Electrical question for the pro's (ceiling fans)

[Mark Bolton]

I am going to be installing a run of ceiling fans in my shop. Its a commercial building, 10.5' ceilings. Going to install simple 3 blade white metal fans to move heat back down to the floor in the winter. In the past when I have installed fans in these situations for customers I have always run equal length wire runs to so the fans all rotate at the same speed from a single fan control. These fans are going to be fed via surface mounted EMT. So I am basically coming out of the panel (EMT) to a fan control, conduit bend, up the wall, conduit bend, and a straight shot 80' across the shop ceiling picking up the 4 fans (deadheading at the last). Running equal length runs is a pain but I am wonder if there is a trick like perhaps running a 3 wire so you'd be feeding from both ends? It wouldnt be a dual feed but just a loop? Would that achieve anything?

I have a customer who did his own wiring and told me I was crazy and just ran from one fan to the next. With three fans, when he kicks on his fan control the farthest fan in the circuit spins about half as fast as the first.

Thanks for any input.

[Chris Padilla]

240V? 30A? What is the expected load on this circuit? What is the exact fan model/type you are planning to use?

[Mark Bolton]

Chris, they will just be simple 3 blade industrial fans. 120v. I'd guess .5-.6 amps per fan. The load for most average ceiling fans is trivial which (to me) seems to be why the voltage drop over the run length, combined with the draws of each fan in the run, affect each subsequent fan so greatly.

I have run into this in the past numerous times and my electrical subs have always said the work around is equal length wire runs which is what I have always done but its always been residential for me where I can bury a whip in a stud bay or roof cavity.

The EMT situation got me thinking of running a second feed (same circuit, even up-sized) to the end of the run wondering if that would work.

[Lee Schierer]

What about running the main lead to the middle fan and then feed the other two fans from that point or to a central point in the ceiling between all three. The difference in run lengths would be minimal.

[Chris Padilla]

Can you run a pair in series (use 240 V to get 120 V across each fan)? This will keep the current the same for each fan.

[Duane Meadows]

Can you run a pair in series (use 240 V to get 120 V across each fan)? This will keep the current the same for each fan.

IF you run them both at the same speed and everything is ideal. Otherwise you could have 80V on one and 160V on the other! I wouldn't go that route. Kinda like an open neutral... the middle just floats.

Not to mention, you could not use a single control that way!

[Mark Bolton]

Thanks for the input. I guess with a little more research it may all be in the fan control. The voltage drop thing didnt really make total sense to me but I guess the key will be in the fans and a multiple fan control. I was just hoping to have a single fan control but it seems most of the basic fans come with a fan control. I guess I need to find out if I can ditch the included fan control and go with a multiple control but still not sure about the speed issue.

[Jason Roehl]

A year ago, about this time, I was on a Caribbean cruise, which stopped in the Bahamas. We took a tour of a rum distillery in Nassau. In their tasting room (I plead the fifith!) they had 3 ceiling fans, all in a row, and all run by a single motor, connected by belts. I thought it was pretty cool.

301518

What you could also do, is simply power all the fans, and install remote controls. Get 3 of the same brand and model, and you can set the DIP switches so that all the fans are controlled by one remote. They usually come with a wall-mount holster, so you could even put the extra 2 remotes in other convenient locations.

[Mark Bolton]

A year ago, about this time, I was on a Caribbean cruise, which stopped in the Bahamas. We took a tour of a rum distillery in Nassau. In their tasting room (I plead the fifith!) they had 3 ceiling fans, all in a row, and all run by a single motor, connected by belts. I thought it was pretty cool.

301518

What you could also do, is simply power all the fans, and install remote controls. Get 3 of the same brand and model, and you can set the DIP switches so that all the fans are controlled by one remote. They usually come with a wall-mount holster, so you could even put the extra 2 remotes in other convenient locations.

I have seen that same belt drive setup and it is indeed cool. Probably more costly than id care for in a cabinet shop lol.

