I am installing a small transformer to supply a fire alarm panel with 120v. Is it necessary to provide protection for the transformer? The load required for the panel is less than 2 amps. I haven't done much work involving a fire alarm system, and I'm having trouble finding a clear answer in either Art. 450 or 760, so any help is appreciated.
Transformer Prot. for Fire Alarm Panel
- Thread starter beegee
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Re: Transformer Prot. for Fire Alarm Panel
Generally, all xfmrs require some type of primary O/C protection. The rules are in article 450.
I assume 120v. is your secondary voltage. If this is a 1-phase xfmr with a primary voltage of 600,480,277,240, or 208, usually "slow blow" fuse(s) are used in the primary. Size at 300%, 167%, or 125% as per Art.450.
Generally, all xfmrs require some type of primary O/C protection. The rules are in article 450.
I assume 120v. is your secondary voltage. If this is a 1-phase xfmr with a primary voltage of 600,480,277,240, or 208, usually "slow blow" fuse(s) are used in the primary. Size at 300%, 167%, or 125% as per Art.450.
Re: Transformer Prot. for Fire Alarm Panel
The primary is 277v. The Secondary is 120v(500VA). I can't feed it from a normal low voltage panel because it is required to be on an emergency circuit and the only emergency power is 277v. I talked to the inspector today and he said that he would not require me to install any type of fuse protection.........but he didn't seem too certain about his response.
The primary is 277v. The Secondary is 120v(500VA). I can't feed it from a normal low voltage panel because it is required to be on an emergency circuit and the only emergency power is 277v. I talked to the inspector today and he said that he would not require me to install any type of fuse protection.........but he didn't seem too certain about his response.
ron
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- New York, 40.7514,-73.9925
Re: Transformer Prot. for Fire Alarm Panel
Sounds like a pretty small fire alarm system.
It needs overcurrent protection. If your jurisdiction has adopted the 2005 NEC, it needs to be selective with the upstream protection too!
Sounds like a pretty small fire alarm system.
It needs overcurrent protection. If your jurisdiction has adopted the 2005 NEC, it needs to be selective with the upstream protection too!
ron
Senior Member
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- New York, 40.7514,-73.9925
Re: Transformer Prot. for Fire Alarm Panel
If there is no upstream overcurrent protection, what will prevent a short or overload on the control panel from turning into a fire? If the AHJ doesn't require overcurrent protection, then I guess it is your choice to follow his minimum code interpretation, or go over and above the minimum.
If there is no upstream overcurrent protection, what will prevent a short or overload on the control panel from turning into a fire? If the AHJ doesn't require overcurrent protection, then I guess it is your choice to follow his minimum code interpretation, or go over and above the minimum.
Re: Transformer Prot. for Fire Alarm Panel
I agree with Ron. Looks like article 760 refers back to 450.3(B). So I just put a fuse on the primary side of the transformer. I would use 300% of the primary current, and round up to the next standard size fuse.
The FACP should have a battery backup if the fuse blows, and should also give a trouble signal if the fuse blows.
STeve
I agree with Ron. Looks like article 760 refers back to 450.3(B). So I just put a fuse on the primary side of the transformer. I would use 300% of the primary current, and round up to the next standard size fuse.
The FACP should have a battery backup if the fuse blows, and should also give a trouble signal if the fuse blows.
STeve
Re: Transformer Prot. for Fire Alarm Panel
Well, I already have the transformer. Plus, and I hate to admit this, but hooking up a battery for backup power is not something I do everyday! Anyway, a battery will run out, but an emergency circuit fed from a generator will not. Right?
Well, I already have the transformer. Plus, and I hate to admit this, but hooking up a battery for backup power is not something I do everyday! Anyway, a battery will run out, but an emergency circuit fed from a generator will not. Right?
Re: Transformer Prot. for Fire Alarm Panel
I don't know of any code reference, but I kind of assumed fire alarm panels required a battery backup. Maybe it depends on the type or size of occupancy?
I guess a 10 sec hiccup for the generator to start won't be a major problem for the FACP.
