Restaurant Type-1 Hood KP Control Wiring
Why this matters
A restaurant Type-1 grease hood with a wet-chemical fire suppression system (Ansul R-102, Amerex KP, Pyro-Chem PCL-300) is wired through a "KP control" interlock that shuts off cooking-appliance fuel or power when the suppression system actuates. NFPA 96-2021 Section 10.4 requires the interlock; a hood install without it fails the fire-marshal inspection and the restaurant cannot operate. The KP control microswitch sits inside the suppression system head and the wiring runs to a shunt-trip breaker, gas valve solenoid, or contactor that drops cooking equipment when the suppression fires. Get this wrong and the suppression discharges but the cooking equipment keeps feeding fuel into the fire.
What KP control actually means
"KP" stands for Kitchen Protection control; in practice it is a contact set in the fire-suppression system control head, mechanically actuated when the cartridge releases. The contact set typically provides:
- One Form C (single-pole double-throw) set for the gas valve / shunt-trip output.
- One additional set for alarm system notification.
- One additional set for hood exhaust fan (interlock to keep fan running during discharge per NFPA 96 10.4.4, or shut fan off per AHJ - varies).
The contacts are dry (no internal voltage); the installing electrician brings the control voltage. For a gas-fueled cooking line, the control voltage feeds a normally-energized gas safety valve (Asco 8210, Maxitrol GV-50 with electric reset) downstream of the gas meter. KP discharge opens the contact, drops the valve, gas stops. For an electric cooking line, the control voltage feeds a shunt-trip coil on the kitchen-equipment breaker (Square D MH-frame with shunt-trip accessory, Eaton CHP shunt-trip). Discharge fires the shunt-trip, breaker opens, electric cooking equipment de-energizes.
NFPA 96 requirements
NFPA 96-2021 Section 10.4 governs the interlock:
- 10.4.1 Upon actuation of the fire-suppressant agent, all sources of fuel and electric power that produce heat to equipment under the hood shall automatically shut off.
- 10.4.3 The shutoff valve shall be of the manual reset type. Gas valves with electric reset (push-button after fault clears) are common; spring-return self-resetting valves are NOT compliant.
- 10.4.4 The hood exhaust fan shall continue to operate during fire-suppression discharge (most AHJs interpret this as required; verify locally because some AHJs allow fan shutdown to prevent oxygen feed to the fire).
- 10.4.6 The make-up air supply to the hood shall be shut down upon discharge.
Typical wiring topology
For a gas cooking line:
- 120V or 24V control line from the kitchen control panel through the KP contact in the suppression system head to the gas valve coil.
- Manual reset gas valve (Maxitrol GV-50 series, Honeywell 8200 series with reset, ASCO 8210 with reset feature) holds open with continuous control voltage. KP discharge opens the contact, valve de-energizes, valve closes, valve stays closed until manual reset.
- A test pushbutton in series with the KP contact (or in parallel via a test position) allows the inspector to verify gas shutoff during the annual inspection without firing the suppression cartridge.
For an electric cooking line:
- 120V control line from the panel through the KP contact to the shunt-trip coil on the kitchen-equipment breaker.
- KP contact normally closed (held closed by the suppression system head). On discharge, opens.
- The shunt-trip coil ON 120V trips the breaker when energized; the wiring must invert the KP contact (use the normally-open KP contact, energize the shunt-trip on discharge), OR use a control relay with normally-closed contacts feeding the shunt-trip coil so the shunt is energized only when the KP contact opens.
The second method is the more common and the more reliable: a holding relay (energized continuously by the KP normally-closed contact) drops out on discharge and its own normally-closed auxiliary contact closes to feed the shunt-trip.
Hood exhaust fan handling
The hood exhaust fan typically runs through a contactor controlled by a fan switch at the hood and an interlock with the cooking equipment. NFPA 96 10.4.4 (most jurisdictions) requires the fan to continue running during fire suppression. The KP discharge must NOT shut off the fan contactor; many code-officials want a separate signal that energizes the fan if it is off, ensuring the fan runs through and after discharge. Verify the AHJ position.
Make-up air supply shutdown
NFPA 96 10.4.6 requires the make-up air (MAU) unit serving the hood to shut down on discharge. The KP control's additional contact set or an additional control relay drives the MAU's contactor open. This prevents the MAU from feeding outdoor combustible-debris-laden air to the suppression-active hood.
Test procedure for annual inspection
NFPA 17A-2024 (wet-chemical extinguishing systems) Section 7.4 requires semi-annual maintenance of the suppression system; the KP interlock is tested as part of that:
- Coordinate test with the restaurant manager; gas service will be off for the test duration.
- Manually actuate the KP contact at the system head (most have a manual test position that breaks the contact without firing the cartridge).
- Verify gas valve de-energizes and stays closed; cooking equipment cannot ignite.
- Verify electric cooking equipment breakers trip if applicable.
- Verify hood exhaust fan continues running.
- Verify MAU shuts down.
- Reset gas valve, restore make-up air, return system to service.
- Tag the system with test date, technician identification, and result. NFPA 17A and the AHJ require the tag and a written report.
Never wire the KP control to a gas valve that resets automatically on signal return. NFPA 96 10.4.3 explicitly requires manual reset; an automatic-reset valve restores gas to a kitchen that just had a fire, and that is the exact failure mode the interlock was created to prevent. The annual inspection will reject the install and the fire marshal can red-tag the kitchen.
References
- NFPA 96-2021 Standard for Ventilation Control and Fire Protection of Commercial Cooking Operations
- NFPA 17A-2024 Standard for Wet Chemical Extinguishing Systems
- Ansul R-102 Restaurant Fire Suppression System Design, Installation, Recharge, and Maintenance Manual
- Amerex KP and Pyro-Chem PCL-300 System Design and Installation Manuals
- UL 300-2019 Fire Testing of Fire Extinguishing Systems for Protection of Commercial Cooking Equipment