Fault path and protection

[Isaiah]

I’m concerned with this design from the engineering firm. There’s no CB or Fused switch on two of the feeders. The upstream CB at the SWGR protects both. The cables are all the same size, but it just doesn’t look right. Shouldn’t there be additional OCPDs on the two?


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[ptonsparky]

Distance will make a difference when using taps.
Explain 800AF & 320AT. I'm drawing a blank on them.

 

[jim dungar]

The 350A trip setting of the 800A frame upstream breaker protects the downstream conductors which are 2 paralleled 2/0 conductors.
What is the 400A device, where you show the faults?
From this device you show 2 sets of parallel conductors feeding a common bus which has 2 300A fused switches.

It looks like you are showing current flowing from a fault into the 400A bus and then back down into the common bus, as if it was in a loop. Fault current would not flow in this path, as it can only come from a source.

Can you provide some identifiers on your drawing?
What do you think is happening?

 

[Isaiah]

The 350A trip setting of the 800A frame upstream breaker protects the downstream conductors which are 2 paralleled 2/0 conductors.
What is the 400A device, where you show the faults?
From this device you show 2 sets of parallel conductors feeding a common bus which has 2 300A fused switches.

It looks like you are showing current flowing from a fault into the 400A bus and then back down into the common bus, as if it was in a loop. Fault current would not flow in this path, as it can only come from a source.

Can you provide some identifiers on your drawing?
What do you think is happening?

I believe the circuitry is ok I just wanted to check with code forum to make sure I wasn’t crazy. There is no 400A device just a 400A bus


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[Isaiah]

Distance will make a difference when using taps.
Explain 800AF & 320AT. I'm drawing a blank on them.

You’re right. I need to check on the distances here but I don’t think anything is over 75 feet or so.


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[jim dungar]

You’re right. I need to check on the distances here but I don’t think anything is over 75 feet or so.


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You don't have a tap.
You have paralleled 2/0 conductors protected at 320A. It looks strange, but it meets code.

My concern would be the (2) paralleled sets of (2) paralleled conductors between your 400A equipment and the common bus.