Disconnect vs. Circuit Breaker?

[MD88]

Hello,

I have a question about the difference between disconnect switches and circuit breakers, especially at voltage classes 5kV and above.

It's my understanding that circuit breakers are used to make/break current but disconnect switches are only to be used once the power is already cut to the line. So is the only point of having a disconnect switch that you have some added confidence that the power will stay off to a piece of equipment while it's being worked on? Thanks!

 

[zog]

Hello,

I have a question about the difference between disconnect switches and circuit breakers, especially at voltage classes 5kV and above.

It's my understanding that circuit breakers are used to make/break current but disconnect switches are only to be used once the power is already cut to the line. So is the only point of having a disconnect switch that you have some added confidence that the power will stay off to a piece of equipment while it's being worked on? Thanks!

MV switches come in 4 classes

Dead break
No load break
Load break
Interuptors


So the answer to your question depends on the class of switch you are refering to

 

[charlie b]

Circuit breakers and disconnect switches are equally capable of preventing the return of power, once they are opened and properly locked and tagged. The real difference is that a circuit breaker can trip open when it detects an overcurrent situation.

 

[rcwilson]

Depends on the rating of the disconnect. Some are rated for load breaking/making and can be used to turn onand off loads. Others are no load devices or have such a low rating that they are only good for energizing a short distribution line or an unloaded transformer that has the low voltage breaker open. In some cases the engineer uses a key interlock so the low voltage breaker must be open before the switch can be operated, like you guessed.

A fused disconnect is much cheaper than a circuit breaker and will do the job in most cases. The switch is used to turn on and off the circuit, the fuses provide the protection, just like at low voltage.