Fused Contactor without Overload Relay

[elmatador]

Hi All,

I have run into an existing installation where a 4.16kV Fused Contactor (360A) with 100E fuses feeds a 500kVA 4.16kV/480V transformer. There is a zero sequence CT and ground fault relay for the feeder which trips the contactor but there isn't any overload relay nor phase CT's. This is rather strange for me as there is no overload protection provided on this feeder cell. The fuses will only interrupt the higher fault currents but won't provide overload protection. On the 480V side there is a 600AT circuit breaker. In an overload situation the 600AT breaker would trip, line-line faults would be covered by both the fuse and the 600AT breaker, and line to ground faults will be covered by the ground fault relay opening the contactor. Looks like all the bases are covered.

Are there any issues here? I would imagine that a manufacturer wouldn't build something like this if it was a safety concern. It's just something I have never seen.

Please let me know your thoughts on this.

 

[waross]

Overload protection may be provided on the secondary side of a transformer. Under normal operations including overloads, the current on the secondary is proportional to the primary current.
Under fault conditions, including internal transformer faults, the fuses will provide protection.

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

 

[elmatador]

Thanks for your response Waross. I take it then this type of setup is acceptable?

 

[waross]

Yes. If the overload protection is on the secondary, the primary fuses may be more easily selected to withstand the transformer inrush.

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

 

[jraef]

Overload relays are for motors anyway. They do not count as OCPD devices for loads other than motors.

"Will work for (the memory of) salami"

 

[elmatador]

Thank you all for your response. What I meant was overcurrent protection. But either way the secondary protection would trip on overcurrent. Looks like this is fine.

 

[oldfieldguy]

The contactor is not rated to interrupt fault current. The fuses handle that, and should be sized accordingly.

old field guy