Single point ground on a ct circuit

[111ggg]

After much on the job discussion, what is the primary reason to have just a single point ground on a CT circuit?

 

[scottf]

So you don't get circulating ground currents that would impact the accuracy of the measurement.

Steadfast rule for secondary grounds on VT and CT circuit is the secondary circuit must have a ground reference and it should only be grounded at one point.

 

[waross]

When a circuit is grounded at more than one point, the ground path becomes an impedance in parallel with the intended current path. The circuit voltage drop may not be as calculated.
An even more serious issue is related to scottf's post. In the event of a major system fault, there may be high ground fault currents that may cause voltage gradients. A voltage gradient between multiple ground points of a protection circuit may cause unintended results such as a failure to trip or a false trip. A voltage gradient between multiple ground points may cause unintended currents in CT metering or protection circuits.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[davidbeach]

Or the multiple grounds could be such that some of the current by-passes the relay and it fails to trip when it should.

 

[Kiribanda]

111ggg,
Ground faults on secondary wiring are possible. When there is a ground fault on any of the two wires then both wires are grounded
and there is no open circuit in the secondary circuit.