Electricians? Weird problem!!!!!

[DarkBlack]

Op: Can you better explain exactly where you measured 108volts? Looks like you’re dropping 16 volts somewhere, which maybe due to a loose connection. Does the fan have a locked rotor amp rating? Your complete wiring path may be inadequate.
Did you try it back through the cord that it worked with originally?

 

[LittleBittyBigJohn]

fan motor hummed & tiny bit smoke came out!!!!!

They only put so much smoke in those things. I think it requires ALL the smoke to function properly. But anything can be a smoke machine if it is operated poorly enough .

I didn't see anything wrong with your diagram either. I would still check hot to neutral just to be sure you don't have some wires touching that shouldn't be. It is really tight in those quad/duplex boxes for all the wire you have to cram in there.

 

[CobyRupert]

I agree with the above poster who said to find out where / why you measured 108V.
Also check connections are good.

Did you measure the 108V when fan was humming and stalled (in a locked rotor condition)? Basically, the large locked rotor current would cause a voltage drop in the wiring from the panel so that the 120V (124.5V) is dropped to 108V. (Knowing circuit length and wire gauge, one could calculate how much current it takes to drop 16 volts (or whatever it is) in a #12 AWG wire).
I’m surprised the breaker doesn’t trip. Maybe it would eventually. It’s probably a race between the breaker and the motor making smoke because it’s wires can’t handle large locked rotor currents for very long before burning up.
Motor starting capacitor may be toast.

For giggles let’s say circuit’s length from panel is 100’, so 200’ total travel in hot and neutral conductors. Say #12 gauge wire has resistance of 1.93 ohms/1000’. So 200’ of wire would be .386 ohms. 16 volts drop through .386 ohms only happens when 41 amps is “humming” through the fan.
As a rule of thumb, the “locked rotor” (aka “stalled”) current of a motor is about 6 times its normal current. So 41 amps is in the ballpark.
If you look at the trip times (curves)of a 20amp circuit breaker experiencing 41 amps, I bet your breaker would of tripped right on schedule, probably around 10 seconds.
If you had wires crossed and a dead short, breaker would of tripped in about .01 seconds.

 

[3Ts]

When I wired my barn I had something similar happen. Turned out that when I pushed the wires back into the box, the sharp end of the bare ground wire cut thru the insulation of the white neutral wire and put voltage on the ground wire. And this was on a different circuit from the main breaker panel. You may want to pull all the wire connections out of the box and recheck to see if it all operates properly and put things back in one at a time.

I agree, your wiring schematic should not be a problem and should work correctly.

 

[TheMan419]

I’ve never seen, or heard of a 3 speed fan, that was designed so it would burn up, if started in low or medium speed

Exactly. Ceiling fans have a chain to pull to switch the speed, but are turned off and on with a switch. They can be left in low/med speed and turned on/off with the switch with no problem.

 

[kenmbz]

Could be a floating ground or neutral too. But fan smoke is long gone, sometimes ok, but not often.
Cross wired, or wires touching also could be the issue.

 

[Fuddy1952]

Here's what I did this morning as I explained it to the contractor friend who was helping me:
"The motor is bad.
I tried down below connecting motor to extension cord...hummed & didn't turn. So I went up on scaffolding connecting motor wires right to cord like we had before & same thing.
An electrician wrote me and said little puff of smoke meant start winding burned up. One he had he got lucky & it opened winding where he could resolder it. Most motors you can't get to it.
Now if I plug it into a ground fault breaker circuit it trips instantly. Plugging into another outlet breaker doesn't trip but you can tell it's drawing lots of current.
It (motor hot & neutral) measures 4.6 ohms.
I took front off panel box and everything is wired ok...it's just too weird.
My plug in tester says it's OK. I measure zero ohms ground to neutral. 123.6 vac black to ground or white neutral.
Electrician said motor had "the smoke of death"!
I'll have to get another fan, electrician said rewinding is more expensive, probably motor is too.
I do have a very large squirrel cage fan, about same cfm I'm thinking, but outlet is rectangle I'm guessing 30"X 18". Heavy...probably weighs 50-60#. That one is belt drive motor to squirrel fan blades."

 

[Fuddy1952]

Oh...I forgot to thank everyone for replies.
Thank you!

 

[Midniteoyl]

I’ve never seen, or heard of a 3 speed fan, that was designed so it would burn up, if started in low or medium speed

Never said it was designed to, but 'could' and 'might'.

 

[Lineman North Florida]

Just out of curiosity where you say you picked up power at a simple single light fixture, are you sure that the black wire is the hot wire? Many people will use the white wire on a single run from the switch to the light fixture as their hot wire, and very few mark it with a ring of black tape. Only way to be sure is check white to bare ground to be sure, inside wiring is one of those things that sometimes will still work even when someone has wired it up wrong.