Service Entrance Conductor Grounding to Substation

[OdessaEE]

Here is the scenario:

There is a substation outside our gas facility (approximately 800'). We are running a set of conductors (6 -750MCM per phase underground) from a dedicated substation breaker to the main switchgear at the gas plant (MLO). This is the only connection to the substation from this facility. The transformer feeding the substation breaker is solidly grounded (they are considering installing a NGR). The breaker has 3 phase and ground fault protection only.

Here is my question:

There was no ground conductors ran from the substation to the plant switchgear. Is this required per the NEC? All the plant equipment is grounded adequately to the plant ground loop there is just no ground connection back to the substation. How does this change if there was a main breaker installed at the main switchgear at the plant instead of the MLO? Also if more than one piece of switchgear is fed from the breaker in the substation (tapped at the substation breaker).

I appreciate the help.

John

 

[dpc]

Ignoring the NEC for a moment - strictly from an engineering and safety perspective there should be a ground connection to the utility ground. You don't want the utility substation ground to be a different potential than your ground system. In addition, the utility ground may be one of the best grounding connections you have available.

You don't say what voltage this service is so it is difficult to be specific.

As for the NEC, Section 250.24 covers grounding connections for ac services. Basically, the NEC requires a grounding electrode conductor to be bonded to the grounded service conductor. As usual, there are some exceptions to this.

It's also difficult to see how a service with no main disconnect on premises is going to meet the NEC unless you meet the "six handle" rule at your main switchboard.

"An 'expert' is someone who has made every possible mistake in a very narrow field of study." -- Edward Teller

 

[OdessaEE]

The voltage is 4160V.

 

[rbulsara]

Short answer is yes, you need an equipment grounding conductor(s) (EGC) at the least. Building steel or other grounded surfaces are not a substitute for EGC (and NEC clarifies that). If you are lucky, and these feeder is in metal conduits, the conduits may be acceptable as EGC. I would not recommend it.

As dpc said you also need to have a main disconnect for the facility. NEC has explanation as to how to ground a campus style distribution system which you seem to have (feeding a building from a building).

If you are still confused, you need to hire a competent electrical engineer.