Lighting Circuits

[mbrooke]

Is it correct to assume that a where emergency lighting is required in a building, that any space in said building is required to have least a few lights on a circuit not protected by generator or UPS? Basically that no ATS location, electrical room, hallway, or stairwell can be on 100% emergency power?

 

[infinity]

Why couldn't a room or rooms be on 100% emergency power if the system were large enough to do so?

 

[jusme123]

Look at Hospitals

 

[mbrooke]

Why couldn't a room or rooms be on 100% emergency power if the system were large enough to do so?

Good question- but as I'm reading article 700 it hints at least two circuits.

 

[charlie b]

. . . but as I'm reading article 700 it hints at least two circuits.

Can you cite a specific article? I am not familiar with any requirement to have both normal and emergency circuits providing lights in all rooms.

 

[mbrooke]

Can you cite a specific article? I am not familiar with any requirement to have both normal and emergency circuits providing lights in all rooms.

I'll dig through right now.

 

[mbrooke]

Can you cite a specific article? I am not familiar with any requirement to have both normal and emergency circuits providing lights in all rooms.

700.17 Branch Circuits for Emergency Lighting. 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 branch circuit

(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 source and system. Each system
shall provide sufficient power for emergency lighting
purposes.
Unless both systems are used for regular lighting purposes
and are both kept lighted, means shall be provided for
automatically energizing either system upon failure of the
other. Either or both systems shall be permitted to be a
part of the general lighting of the protected occupancy if
circuits supplying lights for emergency illumination are
installed in accordance with other sections of this article.

Here is one being more explicit. 700 keep making a distinction between "normal" and "emergency" circuits.

I'm thinking that a single ATS can cover every light in a building provided a select few lights (for egress) can not be turned off by occupants or light upon failure of the utility.

 

[mbrooke]

Ok, say I had a single life safety or lighting ATS which fed every light in the building... how would an inspector/AHJ fail me?

 

[rjk_cmh]

It's because "emergency" and "legally required" systems are distinct from "optional standby" systems and must be kept separate. Any system designated as "emergency" is critical for life-safety, and therefore is isolated from general-purpose systems, whether or not the general-purpose loads have a backup power source.

Read http://www.mikeholt.com/download.php?file=PDF/11_Standby_Power_Systems.pdf for a really good overview of article 700-702 relating to this topic. It essentially comes down to life safety and reliability - I'll attach this blurb from that PDF here:

Emergency systems are legally required, often as a condition of an operating permit for a given facility. The authority having jurisdiction
makes the determination as to whether such a system is necessary for a given facility and what it must entail. Sometimes, it simply
provides power for exit lighting and exit signs upon loss of main power or in the case of fire. Its purpose isn’t to provide power for normal
business operations, but rather to provide lighting and controls essential for human life safety.
The general goal is to keep the emergency operation as reliable as possible. The emergency system must be able to supply all emergency
loads simultaneously. When the emergency supply also supplies power for other nonemergency loads, the emergency loads take priority
over the other loads, and those other loads must be subject to automatic load pickup and load shedding to support the emergency loads if
the emergency system doesn’t have adequate capacity and rating for all loads simultaneously.
As you study Article 700, keep in mind that emergency systems are essentially lifelines for people. The entire article is based on keeping
those lifelines from breaking.

 

[mbrooke]

It's because "emergency" and "legally required" systems are distinct from "optional standby" systems and must be kept separate. Any system designated as "emergency" is critical for life-safety, and therefore is isolated from general-purpose systems, whether or not the general-purpose loads have a backup power source.

Read http://www.mikeholt.com/download.php?file=PDF/11_Standby_Power_Systems.pdf for a really good overview of article 700-702 relating to this topic. It essentially comes down to life safety and reliability - I'll attach this blurb from that PDF here:

But nowhere is the size specified. Nowhere does it say you couldn't have all lighting on life the emergency or legally required branch.

 

[rjk_cmh]

But nowhere is the size specified. Nowhere does it say you couldn't have all lighting on life the emergency or legally required branch.

No, that would come down to economics and engineering. An engineer could specify that every single fixture in the back hallway was critical for life safety, and cause the generator to be oversized for that, but it would cost more. But the relevant section would be 700-4 as shown here:


This arrangement allows non-critical loads to be shed if the genset is getting overloaded, and helps with the selective coordination that is required to protect the emergency loads from being disconnected in a fault event.

 

[mbrooke]

No, that would come down to economics and engineering. An engineer could specify that every single fixture in the back hallway was critical for life safety, and cause the generator to be oversized for that, but it would cost more. But the relevant section would be 700-4 as shown here:

View attachment 2552782
This arrangement allows non-critical loads to be shed if the genset is getting overloaded, and helps with the selective coordination that is required to protect the emergency loads from being disconnected in a fault event.

That is unless the occupants want 100% of the building on backup.

 

[rjk_cmh]

That is unless the occupants want 100% of the building on backup.

I don't know enough about how the loads are differentiated by the AHJ or engineers, but the fact that the circuits are always separate in hospital environments would indicate that there is a prevailing methodology for specifying critical versus general purpose loads, even when the owner wants everything to have backup power available. I think it would probably come down to minimizing the number and size of loads designated as Emergency, solely for reliability purposes, but I don't have that particular expert insight.

 

[mbrooke]

I don't know enough about how the loads are differentiated by the AHJ or engineers, but the fact that the circuits are always separate in hospital environments would indicate that there is a prevailing methodology for specifying critical versus general purpose loads, even when the owner wants everything to have backup power available. I think it would probably come down to minimizing the number and size of loads designated as Emergency, solely for reliability purposes, but I don't have that particular expert insight.

Hospitals want 3 separate branches for everything considered essential- 4th if the patient bad area doesn't have normal power.

There is a list of what is considered essential. However 700 leaves a lot up to the EE/AHJ.

 

[roger]

700.17(1) allows it, note it is talking about an "emergency lighting supply" it doesn't care if the designer or owner wants the whole facility to be backed up. If the EPSS can handle it the lighting can remain at 100%. Remember, the Emergency System is Normal Power until it transfers to Emergency.

700.17 Branch Circuits for Emergency Lighting. 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 branch circuit

Roger

 

[hillbilly1]

That is unless the occupants want 100% of the building on backup.

Then you would need a minimum of two transferswitches to seperate the loads, unless the egress lighting has a seperate power source such as a battery backup.

 

[mbrooke]

700.17(1) allows it, note it is talking about an "emergency lighting supply" it doesn't care if the designer or owner wants the whole facility to be backed up. If the EPSS can handle it the lighting can remain at 100%. Remember, the Emergency System is Normal Power until it transfers to Emergency.

700.17 Branch Circuits for Emergency Lighting. 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 branch circuit

Roger

Alright, good to know.

 

[mbrooke]

Then you would need a minimum of two transferswitches to seperate the loads, unless the egress lighting has a seperate power source such as a battery backup.

True, but you could have on ATS for all the lighting and fire alarm panel, another ATS for all the COPs equipment (continuity of government operations) and another for everything else. Just something that went through my mind.