Contactor for 3 devices

[patricknola]

Hey Guys, I'm bidding a job where I supply power to a Wells wvu-72 ductless vent hood. The hood system needs (2) 208v 3 phase 40 amps circuits for deep fryers, (1) 208v 90 amp circuit for a range oven, and it needs a 20 amp circuit that feeds the ventless hood. The hood has a terminal block to land 1 electrical circuit , input and output , a contactor and the alarm interface. I spoke to the manufacturer to see if they had any recommendations about a contactor and the did not, but i was told I need a contactor that will open (shut down) all appliances in the case of an emergency. Can anyone recommend the best configuration or what type of contactor to use that will open all appliance circuits?

 

[infinity]

We typically feed these types of loads from a shunt trip main CB in the panel to switch off all of the circuits at one time.

 

[hbiss]

Yes. I would install a 200A ML sub panel for those circuits and feed it from a 200A 3 pole shunt trip breaker in the main panel.

In looking at the installation instructions:

https://wells-mfg.com/wp-content/upl..._E-05-2019.pdf


Page 12 shows the electrical, and they do indicate a contactor. Also, the contacts to control the contactor are (unfortunately) only SPST and closed when the hood is operating normally (which would make sense for controlling a contactor). BUT that's going to be a BIG contactor (or contactors) for those loads and it's going to have to be energized all the time.

The correct way to do this is with a shunt trip breaker as above, but you are going to have to use a small SPDT control relay off the SPST hood contacts to "reverse" the logic. In other words that relay will be pulled in all the time by the hood but you use its normally closed contacts (those contacts that are closed when the relay is de-energized) to control the shunt trip breaker. You would do that with power from another 20 or 15A breaker in the sub panel so that when the system trips, the shunt trip breaker trips then there is no longer power applied to its coil. You need to do this because most shunt trip breakers are not designed to have power applied continuously to its coil.

-Hal

 

[petersonra]

Yes. I would install a 200A ML sub panel for those circuits and feed it from a 200A 3 pole shunt trip breaker in the main panel.

In looking at the installation instructions:

https://wells-mfg.com/wp-content/upl..._E-05-2019.pdf


Page 12 shows the electrical, and they do indicate a contactor. Also, the contacts to control the contactor are (unfortunately) only SPST and closed when the hood is operating normally (which would make sense for controlling a contactor). BUT that's going to be a BIG contactor (or contactors) for those loads and it's going to have to be energized all the time.

The correct way to do this is with a shunt trip breaker as above, but you are going to have to use a small SPDT control relay off the SPST hood contacts to "reverse" the logic. In other words that relay will be pulled in all the time by the hood but you use its normally closed contacts (those contacts that are closed when the relay is de-energized) to control the shunt trip breaker. You would do that with power from another 20 or 15A breaker in the sub panel so that when the system trips, the shunt trip breaker trips then there is no longer power applied to its coil. You need to do this because most shunt trip breakers are not designed to have power applied continuously to its coil.

-Hal

the only problem with this kind of arrangement is every time you get a few cycles of power outage your shunt trip breaker will open.

 

[hbiss]

Because of the constantly energized control relay? Maybe. Remember that any interruption will cause the power to drop on the shunt trip circuit also. So it's a matter of how fast that relay operates. If I had a problem with it, I would use a relay with a low voltage DC coil with a small power supply and put a cap across the coil to keep it pulled in for at least a second after power disappears.

But this whole work around all can be blamed on the hood manufacturer not providing at least one set of SPDT contacts like every other one does with a micro switch. Then we could do away with that control relay. I would contact them and ask if there is something we are not seeing or if not, could they provide SPDT contacts. They do mention alarm contacts but nothing is shown.

-Hal

 

[patricknola]

Hey Guys , thanks for the response. I spoke to wells mfg. and i was told not to use a shunt trip breaker. I was told that everything i need is in the hood and it is made to drop out power to all appliances if there is an emergency. They told me to run 4 circuits to the hood, 2 for the fryers, 1 for the range and one for the hood power that will also power the pressure switches I/m trying to figure out how to configure the contactors I must choose and supply. There is only one terminal on the block to feed all 3 contactors.

