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"?

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.

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.

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.

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.

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>

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

"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.

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.

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.

Reno, Of course the NEC required overload protection



Overload protection will seldom (ever?) be provided by the same device that gives you over current protection since that must be able to sustain starting current. Typically in an inverse time breaker that will still be 250% of FLA and if you have an instantaneous trip device, it reaches scary numbers. Thermal and overload protection is commonly the same device. Maybe that is what you were thinking.

Reno:

Greg is correct - the term is "overload" when we are talking about motor protection. The term is "branch circuit, short circuit and ground fault protection" when we are talking about the circuit protection. I would also draw your attention to 430.55 ('08 NEC) where we are permitted to use a single device to serve both needs. The caveat being we must protect the motor from overload based on 430.32 in the process. The reality of it is this only works on smaller motors.

I know others out here have had to replace a complete overload relay assembly and it's heater element because the co-ordination was not proper in the circuit and something had to give and it was the heater element melting and destroying the overload assembly.

Just a side note since Greg mentioned disconnect, we would need a disconnect within sight of the motor and the controller if it were a non-combination type starter.

Greg, you are correct, and I thank you for the clarification.

However, there are plenty of situations where even motors are not required to have any manner of 'overload' protection - whether internally, or as part of a separate starter. That these are invariably either small motors, or part of a specific appliance really isn't the point.

Rather, the question was whether 'starters' were required. There is no such requirement. While it's been a while, I recall seeing motors controlled by a collection of separatly enclosed widgets - one for the disco, one for the fuses, one for the contactor - and it being anyone's guess where the 'heaters' might be located.

After all, we've all seen motors that 'let the smoke out.' and I think this manner of 'enforcement' beats any codebook for effectiveness.

We can't, as Bill Engvalls observed, fix 'stupid.'

It's not all doom and gloom, though. I've been quite impressed by the newer 'electronic overloads' some starters have. These gizmos protect the motor from a number of things in addition to a basic overload. With all this focus on 'code,' sometimes we overlook the effect the free market can have.

Another detail ....

Remember that another component of a 'starter' is the contactor. I can think of no code requirement for there to be any manner of contactor; the use of full-power rated switches and plugs is allowed.

If you had 'heaters' but no contactor, you would not have a 'starter.'

Lest some newcomer try to read something into my comments that I'm not saying, I'll be the first to extoll the advantages of using a contactor; that's another discussion.

I suspect that even the small motors that have no obvious O/L protection will still have a thermal fuse in them if they want the U/L seal of approval.
There are still a lot of hand held tools that will go until they burn up.

I'm not sure that all motor starters necessarily contain overload protection.
I know that Hubbell/Bryant makes 30A 3-pole manual motor starters with no overload protection. I've installed them on 5HP 208V 3-phase disposals in commercial kitchens before. The disposals had their own built in thermal protector.

The only heaters I'm familiar with use bimetallic physics to break the hold circuit for the contactor coil.

I'm trying to imagine any other layout...

How would a heater operate without a contactor?

Again, it comes down to vocabulary - and out maddening exceptions to our rules!

A 'starter,' by definition, has an overload protective element in it .... except for the 'drum switch,' which is considered a reversing motor starter, though there is no overload protection in it.

As for the term 'heater,' that seems to be trade slang for 'overload protection element.' I suppose that's because it takes heat to make most of them trip. While there are some that use a bimetallic element, most seem to use some manner of ratching mechanism, springs, and solder. When the solder melts, the 'gear' is rotated by the spring and the connection opens. Once the solder cools, your reset button re-loads tension on the spring as it closes the contacts.

"Heater" contacts are fairly small, so they are not capable of handling very much current. They only need to open the control circuit. The solder, by contrast, is directly heated by the full load current. Open the control circuit, and the contactor opens - interrupting the current flow through the solder.