motor overload

[aarifisher]

If a motor has a service factor of more then 1.15 but has a temperature above 40c,
What do I choose 1525% or 1.15%. ???

 

[tom baker]

Its per the overload mfg instructions. And what motor temp are are referring to? Ambinent air? Winding temp?
One very good solution is to use ambient compenstated overloads, such as the IEC type.

 

[poeboy]

I usually size o/l's at 125% of FLA, unless for the specific application, the manufacturer suggests otherwise. Different applications have different standards as well..... I think Fire Pumps are allowed to be way over that 125% figure.

 

[aarifisher]

Its per the overload mfg instructions. And what motor temp are are referring to? Ambinent air? Winding temp?
One very good solution is to use ambient compenstated overloads, such as the IEC type.

I'm talking about Ambient temp, and about the code not mfg instructions.

 

[John Valdes]

There is only one thing on that nameplate you need to be looking at for sizing the overload. (FLA). Never consider SF for the overload setting. Running in the SF can and will shorten the life of the motor.

 

[iwire]

There is only one thing on that nameplate you need to be looking at for sizing the overload. (FLA). Never consider SF for the overload setting. Running in the SF can and will shorten the life of the motor.

I would say that is a design choice, it also means you might has well bought a motor with a 1.0 SF.

If I recall the overload selection tables are different for different service factors.

 

[kwired]

Setting of overload protection according to NEC is maximum allowed setting. There are times by personal choice that I have set protection at a lower value. This works well on a motor that has a fixed load that is less than motors maximum to detect other conditions that are abnormal but add to the load.

I think all too often anymore equipment if powered by a motor that is absolutely maxed out, in fact they often modify the driven load so the motor can power it, instead of using the next larger motor.

I have seen motors on older equipment that are not undersized or loaded to the max that have been used hard for a long time and then you run into something newer that needs new motor - usually the day after any warranty expires.

Higher temperature ratings, higher efficiency ratings, and other technologies are good but allowing a little extra capacity in the design will usually result in longer life.

 

[tom baker]

I'm talking about Ambient temp, and about the code not mfg instructions.

My point is the code is the maximum value, but you must go by the mfg instructions for each overload device. As pointed out, you can go above the NP value, if you have a motor with a SF above 1.0. Running in the SF generates more heat, less motor life.

 

[Dave58er]

Unless I am misunderstanding the question the OP hasn't really been answered directly.
So adding to what others have said, from a strictly code point of view, the two ways you can get to125% are:
motor marked with a SF of 1.15 or greater,
motor marked with a temperature rise of 40C or less.

These are either/or requirements, you only need to meet one of them to allow you to size the OL at a max of 125%.

All motors not meeting one of these must be sized no higher than 115%.

Overload article is 430.32

BTW, I would NEVER size an overload at 1525%! That's just crazy!