Attic Fan Wiring


Old 10-05-01, 10:23 AM
Visiting Guest
Posts: n/a
I have a 220 Volt 1930's attic fan. I want to wire this with two switches, one on main floor and one on second floor:
1) Do they make 220V three way switches?
2) If they don't make 220V three way switches: Can I wire a circuit with two double pole switches in series with each other so each has a direct run to the fan and when either is turned on it puts power to the fan?
Thanks, FH
Sponsored Links
Old 10-05-01, 03:02 PM
green jacket's Avatar
Join Date: Sep 2000
Location: Williamsport and Blue Bell, Pennsylvania
Posts: 502
Cool how much do you want to spend?

Multi location switching can be acheived with a contactor and start-stop stations. The wiring of this might be best for a professional to do, unless you are up to the challenge. Somebody would need to email you some diagrams of what to do. (how to wire)

The swiches you want are not made explicitly for your application. IS this fan currently installed with permanent wiring that includes a switch nearby, within 50 feet and within sight of the fan?
There are NEC articles pertaining to motor control.

Old 10-05-01, 03:22 PM
Visiting Guest
Posts: n/a
You are allowed to disconnect only one of the two hot conductors serving that motor when using a switch as a controller. If you use a snap switch to control a motor that snap switch must be rated in amps equal to twice the full load current rating of that motor. If the full load current of your attic fan is 10 amps then you may use three way switches to control you motor only if you buy 20 amp rated three way switches. This three way would be wired with the normal 15 or 20 amp rated wire 12 or 14 awg conductors if copper. The second hot conductor would be hot to the motor 24 hours a day 7 days a week. The break of the second hot wire by way of the two three way switches would be the controlling method of the motor and the switches would be considered as the controller devices operating that switch. There would have to be a 220 volt rated plug and receptacle installed or a non fused disconnect that disconnects all hot conductors from that motor in sight of that attic fan motor as the required disconnect form for that motor.

Hope this helps

Old 10-09-01, 06:53 AM
Visiting Guest
Posts: n/a
One lead hot?

How do you decide which line stays hot 24 hours? This motor is old and there is no serial number plate or anything on it. It is hooked up by a belt to the 5 foot fan and I guess I can trial and error put power to the seperate wires before I mount it to decide which will control it. I feel that it is a ten amp motor but it could be larger. Do they make a 3-way switch rated higher than 20 amps?
Thanks, FH
Old 10-09-01, 10:10 AM
Visiting Guest
Posts: n/a
You are going to have to do some experiments and push that motor through some tests. How are you sure that this motor is 220 volts? This is a must to know first.

If it were my motor, I would hook 120 volt 20 amp protected to that motor and see if it just hums or takes of normally. If the motor starts up normally and turns the fan as it should on 120 volts then you can go to the next tests. If the motor just sets and hums then you can put 220 volts to the motor. Once you test the motor to just hum for a few seconds on 120 volts then hook a 220 volt 20 amp breaker 12 awg copper cable to that motor. Just energize the motor a few seconds testing to see if the motor comes to speed normally. If the motor still hums only then you have wired the motor wrong or you have bad capaciters or the centrifical switch is stuck in the run mode instead of the start mode. If the motor operates normally without becoming hot to the touch for about 3 minutes you have found the right voltage and you can go to the next test.

Once you have the right voltage and the motor is running properly without getting hot, you need to take an amp probe tester and test the amps being used under normal running. This will tell you the running amp ratings of the motor with the fan running. Then come back in and tell us what that amp reading was and we should be able to help set up the wire and breaker sizing once we have that info.

Once you have knowledge that the motor is running properly and is not getting hot and you know the running amps pulling on the circuit then you need to increase the load on the motor until the motor kicks off. This will tell us that you have a thermal cut out on the motor. If you increase the motor load on that motor to the point of stopping the motor or smoke starts coming out immediately shut off the motor. This will tell us if you have a thermal overload built into that motor or if we have to include an overload in the motor wiring design. You can increase the motor load to that motor while the fan is running by apply pressure to a wood board touching the pulley of the fan. This will increase the motor load pushing the motor to the point of causing the overload or thermal to react and shut off the motor. IF you hear a click and the motor stops trying to run then later starts back up then you have a thermal overload built into that motor.

Leave the amp probe connected measuring the amps being pulled on that motor. Remember what the motor amps were while the motor was running normally. If you increase the motor amps being pulled more than a 40% increase above the running amps under normal loads then you have no thermal cut out or overload. Stop the test and we will install an overload in the wiring design to that motor to protect it from overheating.

Then we will worry about the three way switching after we know what we have.

