No GFP on Existing 2500A Meter/Main....

[rr]

We're doing some modernizations for a school that was built in the 1970's.

We're replacing the original Switchgear with newer equipment. However, the 2500A Meter/Main will be existing to remain.

The Electrical Contractor has brought to our attention that the existing Meter/Main does not have GFP. The service is 120/240V, 1PH, 3W High Leg Delta. According article 230.95, it is required to have GFP.

However, since the Meter/Main is "existing to remain" are we still required to update the Main with GFP?

The Code is silent on this issue. I looked in the California Building Code in Chapter 34 Existing Structures and found this:

"3403.2 When Allowed. Additions, alterations or repairs may be made to any building or structure without requiring the existing building or structure to comply with all the requirements of this code, provided the addition, alteration or repair conforms to that required for a new building or structure."

I'm not sure which direction to go in. Any advice would be appreciated.

Thanks!

[ February 10, 2006, 02:43 PM: Message edited by: rr ]

 

[bob]

Re: No GFP on Existing 2500A Meter/Main....

The Electrical Contractor has brought to our attention that the existing Meter/Main does not have GFP. The service is 120/240V, 1PH, 3W High Leg Delta. According article 230.95, it is required to have GFP.

230.95 refers to a grounded Wye system.

 

[pierre]

Re: No GFP on Existing 2500A Meter/Main....

230.95... also greater than 150V to ground.

 

[jim dungar]

Re: No GFP on Existing 2500A Meter/Main....

Pierre,

The voltage from the high leg to grounded conductor is 208V. So IMO the only valid reason not to add GFP is the requirement that it be a wye system.

 

[pierre]

Re: No GFP on Existing 2500A Meter/Main....

Jim
That works for me.

 

[bob]

Re: No GFP on Existing 2500A Meter/Main....

Jim
How would a gfp work if the system is not grounded?

 

[jim dungar]

Re: No GFP on Existing 2500A Meter/Main....

A zero sequence sensor can be used on an ungrounded system. These sensors look at the magnetic field around a set of conductors. If all of the current flowing "out" is not balanced by the current flowing "back" then the system will operate.

A typical example is the use of a GFCI receptacle on a 2 wire ungrounded circuit.

 

[Zifkwong]

Re: No GFP on Existing 2500A Meter/Main....

Couldnt you also use an open delta to determine ground faults? It would probably be more expensive.

 

[templdl]

Re: No GFP on Existing 2500A Meter/Main....

If you're considering adding ground fault, yes you can do it with a zero sequence GFP by running all current carrying condictors through the center of the CT including the grounded conductor.

Or, you can can run the gounding conductor and through the CT which may be simpler that running all of the phase conductors an grounded conductor through the window of the CT. It's 6 of one 1/2 doz of the other as the current induced into the secondary of the CT will be the same. If you monitor the current on the grounding conductor it is as of a result of a GF. There are any number of these devices available.
Then, hopefully your breaker has the ability to add an optional shunt trip accessory for use with the GFR.

 

[rcwilson]

Re: No GFP on Existing 2500A Meter/Main....

I don't think open-delta ground fault detection system would work on a 120/240V delta system with a wild leg. The phase voltages to ground are not balanced.

The open-delta ground detector uses three identical voltage transformers with the primary windings connected phase-ground and the secondary windings connected in delta. One corner of the delta connection is left open and connected to a voltage relay and a stabilizing resistor. Theoretically, if all phases are balanced to ground, the secondary winding voltages add to zero in the delta and the relay sees nothing. When a phase is grounded, the corresponding leg of the delta secondary goes away, the relay sees a voltage and sends a trip signal.

One problem is this system does not respond to ground fault current. It can only be coordinated with other downstream protection by adding a time delay.