480 volt grounded B on parking lot lighting....grounding questions

[mollydodger]

I have an existing installation at a shopping center. I believe a non licensed sign company did it orriginally. I was called out because another sign company was changing some lamps/ballasts and the technician said he was getting shocked when in contact with one of the poles. I realize there are too many NEC issues with the installation to list here so I will try to address a couple of questions. First, the lighting circuit conductors are run underground (in conduit). There are a total of 9 circuits. Each circuit consists of ONLY two conductors. There are NO equipment grounding conductors present and no "grounded" conductors. I believe they should be run with the ungrounded conductors for each circuit. Am I correct?

As I see it, if there is presently a fault to ground at a pole there is no way the OCPD will "see" it and there is a strong possibility that a voltage potential could be imposed at the pole resulting in the shocking.

All advice appreciated.

 

[PEDRO ESCOVILLA]

if i read your post right, no equipment ground and no neutrals (grounded conductors) . how are the lights working. an egc and neutral needs to be pulled. theres probably an neutral, just no egc and none back to the panel. and yeah, thats probably why he's getting shocked. no cb will pick up fault w/o egc

 

[petersonra]

no need for a grounded conductor (the B phase in this case) if it is not being used.

they do need EGCs though.

you would have thought someone would have mentioned being shocked by light poles a long time ago.

is there some chance they are using the light pole as the return?

 

[Smart $]

.... There are a total of 9 circuits. Each circuit consists of ONLY two conductors. ...

no need for a grounded conductor (the B phase in this case) if it is not being used.

...

Seems odd with 9 circuits on a 3? and all are connected A to C...

...but considering OP believed a non-licensed (and perhaps more to the fact, unqualified) sign contractor installed them, they were probably not aware A to grounded-B and C to grounded-B circuits would give them 480V circuits too.

Actually, they could run 3? circuits. Hmm... have to think about if the existing conductors could be reconfigured to change at least one to an EGC. Need more info on how the circuit are routed: conduits plus number and size of wires in each, number of poles and load contribution of each...

 

[augie47]

It makes no difference in the fact that an equipment grounding conductor is essential for safety, but from your original post I'm unsure if you are telling us "B" went to ground, or you have a B phase grounded system. Since it's a shopping center, I would imagine the 1st assumption and the premises service is 480/277.
On a 480/277 grounded supply, your hit the nail on the head that without an equipment ground you have no way of tripping the over-current device on a one phase fault.
On either system you have a significant shock hazard.

 

[hillbilly1]

It makes no difference in the fact that an equipment grounding conductor is essential for safety, but from your original post I'm unsure if you are telling us "B" went to ground, or you have a B phase grounded system. Since it's a shopping center, I would imagine the 1st assumption and the premises service is 480/277.
On a 480/277 grounded supply, your hit the nail on the head that without an equipment ground you have no way of tripping the over-current device on a one phase fault.
On either system you have a significant shock hazard.

I agree, this most likely is a 277/480 volt system, and one phase has went to ground. Because a plain earth return, and even though the poles likely have ground rods in them, will have high enough resistance to not trip the ocp. If all the loads are straight 480, take an ammeter and clamp it around all three phases at the same time of each three or two breaker (whichever is used) with all loads on. You will probably find that one of the 9 (3 if you are meaning 9 wires) will show an amp draw, probably 3-10 amps. That circuit will be the one with the fault. That still does not solve your ground problem, but at least you can narrow down where the fault is, and remove the exsiting shock hazard.

 

[hillbilly1]

Re-read your post, and you did say two wire, so it should be two pole breakers.

 

[kwired]

First thing you need to do is confirm whether or not this is a grounded B phase system or a 277/480 volt system.

Next confirm what operating voltage is supposed to be with ballasts. If they are 480 volt ballasts then you need at least two conductors with 480 volts between (any of them can be the grounded B phase conductor) them plus an equipment grounding conductor that carries no current except in a fault condition.

If they are 277 volt ballasts then you need one ungrounded conductor and the grounded neutral conductor at each ballast - plus an equipment grounding conductor that carries no current except in a fault condition.

If in either case the grounded circuit conductor is relying on the pole, base, or ground rod for circuit continuity, you will have shock hazards.

 

[charlie b]

I used to be good at math. :huh: Nine conductors are in the conduit, and each circuit has two wires. 9/2 = 4.5. What's with the half-circuit? :?

You don't need a neutral (grounded) conductor, if the lights are all 480 volt single phase. Are you dealing with a grounded delta, as some have suggested? Or are you dealing with three circuits, each a 3-phase circuit with a 3-pole breaker, and with lights along the run alternately being wired A-B for one light, and B-C for the next light, and C-A for the next light, and so on?

As to the shock, the presence of an EGC would have prevented that. It would also have caused a breaker to trip, which would have alerted someone to the problem before a person received a shock.

