Help with Riser Diagram Question

[designer82]

Please see attached riser diagram for question.

I am reviewing a project and I think they came off the wrong place for the normal feed to the Life Safety ATS. They came off the house panel which is downstream of the Normal ATS.
They should come ahead of the normal ATS.

The second question I have is I think they have put in a lot of unnecessary OCPDs.

This is clearer in the picture... Thank you for your help.

Better pic here: https://ibb.co/P6gByFG

 

[GoldDigger]

It does not seem totally clear in this case. The operation of the Life Safety circuit is in no way dependent on the correct operation of the main ATS.

All this configuration does is remove the need for the circuit to transfer if the main alternate power is satisfactory. On the other hand it could unnecessarily cause the Life Safety ATS to transfer during a failed test of the main system.
Feeding the LS ATS from the output of thje main ATS could technically compromise the formal separation of the two circuits.

 

[designer82]

In this configuration....

Wouldn't the LS ATS transfer back to normal once the Main ATS transfers to the generator? Then you're feeding optional standby and LS from the Generator optional standby branch?


That's why I would think you'd want the normal feed to the LS ATS ahead of the main ATS.

 

[charlie b]

I agree that the normal source feeder to the life safety ATS should have originated upstream of the house panel ATS. Is this a code violation? Not so easy to tell. I think not. Is it a bad design? I think so. It places more components than are needed in the path of power to the LS panel, and that means there are additional failure modes.

I also agree that the two breakers immediately upstream of the LS ATS are unnecessary. But I don't see a code violation there either.

By the way, is there really a "life safety" panel? Is this a hospital? Is this a power source to emergency (article 700) components?

 

[charlie b]

Wouldn't the LS ATS transfer back to normal once the Main ATS transfers to the generator?

Depends on the type of ATS. If it is "normal seeking," meaning that it will automatically transfer to its normal source when it becomes available, then you are right. If it is "power seeking," meaning that it will stay on whatever source is presently powering it as long as that source remains available, then the answer is no.

Then you're feeding optional standby and LS from the Generator optional standby branch?

Since the optional standby system is not required to have selective coordination, a fault in that system could take out the main breaker on NPPH1. That would force the LS ATS to transfer to its backup source. Again, I would call this a poor design, but I still don't see a code violation.

 

[designer82]

Thanks Charlie.

I didn't know the level of detail available with ATS's (normal/power seeking). Maybe their intention is to have the main ATS "normal seeking" and have the LS ATS "power seeking". I guess in that case it would work fine. That would just leave the too many components ahead of the LS panel issue.