480v service

[mitch cochrell]

I am bidding on a lift station that someone has vandelized and I am kind of stumped. The original service entrance conductors were installed in conduit under ground but there was no equipment ground or grounded conductor pulled in at the time of the installation. The voltage is 480v, 3 ph. Is this OK to do or does there need to be a ground pulled to the utility pole?

 

[Dennis Alwon]

If there is no disconnect at the pole then there is no need for an egc. Are these service conductors? Is there no neutral? Then it is a violation

 

[mitch cochrell]

Yes sir. They are service entrance conductors. There were three conductors installed and the service is 480v 3ph. The conductors enter into a disconnect. The ground rod is the only source of grounding.

 

[jumper]

Yes sir. They are service entrance conductors. There were three conductors installed and the service is 480v 3ph. The conductors enter into a disconnect. The ground rod is the only source of grounding.

As Dennis said, services require a neutral/grounded conductor, 250.24(C).

 

[iceworm]

Mitch -
There are a couple of possibilities I can think of besides, "The original installation was in violation."

The service could easily be corner grounded 480V 3 phase Delta.

The service could be un-grounded 480V 3 phase Delta. Not common for a utility to supply this - I don't recall having ever seen one.

I suggest asking the utility what the service is susposed to be - beats guessing.

ice

 

[Dennis Alwon]

If it is an ungrounded system then there is no need but somehow you need to bond the enclosures etc. if it is a grounded system. Is that the only voltage(service) at the building?

 

[tom baker]

I have seen this before, where there is a three phase service with no loads to neutral, the designer ( I did not say engineer) sees no need for a neutral. For 480V motors there is no neutral past the service but the neutral is actually a white wire with a green stripe.

And as pointed out make sure this is not a delta service.

 

[mitch cochrell]

If this service is corner grounded does that mean the equipment is rated differently or does it not matter? The equipment is 2 - 150 hp moters. There is a control panel as well.

 

[jumper]

If this service is corner grounded does that mean the equipment is rated differently or does it not matter? The equipment is 2 - 150 hp moters. There is a control panel as well.

Motors do not care which conductor, if any, is grounded. Grounded conductor should not be fused IIRC.

 

[Dennis Alwon]

Here is an article on the corner grounded delta. This is a system where one of the phase conductors of the 3-phase delta bank is intentionally grounded. Corner-grounded systems were used to supply services serving only a 3-phase load.

 

[jumper]

Motors do not care which conductor, if any, is grounded. Grounded conductor should not be fused IIRC.

Let me clarify what I meant: A 480V 3p motor will run off a ungrounded, corner grounded, or wye system just the same AFAIK.

If it gets 480V, it should be happy.

 

[kwired]

Is one of the three conductors connected to the grounding electrode and service enclosure somehow? If so that is the grounded phase. There can not be fuses in the grounded conductor if that is what you have, circuit breakers that break all lines (common trip) are acceptable.

 

[petersonra]

A few years ago we did a series of MCCs for some upgrades to wells in the area.

They were all previously 480V ungrounded delta.

For whatever reason, they were all being changed to 480/277 Y.

It did not affect us very much. none of the motors cared. we had to get service rated MCCs. As best I can tell the only difference was a terminal block installed in the incoming section labeled N for the neutral coming from the pole.

IIRC, on one of them Siemens sent us the terminal and nameplate for us to add as they had forgotten to put it in.

 

[kwired]

A few years ago we did a series of MCCs for some upgrades to wells in the area.

They were all previously 480V ungrounded delta.

For whatever reason, they were all being changed to 480/277 Y.

It did not affect us very much. none of the motors cared. we had to get service rated MCCs. As best I can tell the only difference was a terminal block installed in the incoming section labeled N for the neutral coming from the pole.

IIRC, on one of them Siemens sent us the terminal and nameplate for us to add as they had forgotten to put it in.

Ungrounded system will not need a terminal for an incoming neutral but will still need a grounding electrode system and all non current carrying metallic parts of the system including raceways, boxes, etc connected together via equipment grounding conductors just like a grounded system does. The ungrounded system does require ground fault detection system - once there is a fault the system still operates but is now grounded through that fault. If there would be a second fault on another phase it will be no different from when this happens on a grounded system. The whole idea of an ungrounded system is to allow for orderly shutdown instead of immediate shutdown when a ground fault occurs where there is a process that may possibly have catastrophic results if it is not shut down in an orderly manner.

 

[petersonra]

Ungrounded system will not need a terminal for an incoming neutral but will still need a grounding electrode system and all non current carrying metallic parts of the system including raceways, boxes, etc connected together via equipment grounding conductors just like a grounded system does. The ungrounded system does require ground fault detection system - once there is a fault the system still operates but is now grounded through that fault. If there would be a second fault on another phase it will be no different from when this happens on a grounded system. The whole idea of an ungrounded system is to allow for orderly shutdown instead of immediate shutdown when a ground fault occurs where there is a process that may possibly have catastrophic results if it is not shut down in an orderly manner.

We have done some service rated MCCs that are for 480 delta ungrounded. we used the three light scheme to detect ground faults.

afaik, the gec on those just connected to the normal ground bar down in the bottom wireway of the mcc.