 

[LarryFine]

I/m trying to figure out how to configure the contactors I must choose and supply. There is only one terminal on the block to feed all 3 contactors.

Simply parallel the contactor coils, supplied from that wire and neutral at 120v.

 

[hbiss]

Hey Guys , thanks for the response. I spoke to wells mfg. and i was told not to use a shunt trip breaker. I was told that everything i need is in the hood and it is made to drop out power to all appliances if there is an emergency. They told me to run 4 circuits to the hood, 2 for the fryers, 1 for the range and one for the hood power that will also power the pressure switches I/m trying to figure out how to configure the contactors I must choose and supply. There is only one terminal on the block to feed all 3 contactors.

Gee, I thought they just said that everything you needed was in the hood? Yeah, don't use a shunt trip breaker because we don't provide the contacts so you can- like every other manufacturer does.

Now you have to buy some big 3 pole contactors and a cabinet to put them in. Probably going to cost as much as that hood.

And as Larry says, just wire the 120V coils all in parallel, hot through TB5 and TB6 from a breaker that you want to supply the control power from. Alternately you can use contactors with 208V coils, again all in parallel and one hot through TB3 and the other through TB4. Then you can jumper to L1 and L2 for power.

-Hal

 

[LarryFine]

It would be simple to interface a shunt-trip beaker with the hood panel if you want to. You just need a 1p breaker in the shunt-equipped panel that supplies 120v to the COM of an available relay, and run the N.O. contact back to the shunt in the panel. Don't forget the hood panel still needs an uninterrupted source.

 

[Stebs]

It would be simple to interface a shunt-trip beaker with the hood panel if you want to. You just need a 1p breaker in the shunt-equipped panel that supplies 120v to the COM of an available relay, and run the N.O. contact back to the shunt in the panel. Don't forget the hood panel still needs an uninterrupted source.

Every time they shut the hood down, the shunt trip breaker would trip. That means every morning, they would have to turn the hood on and then go reset the breaker to get the appliances back. With contractors, it would all be automatic.

 

[hbiss]

It would be simple to interface a shunt-trip beaker with the hood panel if you want to. You just need a 1p breaker in the shunt-equipped panel that supplies 120v to the COM of an available relay, and run the N.O. contact back to the shunt in the panel. Don't forget the hood panel still needs an uninterrupted source.

Isn't that what I showed him how to do in post #3?

Every time they shut the hood down, the shunt trip breaker would trip. That means every morning, they would have to turn the hood on and then go reset the breaker to get the appliances back. With contractors, it would all be automatic.

We don't know that turning the hood off opens the contacts that control the contactors or in my case the control relay, but you have a good point. Now that you got me thinking about it, betcha it does. What happens with the fire contacts?

This is just a poor design that doesn't give the installer the flexibility that normal systems do. On top of that it would be nice of them to include a schematic of the way the thing is wired. My guess is there isn't a whole heck of a lot of demand for a ventless commercial kitchen hood so they aren't going to put a lot of effort into it. I can't see it being allowed at all with gas appliances.

-Hal

 

[Stebs]

We don't know that turning the hood off opens the contacts that control the contactors or in my case the control relay, but you have a good point. Now that you got me thinking about it, betcha it does. What happens with the fire contacts?


-Hal

Page 12 of the linked to manual states that the contacts open when the hood is turned off, there’s a fire, or a malfunction.

 

[hbiss]

Yes, I see that now.

Digging deeper I also see:

Air flow sensors continually monitor air flow optimizing performance and grease removal while an interlock system will not allow cooking appliances to function if filters are missing, clogged...

The manufacturers instructions and design provide for no other way except contactors so on that alone we need to follow those instructions if for no other reason than to minimize liability if that thing ever were to malfunction and result in a fire.

-Hal