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#129825 - 09/16/05 08:50 AM Circuiting  
Traineeeee  Offline
Junior Member
Joined: Sep 2005
Posts: 2
New to this forum.
I need help in showing a circuit diagram.
There is an exhaust fan in a hood over a convection oven. The exhaust fan motor needs to be circuited in such a way that the fan must run all the time as long as the oven is ON. In other words the oven and the fan motor are tied together thru a common switch.
The fan motor specs are: 208V, 60 HZ, 3phase, 1725 RPM, 1/2 Horsepower, Vol(CFM):1300.
Also what would the load of this fan motor in terms of KVA??
Thanks in advance.

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#129826 - 09/16/05 09:01 AM Re: Circuiting  
iwire  Offline
Joined: Jan 2003
Posts: 4,391
North Attleboro, MA USA
Welcome to ECN

This is tricker then it sounds as you should not be modifying the wiring in the convection oven. And the oven should probably not be controlled on a regular basis from an external switch. It may have electronics or built in cool down modes that will not like having the power killed like that.

My first thought is to use a current sensing switch installed in the branch circuit to the oven. When the oven is turned on the current sensing switch closes and starts the fan.

If this is commercial you may also want to provide an off delay for the fan of 15 - 30 minutes after the oven shuts down for a cool down period.

Sometimes we also have to provide proof of air flow before the oven can start that can be a problem also.

Bob Badger
Construction & Maintenance Electrician

#129827 - 09/16/05 09:15 AM Re: Circuiting  
iwire  Offline
Joined: Jan 2003
Posts: 4,391
North Attleboro, MA USA
Here is a current sensor that I mentioned.

[Linked Image]

You run one leg of the load you want to monitor through the hole in the unit, the trip point on this one is adjustable from 2 to 20 amps.

This is handy as it can ignore a few amps of control power but activate when the running load is on.

[This message has been edited by iwire (edited 09-16-2005).]

Bob Badger
Construction & Maintenance Electrician

#129828 - 09/16/05 10:24 AM Re: Circuiting  
Traineeeee  Offline
Junior Member
Joined: Sep 2005
Posts: 2
Thanks for the response.
But here is the situation. The electronics involved in oven is not at all a concern. The project is in the construction phase and the electrician is on the job. I need to provide him a circuit diagram just to show that the switch for the oven is directly hooked on to the fan motor. Can u draw a simple circuit showing 3 phase 208v coming to the oven and also going to the fan siting right above it. The main branch circuit is 20 Amps for a panel. Appreciate. And yes what would be the load of the fan motor, 1/2 HP?

#129829 - 09/18/05 02:00 PM Re: Circuiting  
Tesla  Offline
Joined: Jun 2004
Posts: 1,273
Sacramento, CA
Traineee you are in over your head.

Get a real electrician involved as soon as possible.

Your situation is not simple at all and would typically be drafted by a licensed electrical engineer and provided as a detail in the prints.


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