Shunt trip breakers/Kitchen Hoods

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new_ee

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I think I have a few good questions here for a beginning engineer.

What equipment do you use a shunt trip breaker for?

Do you shut the hood itself down (exhaust fan)?

Do you also shut cooking equipment under the hood down (fryers, ovens, etc)?

Is this a code requirement? If so, what code do these requirements come from?
 
Re: Shunt trip breakers/Kitchen Hoods

One more question: Do shunt trip breakers require an extra pole? For example a 3 pole piece of equipment would require 4 poles for a shunt trip breaker?
 
Re: Shunt trip breakers/Kitchen Hoods

One more question: Do shunt trip breakers require an extra pole? For example a 3 pole piece of equipment would require 4 poles for a shunt trip breaker?
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Depends upon the breaker frame size. Usually 2 and 3p 100a frames and above don't require extra space and they are capable of being contained within the frame of the breaker. The ST solenoid is installed to the right or left pole from the handle. On smaller breakers the ST must be installed in a separate addition to the breaker that takes up an extra pole space.
With regard to code requirements, it would be best if you obtain a copy of the code requirements in your area to assure that you meet your local code reqirement which may be different than others.
 
Re: Shunt trip breakers/Kitchen Hoods

new_ee - You want NFPA 96. Read it closely. Generally you will find that supply fan should shut off & exhaust fan remains enabled.
 
Re: Shunt trip breakers/Kitchen Hoods

got it thanks. is there any way to shut the equipment down without a shunt trip breaker? some type of contact or something?
 
Re: Shunt trip breakers/Kitchen Hoods

The last responder indicated that the supply fan should be shut off, but the exhaust fan is enabled.

That indicates that the purpose of the shunt trip is to shut off the supply fan, but maybe leave the fryer,oven and exhaust fan on.

I know that a shunt is a parallel path around a device often used for meters (i.e. shunt meter). When used as a breaker (i.e. shunt trip breaker), it must be used for items in this cooking device (supply fan) that need to be shut off earlier, i.e. require less current, so a parallel path is set up to by-pass the exhaust fan, fryer and stove in this case, which would require more current before it trips.
 
Re: Shunt trip breakers/Kitchen Hoods

This is a different connotation of the word "shunt," and it has nothing to do with parallel conditions. A "shunt breaker" receives an external signal that activates a trip mechanism internal to the breaker. This has nothing to do with the amount of current any single device would draw. You use a "shunt breaker" to force one load to turn off, whereas you may wish other loads to continue to run.

In the case of a fire in a kitchen, you don't want supply fans to blow fresh air into the space, because that would feed the flames. On the other hand, you may wish to continue operating the exhaust fans, to remove smoke from the space. So the external signal that activates a "shunt trip" device on the breaker for the supply fan might come from the Fire Alarm System.

{Edited to add: I do not know why the word "shunt" is used in this application. My guess is that the mechanism through which the breaker is forced to trip takes the external trip signal and operates the breaker's trip coil in parallel with the circuit that would have tripped the breaker on an overload. Someone more familiar with the internal operation of breakers may confirm or refute this guess.}

[ September 26, 2005, 03:47 PM: Message edited by: charlie b ]
 
Re: Shunt trip breakers/Kitchen Hoods

Originally posted by charlie b:
This is a different connotation of the word "shunt," and it has nothing to do with parallel conditions. A "shunt breaker" receives an external signal that activates a trip mechanism internal to the breaker. This has nothing to do with the amount of current any single device would draw. You use a "shunt breaker" to force one load to turn off, whereas you may wish other loads to continue to run.

In the case of a fire in a kitchen, you don't want supply fans to blow fresh air into the space, because that would feed the flames. On the other hand, you may wish to continue operating the exhaust fans, to remove smoke from the space. So the external signal that activates a "shunt trip" device on the breaker for the supply fan might come from the Fire Alarm System.

{Edited to add: I do not know why the word "shunt" is used in this application. My guess is that the mechanism through which the breaker is forced to trip takes the external trip signal and operates the breaker's trip coil in parallel with the circuit that would have tripped the breaker on an overload. Someone more familiar with the internal operation of breakers may confirm or refute this guess.}
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correct as always. thanks. now does anyone know of another way to shut the fryers, ovens, etc off without using a shunt trip breaker?
 
Re: Shunt trip breakers/Kitchen Hoods

If the fryers ovens etc are electric the cheapest way out is usually a dedicated panel with a shunt trip main or a number of branch circuit shunt trip breakers for each piece of equipment.

Other than that you would be using contactors which will end up costing more.

However if the equipment under the hood is gas fired usually the plumber installs a manual operated valve that shuts when the ansual system trips. That gets us electricians off the hook.
 
Re: Shunt trip breakers/Kitchen Hoods

As with all codes, I've seen different requirements in different AHJ areas.
In all areas I've experienced it has been required to turn off fresh air make-up and any cooking device that produces direct heat (electric heating elements). If the fire suppression system is "wet", normally any power under the hood (outlets, motors, etc.) must be shut down due to electrical hazards associated with the "wet" fire chemical.
In several jurisdictions, the fire alarm trip must also activate the exhaust fan if it is not "on".
I did not see anyone answer your "alternative method" question. But yes can can?also accomplish the task with contactor(s). Several of the fast food chains have a "prewired" hood control system that accomplishes all of the above with contactors and only require input power and possibly some inner-connections.
 