 

[petersonra]

I used to be good at math. :huh: Nine conductors are in the conduit, and each circuit has two wires. 9/2 = 4.5. What's with the half-circuit? :?

You don't need a neutral (grounded) conductor, if the lights are all 480 volt single phase. Are you dealing with a grounded delta, as some have suggested? Or are you dealing with three circuits, each a 3-phase circuit with a 3-pole breaker, and with lights along the run alternately being wired A-B for one light, and B-C for the next light, and C-A for the next light, and so on?

As to the shock, the presence of an EGC would have prevented that. It would also have caused a breaker to trip, which would have alerted someone to the problem before a person received a shock.

The OP is pretty unclear about a lot of things. It does seem clear that whoever wired this thing up might have done so incorrectly. However, it is not clear that the EGC is missing as the OP mentions the wiring was run in conduit UG, but does not say what kind of conduit was used. metal conduit would make for an acceptable EGC if it was properly bonded to the light pole and at the source.

 

[augie47]

Mollydodger, Let us know how things turned out, please.

 

[Electric-Light]

Do corner ground delta loads on A-B, B-C require one pole while A-C requiring two pole switching?

I understand that B is treated as neutral and shouldn't be fused at subpanel.

 

[Smart $]

Do corner ground delta loads on A-B, B-C require one pole while A-C requiring two pole switching?

I understand that B is treated as neutral and shouldn't be fused at subpanel.

Yes... I think.

One phase AB or BC loads = one-pole breaker
One phase AC loads = two-pole breaker
Three phase ABC loads = two-pole breaker

 

[Electric-Light]

Yes... I think.

One phase AB or BC loads = one-pole breaker
One phase AC loads = two-pole breaker
Three phase ABC loads = two-pole breaker

I wonder how ballast durability compare in long term, especially for those newer 347-480v rated electronic ones.

In Canucka and newish US setup, the case to inside is 277 to 347v, but when used in corner ground, everything is subject to 480v against the case.

Wouldn't two pole for corner ground delta require a higher rated gear than two pole 480 wye, much like 240 rated as opposed to 120/240 two pole since a phase to ground shorts places the need for one pole to interrupt 480v?

 

[Smart $]

I wonder how ballast durability compare in long term, especially for those newer 347-480v rated electronic ones.

In Canucka and newish US setup, the case to inside is 277 to 347v, but when used in corner ground, everything is subject to 480v against the case.

Wouldn't two pole for corner ground delta require a higher rated gear than two pole 480 wye, much like 240 rated as opposed to 120/240 two pole since a phase to ground shorts places the need for one pole to interrupt 480v?

Yes, breakers must be full-rated 480V. Have no info on ballast durability.

 

[GoldDigger]

However, it is not clear that the EGC is missing as the OP mentions the wiring was run in conduit UG, but does not say what kind of conduit was used. metal conduit would make for an acceptable EGC if it was properly bonded to the light pole and at the source.

But getting a shock from touching the pole while grounded argues that even if the conduit is suitable for use as an EGC, it is not correctly installed or is not bonded to the pole.

 

[kwired]

Do corner ground delta loads on A-B, B-C require one pole while A-C requiring two pole switching?

I understand that B is treated as neutral and shouldn't be fused at subpanel.

B phase is not neutral it is simply "grounded conductor" and the ungrounded conductors of the system just happen to have 480 volts to this conductor. All three phases of the system are still 120 degrees apart, and a three phase motor runs just fine, just so happens one conductor is grounded. It is no different than the grounded conductor of a system that has 120 volts to ungrounded conductors. Connect a load rated for 120 volts between the grounded conductor and an ungrounded conductor and the load operates normally. People seem to go blank when they hear the term corner ground, they are simpler than most seem to think. You still run the grounded conductor to the service equipment or first disconnect and then from that point separate it into two conductors - grounded conductor, and equipment grounding conductor. Since it is grounded you don't put any overcurrent devices in it, except for exceptions allowed - generally a multipole breaker that opens all circuit conductors simultaneously.

I wonder how ballast durability compare in long term, especially for those newer 347-480v rated electronic ones.

In Canucka and newish US setup, the case to inside is 277 to 347v, but when used in corner ground, everything is subject to 480v against the case.

Wouldn't two pole for corner ground delta require a higher rated gear than two pole 480 wye, much like 240 rated as opposed to 120/240 two pole since a phase to ground shorts places the need for one pole to interrupt 480v?

You will have 480 volts from equipment to case, doesn't matter if you are using grounded phase in the circuit or not. It could be possible to find equipment marked with something like "voltage to ground not to exceed xxx volts". I do see this frequently on 240 volt rated equipment.

But getting a shock from touching the pole while grounded argues that even if the conduit is suitable for use as an EGC, it is not correctly installed or is not bonded to the pole.

Getting a shock could also mean that installer thought a ground rod was an acceptable equipment grounding method or even substitute for an actual grounded current carrying conductor.