480V 3W/4C Wye/Delta? Bare neutral?

[schmieden]

I'm working in a building in an industrial park where there is 100amp 480v 3~ service being fed from a non-fused disconnect that is attached directly to the supply side of a meter, and is located within a "meter shed" about 150' away from the building I'm working in. The "meter shed" is being fed from a substation on the other side of the park where the utility comes in. The service is carried over for that 150' or so, from the non fused disconnect in the shed to a fused disconnect (fused at 90A) within the building I'm working in, via a 2-2-2-4 aluminum SER cable. The three insulated conductors are connected to the line terminals of the disconnect and the bare conductor is attached to a lug that is thru-bolted to the case of the disconnect.

Judging by the appearance of this service, it physically looks like it would be 3 wire 480 Delta, and the conductors are coded brown/orange/yellow like it's a Delta. When I put my volt meter on these conductors, i get approx. 480V between each of the three phases, however, I get approx. 277 volts from each phase to the bare conductor. It's my understanding that this would not be possible from a Delta configuration, but with a WYE configuration, there should be 4 insulated conductors and one bare EGC, thus the SER cable should be a 5C. I would not be at all surprised if the park owners had a 4C cable run to save $$$.

My question, is it possible that the bare conductor is being used as the neutral and as an EGC simultaneously? This sounds like it would be a violation and unsafe. Can this bare conductor carry current like in SEU cable in residential service? I've heard of situations like in MCC's where the supply is a 4W - WYE config. but only the three ungrounded conductors and an EGC are utilized and the neutral isn't pulled for cost savings. If that's the case here and the bare conductor is just an EGC, where is the reference back to the center point of the WYE coming from?

I've attached 3 pictures, 1 of the Meter/NF disconnect in the the meter shed, 1 closeup of the NF disconnect, and 1 of the Fused disconnect in the building.

Please enlighten me

 

[Jim1959]

If there are no 277 volt line to neutral loads, it is just a 480 volt 3 wire system sourced from a wye connected transformer and the bare conductor is indeed an EGC and you should be fine. Depending on when it was installed, it may have met code at that time, however current code would require a grounded conductor to the service disconnect if I'm not mistaken.

 

[drcampbell]

What is it feeding? If none of the loads use 277 volts, there's no need for a neutral and the bare wire is only a ground.

 

[texie]

I'm working in a building in an industrial park where there is 100amp 480v 3~ service being fed from a non-fused disconnect that is attached directly to the supply side of a meter, and is located within a "meter shed" about 150' away from the building I'm working in. The "meter shed" is being fed from a substation on the other side of the park where the utility comes in. The service is carried over for that 150' or so, from the non fused disconnect in the shed to a fused disconnect (fused at 90A) within the building I'm working in, via a 2-2-2-4 aluminum SER cable. The three insulated conductors are connected to the line terminals of the disconnect and the bare conductor is attached to a lug that is thru-bolted to the case of the disconnect.

Judging by the appearance of this service, it physically looks like it would be 3 wire 480 Delta, and the conductors are coded brown/orange/yellow like it's a Delta. When I put my volt meter on these conductors, i get approx. 480V between each of the three phases, however, I get approx. 277 volts from each phase to the bare conductor. It's my understanding that this would not be possible from a Delta configuration, but with a WYE configuration, there should be 4 insulated conductors and one bare EGC, thus the SER cable should be a 5C. I would not be at all surprised if the park owners had a 4C cable run to save $$$.

My question, is it possible that the bare conductor is being used as the neutral and as an EGC simultaneously? This sounds like it would be a violation and unsafe. Can this bare conductor carry current like in SEU cable in residential service? I've heard of situations like in MCC's where the supply is a 4W - WYE config. but only the three ungrounded conductors and an EGC are utilized and the neutral isn't pulled for cost savings. If that's the case here and the bare conductor is just an EGC, where is the reference back to the center point of the WYE coming from?

I've attached 3 pictures, 1 of the Meter/NF disconnect in the the meter shed, 1 closeup of the NF disconnect, and 1 of the Fused disconnect in the building.

