Panelboards

[roger]

Not quite the same problem if the opening of that breaker on the service input side of the ATS triggers the generator to start and pick up the load through the ATS.
You would need two points of failure to create the same outage as the single point downstream of the ATS.

True, but if the EPSS is already running the show and whatever caused the normal side to go has not been cured we still have a single point of failure that is the concern.

The point is, if there is a problem with the loads or a fault from the Critical Panelboard opening the feeder OCPD, it is going to happen on both devices assuming they are the same values.

Roger

 

[Maders]

But, back to my earlier post, why would a designer want to put a main where one is not wanted or needed?

Roger

Great question. Depending on the location of the ATS there could be a perceived need for a local isolation means for maintenance, etc (which can conveniently be provided via a MCB in lieu of a MLO). There certainly is no prohibition on this practice. But like Pharon mentioned there probably should be.

 

[GoldDigger]

Great question. Depending on the location of the ATS there could be a perceived need for a local isolation means for maintenance, etc (which can conveniently be provided via a MCB in lieu of a MLO). There certainly is no prohibition on this practice. But like Pharon mentioned there probably should be.

Which leads to the very interesting question of whether you can put a grossly oversized CB into an MCB panel just for use as a switch, as long as the panel is properly protected by an upstream OCPD? I am sure it would really surprise someone looking at it later, but would it pass code?

 

[Pharon]

Or you could just make it a molded case switch - it would have instantaneous protection still, though. Better off to eliminate it completely. Otherwise you eliminate the reason you added the extra source in the first place.

It's funny to see so much energy focused on selective coordination being justified as such a "safety" issue, but when it comes to allowing a single point of failure like this in an emergency system it's simply a "design" issue.

 

[Maders]

Which leads to the very interesting question of whether you can put a grossly oversized CB into an MCB panel just for use as a switch, as long as the panel is properly protected by an upstream OCPD? I am sure it would really surprise someone looking at it later, but would it pass code?

Unless the ATS serves optional stand by loads, I'm pretty sure the selective coordination zealots would take issue with this practice. (assuming we are still discussing OCPDs downstream of an ATS)

 

[david]

Isn't the issue of an ATS frailer the reason why critical loads in a hospital have outlets on both the normal branch and the critical branch or outlets from two different ATS. A hospital has the design choice of serving these critical areas from two different ATS

I can see though manually transferring equipment from one outlet to another serving the same area could be time critical but at least if the area was served through two different critical branches they would at least have that option.

 

[Pharon]

Time critical is an understatement. 10 patient care floors, half of which contain ICUs - let's just say 'hypothetically' that exercise might take 12 hours or so. Good thing it wasn't the Friday before Christmas or anything. Hypothetically.

 

[Maders]

Time critical is an understatement. 10 patient care floors, half of which contain ICUs - let's just say 'hypothetically' that exercise might take 12 hours or so. Good thing it wasn't the Friday before Christmas or anything. Hypothetically.

losing one ventilator in a NICU for 12 seconds is a nightmare.