Bleacher Motors

[RogerD]

Need some help,

I've got a bleacher system in a high school that has 5 - 1/2 HP motors with name plate ratings of 115V / 6.2A and are not thermally protected. The Manufacturers recommendation is a single circuit with a 40A circuit breaker.

I'll admit it's been sometime that I've had to address code issues so I might be mistaken so some input would be appreciated.

Article 430.33 states;

"A motor used for a condition of service that is inherently short-time, intermittent, periodic, or varying duty, as illustrated by Table 430.22 (E), shall be permitted to be protected against overload by the branch-circuit short-circuit and ground-fault protective device, provided the protective device rating or setting does not exceed that specified in Table 430.52.
Any motor application shall be considered to be for continuous duty unless the nature of the apparatus at drives is such that the motor cannot operate continuously with load under any condition of use".

The bleachers take about 15 seconds to fully extend and rest at a minimum of 2 hrs. so each motor could be classified as a short time or intermittent motor. My question is can this article be applied to a multi-motor circuit?

 

[iwire]

In my opinion you could use one circuit, one controller but need five thermal overload units.

 

[steve66]

In my opinion you could use one circuit, one controller but need five thermal overload units.

Just looking at the code section quoted, it seems like bleachers would meet the exception, and the thermal overloads would not be required.

I'm curious if you are seeing seeing something else, or if you just don't think the exception applies?

 

[iwire]

Just looking at the code section quoted, it seems like bleachers would meet the exception, and the thermal overloads would not be required.

I'm curious if you are seeing seeing something else, or if you just don't think the exception applies?

I think it would be difficult if not imposable to size the branch circuit breaker large enough for 5 motors to start but small enough to comply with the exception. I may be wrong.

 

[petersonra]

Need some help,

I've got a bleacher system in a high school that has 5 - 1/2 HP motors with name plate ratings of 115V / 6.2A and are not thermally protected. The Manufacturers recommendation is a single circuit with a 40A circuit breaker.

I'll admit it's been sometime that I've had to address code issues so I might be mistaken so some input would be appreciated.

Article 430.33 states;

"A motor used for a condition of service that is inherently short-time, intermittent, periodic, or varying duty, as illustrated by Table 430.22 (E), shall be permitted to be protected against overload by the branch-circuit short-circuit and ground-fault protective device, provided the protective device rating or setting does not exceed that specified in Table 430.52.
Any motor application shall be considered to be for continuous duty unless the nature of the apparatus at drives is such that the motor cannot operate continuously with load under any condition of use".

The bleachers take about 15 seconds to fully extend and rest at a minimum of 2 hrs. so each motor could be classified as a short time or intermittent motor. My question is can this article be applied to a multi-motor circuit?

T430.52 requires no more than 250% for a CB. That would be a 20A CB (rounding up). I don't see how you can go higher than 20A on a single CB.

It would not bother me any if they put them all on the same 20A CB. What chance is there they will run all 5 at once anyway?

 

[Besoeker]

In my opinion you could use one circuit, one controller but need five thermal overload units.

Whether or not required by code, I think that would be good engineering practice.

 

[iwire]

It would not bother me any if they put them all on the same 20A CB. What chance is there they will run all 5 at once anyway?

My guess is that they must run at the same time.

 

[Jraef]

To my mind, the cost to put in even just some simple little "toggle switch" type 1 pole manual motor starters would make this all a moot point.

Use one in this style of enclosure as your J-Box near the motor, and you end up with a local LO/TO point as well.

 

[steve66]

I think it would be difficult if not imposable to size the branch circuit breaker large enough for 5 motors to start but small enough to comply with the exception. I may be wrong.

Sounds like a good point - you are probably right.

 

[kwired]

Need some help,

I've got a bleacher system in a high school that has 5 - 1/2 HP motors with name plate ratings of 115V / 6.2A and are not thermally protected. The Manufacturers recommendation is a single circuit with a 40A circuit breaker.

