Kitchen Hood Fire Suppression sytem questions.

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Hawkins

Member
Location
Tennessee
Hello all,
I have a small commercial job I am finishing, (my first restaurant), and I would like some advice about the fire suppression system. Here is what I have:

2 exhaust fans & a MUA unit, all powered via contactors (motor starters).

Simplex G. is doing the under the hood fire system and they have installed pyro-chem microswitches.
The microswitches have 3 wires:
Red/Hot
Black/N.O.
Brown/N.C.

The paper work for the microswitches says they can handle 21A 120v, so it does not look like a need a relay for this model.

My question is about the micro switches, if I run a 120v control circuit to the switches, am i supposed to run a wire from the black/N.O. to the normally open terminal on my contactor. (I want the exhaust to kick on or continue running when the fire system is activated).

I just want to make sure method is correct. I am worried about the 120v from the microswitch causing a short on the contactors, as the power would be from a different phase than the contactor control circuit.
 

luckylerado

Senior Member
Hello all,
I have a small commercial job I am finishing, (my first restaurant), and I would like some advice about the fire suppression system. Here is what I have:

2 exhaust fans & a MUA unit, all powered via contactors (motor starters).

Simplex G. is doing the under the hood fire system and they have installed pyro-chem microswitches.
The microswitches have 3 wires:
Red/Hot
Black/N.O.
Brown/N.C.

The paper work for the microswitches says they can handle 21A 120v, so it does not look like a need a relay for this model.

My question is about the micro switches, if I run a 120v control circuit to the switches, am i supposed to run a wire from the black/N.O. to the normally open terminal on my contactor. (I want the exhaust to kick on or continue running when the fire system is activated).

I just want to make sure method is correct. I am worried about the 120v from the microswitch causing a short on the contactors, as the power would be from a different phase than the contactor control circuit.

In my experience, in addition to turning on the exhaust, you must kill the makeup air and shunt all power under the hood. In a couple of cases I have also had to de-energize low voltage gas valves as well.

I cannot think of a case that at least one relay was not required to make it all work and it is highly unlikely that the fans are 120v single phase.

One NO contacts should energize a contractor for the exhaust
One NC contact to kill the MAUs via safety loop or via de-energize contractor
One (or more) NO contact to shunt power under the hood via shunt trip breaker
 

Hawkins

Member
Location
Tennessee
In my experience, in addition to turning on the exhaust, you must kill the makeup air and shunt all power under the hood. In a couple of cases I have also had to de-energize low voltage gas valves as well.

I cannot think of a case that at least one relay was not required to make it all work and it is highly unlikely that the fans are 120v single phase.

One NO contacts should energize a contractor for the exhaust
One NC contact to kill the MAUs via safety loop or via de-energize contractor
One (or more) NO contact to shunt power under the hood via shunt trip breaker


This is actually part of my issue. The coil contactor on each of the 3 "weg motor starters" is powered via 208v-240v, meaning they share a double pole breaker for the control circuit (going with 240v).

The 2 exhaust fans are 220v, each on a separate circuit.

The MUA is 3 phase...

is it permissable to break one phase of the 220v control circuit via the microswitches? If the control circuit (coil voltage) was 120v, I could easily set this up with a relay connecting into the load side of the switches via the microswitch control circuit, and cutting the control circuit power to the MUA.

All appliances are gas, fire inspector said hood lights are not required to shutoff if in explosion proof fixtures, which they are.
 

luckylerado

Senior Member
This is actually part of my issue. The coil contactor on each of the 3 "weg motor starters" is powered via 208v-240v, meaning they share a double pole breaker for the control circuit

How does the cook turn on the EF? 2 double pole switches? Put your NO contacts in parallel with those switches.

The MUA is 3 phase...
Does it have a safety loop or EM shutdown? May just need to open the low volt side. It is better to let the equipment go through the shutdown process if one is built in. I could see using the micro switch for this if you are just breaking the low volt side.


is it permissable to break one phase of the 220v control circuit via the microswitches?
It seems to me that you need to open all ungrounded conductors. I do not have a reference at the moment. Regardless, I would not recommend it. Need to leave a set of contacts for the fire alarm system as well if there is one available.

All appliances are gas
They have no power?? Can't be.

