Intermittent duty

[NeilG]

Hi

Can I always consider an elevator motor and pump motors intermittent duty and if it's not specified do I have to assume it's 5, 15, 30 or 60 minute rated motor?

 

[jusme123]

sec 430.22(E) also see note below table 430.22(E)

 

[NeilG]

Can I assume that an elevator will not operate on continuous load under any condition since every time it stops on a floor the motor stops?

 

[Julius Right]

As jusme123 already said according to Art430.22E if you are not sure what kind of duty

it is about you have to consider it as continuous.

 

[NeilG]

Correct but I'm asking more of a technical question since the note doesn't say that it has to be marked for non continuous duty it just depends on the nature of what the motor is being used...
Now an elevator in my humble opinion can never work for 60 minutes without stopping probably way less than that
now can I use the 30&60 min column to size the wire?

 

[bwat]

Correct but I'm asking more of a technical question since the note doesn't say that it has to be marked for non continuous duty it just depends on the nature of what the motor is being used...
Now an elevator in my humble opinion can never work for 60 minutes without stopping probably way less than that
now can I use the 30&60 min column to size the wire?

Never? I disagree.

Highly unlikely? Absolutely. But I’d think it’s technically possible and the section states “under any condition of use”. Although bizarre, we could come up with some strange scenario where it did run basically non stop.

 

[NeilG]

Let's assume it's 100 flights If the elevator goes straight up from level 1 to 100 it has to stop for a few seconds and open the door in order to go back down.. That's the way I look at it please correct me if I'm wrong

 

[GoldDigger]

Let's assume it's 100 flights If the elevator goes straight up from level 1 to 100 it has to stop for a few seconds and open the door in order to go back down.. That's the way I look at it please correct me if I'm wrong

A few seconds pause between 100 second run times is not, IMHO, sufficient to cause the motor's heating regime to be intermittent rather than continuous. Especially given that the act of starting will probably generate more heating than was saved during the several second pause.

 

[kwired]

Let's assume it's 100 flights If the elevator goes straight up from level 1 to 100 it has to stop for a few seconds and open the door in order to go back down.. That's the way I look at it please correct me if I'm wrong

That would mean it is not a continuous load but doesn't disqualify use of code posted in post 4. If your motor is not actually marked with a duty rating you actually do need to use 140 percent factor though that maybe is overlooked quite often. But at same time the more a motor is cycled the more it needs to be derated if you want it to last a long time, take something that reverses pretty frequently, it spends a lot of time accelerating, possibly from almost -100% through zero and then to + 100%, it is going to need derated to last very long and will draw more average current on the supply conductors then one that just accelerates once and stays at a certain level/range for extended periods.

 

[Julius Right]

In my opinion in 430.22 E it is not about motor but conductor ampacity.

 

[kwired]

In my opinion in 430.22 E it is not about motor but conductor ampacity.

It is, but properties and use of the motor have an impact on which multiplier you use.

My mentioning the frequent reversing motor - I had a dual head bagging machine once that had final bag feed auger that would reverse to change product flow from one head to the other. product feed was in center of auger and it went either right or left depending on which bag you were filling, and was controlled by the bag scales. Operator would change filled bag while other bag was filling, took maybe couple minutes to fill a bag. Reversing was instant, across the line reverse so that motor saw a lot of near locked rotor current during a shift, and at one time this plant did run 24/7 although production might have had occasional break in product flow. Motor was general purpose continuous duty motor. If it weren't for the frequent reversing probably could have been 1/4 hp or less as it was a 4 inch auger moving powder at a relatively slow rate through only a 24-36" long tube either direction from the center supply. 430.22 had nothing to do with determining how big the motor needed to be to be able to handle the frequent reversing, but at same time was somewhat insignificant as a 14 AWG supply conductor had well over the 140% ampacity the table requires as well on this particular application.

This auger had motor fail one time don't recall original motor HP probably 1/2, but the only 56C motor they had on hand at the time was a 2HP so it got put on there. Next failure, did take some time but was maybe less than a year wasn't any electrical component failure but the output shaft failed from all the excess torque upon each reversing cycle.