Utility C/T ?

[Mike01]

On utility secondary services are C/T cabinets usually grounded? From the C/T cabinet drawing from the utility It indicated three phases and neutral from the utility xfmr. (not bonded N-G until it lands in the switchboard inside the building however the C/T is on the exterior of the bldg between the xfmr, and switchboard? Does this mean that the conductors from the xfmr to main switch are "ungrounded" since not N-G connection is made in the xfmr, and only 4-conductors are installed from the xfmr to the main switch?

 

[roger]

I always bond the CT can one way or another regardless of any drawings from a POCO.

Nowdays most CT services I install the CT's are located in the pad mount utility owned transformer.

Roger

 

[Mike01]

ct

ct

I was just curious about this and was interested in others opinions and experiences; thanks roger. The other alternative I just discovered is to intergraded the C/T compartment into the incoming on the switchboard where applicable. (Utility requires this for services over 1200A according to their literature).

 

[tryinghard]

On utility secondary services are C/T cabinets usually grounded? From the C/T cabinet drawing from the utility It indicated three phases and neutral from the utility xfmr. (not bonded N-G until it lands in the switchboard inside the building however the C/T is on the exterior of the bldg between the xfmr, and switchboard? Does this mean that the conductors from the xfmr to main switch are "ungrounded" since not N-G connection is made in the xfmr, and only 4-conductors are installed from the xfmr to the main switch?

Yes they should be bonded (grounded) especially when remote. If a XRMR is bonded to it's frame and ground (like the XO) the system is a "grounded type" it is this bonding that qualifies the type as grounded or ungrounded.

 

[Mike01]

Utility

Utility

Yes they should be bonded (grounded) especially when remote. If a XRMR is bonded to it's frame and ground (like the XO) the system is a "grounded type" it is this bonding that qualifies the type as grounded or ungrounded.

Yes the transformer is "grounded" the frame is connected to ground on the delta primary side the wye secondary is grounded at the first disconnecting means (MCB) located about 200' from the xfmr. The utility does not bond the N-G at their (utility owned) xfmr. However the C/T cabinet is located only 50' from the xfmr. on the exterior of the building.

 

[pete m.]

Yes the transformer is "grounded".... However the C/T cabinet is located only 50' from the xfmr. on the exterior of the building.

I think that 250.4(A) 3-5 addresses the requirements for bonding the C/T cabinet.

250.92(A) and (B) give you the "things" that are required to be bonded and the method for the bonding.

Pete

 

[kwired]

Yes the transformer is "grounded" the frame is connected to ground on the delta primary side the wye secondary is grounded at the first disconnecting means (MCB) located about 200' from the xfmr. The utility does not bond the N-G at their (utility owned) xfmr. However the C/T cabinet is located only 50' from the xfmr. on the exterior of the building.

Are you sure the neutral is not bonded at the transformer, Utilities will not run separate neutral and ground but their grounded conductor is usually bonded to everything in close proximity on all installations as well as to at least one man made electrode.