motor starter without overload relay / protection?
- Thread starter anbm
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petersonra
Senior Member
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- Northern illinois
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- engineer
If the tm cb is a mpcb
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- Bremerton, Washington
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- Master Electrician
Or if the motor is thermally protected.
And there is an exception, for a motor that is manually controlled if under 1 hp, where you are at the motor, so this would be seldom used.
And a mpcb can only be used as part of a listed controller.
And there is an exception, for a motor that is manually controlled if under 1 hp, where you are at the motor, so this would be seldom used.
And a mpcb can only be used as part of a listed controller.
petersonra
Senior Member
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- Northern illinois
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- engineer
Mpcb are not mcps. Mcps can only be used as part of a listed controller.
- Location
- Bremerton, Washington
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- Master Electrician
Thanks I made a typo.
petersonra
Senior Member
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- Northern illinois
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- engineer
It does. But it does not have to be an overload relay
What's the difference between overload protection and overload relay in starter? I thought they are same?
petersonra
Senior Member
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- Northern illinois
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- engineer
They often are, but don't have to be. Google type f combination starter.
Nope.
Overload protection means you protect the stator coils from burning up. As an obvious example in a submersible motor it’s water cooled. Using a current simulation is a waste of time. Virtually all of these have Klixxons epoxied into the stator coils and are wired in series with the starter coil. This is an extremely reliable and inexpensive way of protecting the stator that does not need an overload relay.
Stepping up to the 250+ HP world at this point the rotor is more thermally limited than the stator. At this point typically we have microprocessor motor protection relays. It uses CTs and they are typically door mounted but don’t need to be. Some older starters use a fixed current relay set to say 4-5x FLA with a timer in conjunction with the traditional overload relay. Often these also use RTDs which are more effective than overload relays except again during startup. So it’s a “starter relay” in the end but it’s not a bimetallic or eutectic overload relay.
Finally the overload relay doesn’t need to be on the contactor. It is very common for IEC starters to use an MMS (manual motor starter) with an integrated bimetallic relay. In this configuration the contactor is optional and is only needed for automatic control. So technically we’ve just rearranged the parts. It’s not fundamentally different,
And as another Code/direction with fire pumps the wiring is oversized and they are installed without an overload relay at all. Unless the motor burns up (shorts out) we do not trip.
David Castor
Senior Member
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- Washington, USA
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- Electrical Engineer
An overload relay is a type of motor overload protection - but not the only type.
I appreciate your response but this is way beyond what I need to know
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- Bremerton, Washington
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- Master Electrician
Like an overload?
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- San Francisco Bay Area, CA, USA
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- Electrical Engineer
A "motor starter" moniker does imply that the device INCLUDES an OL relay. Without the OL relay, is is just a motor contactor. Motor contactors are perfectly valid for motors that have some other means of OL protection. The NEC dictates that there must be "running overload protection" in a motor circuit and what levels of protection are provided at a minimum, but does not dictate how that is accomplished. As said, there are several ways to achieve this.
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