Why the need for a second disconnect?

[mbrooke]

Why would you need a disconnect between the two bus disconnects and circuit breaker? It seem completely redundant to me- but a well respected EE book seems to make it out as necessary (see #2 to the right in the second picture). :huh:

 

[GoldDigger]

I would say that it is there so that you can always have one switch that opens the circuit regardless of which bus it is connected to.
Only one switch to lockout instead of two when the load or circuit is to be maintained

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[mbrooke]

I would say that it is there so that you can always have one switch that opens the circuit regardless of which bus it is connected to.
Only one switch to lockout instead of two when the load or circuit is to be maintained

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Switching, lockout, and tagging type deal then?

 

[Tony S]

I don’t know if it is still the case, early HV live tank breakers had accompanying isolators to reduce the stress on the primary breaker once it had opened.

Look for ISBN 095389712-1-4

 

[mbrooke]

I don’t know if it is still the case, early HV live tank breakers had accompanying isolators to reduce the stress on the primary breaker once it had opened.

Look for ISBN 095389712-1-4

I hear you, but not getting anything on Google

 

[rian0201]

Why would you need a disconnect between the two bus disconnects and circuit breaker? It seem completely redundant to me- but a well respected EE book seems to make it out as necessary (see #2 to the right in the second picture). :huh:

The answer is already provided in your 2nd pic.


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[GoldDigger]

The answer is already provided in your 2nd pic.


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I see it saying that it is necessary. I do not see it explaining why.

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[rian0201]

maintenance for the buses, is that not a reason? maybe we are expecting something big..


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[GoldDigger]

maintenance for the buses, is that not a reason? maybe we are expecting something big..


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Would not opening the bus switches be sufficient for that even without the additional switch at the load side?

 

[adamscb]

It could have something to do with the location of the disconnects. For example, let's say the two Bus disconnects are in a separate room from the circuit breaker. In that case, doesn't it say in the NEC that the disconnecting means must be in line-of-sight of the equipment it disconnects? May be wrong.

 

[mbrooke]

maintenance for the buses, is that not a reason? maybe we are expecting something big..


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But you already have one switch for each bus, and in turn each switch for the breaker.