Scenario:
Small mantrap that is part of egress route and is the pair of doors between the outdoor exit and the interior of building. Currently there is only one exit sign and one linear light fixture in this space, both are circuited to an ATS backed EM panel.
700.16(B) states:
"Emergency lighting systems shall be designed and installed so that the failure of any illumination source cannot leave in total darkness any space that requires emergency illumination"
700.17 states:
"Branch circuits that supply emergency lighting shall be installed to provide service from a source complying with 700.12 when the normal supply for lighting is interrupted. Such installations shall provide either of the following:
(1) An emergency lighting supply, independent of the normal lighting supply, with provisions for automatically transferring the emergency lights upon the event of failure of the normal lighting supply.
(2) Two or more branch circuits supplied from separate and complete systems with independent power sources. One of the two power sources and systems shall be part of the emergency system, and the other shall be permitted to be part of the normal power sources and system. Each system shall provide sufficient power for emergency lighting purposes."
This mantrap was flagged because per 700.16, the exit sign does not provide sufficient illumination for the space on its own, so another source of illumination is required for this area as a form of redundancy.
Typically, under the 2008 NEC we would just place another fixture in the area and circuit back to the same panel EM ATS backed panel. However, our AHJ has recently updated from enforcing 2008 to 2020 which caused some debate as to how to comply with 700.17 internally. Under 2008, 700.17(2) was written as follows: "Two or more separate and complete systems with independent power supply, each system providing sufficient current for emergency lighting purposes". Under the 2008, it was interpreted that having all lighting be fed off the same branch circuit was acceptable, however the most recent revisions of the code very explicitly say you must use two or more separate branch circuits as shown above in the excerpt.
Solution:
I think that it is easiest to comply with 700.17(1) in the case of this mantrap. We are going to spec a UL 924 battery backed bug-eye exit sign that can provide the necessary illumination. This way the mantrap can comply with both 700.17 and 700.16.
Remaining question about 700.17:
I am still confused about how 700.17(2) works under the latest revisions... in this exact same scenario, assuming I wanted to instead place another linear light fixture and keep the existing exit sign, I'd now have two lights in this space. Then I can go one of two routes:
(i) If I circuited one light to the EM ATS backed panel, and the other one to the normal power supply, this is now compliant because the area is being served by two separate power sources. Under an EM condition where all power is running off of generators, only the one light would be running now.
(ii) If I were to circuit both lights to the same EM ATS backed panel (even on different circuit breakers) this would now not be a compliant solution because they're not fed from independent power sources? Under an EM condition, now both lights would be running yet it would be less compliant than the previous situation of one EM / one normal supplied light described previously. Is there an error in my understanding here?
Final thought, if you went with route (i), would you then be violating 700.16 under EM circumstances? What would happen if that fixture was broken the one day you need it?
Small mantrap that is part of egress route and is the pair of doors between the outdoor exit and the interior of building. Currently there is only one exit sign and one linear light fixture in this space, both are circuited to an ATS backed EM panel.
700.16(B) states:
"Emergency lighting systems shall be designed and installed so that the failure of any illumination source cannot leave in total darkness any space that requires emergency illumination"
700.17 states:
"Branch circuits that supply emergency lighting shall be installed to provide service from a source complying with 700.12 when the normal supply for lighting is interrupted. Such installations shall provide either of the following:
(1) An emergency lighting supply, independent of the normal lighting supply, with provisions for automatically transferring the emergency lights upon the event of failure of the normal lighting supply.
(2) Two or more branch circuits supplied from separate and complete systems with independent power sources. One of the two power sources and systems shall be part of the emergency system, and the other shall be permitted to be part of the normal power sources and system. Each system shall provide sufficient power for emergency lighting purposes."
This mantrap was flagged because per 700.16, the exit sign does not provide sufficient illumination for the space on its own, so another source of illumination is required for this area as a form of redundancy.
Typically, under the 2008 NEC we would just place another fixture in the area and circuit back to the same panel EM ATS backed panel. However, our AHJ has recently updated from enforcing 2008 to 2020 which caused some debate as to how to comply with 700.17 internally. Under 2008, 700.17(2) was written as follows: "Two or more separate and complete systems with independent power supply, each system providing sufficient current for emergency lighting purposes". Under the 2008, it was interpreted that having all lighting be fed off the same branch circuit was acceptable, however the most recent revisions of the code very explicitly say you must use two or more separate branch circuits as shown above in the excerpt.
Solution:
I think that it is easiest to comply with 700.17(1) in the case of this mantrap. We are going to spec a UL 924 battery backed bug-eye exit sign that can provide the necessary illumination. This way the mantrap can comply with both 700.17 and 700.16.
Remaining question about 700.17:
I am still confused about how 700.17(2) works under the latest revisions... in this exact same scenario, assuming I wanted to instead place another linear light fixture and keep the existing exit sign, I'd now have two lights in this space. Then I can go one of two routes:
(i) If I circuited one light to the EM ATS backed panel, and the other one to the normal power supply, this is now compliant because the area is being served by two separate power sources. Under an EM condition where all power is running off of generators, only the one light would be running now.
(ii) If I were to circuit both lights to the same EM ATS backed panel (even on different circuit breakers) this would now not be a compliant solution because they're not fed from independent power sources? Under an EM condition, now both lights would be running yet it would be less compliant than the previous situation of one EM / one normal supplied light described previously. Is there an error in my understanding here?
Final thought, if you went with route (i), would you then be violating 700.16 under EM circumstances? What would happen if that fixture was broken the one day you need it?