How do I calculate the size of a shunt trip breaker for hood

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elitegrp100

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DETROIT MI 48221
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electrical contractor
I have 20amp hood light , 20 amp fryer controls , 20 amp refrigerated base, 20amp 3 phase supply fan , 20amp 3 phase make up air , 60 amp 3 phase rtu -1,,, and 60amp 3 phase rtu-2
 
Welcome to the forum.

You don't want "a" shunt-trip breaker. There are rules for how the system should behave when there's a trip. They might vary slightly in some localities, but here's the rules in my area:

Exhaust fan must turn on or stay on.
Make-up fan must turn off or stay off
All appliances must lose power
All receptacles must lose power
Hood lights must turn off

The RTU shut-down is not something I have had to do, so check that and the above list with your local building inspection dept.

Some hood systems come with pre-wired control packages, so we need to know more about your specific installation.
 
elitegrp100 said:
I have 20amp hood light , 20 amp fryer controls , 20 amp refrigerated base, 20amp 3 phase supply fan , 20amp 3 phase make up air , 60 amp 3 phase rtu -1,,, and 60amp 3 phase rtu-2
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Are you thinking of using a sub panel fed by a shuntrip breaker? As Larry said, normally the rtu is not required, usually because they are controlled by the fire alarm, or a duct detector.
 
LarryFine said:
Welcome to the forum.

You don't want "a" shunt-trip breaker. There are rules for how the system should behave when there's a trip. They might vary slightly in some localities, but here's the rules in my area:

Exhaust fan must turn on or stay on.
Make-up fan must turn off or stay off
All appliances must lose power
All receptacles must lose power
Hood lights must turn off

The RTU shut-down is not something I have had to do, so check that and the above list with your local building inspection dept.

Some hood systems come with pre-wired control packages, so we need to know more about your specific installation.
Click to expand...
ok i in michigan and i put in a shunt trip breaker on commerial job , ifind with the rule you gave,,, but woul i size a breaker base on those rule ,,, ty
 
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ok so i have a 20 amp. for hood light ,20 amp. hood fan, 20 amp 3 phase mak-up air , 20 amp fryer , 20 amp stove , and 20 amp base ref, under the hood fan
 
The only way to shut down multiple circuits with a single shunt-trip breaker is to have it feed a sub-panel that supplies every circuit that needs to lose power upon a trip.

Side note: Most shunt-trip breakers can not withstand having the trip coil continuously energized, so you might need to have it fed from a circuit from the panel it supplies.
 
elitegrp100 said:
ok so i have a 20 amp. for hood light ,20 amp. hood fan, 20 amp 3 phase mak-up air , 20 amp fryer , 20 amp stove , and 20 amp base ref, under the hood fan
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Strange that make-up fan is larger than exhaust.

Everything except the exhaust needs to lose power. The lights and both fans should be controlled by the hood switches, and the appliances shut down by either several shunt trip breakers, by one as I described above, or with contactors normally held on that lose power when there's a trip.

I need to ask a few more questions:

Existing or new installation?
Hood fan 120 or 208/240v?
Hood have a control box?
One or two fan switches?
Separate light switch?
Switches in hood, or you install?
Fans have contactors?
 
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