Small ATS feeding panels- OCPD required?

[greenspark1]

Hello,

I have several buildings that each have their own small 208/120V three phase generators. A typical building has a MDP which feeds the ATS and several other panels. The outdoor generator has a small built-in breaker which feeds the ATS, which then feeds an emergency panel EP nearby that is 100A main lugs only. This is not a required standby or emergency panel, just for prolonged winter outages- lights, some receptacles, boiler, etc.

My first question is if the ATS needs to have an OCPD to protect the load wiring. Otherwise you're relying on the upstream devices.

Second question is that there are some ATSs that are double lugged to EP1, EP2, EP3, etc (see photo). These don't have OCPD on the load side either and the EP panels are all MLO. I'm looking at 240.21(B)(1). Both the line and load side wires look about the same size, so that would comply with 240.21. Any other sections I should be looking to?

Third question- if the generator has an integrated breaker do you also need an external disconnect since it's an outside feeder? Seem a bit redundant, I'm not sure what purpose it serves. Thanks for any help!

 

[augie47]

Several things come to mind.....
(a)The conductors must be protected at their ampacity other than allowed by the tap rules. If your generator has a 100 amp breaker and all wiring is rated 100 amps or greater you should be good to go as far as the generator supply.
(b)You did not mention the utility supply to the ATS. The load side conductors would need to be protected by the utility side ATS breaker also (other than tap rules.
(c) 408.36 requires the panels to have an overcurrent device protecting it.
(with exceptions in that section)
(d) If you are feeding seperate buildings, Art 225 has an number of requirements for the panels in each building in Section II. Among them would be a main (or 6 disconnect rule).
(e) Satisfying Art 225 might cover this, but note the requirement in 702.11.

 

[greenspark1]

Thanks for the quick response. Here's my comments:

Several things come to mind.....
(a)The conductors must be protected at their ampacity other than allowed by the tap rules. If your generator has a 100 amp breaker and all wiring is rated 100 amps or greater you should be good to go as far as the generator supply.
(b)You did not mention the utility supply to the ATS. The load side conductors would need to be protected by the utility side ATS breaker also (other than tap rules.
The normal feed to the ATS is via breaker in the MDP.
(c) 408.36 requires the panels to have an overcurrent device protecting it.
(with exceptions in that section)
I believe one OCPD can supply multiple panels as long as the rating of the OCPD is less than that of each panel. Since both normal and emergency ATS feeds have a breaker, technically the EP panel is protected.
(d) If you are feeding seperate buildings, Art 225 has an number of requirements for the panels in each building in Section II. Among them would be a main (or 6 disconnect rule).
Each building has its own generator located directly outside feeding the ATS within the corresponding building. I don't think this section applies, but am curious if you disagree.
(e) Satisfying Art 225 might cover this, but note the requirement in 702.11.
These aren't portable generators.

 

[GoldDigger]

Re one OCPD protecting multiple panels, do not forget that the OCPD must also protect the wiring to those panels. If the panels are MLO you cannot terminate a tap conductor on them. I believe you also indicated that all of the wiring was protected, but I wanted to re-emphasize that here.

 

[augie47]

Several things come to mind.....
(a)The conductors must be protected at their ampacity other than allowed by the tap rules. If your generator has a 100 amp breaker and all wiring is rated 100 amps or greater you should be good to go as far as the generator supply.
(b)You did not mention the utility supply to the ATS. The load side conductors would need to be protected by the utility side ATS breaker also (other than tap rules.
The normal feed to the ATS is via breaker in the MDP.
Understand. Is that breaker sized at or below the ampacvity of the conductors on the "load" size of the ATS. If so, no problem, your conductors are protected by MDP or the Generator breaker.
(c) 408.36 requires the panels to have an overcurrent device protecting it.
(with exceptions in that section)
I believe one OCPD can supply multiple panels as long as the rating of the OCPD is less than that of each panel. Since both normal and emergency ATS feeds have a breaker, technically the EP panel is protected.
Agree
(d) If you are feeding separate buildings, Art 225 has an number of requirements for the panels in each building in Section II. Among them would be a main (or 6 disconnect rule).
Each building has its own generator located directly outside feeding the ATS within the corresponding building. I don't think this section applies, but am curious if you disagree.
Depends to some degree which Code cycle you are in. The 702.11 requirements relating back to 225.36 are in place in the '08.
(e) Satisfying Art 225 might cover this, but note the requirement in 702.11.
These aren't portable generators.
702 is not limited to portable generators

In summary, if your breakers in MDP and your generator breaker are both sized to protect the
conductors and buss rating of your panels, I see no problem on that issue.
Again, depending on the Code cycle and particulars, you might need a service rated disconnect where the generator supply enters the building to satisfy 225.36 and 702.11
(That may have changed in 2011, I don't have that Code handy)