How to install a AFCI brkr. on a 4 wire circuit?

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Yota Master

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So Cal, Ramona CA
What I have is a Commercial customer that just recently had a small electrical fire in a Fume Hood. It didn't go long enough to cause any real damage. It was caused by a piece of faulty test equipment.

Now they are concerned it could happen again I believe it was just a fluke it is the first in 10 years to happen.

They want to install AFCI breakers for all 15 of their Fume hoods. Not a big deal except each one is fed with a 4 wire circuit 3 hots sharing 1 neutral. The breakers are Siemens type BL well Siemens only makes a 1 pole and 2 pole version I need a 3 pole. I spoke to Siemens tech support but they were really no help. All they could tell me is that they dont make a 3 pole breaker.

Is there any way to install 3 single pole 20 amp AFCI breakers and share the neutral at the panel? Or would I have to pull a seperate neutral for each circuit?

Pulling another neutral would be a bear it's conduit then to MC to the equipment and if I remember the equipment is wired with a shared neutral.

Does anyone know of a point of use device like a GFCI that could be installed in place of the existing outlet?
 
separate neutral is the only way it will work.

i've seen pictures of AFCI receptacles, but never any info on where to buy them.
 
Can you install a small load center at each hood with a seperate AFCI for each one? Your not mandated by code to have it at the begining of the circuit for this installation. (assuming they are 120 single phase)
 
Yes you would need a separate neutral in this situation . I have never used this for application you are suggesting . I would probably not recommend this just because of the possibility of nuisance tripping . I would suggest inspecting the equipment once a year for any defects and look at the rest of the electrical system you still make money and the customer feels more secure .
 
Voluntarily installing ark faults on any type of motor load is always a bad idea. Asking for trouble. Have you considered an induct type detector of some kind. Smoke or flame or even ark detectors are available for in duct use and can be equipped with dry contacts that can operate either a shunt trip style breaker or a 3 pole contactor or possibly grab the start/stop or on/off switch depending on how the control wiring is configured. If you use a shunt trip style breaker be sure to consider the extra space that will be required in the panel for each one.
 
Yota Master said:
Does anyone know of a point of use device like a GFCI that could be installed in place of the existing outlet?
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This wall case mountable AFCI has not been released by any manufacturers yet.

If box mounting a GFCI like device at each fume hood is practical, what about setting a little two pole breaker box per hood, each with its own AFCI breaker?
 
Thanks for everyone's input. After talking with the customer they agreed what would be more practical is to adopt a safety maintenance plan for their equipment and a little more training to their employees.

It was basically user error the employee had submerged a liquid mixer in some kind of liquid, the type where you drop the stirrer into the liquid and it has like magnet that spins it.

Well after he was done using it he turned it off but whatever he submerged it in bypassed the on/off switch and the thing ran all night and over heated.

Stuff happens:)

thanks
 
Maybe a small suppression system in the hood that activates the exhaust and kills power to the receptacles.
 
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