Boy it would have been easier if your nameplate ratings were still on that motor. All these tests would not have to be performed if that nameplate tag were there.

Hope this helps

Old 10-10-01, 09:44 AM
Visiting Guest
Posts: n/a

Yknow, I never pick the easy home inmmprovement projects you see the nice folks on the TV shows do. No I have to find something that I can pull my hair out over (see my other post at thread:
to see!
I will try to get all the info you need. Meanwhile I am more worried about the other thread since it is getting cold. I also have 40 rolls of Miraflex R-25 insulation and 6 bags of loosefill that are calling my name to work in the attic before I can really get back to this fan project.
I will get info as soon as possible.
Thanks, FH
Old 10-11-01, 12:55 PM
Visiting Guest
Posts: n/a
I received an email questioning the safety of just switching one hot conductor to a motor leaving the second hot energized continuously.

I understand his concern and really don't like leaving a hot continuously energized especially in a dwelling where unskilled home owners tend to trust the switch to de-energize a piece of equipment to work on it thus getting a very shocking surprise.

I try my best to respond as to what the Code says is the minimum safety standards with as little personal thoughts or feeling included in my replies. I try to talk minimum safety standards and leave the design more than Code to the installer. At least when they know what the minimum is they then will know just how much more than safe they are going.

The following is a copy of the NEC article dictating the controlling of motors by allowing one hot conductor to remain energized.

430-84. Need Not Open All Conductors
The controller shall not be required to open all conductors to the motor.
Exception: Where the controller serves also as a disconnecting means, it shall open all ungrounded conductors to the motor as provided in Section 430-111.

As you can see the NEC allows this practice. However there is concern about leaving that hot conductor continuously hot. I too don't care for this wiring style.

The main concern to me is not switching a grounded conductor controlling a motor unless both all the hots and the neutral are disconnected simultaniously. If you use a grounded conductor in a controller of a motor and this machine can hurt someone if there is a ghost startup such as having chains, saw blades, belts, etc, then if a person happens to drop a wrench in the switched side of that lone neutral switched in the controler then the motor can start false by the wrench creating a ground path to any nearby metal. This scenerio is extremely dangerous.

If you are concerned about not switching all hot conductors in a motor controller and you still want to use 20 amp three way switches as controllers then you may use a simple contactor then use the three way switches to complete the control circuit of the magnetic coil of that contactor. The contactor can de-energize all conductors going to the motor controlled by the magnetic coil controlled by the smaller three way switches.

The one who emailed me about his concerns and myself both thought this explaination might be worth telling.

Hope this helps promote safety

Old 10-12-01, 03:09 AM
Visiting Guest
Posts: n/a
Previous Wiring

Thanks for previous post. I too don't like leaving a continuous hot to motor. I am trying to figure out old wiring because the old owner said they had two switches controlling fan, one on main floor and one on second floor. I have looked at the switches and they seem to be double pole 20 (possibly 40) amp switches.
It looks like it is not a three way system but instead they kept the second floor always on and switched from the main floor. Maybe they had the second floor switch there in case the upstairs sleepers got tired of hearing the fan run at night. I don't know. This was in an era before AC.
I might go back to this system also since I would do primary controlling on main floor anyway.
Does NEC allow for this type switching???
Thanks, FH
Old 10-12-01, 07:58 AM
Visiting Guest
Posts: n/a
Yes, you can use two double pole switches to control that motor in two locations. However if you do it the way you discrbe you will find that you may hit a situation where you can not shut off the fan without going to the oppisite floor to the second switch and first shut that one off. This wiring design would not operate as and either or, you will often find times when you will have to go to both switches to turn off the motor.

My advise is to install the three way switches [can be either 15 amp or 20 amp rated] controlling the magnetic coil of a double pole contactor. Same as a normal motor controller is done. This way you can turn the fan on or off either location. Run you fan power source to one set of contactor points then run the motor circuit to the load side of that contactor. Then pick up a normal power source from the nearest receptacle and install the three way switch system energizing a 120 volt magnetic coil that will pull in to energize the fan motor. The 3 way switches would only carry the load of the magnetic coil this way and not the load of the motor. The contactor controlled by the three way switches would carry the load through the contacts of that double pole 20 amp rated contactor instead of the three way switches carrying the motor load.

Code does not require this type wiring design. A controller is allowed to shut off only one hot leaving the motor hot continuous and meet the Code requirments. I am just trying to tell you an option, not tell you what is better. The choice is yours as to how much more that minimum safety standards you want to go.

HOpe this helps


Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off

Thread Tools
Search this Thread
Display Modes