A 480V/277Y 2,500 KVA standby generator has a 2,500 amp circuit breaker located at the genset. From there a 2,500 amp feeder supplies a switchboard with a 2,500 amp bolted pressure switch. The feeder section of this switchboard contains 3-1,000 amp switches. One of the feeder switches supplies the elevator loads via a transfer switch, one supplies legally required standby loads via a transfer switch, and the other supplies emergency loads via a transfer switch. Which one of these circuit breakers is the "emergency source distribution overcurrent protective devices" referenced in 700.9(b)?
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Emergency Source Distribution Overcurrent Protection
- Thread starter rb
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david
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Re: Emergency Source Distribution Overcurrent Protection
700.9 Wiring, Emergency System.
(B) Wiring. Wiring of two or more emergency circuits supplied from the same source shall be permitted in the same raceway, cable, box, or cabinet. Wiring from an emergency source or emergency source distribution overcurrent protection to emergency loads shall be kept entirely independent of all other wiring and equipment, unless otherwise permitted in (1) through (4):
Which one of these circuit breakers is the "emergency source distribution overcurrent protective devices" referenced in 700.9(b)?
Is this a trick question? Basically this section is calling for emergency wiring to be kept separate from non- emergency wiring. Emergency wiring, from the same emergency source can be run together.
You question ask about the over current devices at the point of distribution to the emergency loads. This normally would be the branch circuit over current protection.
700.9 Wiring, Emergency System.
(B) Wiring. Wiring of two or more emergency circuits supplied from the same source shall be permitted in the same raceway, cable, box, or cabinet. Wiring from an emergency source or emergency source distribution overcurrent protection to emergency loads shall be kept entirely independent of all other wiring and equipment, unless otherwise permitted in (1) through (4):
Which one of these circuit breakers is the "emergency source distribution overcurrent protective devices" referenced in 700.9(b)?
Is this a trick question? Basically this section is calling for emergency wiring to be kept separate from non- emergency wiring. Emergency wiring, from the same emergency source can be run together.
You question ask about the over current devices at the point of distribution to the emergency loads. This normally would be the branch circuit over current protection.
Re: Emergency Source Distribution Overcurrent Protection
From the set up you describe the cb at the gen set is the emergency source distribution over current device. The other cb's are feeder protection devices. I believe the intent in this article is to keep normal power and emegency power over current devices seperate except in the required transfer equipment.
From the set up you describe the cb at the gen set is the emergency source distribution over current device. The other cb's are feeder protection devices. I believe the intent in this article is to keep normal power and emegency power over current devices seperate except in the required transfer equipment.
david
Senior Member
- Location
- Pennsylvania
Re: Emergency Source Distribution Overcurrent Protection
1. a 2,500 amp circuit breaker located at the genset.
2. a switchboard with a 2,500 amp bolted pressure switch.
3. a feeder switch that supplies the elevator loads via a transfer switch,
4. a feeder switch that supplies legally required standby loads via a transfer switch
5. A feeder switch that supplies emergency loads via a transfer switch.
If this is a test question and the above are you choices one has a circuit breaker so I would agree one is your best choice of possible answers. However when I consider that this GEN is not dedicated to emergency loads and legally required standy by system wiring is allowed to be mixed with non emergency loads I rule one out.
But you ask,? which one of these circuit breakers is the "emergency source distribution over current protective devices" referenced in 700.9(b)??
When you say which one of these circuit breakers I am lead to believe the feeder switches are circuit breakers and I assume all these circuit breakers are over current devices. So that is why I ask is this trick question? So from the choices above I have to go with 5 as the best answer to this question.
caj1962
?I believe the intent in this article is to keep normal power and emergency power over current devices separate except in the required transfer equipment?
This section is about the emergency wiring and by default if the emergency wiring is kept separate from non-emergency wiring the distribution (over current) devices will have to be separate from non-emergency wiring.
[ August 12, 2003, 01:56 PM: Message edited by: david ]
1. a 2,500 amp circuit breaker located at the genset.
2. a switchboard with a 2,500 amp bolted pressure switch.
3. a feeder switch that supplies the elevator loads via a transfer switch,
4. a feeder switch that supplies legally required standby loads via a transfer switch
5. A feeder switch that supplies emergency loads via a transfer switch.
If this is a test question and the above are you choices one has a circuit breaker so I would agree one is your best choice of possible answers. However when I consider that this GEN is not dedicated to emergency loads and legally required standy by system wiring is allowed to be mixed with non emergency loads I rule one out.