I'll admit it's been sometime that I've had to address code issues so I might be mistaken so some input would be appreciated.

Article 430.33 states;

"A motor used for a condition of service that is inherently short-time, intermittent, periodic, or varying duty, as illustrated by Table 430.22 (E), shall be permitted to be protected against overload by the branch-circuit short-circuit and ground-fault protective device, provided the protective device rating or setting does not exceed that specified in Table 430.52.
Any motor application shall be considered to be for continuous duty unless the nature of the apparatus at drives is such that the motor cannot operate continuously with load under any condition of use".

The bleachers take about 15 seconds to fully extend and rest at a minimum of 2 hrs. so each motor could be classified as a short time or intermittent motor. My question is can this article be applied to a multi-motor circuit?

Sounds to me like you have 5 units that each need maximum of 20 amp overcurrent protection. Why not run a 40 amp feeder or even less if done with a multi-wire feeder and tap a 20 amp max circuit at each one? You need disconnect near each one anyway.

I may even be tempted to run a 20 amp 4 wire MWBC if the supply is 120/208 three phase and run up to six units on one 20 amp 3 pole breaker, then no overcurrent device would even be necessary at the motor disconnects, as mentioned with the feeder scenario.

 

[RogerD]

T430.52 requires no more than 250% for a CB. That would be a 20A CB (rounding up). I don't see how you can go higher than 20A on a single CB.

It would not bother me any if they put them all on the same 20A CB. What chance is there they will run all 5 at once anyway?

All 5 motors do run simultaneously, that's the issue. Design engineer is seeing it as applying as myself, however local inspector is not and has asked for further info.

 

[kwired]

All 5 motors do run simultaneously, that's the issue. Design engineer is seeing it as applying as myself, however local inspector is not and has asked for further info.

Do you have one utilization equipment with 5 motors, or do you have 5 separate motors? If it is one utilization equipment then there should be one nameplate, controller, etc. that is for all 5 of them. If they are individual units (even though they may run at same time) then they essentially need 5 circuits. If they were larger motors it would not be as tempting to try to put them on one circuit. These are just right size they may actually work on one circuit - mostly depends on if the breaker will hold during starting, but I still think it would be best to either use the 3 phase MWBC I mentioned earlier if that is possible, otherwise use a feeder and individual branches for each motor if you don't want 5 circuits from the panel. I would probably use 15 amp breakers on these unless they will not allow starting (they likely will though).

 

[dicklaxt]

40amp breaker and 5 manual motor starters with LO is my vote.I think the motors will be at max torque almost immediately and the 40 will/should carry the inrush.

dick

 

[JoeStillman]

I believe the short-circuit protection size is specified in 430.53(C)(4), but that article stipulates individual overload protection. It might be hard to argue that 430.33 applies because the 40A breaker might never trip on locked-rotor current. I can see how they came up with 40A though. It's (6.2x2.5)+6.2+6.2+6.2+6.2 = 40.3. (That's 6.2x6.5 for you algebrains)

What makes the motors run? Is there a control panel? Wall switch? If it was my project, I'd put an Allen-Bradley bulletin 600 motor-rated switch with overloads at each motor.

 

[USMC1302]

Sounded to me like a motorized bank(s) of telescopic bleachers. All I have seen have (1) controller w/overload, usually located somewhere terribly inconvenient if it trips(behind the retracted bleachers). If that is the case separate overloads could be trouble for the bleachers if a motor quits and the others continue to run. Some people aren't too quick on the trigger of the pendant control

 

[steve66]

Sounded to me like a motorized bank(s) of telescopic bleachers. All I have seen have (1) controller w/overload, usually located somewhere terribly inconvenient if it trips(behind the retracted bleachers). If that is the case separate overloads could be trouble for the bleachers if a motor quits and the others continue to run. Some people aren't too quick on the trigger of the pendant control

I'm also wondering if the unit has overloads or thermal protection somewhere. If the instructions just call for a 40A circuit, I would think the manufacturer has used some method to make this comply with the code. There are impedence protected motors, and internal motor cutouts that can eliminate the requirement for separate overloads. Maybe the bleacher motors comply with one of these.

