said, Egc is broken, and one leg is faulted.

Essentially the same result, just floating there at 120v to ground. One bare phase wire, waiting.

 

[tom baker]

Sorry I missed the no bastard leg comment

 

[Jraef]

After re-reading the op’s post, it is probably what Larry said, Egc is broken, and one leg is faulted.

Tweaker cut off the GEC because it was exposed and accessible.

 

[hillbilly1]

Tweaker cut off the GEC because it was exposed and accessible.

You would not believe how many cell towers have the grounding electrode cut at about 8’ going up the towers. Happens so much in certain areas, they don’t even bother repairing it!

 

[TwoBlocked]

OP says correct voltage at handhole, but incorrect at vac, with vac not working, frozen water in conduit. I'd say the black leg broke in the conduit, but too much resistance in the water/ice to trip a breaker, and also too much resistance to run the vac, yet low enough resistance to energize the part of the black conductor going to where it can be read by the meter. A lower impedance meter (like the vac itself ) would show little voltage between the legs.

Yep "...rip out the vac, pull new wires, put the vac back gingerly without damaging the conductors."

 

[jaggedben]

After re-reading the op’s post, it is probably what Larry said, Egc is broken, and one leg is faulted.

Either way, OP is measuring to a box he thinks is bonded to neutral but it's not, and another leg is faulted.

 

[jaggedben]

... I tested at the pole vac to find 0 volts on the black and somehow 208 volts on the red conductor. ...

I'm assuming you're measuring from each conductor to the metal bell box or something else you're assuming is ground. Always helps to be clear; voltage is always between two points. As discussed above, the explanation probably includes that the thing you're measuring to that you think is bonded or grounded is not.