Hi!,to all. Need Help. Wired a hood exhaust fan so the fan would run in alarm mode (dry ansul system) even if tenant forgot to turn the exhaust switch on. Here,s the situation. One ckt for hood supply, one for exhaust. The hot of exhaust ckt fed common of ansul microswitch.No common trip for the two ckts. This was existing. I understand Multiwire ckts must be grouped and have common trip per 2008 NEC. They installed new exhaust fan motor. 110V. single phase. Old one ran fine. pulled lower amps. Did load calc and I either need to run #10,s with a 30 amp s.pole breaker or go 230 V. Sorry! the motor is 115/2320 volts optional. I decided to go with 230 V because existing wires are # 12,s And would meet code on 125% conductor calc for load. supply and exhaust ckts share common neutral. Wired microswitch so supply fan, hood lights, and GFI duplex receptacle of which two convection circulating fans for oven, all go off in alarm condition. Also exhaust fan would stay on or be shunted to come on off n.c.microswitch. problem is I want to install 230 volt breaker for motor I don,t mean to type so much but I wish I could talk to someone.I have been a loyal Mike Holt member for a long time. He is the best! have bought much merchandise from him complete journeyman series and lots of other stuff. Can anyone give me possible options? Greatly appreciated!!!
Ansul hood and exaust supply dilemma
- Thread starter tld38
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Ever heard of a thing called a relay? 
You'll need a DPST 120V relay with contacts rated for the hp of the fan motor or greater. If the old circuit worked fine, just wire in the coil as if it were the old motor. Take your hots directly to one "side" of the contacts and motor feeders of the other "side". Put the relay in its own enclosure.
Additionally, you likely have to change the fan disconnect (switch) to a 2-pole motor hp rated one, not to mention replacing the neutral to the old motor.
You'll need a DPST 120V relay with contacts rated for the hp of the fan motor or greater. If the old circuit worked fine, just wire in the coil as if it were the old motor. Take your hots directly to one "side" of the contacts and motor feeders of the other "side". Put the relay in its own enclosure.
Additionally, you likely have to change the fan disconnect (switch) to a 2-pole motor hp rated one, not to mention replacing the neutral to the old motor.
electricguy61
Senior Member
I'm doing a job right now that spec'd all ovens, supply air, exhaust air, lights, natural gas, etc. to be disconnected in the event the ansul system activates.
I bought a 12 pole maintained, mechanical contactor & put it in a NEMA 4 can. We'll pull all circuits in the hood back to the contactor (rated 30 amps @ 250v) and use the dry contact from the ansul to drive it.
Nice job for us!
I bought a 12 pole maintained, mechanical contactor & put it in a NEMA 4 can. We'll pull all circuits in the hood back to the contactor (rated 30 amps @ 250v) and use the dry contact from the ansul to drive it.
Nice job for us!
You sure about exhaust?
electricguy61
Senior Member
Interesting you should ask that. The OSHPOD inspector thought yes on the exhaust being shut down, the ansul guy said no.
I'm not a fire engineer (but I was a firefighter many moons ago), and I would think that if the exhaust was running, you'd be drawing air into a fire, hence it should be shut down. I suppose the other thought is it would clear the smoke out.
What's your experience/expertise say?
I've always had the exhaust fan stay/turn on when the fire supression system discharges.
LarryFine
Master Electrician Electric Contractor Richmond VA
- Location
- Henrico County, VA
- Occupation
- Electrical Contractor
Exhaust and horn/strobe (or building alarm) on, all else off. Yes, for a 240v motor, install a 2-pole contactor in place of 120v motor.
A lot of the supression work I have done has been for retro-fits of exiating systems, which need to be re-wired to meet new rules.
I have made a few diagrams for variations I've run into. Circuit hot to the micro COM terminal is not the only way to do it. For example:
If you only have a pair of blowers on one circuit, and using one micro for both (substitute your wire colors):
Before:
After:
Also, the same circuit plus additional stuff, like lights and appliance/receptacle contactors:
Around here, the gas valve must de-energize even when the exhaust is shut off manually. The place for that connection is where the intake fan is wired.
Added: Use 2p or 3p contactors where motors are not 120v, and also for appliances and receptacles. Much cheaper than a single 12p contactor.
A lot of the supression work I have done has been for retro-fits of exiating systems, which need to be re-wired to meet new rules.
I have made a few diagrams for variations I've run into. Circuit hot to the micro COM terminal is not the only way to do it. For example:
If you only have a pair of blowers on one circuit, and using one micro for both (substitute your wire colors):
Before:
After:
Also, the same circuit plus additional stuff, like lights and appliance/receptacle contactors:
Around here, the gas valve must de-energize even when the exhaust is shut off manually. The place for that connection is where the intake fan is wired.
Added: Use 2p or 3p contactors where motors are not 120v, and also for appliances and receptacles. Much cheaper than a single 12p contactor.
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LarryFine
Master Electrician Electric Contractor Richmond VA
- Location
- Henrico County, VA
- Occupation
- Electrical Contractor
Exhaust on to eject smoke, intake off to reduce fire air.
justin59
Member
- Location
- loma linda, ca
we always have the exhaust stay on. i've been told hood lights can remain on as well. everything else off. KFC's and Taco Bells spec a shunt trip main breaker to accomplish this.
electricguy61
Senior Member
EE spec'd the 12 pole contactor, so that's what I installed.
We have also have one of the 12 feeding to the FA panel.
We have also have one of the 12 feeding to the FA panel.
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