Steve
I don't know of any code reference, but I kind of assumed fire alarm panels required a battery backup. Maybe it depends on the type or size of occupancy?
I guess a 10 sec hiccup for the generator to start won't be a major problem for the FACP.
Steve
Re: Transformer Prot. for Fire Alarm Panel
Fire alarm system installer has to provide battery calcs for approval. Typically, wiring to batteries are not required. It is part of FACP or NAC and all you have to do is to provide 120V power to FACP or NAC.
By the way, 10 second delay is allowed for power transfer.
[ October 20, 2005, 12:11 PM: Message edited by: jkim780 ]
FACP always have to have a battery as a secondary power supply no matter what. 4 hrs of capacity under normal condistion followed by 5 minutes of alarm capacity with generator. 24 hrs/5min. without generator. Alarm capcity goes up to 15 min. for voice/evac. NFPA 72 (2002) 4.4.1.5.
Fire alarm system installer has to provide battery calcs for approval. Typically, wiring to batteries are not required. It is part of FACP or NAC and all you have to do is to provide 120V power to FACP or NAC.
By the way, 10 second delay is allowed for power transfer.
[ October 20, 2005, 12:11 PM: Message edited by: jkim780 ]
Re: Transformer Prot. for Fire Alarm Panel
Hey Ron. On a normal installation the panel would be fed from a 120v emergency circuit that would land directly in the panel. I have never seen an installation where an electrician installed overcurrent protection, so I assumed that if there was ocp, it was already installed in the panel. The only reason I was curious as to whether it was required for this installation, is because of the transformer I have to install. If there wasn't a transformer, I wouldn't be considering it, I would land my wires on the 120v terminal blocks and be done with it.
Hey Ron. On a normal installation the panel would be fed from a 120v emergency circuit that would land directly in the panel. I have never seen an installation where an electrician installed overcurrent protection, so I assumed that if there was ocp, it was already installed in the panel. The only reason I was curious as to whether it was required for this installation, is because of the transformer I have to install. If there wasn't a transformer, I wouldn't be considering it, I would land my wires on the 120v terminal blocks and be done with it.
ron
Senior Member
- Location
- New York, 40.7514,-73.9925
Re: Transformer Prot. for Fire Alarm Panel
On a normal installation, the 120V circuit hopefully has some protection upstream (20A or smaller).
On a normal installation, the 120V circuit hopefully has some protection upstream (20A or smaller).
ron
Senior Member
- Location
- New York, 40.7514,-73.9925
Re: Transformer Prot. for Fire Alarm Panel
Sounds fine. A 20A breaker at the panel protects the downstream wire and transformer.
Sounds fine. A 20A breaker at the panel protects the downstream wire and transformer.
Re: Transformer Prot. for Fire Alarm Panel
I guess Ron & I don't agree, but I am going to change my answer slightly.
If you are providing a transformer separate from the panel, I still think you have to meet table 450.3. But on the primary side of the transformer, I think you can use a circuit breaker, and round up to the next standard size. That would require a 15A circuit breaker, not a 20A.
On the secondary side, the wires would be taps, so I would keep them short. The FACP probably contains some type of OCP for the secondary of the transfomer. Or the secondary conductors might be considered protected by the primary OCP, if they are sized large enough.
Steve
I guess Ron & I don't agree, but I am going to change my answer slightly.
If you are providing a transformer separate from the panel, I still think you have to meet table 450.3. But on the primary side of the transformer, I think you can use a circuit breaker, and round up to the next standard size. That would require a 15A circuit breaker, not a 20A.
On the secondary side, the wires would be taps, so I would keep them short. The FACP probably contains some type of OCP for the secondary of the transfomer. Or the secondary conductors might be considered protected by the primary OCP, if they are sized large enough.
Steve
ron
Senior Member
- Location
- New York, 40.7514,-73.9925
Re: Transformer Prot. for Fire Alarm Panel
I agree with you Steve. 15A upstream breaker would be the way to go, for a small transformer.
I agree with you Steve. 15A upstream breaker would be the way to go, for a small transformer.
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