NEC 230.95 Ground Faulty Requirements

[mcnichol]

I am checking a project that involves the installation of a new electrical service for a Waste Water Treatment Process. The service is from the secondary of a new 480/277V wye connected 1500 KVA utility transformer. The secondary conductors are routed underground to a new standalone 2000 amp circuit breaker located outdoors near the transformer. The breaker load side conductors are routed to a Process Motor Control Center via a service entrance rated transfer switch. The MCC serves only 480V three phase three wire loads.
Given that there are no 277V single phase loads:
1) Do we have to run the neutral to the Motor Control Center?
2) Are we bound by the requirements of 230.95?

 

[jtester]

I believe the circuit to the MCC would be a feeder, and you wouldn't need a neutral. Your 2000 amp circuit breaker service disconnect does need a neutral, if available, run to it, and would need to offer GFI protection.

Jim T

 

[iwire]

Don't forget 215.10 as well if the feeder to the MCC is larger than 1000 amps.

Now I have question.

What does exception 3 of 215.10 mean?

 

[cpal]

Don't forget 215.10 as well if the feeder to the MCC is larger than 1000 amps.

Now I have question.

What does exception 3 of 215.10 mean?

Bob
The HB has an explanation that seem to answer your question,

The requiments are minimum standard and there is no restriction on providing GFPE on down stream feeders that are supplied by GFPE OCPD's upstream. But it appears to not be required.

 

[mcnichol]

NEC 230.95 Ground Fault Requirements

NEC 230.95 Ground Fault Requirements

I believe the circuit to the MCC would be a feeder, and you wouldn't need a neutral. Your 2000 amp circuit breaker service disconnect does need a neutral, if available, run to it, and would need to offer GFI protection.

Jim T

When you say that the 2000 amp circuit breaker does need a neutral " if available" do you mean at the transformer secondary terminals? In other words the secondary configuration dictates whether or not the neutral is run to the breaker.

 

[jtester]

When you say that the 2000 amp circuit breaker does need a neutral " if available" do you mean at the transformer secondary terminals? In other words the secondary configuration dictates whether or not the neutral is run to the breaker.

To be technically correct, I should use the term grounded conductor. 250.24(C) requires the grounded conductor to be run to the service disconnect where the AC system is grounded. If the utility offers a 277/480 volt service that is grounded, you must connect the neutral at the service disconnect. It doesn't have to be run in feeders, but does to the service.

Jim T

 

[mcnichol]

Isn't the ground fault protective equipment designed to protect the load side conductors and equipment? How would this be possible if we only run a grounded conductor to the service breaker and not from it to the downstream service equipment. Did I misunderstand?

 

[pete m.]

At your 2000 amp service disconnect the grounded conductor(s) that you brought from the utility transformer will be bonded to the equipment enclosure, GES, etc...

From the service disconnect you will be entering the building with a feeder assembly that will most likely contain equipment grounding conductors sized in accordance with 250.122(f) for a parallel installation.

In the event of a ground fault the fault current will utilize the equipment grounding conductors back to the service disconnect which has the GFP.

Pete

 

[steve66]

What does exception 3 of 215.10 mean?

It just means you don't have to provide more than one Ground fault Protection device per feeder. It's for the times when additional disconnects on the same feeder are either required or installed for convience. (Notice the basic requirement says each "disconnect" requires GFPE).

So you basically put the GFPE on the first disconnect.

It might also be used in the case of a 2000A feeder supplying two 1000 amp feeders. GFPE is required for the 2000A feeder. Since the 1000 amp feeders are also protected by the 2000A GFPE, you don't have to install additional GFPE sensors and trip units.

Steve

 

[acrwc10]

It just means you don't have to provide more than one Ground fault Protection device per feeder. It's for the times when additional disconnects on the same feeder are either required or installed for convience. (Notice the basic requirement says each "disconnect" requires GFPE).

So you basically put the GFPE on the first disconnect.

It might also be used in the case of a 2000A feeder supplying two 1000 amp feeders. GFPE is required for the 2000A feeder. Since the 1000 amp feeders are also protected by the 2000A GFPE, you don't have to install additional GFPE sensors and trip units.

Steve

would this mean that you could use two 1000a gfpe's to keep the loads protected but sepperate, so if one trips the other would remain on?and not use the 2000a main gfpe ?