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#194045 05/06/10 09:42 AM
Joined: Jan 2004
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An interesting question was presented to me recently and I wonder how a person would respond. " When do I have to use a starter in a motor circuit"? and another way of putting it would be "If a motor has a thermo overload built in to the motor do I need a starter in the circuit"?


George Little
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Joined: Jul 2004
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First you have to ask, what is a motor starter?

In a strict code sense you just need to satisfy all the requirements of 430. A packaged motor starter is the easiest way to do it.
When the overload protection is internal you are basically just looking for a way to start and stop the motor. At that point the size of the motor is probably the determining factor.
The magnetic starter (contactor) allows a fairly small switch to control a large motor. There are drum switches that will run motors up into the 10HP range tho.
I think most fractional HP motors are going to be controlled by a switch with internal O/L protection unless they are part of a larger machine that controls them with a relay.


Greg Fretwell
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My response was that a motor needs to have overload protection usually 125% in addition to ground fault and short circuit protection. If a motor does not have that protection built in and there is no fuse or circuit breaker that meets the need at 125% you end up with a starter or contactor either manual or electrically operated that can contain the proper size overloads. This can also be an issue with small motors such as I've seen on roof-top exhaust fans where usually they field install a small toggle type switch that can accommodate an overload element.


George Little
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What sized motor are we talking about here?

Until you get into large industrial motors, overload protection is usually built into the motor from what I have seen. Then you are really just talking about the branch circuit O/C device to give you short circuit/GF protection. As long as that is selected per 430.52 (generally 250% of FLA up to the next standard breaker) you should be good to go. Fractional HP motors are usually listed for 15 or 20a circuits and usually have internal O/L protection.

The labeling of the motor is the key indicator and replacements might create a troubling situation but we have to inspect what is there.

I would use figure 430.1 and verify that every step was satisfied in one way or another (understanding there may not be a feeder or secondary controller or resistor).
A packaged motor starter properly sized to the motor makes it easy but it is not the only way to comply.

Motors are really the most interesting part of the code as far as all the different situations that might arise. It ranges all the way from a big factory with hundreds of motors the size of small cars to plugging in your blender to make a frozen margurita. It may take different forms but
figure 430.1 applies to all of them.



Greg Fretwell
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I agree with you Greg, about the 430.1 approach. The question came up with an air compressor where the only thing provided was a pressure switch. I think the HP was somewhere around 7.5 and the voltage was 240v. I didn't inspect it but got the call from another inspector.


George Little
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If the motor was internally protected you end up with the need for a properly sized branch circuit OC device (part IV) and a disconnecting means(part IX). The pressure switch is just the controller(part VII).
This might best be done at the panelboard with a properly sized breaker if it is within sight.
If the disconnect was a separate device at the compressor you will be enforcing 110.26 won't you? <ducking for cover> wink


Greg Fretwell
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BTW not to state the obvious, what do the manufacturer's installation instructions say? When all else fails, read the book wink


Greg Fretwell
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G
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"If the disconnect was a separate device at the compressor you will be enforcing 110.26 won't you"?

But of course. I would but I can't guaranty he will.


George Little
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Actually I was looking at the pressure switch on my compressor and it has a lever that locks the contact points in the open position with a marked "off" position. That probably meets the requirement of a disconnect. I have the breaker right there so I never though of it.



Greg Fretwell
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I am not aware of any CODE requirement to use a 'starter' anywhere. Perhaps we need to clear up our terms a bit.

A 'starter' is defined as a contactor with the addition of motor overLOAD protection. This is not to be confused with other functions that packaged starters commonly perform in addition to those first two.

The NEC provides, in various places, for there to be a disconnecting means. If a 'starter' contains a disconnecting means, it is called a 'combination starter.' These days, thats what most of us really mean when we say 'starter.' Keep in mind that, if used as a disconnect, the starter needs to open ALL the 'hot' wires (many starterrs within HVAC equipment don't do this).

OverLOAD protection is not required by the NEC; overCURRENT protection is. While in many cases the two functions are served by the same fuse or circuit breaker, in a starter a different element is used. The 'heaters' in a starter are absolutely useless in protecting the motor from, say, a shorted winding; their response is far too slow. The 'heaters' are very good, however, at protecting the motor from being asked to do more than it is expected to do. That is, they'll limit the time a 1hp motor will be allowed to provide 1.1hp of work. Fuses and circuit breakers would trip on the start-up current if they were set this close to the capacity of the motor.

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