Motor rotating after being lock out/ tag out

[mtnelectrical]

I started a conversation while waiting for my van to be fixed with a fire contractor that was servicing the extinguishers of this shop. He had an accident 3 months ago, lost the tip of one his fingers while servicing a roof top exhaust fan part of the range hood commercial top on a commercial place he was working. He said he found the breaker for the exhaust fan locked out the breaker and went up to service the unit, when he opend the exhaust fan he manually move the pulley and belt of the motor and the motor suddenly started rotating and cut the tip of his finger. He went to the ER with this part of his finger on ice to see if it could be reattached by unfortunately they couldn't. I asked him if there was other controls for that motor but he says there is only one, but he said that he was found out that the capacitor of the motor (motor is wired for 120v) might did that. That is the question, Is it possible for a capacitor to suddenly start a motor for a fraction of time? I know defenetly that does not happen in 3 phase motors unless there is some conttrol problems. Sorry from the long post.

 

[mxslick]

My "bull puckey" meter pegged on this one..there are some things that make me doubt that this is possible.

First off, what is the "fire contractor" doing by messing around with a commercial exhaust fan? That is usually the HVAC guy's territory.

Even if the cap stored a charge (which it wouldn't as it is directly connected to the start/run windings) it wouldn't have enough kick to rotate a motor with a blower wheel hard enough to cut someone's finger tip OFF, or even cause a deep enough cut that it couldn't be saved. (Even a motor with a start switch needs a fast enough rotation to activate the switch and you'll not be able to get it going that fast by hand. Further, rotation would OPEN the switch not close it.)

How does he KNOW it was the right breaker that was locked out? Did he check the motor terminals for voltage?

I noticed it was a belt driven fan. One possibility would be if there was a gust of wind that hit the blower wheel just right it could, maybe, turn it hard enough to cause a cut.

Finally, don't most roof-top exhaust fans have a local disconnect, which I'm pretty sure is required by Code?

There are way too many holes in that guy's story. I think he was just clumsy and is looking for something (read: someone) to blame.

My experience in this area? Years of fixing roof-top exhaust blowers for film projectors.

 

[augie47]

My money would be on "he found the breaker labeled exhaust fan" and not necessarily the exhaust fan breaker. As mxslick noted, 430.102 would require an insight disconnect.

 

[LarryFine]

One possibility would be if there was a gust of wind that hit the blower wheel just right it could, maybe, turn it hard enough to cause a cut.

That's my first thought.

Finally, don't most roof-top exhaust fans have a local disconnect, which I'm pretty sure is required by Code?

Yep.

 

[iwire]

I will go with 'Too embarrassed to tell the real story'.

 

[charlie b]

He said he found the breaker for the exhaust fan (and then he) locked out the breaker. . . .

Since we are not dealing with an electrician, he probably doesn't speak the same language. When a person who is not in the profession uses a word or phrase that has a particular meaning to members of the profession, we should not presume that he thinks he is saying what we think we are hearing. What does the phrase "locked out the breaker" mean to the person telling this story? We see that phrase, and we think LOTO. He says that phrase, and he may simply mean that he turned it off. Thus, absent a tag, another person sees the breaker turned off, does not know why, and turns it back on.

I don't, of course, know what actually happened. My comment is simply a caution to take a little extra effort to make sure there is no miscommunication, when a non-professional uses a professional term.

 

[One-eyed Jack]

It could be he was trying to trip the belt off and used his finger as a pry bar. Not a smart move but it will cut the meat part of a finger off.

 

[LarryFine]

It could be he was trying to trip the belt off and used his finger as a pry bar.

I've replaced too many motorcycle tires to try that.

 

[gadfly56]

...

First off, what is the "fire contractor" doing by messing around with a commercial exhaust fan? That is usually the HVAC guy's territory.

..

Around here, fire contractors often clean the hoods served by the suppression systems they maintain. That means popping the fans off or otherwise getting access to the duct leading down to the hood to clean it. I will agree that LOTO isn't a very familiar concept in the industry, especially for "mom & pop" outfits.

 

[Article 90.1]

If he was following proper LOTO procedures he would have placed his own LOTO device, or supplemental device to lock the breaker out. Just seeing that someone else has a lock, tag, tape, or otherwise does not insure your safety.

Scenario 2: Breaker may have been labeled properly, but there is a make up air fan and motor, and en exhaust fan and motor with separate OCPD's.

How many times have we tried to work on a roof top unit for a multi family dwelling, etc. and when we got to the roof there were dozens of RTU's and none of them were labeled.

"Measure twice, cut once" or "Meter twice..."

 

[mtnelectrical]

I got all you guys excited, that's good. My question was if the capacitor might've been able to rotate the motor for a split second, yes or no? Well the guy was servicing the fan like gadfly56 said fire contractors can open this units and work on them,service, maintain them, and yes it is supposed to have a disconnect but the guy told me he had serviced this units before and know the breakers location and before I mentionated the LOTO procedures he did so, there was no power coming from panel. I think that if you start MUA fan it might move the exhaust fan if it is powerful enough and there is no way to air to escape (all doors closed in kitchen), but powerful to move enough to cut some meet and bone, I don't know.

 

[LarryFine]

I've worked on many kitchen exhaust systems. The drafts can be rather strong, even with no fans on.

The blower wheel's larger diameter gives it plenty of mechanical advantage over the belt and pullies.

 

[sii]

Several years ago, one of my coworkers was replcing the belt on a 50 hp blower at work. He used his hand to roll the motor around and managed to leave his index finger under the belt. He got what the doctor called a "glove extraction"; basically it pulled all of the meat off the bone of his entire finger. I didn't get to see it but they said it looked like Skeletor from the He-Man cartoon series.

Anyway, the company president comes out to do a walk through of the scene a couple days later, after the machine is up and running again. He freaks out and tries to fire the guy saying that he must not have taken the proper LOTO precautions and so forth. We tried to explain to him that LOTO does nothing to prevent that motor from turning, only prevents it from becoming energized but he wouldn't buy any of it.

The only thing that saved his job was that the HR assistant came out and took extensive pictures of the machine immediately after the accident, including the lock on the main disconnect for the machine.

 

[jmellc]

Not sure about the cap. Never heard of it kicking a motor like that. My bet is the improper labeling. I have seen that time after time. Labeling is often poorly done to begin with and gets worse with time, as new units are added, old ones discontinued, etc. I guess the wind issue could be valid, haven't seen it firsthand. I forget when on site disconnects became code, but I have seen a lot of older units without them.