But you ask,? which one of these circuit breakers is the "emergency source distribution over current protective devices" referenced in 700.9(b)??
When you say which one of these circuit breakers I am lead to believe the feeder switches are circuit breakers and I assume all these circuit breakers are over current devices. So that is why I ask is this trick question? So from the choices above I have to go with 5 as the best answer to this question.
caj1962
?I believe the intent in this article is to keep normal power and emergency power over current devices separate except in the required transfer equipment?
This section is about the emergency wiring and by default if the emergency wiring is kept separate from non-emergency wiring the distribution (over current) devices will have to be separate from non-emergency wiring.
[ August 12, 2003, 01:56 PM: Message edited by: david ]
Re: Emergency Source Distribution Overcurrent Protection
This is not a trick question.
If the 2,500 amp circuit breaker located at the generator is the emergency source distribution overcurrent device referenced in 700.9(b), then the feeder switches serving the legally required standby loads and optional loads would not be permitted to be located in the same switchboard as the emergency system feeder switch.
I am interested in how others define "Emergency source distribution overcurrent device." It appears to be a salient point when applying 700.9(b).
This is not a trick question.
If the 2,500 amp circuit breaker located at the generator is the emergency source distribution overcurrent device referenced in 700.9(b), then the feeder switches serving the legally required standby loads and optional loads would not be permitted to be located in the same switchboard as the emergency system feeder switch.
I am interested in how others define "Emergency source distribution overcurrent device." It appears to be a salient point when applying 700.9(b).
david
Senior Member
- Location
- Pennsylvania
Re: Emergency Source Distribution Overcurrent Protection
Rb
This section is addressing wiring of he emergency system. The emergency source being addressed in 700.9 does not have to be the alternate power source in your example this section is also addressing emergency sources such as unit equipment.
I will go back to my first post where I stated that the emergency source distribution overcurrent protection is usually the overcurrent device in the emergency panel. Notice it is saying from the overcurrent at the point of distribution to the emergency loads. The feeder from an alternate power source is allowed to supply other non emergency loads such as legally required standby, and optional standby system loads.
Rb
This section is addressing wiring of he emergency system. The emergency source being addressed in 700.9 does not have to be the alternate power source in your example this section is also addressing emergency sources such as unit equipment.
I will go back to my first post where I stated that the emergency source distribution overcurrent protection is usually the overcurrent device in the emergency panel. Notice it is saying from the overcurrent at the point of distribution to the emergency loads. The feeder from an alternate power source is allowed to supply other non emergency loads such as legally required standby, and optional standby system loads.
Re: Emergency Source Distribution Overcurrent Protection
This is a good discussion. Even though it may meet the requirements of the NEC will the OCPD really protect? Has the OCPD been specifically selected for protecting the generator or is a common breaker? All to ofeten breaker trip curves are forgotten about.
Consider that the generator and prime mover have a specific power output, i.e., 2500a. If it is said to be protected by even a 2000a breaker how much overcurrent can the genset provide for a long enough time that would be enough to trip the breaker in the event of an overload. This would be simple to determine should one look at the time current trip curve for the breaker as compared to the generator output.
Then there is the available short circuit current from the generator in the event that there is a bolted fault. Will the available fault current be high enough to trip the breaker instantaneously?
Often times other means may be considered to monitor and protect the generator tripping the breaker using a shunt trip.
There's one heck of a lot more capacity to sustain an overcurrent or fault available from a utility source than from a generator.
This is a good discussion. Even though it may meet the requirements of the NEC will the OCPD really protect? Has the OCPD been specifically selected for protecting the generator or is a common breaker? All to ofeten breaker trip curves are forgotten about.
Consider that the generator and prime mover have a specific power output, i.e., 2500a. If it is said to be protected by even a 2000a breaker how much overcurrent can the genset provide for a long enough time that would be enough to trip the breaker in the event of an overload. This would be simple to determine should one look at the time current trip curve for the breaker as compared to the generator output.
Then there is the available short circuit current from the generator in the event that there is a bolted fault. Will the available fault current be high enough to trip the breaker instantaneously?
Often times other means may be considered to monitor and protect the generator tripping the breaker using a shunt trip.
There's one heck of a lot more capacity to sustain an overcurrent or fault available from a utility source than from a generator.
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