Please enlighten me

If this is a 480Y/277 grounded system from the POCO you could have a bare grounded conductor up to the service disconnect per 230.41. This conductor must terminate in a neutral bar that has a main bonding jumper. After the service disconnect, if there are no line to neutral loads, you could have a bare EGC and no grounded conductor.
Note that the bare conductor from the POCO to the service disconnecting means is a grounded conductor, not an EGC. There is no EGC on the line side of a service. After the service disconnect it will become an EGC.
If there are any line to neutral loads then you will need both a grounded conductor and an EGC on the load side of the service.

 

[don_resqcapt19]

This could be a 3 wire ungrounded delta. Often the capacitance to ground will give you the 277 volt reading, even on an ungrounded system.

 

[schmieden]

If there are no 277 volt line to neutral loads, it is just a 480 volt 3 wire system sourced from a wye connected transformer and the bare conductor is indeed an EGC and you should be fine. Depending on when it was installed, it may have met code at that time, however current code would require a grounded conductor to the service disconnect if I'm not mistaken.

What is it feeding? If none of the loads use 277 volts, there's no need for a neutral and the bare wire is only a ground.

If this is a 480Y/277 grounded system from the POCO you could have a bare grounded conductor up to the service disconnect per 230.41. This conductor must terminate in a neutral bar that has a main bonding jumper. After the service disconnect, if there are no line to neutral loads, you could have a bare EGC and no grounded conductor.
Note that the bare conductor from the POCO to the service disconnecting means is a grounded conductor, not an EGC. There is no EGC on the line side of a service. After the service disconnect it will become an EGC.
If there are any line to neutral loads then you will need both a grounded conductor and an EGC on the load side of the service.

It's feeding a 480 panel board which is feeding a small load of machine motors and a 480V delta pri. - 120/240 sec. 1~ xfmr, so there are no 277V loads. There is an approved inspection tag on the fused disconnect dating back to 2000/01. I guess what I'm trying to understand then is:

1) will this EGC effectively carry a GFC back to the utility? If you look close in the pics of the NF disconnect at the meter, there is a bare stranded copper conductor nutted to the bare from the SER. I'm guessing that copper comes over from the sub station but I dont know. There def. is no neutral bar in the NF disconnect and therefore no MBJ.

2) If it is indeed a 3 wire service and the bare conductor is just an EGC, how is it referencing 277V from each phase to ground? Is it because somewhere back in the system there is in fact a MBJ making the System Neutral and this EGC common, and therefore I can be confident about the EGC's ability to return a GFC?

 

[schmieden]

This could be a 3 wire ungrounded delta. Often the capacitance to ground will give you the 277 volt reading, even on an ungrounded system.

If that's the case, would it consistently read 277v to ground on each phase or would it vary from time to time.

Other than that, is there a sure fire way to know if it's Delta or does it not matter since there are no loads requiring 277/a neutral/

Are there any safety concerns with that type of Delta service?

 

[GoldDigger]

If that's the case, would it consistently read 277v to ground on each phase or would it vary from time to time.

Other than that, is there a sure fire way to know if it's Delta or does it not matter since there are no loads requiring 277/a neutral/

Are there any safety concerns with that type of Delta service?

The sure fire way to tell a grounded wye from an ungrounded deltta is to try to carry more current than just the input current of a high impedance meter between any line and ground (or the POCO neutral if available.)

A low wattage 277V+ lamp would be one possible load.

 

[don_resqcapt19]

If that's the case, would it consistently read 277v to ground on each phase or would it vary from time to time.

Other than that, is there a sure fire way to know if it's Delta or does it not matter since there are no loads requiring 277/a neutral/

Are there any safety concerns with that type of Delta service?

It will vary, especially if there is any type of ground fault. You could use a digital volt meter and a solenoid voltage tester to check. Hook the digital meter between one phase and ground and the solenoid voltage tester between another phase and ground. If the reading on the digital meter changes, it is an ungrounded system.

It really doesn't matter as long as there are no line to neutral loads.

The biggest safety issue is that a second ground fault creates a line to line fault on the path between the two faults. Current codes require a ground fault alarm for ungrounded systems, but I don't think the older codes did. There is also the possibility of a arcing or restriking ground fault causing high system voltage, in some cases high enough to damage motors and other equipment.

