Single phase motor starter and overload

[JeffKiper]

I'm looking for how others do it. I need to start a 1 phase motor. I have always used a regular 3 phase Motor Protected Circuit Breaker and looped L2 back thru L3 to keep them balanced.

Is there a better or cleaner way of doing it? A standard 3 pole contactor and MPCB?

 

[dummy_bit]

The few times I've dealt with single phase motors, we did the overloads/MPCB the same way looping L2 back through L3. Most equipment OEMs we've dealt with have also done it that way.

 

[mylespetro]

Can confirm this is also how I've done it and seen it done, even on industrial sites.

 

[JeffKiper]

That's the way we have done it for years. Just looking to see if anyone else had a different idea.

 

[John Morris]

That is the way we wire single phase motors. Loop L2 and L3. Actually I've never seen it done any other way.

 

[Robb B]

Just for some clarification for future readers:

The reason for looping the conductors back through the starter is that many modern electronic overload devices have a detection circuit for phase imbalance (current is typically >5% different between phases) or a phase loss detection, both of which will trip the overload.

To the OP: further clarification, these motors are not the normal single phase thermally protected types, correct? They do in fact require a starter for protection?

 

[lfe]

As long as it is a motor with easy starting, it will work well with a standard MPCB, but if it carries a load with more inertia such as the turbine of a fan, it is better to use overcurrent protection and a separate thermal protection relay coupled to the contactor, since you can choose one of class 20 or class 30 that allows a longer starting time due to the low starting torque of those motors. Always using L2 and L3 in a loop.

 

[I_Automation]

A true single phase motor overload would have 2 poles.

Imagine the engineering and production costs to put one on the market - a 3 pole one would be a lot less expensive. and is readily available.

I have seen on older panels a single heater type overload, but for a single phase of 2 line leads that leaves one lead unprotected.
I have also encountered German machines with single phase motors and heaters where they only run one line through a circuit breaker, a single pole contactor like home air conditioning units, and then run the second line (not grounded neutral) straight back to the service disconnect so that line is HOT at all times and the heater/motor runs of the controlled line grounds out and trips the breaker.

 

[Robb B]

A true single phase motor overload would have 2 poles.

Imagine the engineering and production costs to put one on the market - a 3 pole one would be a lot less expensive. and is readily available.

I have seen on older panels a single heater type overload, but for a single phase of 2 line leads that leaves one lead unprotected.
I have also encountered German machines with single phase motors and heaters where they only run one line through a circuit breaker, a single pole contactor like home air conditioning units, and then run the second line (not grounded neutral) straight back to the service disconnect so that line is HOT at all times and the heater/motor runs of the controlled line grounds out and trips the breaker.

https://www.grainger.com/product/SQUARE-D-Manual-Motor-Starter-Non-Reversing-1H416 for $588 USD, comes with a box!

 

[I_Automation]

https://www.grainger.com/product/SQUARE-D-Manual-Motor-Starter-Non-Reversing-1H416 for $588 USD, comes with a box!

That's not a motor overload for using after a contractor.

Plus, no way a 3 pole overload would be near $600. I get up to 25A for under $100 and 40A for $115