I have heard pros and cons about the remotes/dip switch thing and one fan getting out of sync from missing the sigbal ftom the remote but that was years ago and mfrs have maybe come up with a work around. Regardless, these were just going to be simple metal industrial fans so no bells and whistles. Was just trying to decide if I pay the extra 100 smacks each to get reversible models.

[Chris Padilla]

The key is in the fan motor and/or control. We have multiple fans in our large routers and servers and they all must run at the same speed but of course, there are only inches of wire difference in this small area compared to 20-30' of wire in your situation. Unless the fan itself has circuitry that allows it to run in a constant-current mode (over a 'reasonable' range of voltages), it's speed will be dictated by the voltage across it and in your case, the last guy's will be lower than the first guy's voltage and its speed will be slower. If you have a control for each fan, I think you'll be better off if you wish them to run at similar speeds. You might need to spend a bit more for better fans if you want them on a single control.

[Chris Padilla]

I did a little quickie circuit analysis for you, Mark.

I used 120 V for the source voltage.

From there to the first fan is 40 feet.

Then 20 feet from fan 1 to fan 2 and fan 2 to fan 3.

I looked up the DC resistance of #8, #10, #12, and #14 wire and used, respectively, 0.06, 0.1, 0.15, and 0.25 ohms/100 feet.

I also assumed each fan would draw 1 A of current and thus have a resistance of 120 ohms. The numbers can scale easily.

The attached picture file shows some columns of numbers with the voltages fans 1-3 might see using the various gauges of wire and then I went ahead and plotted them on a graph.

Maybe this gives you a better feel for what happens in long runs of cable.

[Mark Bolton]

Makes total sense. This was whybi was thinking of running a three wire with one making a loop to the end of the circuit thinking this would feed the fans from the other end as well and that third lead would only suffer the voltage drop lf the wire itself. Lees option of feeding at the center would be a good solution as well.

Thanks for the leg work. I knew the drop would be considerable but that shows it pretty clearly.

[Anthony Whitesell]

I like the graph, but I think there is something amiss with the numbers.

What was your formula to derive 107V for fan #1?

Looking only at Fan 1, 40 ft, #8 wire at 0.06 ohms per 100 feet, and a 1A current draw.

0.06 ohms / 100 ft = 0.0006 ohms per foot * 40 feet = .024 ohms

V = I*R = 1A * 0.024 ohms = 0.024 volts (or voltage drop or loss)

120V - 0.024V = 119.976 V at fan 1.

Additionally, a general/approximate rule of thumb is 50 feet of a given gauge wire at maximum amperage will result in 3% loss. Ie., 50 feet of 12g wire at 20A has a 3% loss resulting in 117V at the load.

[Chris Padilla]

301582

Here is my quick circuit I used to analyze Mark's situation. This one is set up for the #8 wire. I lumped the wire resistance to one side of the circuit to make things easier. Don't forget that the return wire also adds resistance. :)

I only made the 1 A assumption for the fan to explain why I used 120 Ohm. Imagine the fan is hooked to 120 V with zero ohm wires.

The actual current in the fan is NOT 1 A...it is actually a bit less...according to my circuit.

:)

[Chris Padilla]

Okay, I found my error. All the resistance values for the wire are too high by ONLY 2 orders of magnitude!!! LOL! DOGGONE IT!!!!

I guess something didn't feel right. Mark, ignore my analysis...completely wrong. Even with #14, that last fan will see 119.1 V. I'm not sure why there would be a problem running your wires daisy-chain like you always do.

Tail tucked firmly between legs and backing away.............. :D

[Anthony Whitesell]

The only thing I can think of as to why each of three fans would run slower than the previous is if there was same odd series-parallel wiring combination. Possibly also impacted by the fan controller as well.

If the fans were at 50', 75' and 100' from the source. The difference in voltage from the source to the first and from the first to the third would be 3% each (or 3.6V). I find it hard to believe that a ceiling fan would run noticeably slower on a difference of 3.6V (or 116.4 vs. 112.8).

