Isolating Switch vs Disconnect

[JGinIndy]

I seem to be letting this confuse me when I look at for example 404.8(A) exception 3 and or 501.115(B(2) In definitions is what is throwing me for a loop “ It is intended to be operated only after the circuit has been opened by some other means “ I am new to the Forum and maybe y’all have had this discussion previously. Thanks

 

[paulengr]

In class E2 starters (over 1000 V) and a lot of utility equipment they often use switches that are not load break capable a lot. It is simple and cheap but does not have the capability of safely quenching an arc under load and certainly not during a fault. The major difference is most don’t have springs. Muscle power opens them. In say a starter it relies on the contactor to disconnect the load. Then the switch simply removes power with no load other than control power in the cabinet. Similar isolation switches are often used in utility substations.

In low voltage (under 1000 V) there is no significant cost incentive to do this.

 

[JGinIndy]

In class E2 starters (over 1000 V) and a lot of utility equipment they often use switches that are not load break capable a lot. It is simple and cheap but does not have the capability of safely quenching an arc under load and certainly not during a fault. The major difference is most don’t have springs. Muscle power opens them. In say a starter it relies on the contactor to disconnect the load. Then the switch simply removes power with no load other than control power in the cabinet. Similar isolation switches are often used in utility substations.

In low voltage (under 1000 V) there is no significant cost incentive to do this.

Thanks

 

[JGinIndy]

Thanks