Re: Shunt trip breakers/Kitchen Hoods

sorry Bob,
overlapped you..i was busy typing and spell checking while u posted
 
Re: Shunt trip breakers/Kitchen Hoods

Originally posted by iwire:
If the fryers ovens etc are electric the cheapest way out is usually a dedicated panel with a shunt trip main or a number of branch circuit shunt trip breakers for each piece of equipment.

Other than that you would be using contactors which will end up costing more.

However if the equipment under the hood is gas fired usually the plumber installs a manual operated valve that shuts when the ansual system trips. That gets us electricians off the hook.
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thanks. this is exactly right. unfortunately the equipment is 3 phase electric and i didnt realize that shunt trips required an extra pole. there is not enough room on the panel for the 3 extra poles (oven, fryer, griddle). i realize thats a design flaw (not having any extra spaces on the panel). i think the only way get around this is using a contactor at this point.

[ September 26, 2005, 04:21 PM: Message edited by: new_ee ]
 
Re: Shunt trip breakers/Kitchen Hoods

Should the question originator use a contactor to solve this issue, he will need to provide the correct settings on the contactor (used as a electromechanical relay in this case) so that the correct electromechanical relay signal is sent to trip the single breaker on the corresponding subpanel, correct?

It is interesting to note as explained previously that it depends on whether an extra breaker is even required as to whether extra space on the panel is even required in order to still rule out the shunt breaker.

It is also interesting to note where the shunt breaker gets its external signal if not from a electromechanical relay. Maybe it is a heat heat sensing transducer?
 
Re: Shunt trip breakers/Kitchen Hoods

Newee this is what you want. I highly recommend it. It's all prewired and has plenty of extra dry contacts to use for circuits that you want to stay on or shut off in the event of a fire. You can also add (extra $) ON & OFF controls for the hoods on the outside of the door.
valiantrestrauntequipment_1864_11141384


You can find it here.Captiveaire Web Page

In most cases I believe it will tie into an ANSUL fire suppressant system via a low volt micro switch.

Dave
 
Re: Shunt trip breakers/Kitchen Hoods

Originally posted by iwire:
However if the equipment under the hood is gas fired usually the plumber installs a manual operated valve that shuts when the ansual system trips. That gets us electricians off the hook.
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You remind me of my boring story. :)
 
Re: Shunt trip breakers/Kitchen Hoods

Thanks a lot George!
After using your link and reading your "Not So Boring" story I forgot I was in another thread & I replied as if it was this thread!!!

You did that on purpose! :)
Dave
 
Re: Shunt trip breakers/Kitchen Hoods

Sorry, I forgot to mention the labels on the side of the bottle:

Caution: Side-effects of clicking on this link may include fatigue, drowsiness, incontinence and nausea. Avoid operating heavy machinery while clicking this link. If clicking the link results in an erection lasting longer than four hours, please immediately consult a physician.

Hey, they say it on TV! :D
 
Re: Shunt trip breakers/Kitchen Hoods

New_ee,
If you're doing a hood design that will be installed within a fairly large city, then they will likely have a "hood inspector" who will have his own personal preferences. I just permitted and got a hood installed in the City of Pittsburgh, and they have their own worksheet that must be filled out by the design professional. They also have a rather ugly situation where the hood inspection people and the fire department do their own inspections and do not necessarly coordinate their work with each other. The hood inspector may give you a stamp of approval and the fireman fails you later. Bad stuff but thats how bureaucracy works.

Prior to designing or specifying any equipment, talk to the inspection dept. They reserve the right to require things above and beyond the electrical, mechanical and fire codes. Now, if your job is out in the suburbs, you'll probably have a lot more latitude in what you do.

The situation you want to avoid is where you do a good design by the book and the contractor prices the work accordingly for the owner. Then he goes to get the work permitted and inspected and the city wants the work done in a different manner or using different components. It gets real ugly real fast!!
 
Re: Shunt trip breakers/Kitchen Hoods

Do you also shut cooking equipment under the hood down (fryers, ovens, etc)?
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NFPA96-10.4 requires that ??all sources of fuel and electric power that produce heat to all equipment requiring protection by that system shall be automatically shut off.? Further, the shutoff devices used for this purpose ?shall require manual reset?

got it thanks. is there any way to shut the equipment down without a shunt trip breaker? some type of contact or something?
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I prefer a contactor to the shunt trip breakers. If you can group all your under hood appliances into one panel install a normally open contactor in feed to the panel and your good to go. The control circuit runs through the hood suppression systems n.c. microswitch then to the contactor coil. My problem with shunt trips is that they require an external power source. If you turn off that power source (or it fails) the shunt trip breakers will not trip when you have a fire under the hood.

Another idea (that I have never tried) is to use undervoltage relays wired to n.c. microswitch instead of shunt trips wired to n.o. microswitch. They cost about the same and also require an extra space in the panel (usually). However if control power is interrrupted to the undervoltage relay for any reason devices under the hood will trip.

It is also interesting to note where the shunt breaker gets its external signal if not from a electromechanical relay. Maybe it is a heat heat sensing transducer?
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What? Shunt trip breakers usually get there power from a 120V, 20A circuit somewhere in the kitchen. The relay is used as an alternate to the shunt trip breakers not to supply them.
 
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