Seems like there is another, yet, unknown in the story. My concern with running 3 fans from the same controller would be overloading the controller itself.

[Mark Bolton]

The only thing I can think of as to why each of three fans would run slower than the previous is if there was same odd series-parallel wiring combination. Possibly also impacted by the fan controller as well.

If the fans were at 50', 75' and 100' from the source. The difference in voltage from the source to the first and from the first to the third would be 3% each (or 3.6V). I find it hard to believe that a ceiling fan would run noticeably slower on a difference of 3.6V (or 116.4 vs. 112.8).

Seems like there is another, yet, unknown in the story. My concern with running 3 fans from the same controller would be overloading the controller itself.

There are controllers out there rated for 5 fans. My only guess on the speed issue is the fans being such low amperage but again its a guess.

[Mike Heidrick]

This thread is funny to me. Fan in shop - dust will vary the speed a ton more than length of supply line.

[Bill George]

At 1 amp draw your voltage drop will not be a factor. I have never tried this but, set up each fan on its own controller and adjust the speed on each so they are the same. Feed all the controllers from 1 single pole switch and use it to turn the fans on and off at the same time. You would need to keep the speed fairly fast so the motors will start.

It was always my understanding that unless the motor was DC and its not, the frequency of the controller was the speed control.
This is the Only circuit I could find and its 220 volts > http://www.circuitstune.com/2012/01/ceiling-fan-regulator-speed-controller.html

[Lee Schierer]

Don't most fan speed controllers use sine wave clipping to control fan speed? If that is the case, wouldn't the input voltage to fan #1 be something less than 119 due to the clipping?

[Phil Thien]

An air scrubber mounted in a corner at about shoulder height and aimed (output) at the ceiling, will do an amazing job of equalizing the temps. Even on the lowest setting (which is fairly quiet). And you get the bonus of cleaning the air, too.

[Mark Bolton]

This thread is funny to me. Fan in shop - dust will vary the speed a ton more than length of supply line.

Dust varying the speed of a fan? Thats a funny one. I have been in peoples homes with tendrils of dust trailing off the blades.. doubt it slowed them.

I have seen the progressively slower fan issue first hand. Its completely obvious at all speeds but majorly obvious at very low speed (which is where my fans would mostly run). One instance I saw, at the lowest speed setting the first fan would run like youd think and the last was turning slow enough that you likely could have read something if it were written on the blades.

I was hoping to avoid three fan controls just for ease of installation and to keep it clean but I really dont want the speed ussue. If that's the route then that's the route but as was said, something has to be at play.

[Dick Strauss]

Mark,
I have an idea that might work for you. Use Lee's idea and wire to the center fan. Then add a loop of wire to the center fan circuit only that matches the lengths to the outer two fans. This loop of extra wire could be run into the attic area to hide it. The outer fans will be connected to the straight shot wire coming from the switch and distributed to them through the middle fan. The center fan motor will be connected to the extra loop (that is connected to the main wire feeding all three fans). This way all runs are the same length without messing with conduit lengths, etc, and all the speeds are as close to the same as the resistance in the respective motors.

Exceeding a 3% Voltage Drop
At less than 1A per motor x 3, there should be no reason to run anything bigger than 14g unless you have a run longer than 190 ft one-way. With a 2A total motor draw, you can have 290 ft of one-way run and still make the 3% voltage drop limit.

By the way, I'm not a pro so run it by the other guys to see if there might be an issue with my idea. I have no idea what lengths we are talking about but I know it isn't a good idea to coil too much wire together (it can't dissipate the heat from internal resistance) in the case of the added center loop.

[Ole Anderson]

Before you do this, take time to measure the difference in air temp up and down. I bet you will find that you are wasting your time. Air movement in the summer is of course a whole different matter. I installed three 3 bladed fans in the peaked ceiling (24') of our church 24' on center and we actually used them last night to help cool the choir during rehearsal. And the fans were daisy chain wired. All seem to spin at the same rate off a simple VS fan controller. I think everyone is overthinking this one. Besides even if the air is 5 degrees warmer, the perceived cooling effect of moving air will negate the warmer temp.

