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  1. #1
    Join Date
    Oct 2005
    Location
    B.C. Canada
    Posts
    850

    Kitchen Exaust + MUA Interlock

    Hi
    Its been so long since ive done a kitchen exaust system im having a brain fart.
    How do you guys do your interlock between exaust and MUA?
    Im thinking a current relay to prove exaust is running to energize MUA rather than an air proving switch as I think the air switch would plug up with grease rather quickly.
    The only issue with a current relay is that your not acually proving airflow, just that the motor is running, so if you had a blown belt the mua would still energize.
    Thanks alot for your input.
    Erik

  2. #2
    Join Date
    Jun 2004
    Location
    St Paul, minnesota
    Posts
    1,134
    Quote Originally Posted by coolerik View Post
    Hi
    Its been so long since ive done a kitchen exaust system im having a brain fart.
    How do you guys do your interlock between exaust and MUA?
    Im thinking a current relay to prove exaust is running to energize MUA rather than an air proving switch as I think the air switch would plug up with grease rather quickly.
    The only issue with a current relay is that your not acually proving airflow, just that the motor is running, so if you had a blown belt the mua would still energize.
    Thanks alot for your input.
    Erik
    in my neck of the woods the mua needs to start the exhaust, otherwise they wouldn't even run the mua to save energy. this is accomplished by after they turn on mua, damper opens, starts fan and the mua airflow switch closes then the exhaust starts. since airflow switch is on the mua, no problem with grease. this is code in the state of Minnesota.

  3. #3
    Join Date
    Dec 2004
    Location
    Albuquerque, NM
    Posts
    104
    There are codes that specify how the interlock should operate. At least in my city there are. The fire marshal knows how it is supposed to work, I would suggest contacting the fire department.
    Mark

  4. #4
    Join Date
    Oct 2005
    Location
    B.C. Canada
    Posts
    850
    That was how I thought it sould work aswell but an ex-coworker told me exaust first, then MUA.
    Your way makes more sence to me
    Ya, ill contact the FD to confirm

  5. #5
    Join Date
    Jun 2004
    Location
    St Paul, minnesota
    Posts
    1,134
    again. depends where you are from. here fire dept doesn't give a squat which one starts 1st all they want to see is exhaust on in a fire and MUA off. Mechanical inspector is the one that requires MUA to start 1st and to be interlocked with the exhaust fan per the IMC (international mechanical code)


    just my 2 cents

  6. #6
    Join Date
    Jan 2008
    Location
    Ottawa, Canada
    Posts
    166
    Quote Originally Posted by coolerik View Post
    That was how I thought it sould work aswell but an ex-coworker told me exaust first, then MUA.
    Your way makes more sence to me
    Ya, ill contact the FD to confirm
    You're coworker is right. Exhaust has to be proven before DIRECT FIRED mua. This is to ensure all products of combustion are vented out through exhaust fan. Who cares if you prove mua is on, the danger lies in the exhaust fan not running. If your mua is indirect fired, no problem. This has always been a shady area, I've mostly seen mua started through auxiliary switch on exhaust fan starter, when exhaust fan contactor pulls in mua starts. As you stated, this does not prove air flow, the belt could be blown and the mua would still run. Lately I've been seeing air proving switches used in the exhaust. Code does state AIR FLOW needs to be proven before engaging mua. The problem with air proving switches in the exhaust are plugging issues as well as when it comes to fire code and penetrating steel exhaust ducts for tube intallation.

  7. #7
    Join Date
    Jun 2004
    Location
    St Paul, minnesota
    Posts
    1,134
    Quote Originally Posted by CDNtech View Post
    You're coworker is right. Exhaust has to be proven before DIRECT FIRED mua. This is to ensure all products of combustion are vented out through exhaust fan. Who cares if you prove mua is on, the danger lies in the exhaust fan not running. If your mua is indirect fired, no problem. This has always been a shady area, I've mostly seen mua started through auxiliary switch on exhaust fan starter, when exhaust fan contactor pulls in mua starts. As you stated, this does not prove air flow, the belt could be blown and the mua would still run. Lately I've been seeing air proving switches used in the exhaust. Code does state AIR FLOW needs to be proven before engaging mua. The problem with air proving switches in the exhaust are plugging issues as well as when it comes to fire code and penetrating steel exhaust ducts for tube intallation.
    again it depends where you're from. here we very much care if mua starts if only exhaust starts without the mua many times other combustion equipment in the space (i.e. water heaters),starts down drafting due to the space being under a negative. if they forget to turn on the mua there are heat sensors installed in the exhaust black iron ducts that will start both. maybe you don't have many Asian restaurants, but here they're famous for installing a screened porch around the back door and having their electrician wire in bypasses. inspectors have a hard time enforcing the codes after the job was already signed off, but their is still the lawsuits.

  8. #8
    Join Date
    Aug 2004
    Location
    Des Moines, IA
    Posts
    76
    auxillary switch off exhaust contacter in DSM

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