I would call the company that makes this and ask for clarification.

BTW, I haven't seen an answer to your original question:

My question is can this article be applied to a multi-motor circuit?

In my opinion, if a section applies to a single motor, it would apply to a multi-motor circuit. You are simply applying that code section to each motor in the multi-motor circuit. Although as Bob pointed out, its harder to comply with the OCP limits for a multi-motor circuit.

 

[Jraef]

I'm also wondering if the unit has overloads or thermal protection somewhere. If the instructions just call for a 40A circuit, I would think the manufacturer has used some method to make this comply with the code. There are impedence protected motors, and internal motor cutouts that can eliminate the requirement for separate overloads. Maybe the bleacher motors comply with one of these.

I would call the company that makes this and ask for clarification.

BTW, I haven't seen an answer to your original question:



In my opinion, if a section applies to a single motor, it would apply to a multi-motor circuit. You are simply applying that code section to each motor in the multi-motor circuit. Although as Bob pointed out, its harder to comply with the OCP limits for a multi-motor circuit.

There IS a solution, albeit a complex one.

You could use the new little IEC style "mini-circuit breakers" (MCBs) that are UL listed as UL1077. That is technically the same as a Manual Motor Starter and provides both OL and SC protection. The caveat with using those is that they cannot be used as Branch Circuit Proection, so a UL489 MCCB must be in the circuit ahead of them. In this case, the 40A CB would be that device. You could also add an aux. contact that can be wired into the control circuit and by putting them all in series, you could make it so that if one trips, they all shut down.

 

[dicklaxt]

There IS a solution, albeit a complex one.

You could use the new little IEC style "mini-circuit breakers" (MCBs) that are UL listed as UL1077. That is technically the same as a Manual Motor Starter and provides both OL and SC protection. The caveat with using those is that they cannot be used as Branch Circuit Proection, so a UL489 MCCB must be in the circuit ahead of them. In this case, the 40A CB would be that device. You could also add an aux. contact that can be wired into the control circuit and by putting them all in series, you could make it so that if one trips, they all shut down.

Now we are having fun get some interlocks in the mix,much more enjoyable.

dick

 

[steve66]

There IS a solution, albeit a complex one.

I think the solution may well be that the manufacturer has it covered.

The installation instructions normally tells the electrician exactly what he has to provide. If they say just provide a 40A circuit, the manufacturer probably has the overload requirement covered somehow.

I just had a project that included telescoping bleachers, and the instructions just said to provide a circuit with a disconnect. (The disconnect was similar to the one someone else mentioned -behind the bleachers.)

I just dug into the spec. for that unit, and I found the control panel has a frequency inverter and overload protection for the motors. I'll bet the OP's is similar.

 

[kwired]

I think the solution may well be that the manufacturer has it covered.

The installation instructions normally tells the electrician exactly what he has to provide. If they say just provide a 40A circuit, the manufacturer probably has the overload requirement covered somehow.

I just had a project that included telescoping bleachers, and the instructions just said to provide a circuit with a disconnect. (The disconnect was similar to the one someone else mentioned -behind the bleachers.)

I just dug into the spec. for that unit, and I found the control panel has a frequency inverter and overload protection for the motors. I'll bet the OP's is similar.

If there is overload protection then that is fine - next we need short circuit and ground fault protection. 430.53 still limits us to a 20 amp overcurrent device for this application. Since the OP has said the motors are more than 6 amps we may not even be allowed to use this section to allow multiple motors on the circuit. Now part C may allow a larger circuit but basically says it must be part of a listed assembly - and likely will have overcurrent protection as part of the listed assembly according to what is said in part C.