[Mark Bolton]

At 1 amp draw your voltage drop will not be a factor. I have never tried this but, set up each fan on its own controller and adjust the speed on each so they are the same. Feed all the controllers from 1 single pole switch and use it to turn the fans on and off at the same time. You would need to keep the speed fairly fast so the motors will start.

It was always my understanding that unless the motor was DC and its not, the frequency of the controller was the speed control.
This is the Only circuit I could find and its 220 volts > http://www.circuitstune.com/2012/01/ceiling-fan-regulator-speed-controller.html

Bill,
My entire motivation for the single speed control and feeding from one end (like you'd feed any simple circuit) was just for ease, cost, and clean/simple install and operation. If I have to go to any extremes I will simply three controls and feed to through the single conduit. I was just looking for the optimal solution.

I think both you, and Lee, are on to what may likely be the real culprit here with regard to the progressively slower fans Ive seen. I never had any idea what control they were using on these fans but Im now wondering if the clipping Lee mentions, and your post with regards to the frequency being use to control speed, is what may be at play here. It wasnt my job to do so but it would have been interesting to eliminate the fan control temporarily and see how they ran. For all I know it may not have even been a multi fan control.

It all interesting none the less, and its just a simple little job, but Id rather only fool with it once ;-). Im not a fan of having to go back on things when Im done.

[Mark Bolton]

Before you do this, take time to measure the difference in air temp up and down. I bet you will find that you are wasting your time. Air movement in the summer is of course a whole different matter. I installed three 3 bladed fans in the peaked ceiling (24') of our church 24' on center and we actually used them last night to help cool the choir during rehearsal. And the fans were daisy chain wired. All seem to spin at the same rate off a simple VS fan controller. I think everyone is overthinking this one. Besides even if the air is 5 degrees warmer, the perceived cooling effect of moving air will negate the warmer temp.

Ole,
I experience this on a regular basis. I have high storage in the building and its sweltering up there when its cool down on the floor. I was planning on reversible fans so there really would be no moving air hitting anyone in the space. The fans would be pushing the air down the outside walls of the building (just like your heating system is designed to curtain the exterior walls). Im not saying its an ideal situation, and weatherization would be a much wiser investment. But even if I opted for non-reversing fans, I could do this job in perhaps 4 hours, for 350 bucks or so. That doesnt go too far with weatherization and with the work I have to do the 4 hours as opposed to a longer option, is very pretty serious motivator.
Having the fans running in the summer doing some cooling would be very nice too.

I have wall mounted air moving fans at the moment that help immensely and on one end of the shop I have a modine that moves a lot of air and I keep the fins pointed fairly low which helps. That said, these fans are very directional and they leave a lot of areas of the shop fairly cool.

One entire wall of the shop all overhead doors which is a massive loss. Two of those are going to be eliminated, framed in and insulated, which will make a big difference. That said, we are back to the free time to work on my building as opposed to produce work issue. Hiring it out gets even worse.

Thanks.

[Bill George]

Mark you are on the right track, voltage has little to do with the speed of an AC motor. The speed is controlled by the number of poles in the motor (fixed) and the frequency of the supplied alternating current to the motor. The sine wave clipping is a form of frequency control.

What I have done in the past when working on a control project is do a mock up in the shop and try some ideas. Once again, as Dick has pointed out and proved by the math, at the low amp draw of this circuit voltage drop is not a factor.

[James Tibbetts]

Just reading through the posts, and using a handy online calculator, here's what I think.
Run from panel to junction box at center point of fans. (assuming worst case of 100' run to junction box; 10 ga wire @ 15 amps, 8 ga. @ 20 amps. 3% voltage drop for both.)
Voltage drop from there to the farthest fan on a 12 ga. feed is less than 1 volt.
I'm assuming that the current draw of about .5 amps per was the run current.
Remember that your controller and wiring would need to be rated to handle the start-up draw of 4 loaded motors.