NFPA 17 Standard for Dry Chemical Extinguishing Systems

9.3.5*
Shutoff Devices. Upon actuation of any cooking equipment fire-extinguishing system, all sources of fuel and electricpower that produce heat to all equipment protected by the system shall be shut down.
 

gadfly56

Senior Member
Location
New Jersey
Occupation
Professional Engineer, Fire & Life Safety
How does the cook turn on the EF? 2 double pole switches? Put your NO contacts in parallel with those switches.


Does it have a safety loop or EM shutdown? May just need to open the low volt side. It is better to let the equipment go through the shutdown process if one is built in. I could see using the micro switch for this if you are just breaking the low volt side.


It seems to me that you need to open all ungrounded conductors. I do not have a reference at the moment. Regardless, I would not recommend it. Need to leave a set of contacts for the fire alarm system as well if there is one available.


They have no power?? Can't be.

NFPA 17 Standard for Dry Chemical Extinguishing Systems

9.3.5*
Shutoff Devices. Upon actuation of any cooking equipment fire-extinguishing system, all sources of fuel and electricpower that produce heat to all equipment protected by the system shall be shut down.

Gas range/ovens, griddles, and upright broilers may very well have no electrical components, especially commercial equipment. Even fryers may have mechanical thermostat controls.

The standard you need to quote is NFAP 17A. No one has a listed dry chemical system for kitchen fire suppression.

Don't forget that you will need to connect a micro switch output to the building fire alarm system, or if it doesn't have one, a local notification appliance that is activated when the suppression system is triggered.

The micro switches are rated for 21 A at 250 VAC. They are available as 4PDT
 

luckylerado

Senior Member
The standard you need to quote is NFAP 17A.


NFPA 17A Standard for WET Chemical Extinguishing Systems
4.4.4 Shutoff Devices.

4.4.4.1 On actuation of any cooking equipment fire extinguishing
system, all sources of fuel and electric power
that produce heat to all equipment protected by the system
shall be shut down.
4.4.4.2 · Gas appliances not requiring protection but located
under the same ventilation equipment shall also be shut off.
 

GoldDigger

Moderator
Staff member
Location
Placerville, CA, USA
Occupation
Retired PV System Designer
Probably not relevant to the OP's specific situation, but beware of deciding to use the system microswitch contacts to control a motor load like makeup air fans directly.
This would be a motor load-breaking situation and so an HP rating on the switch contacts would be appropriate, not just a single current value which is most likely for a resistive load.
Now the switch is not likely to be exercised repeatedly and suffer cumulative damage, but you do want it to work well at least once. :angel:
 

K8MHZ

Senior Member
Location
Michigan. It's a beautiful peninsula, I've looked
Occupation
Electrician
Probably not relevant to the OP's specific situation, but beware of deciding to use the system microswitch contacts to control a motor load like makeup air fans directly.
This would be a motor load-breaking situation and so an HP rating on the switch contacts would be appropriate, not just a single current value which is most likely for a resistive load.
Now the switch is not likely to be exercised repeatedly and suffer cumulative damage, but you do want it to work well at least once. :angel:

I just looked at a suppression system for a friend of mine. The micro switches were in one box and a separate box had motor contactors with thermals, controlled by the switches, for each blower, along with a board and some relays to shut off the lights under the hood, one blower and the gas. The pull station was a wire cable (not electric) connected to a whatchamacallit that activated the micro switches. This was in addition to the nitrogen charged extinguisher and the alarm/strobe.

There was also a hood temp and a room temp sensor wired to the unit.

I remember thinking how slick it was and what an expensive PITA it would be to try to build something like this with off the shelf parts.

There were two microswitches in the switch box. One was 120v with the NC side going to the second panel. The other, also 120v, was wired with the NO side going to the alarm/strobe unit.

The 120v was on the common.
 

gadfly56

Senior Member
Location
New Jersey
Occupation
Professional Engineer, Fire & Life Safety
Probably not relevant to the OP's specific situation, but beware of deciding to use the system microswitch contacts to control a motor load like makeup air fans directly.
This would be a motor load-breaking situation and so an HP rating on the switch contacts would be appropriate, not just a single current value which is most likely for a resistive load.
Now the switch is not likely to be exercised repeatedly and suffer cumulative damage, but you do want it to work well at least once. :angel:

That would be 2HP at 250 VAC or 1HP at 125 VAC for the switches under discussion.
 
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