 

[kwired]

If this is still "service conductors" at the destination of the SE cable, then the bare conductor is the grounded service conductor and your fused disconnect is the service disconnecting means. Whether or not the disconnect back near the meter should be fused and be the service disconnecting means might be a good question though and we would need better details of what you have to determine that. If this SE cable is routed inside of building(s) I'd definitely say the service disconnect should be ahead of it, but if outside it may be just fine for it to be used as service conductors.

 

[schmieden]

The sure fire way to tell a grounded wye from an ungrounded deltta is to try to carry more current than just the input current of a high impedance meter between any line and ground (or the POCO neutral if available.)

A low wattage 277V+ lamp would be one possible load.

If I'm understanding correctly, hooking up the 277V load, in this case a lamp, between L-N, if its an ungrounded Delta, the lamp won't light, but if it's a WYE it will?

If the lamp does light, confirming it's a WYE, that doesn't necessarily prove that the bare conductor is the neutral, correct?

 

[schmieden]

It will vary, especially if there is any type of ground fault. You could use a digital volt meter and a solenoid voltage tester to check. Hook the digital meter between one phase and ground and the solenoid voltage tester between another phase and ground. If the reading on the digital meter changes, it is an ungrounded system.

It really doesn't matter as long as there are no line to neutral loads.

The biggest safety issue is that a second ground fault creates a line to line fault on the path between the two faults. Current codes require a ground fault alarm for ungrounded systems, but I don't think the older codes did. There is also the possibility of a arcing or restriking ground fault causing high system voltage, in some cases high enough to damage motors and other equipment.

Does this work on the same principle as GoldDigger's method of using a low wattage 277V load like a lamp, i.e., the current draw of the solenoid tester will cause voltage fluctuation?

 

[kwired]

If I'm understanding correctly, hooking up the 277V load, in this case a lamp, between L-N, if its an ungrounded Delta, the lamp won't light, but if it's a WYE it will?

If the lamp does light, confirming it's a WYE, that doesn't necessarily prove that the bare conductor is the neutral, correct?

only connect one load from line to ground (on an ungrounded delta) and you have no complete circuit for current to flow, but you did effectively "impedance ground" that one line.

connect three loads, one to each line and to a common point - that common point becomes a neutral. If all three loads are of the same resistance then that neutral will be balanced at ~277 volts to each line, if you ground that point you will measure same thing as you would with 480/277 wye system, though the "neutral is not derived from within the source itself.

 

[schmieden]

If this is still "service conductors" at the destination of the SE cable, then the bare conductor is the grounded service conductor and your fused disconnect is the service disconnecting means. Whether or not the disconnect back near the meter should be fused and be the service disconnecting means might be a good question though and we would need better details of what you have to determine that. If this SE cable is routed inside of building(s) I'd definitely say the service disconnect should be ahead of it, but if outside it may be just fine for it to be used as service conductors.

What kind of details would you need? So far the farthest back I've been able to trace the service is this meter shed, but I could probably convince park mtc. to let me into the substation where the service from the POCO comes in. The SER cable exits the meter shed exterior wall, rises about 15' and runs along an exterior wall, outside of the buildings, for the entire ~150', then enters the building I'm working in and drops about 10' to the fused disconnect.

 

[kwired]

What kind of details would you need? So far the farthest back I've been able to trace the service is this meter shed, but I could probably convince park mtc. to let me into the substation where the service from the POCO comes in. The SER cable exits the meter shed exterior wall, rises about 15' and runs along an exterior wall, outside of the buildings, for the entire ~150', then enters the building I'm working in and drops about 10' to the fused disconnect.

Start with locating the "service point". If this "service shed" is on the supply side of the service point, then I'd say the cable is definitely a service cable and separate grounded and equipment grounding conductors are not needed.

If it is an older installation however it once was permitted to supply separate buildings or structures with just one grounded conductor also, and still is exceptions in code to allow those to remain.

The "meter shed" leaves some questions though on whether there should be service disconnecting means in there though, but if it is ahead of the service point, then it is not even covered by NEC.

 

[don_resqcapt19]

Does this work on the same principle as GoldDigger's method of using a low wattage 277V load like a lamp, i.e., the current draw of the solenoid tester will cause voltage fluctuation?

Yes, it will work the same, but in addition, it is unlikely that the lamp will light if it is an ungrounded system.