Motor Starter Definitions 1

[farmape]

Looking at Westinghouse A200 Overload Heater Chart, there are five choices.
1. Non Compensated Open Starters
2. Ambient Comp. Open and Encl. Starters
3. Non-Compensating Enclosed Starters
4. Block Type Overload Using 3 Heaters
5. Single Pole Type Overload
Could someone explain these terms? Specifically, what is the difference between an "open" and "enclosed" starter?
Thanks.

 

[jraef]

"Open" is a starter not in a box (also knows as "chassis mount"). In other words, you bought devices that will be part of a larger assembly such as a control panel, where you are going to take responsibility for maintaining a controlled temperature inside of it, not to exceed the rated temperature of the device (usually 40°C).

"Enclosed" means that you have purchased a standard product offering from that manufacturer of a motor starter in its own specific dedicated (small) box. The reason why they have you pick a different overload heater element is because they may, in the interest of keeping cost and size down, allow the starter to operate at a higher temperature. In doing so, they know that the trip characteristics of the thermal elements will be different.

"Ambient Compensated" means that if the starter and motor are going to be operating at significantly different temperatures, you need(ed) to use heater elements that are compensated for that condition since the thermal characteristics of what the motor can take will be different from what the heater elements will operate at. This concept is not virtually irrelevant because most OL relays are now "ambient insensitive". But since Westinghouse has been gone for years, you are obviously dealing with legacy equipment.

"Block Type Overload Using 3 Heaters" would have meant just what it sounds like; they had a phenolic block which contained a common trip mechanism and spaces into which you mounted 3 separate heater elements. Most modern OL relays now have integrated adjustable heater elements so you no longer mount them separately, or better yet, solid state OL sensing.

"Single Pole Type Overload" would be an even more ancient version where each phase had its own block that contained its own trip element and heater, then you, the customer, would wire your control circuit in series.

 

[farmape]

Thank you for the information, very nicely done.
I'd like to bransch out with two additional questions.
1. Can excessive current draw in any way be related to a motor problem (at rated voltage)?
2. Can the OL's be increased based on the duty cycle of the motor?
One example for specifity: 3HP AC Motor, 460V, 825rpm, 6 FLA 1.15SF. Motor has been in service for 20+ yrs. Avg current draw is 10-12 amps, but the motor only runs about 15 seconds every 15 minutes.
Thanks again.

 

[jraef]

Thank you for the information, very nicely done.
I'd like to bransch out with two additional questions.
1. Can excessive current draw in any way be related to a motor problem (at rated voltage)?
2. Can the OL's be increased based on the duty cycle of the motor?
One example for specifity: 3HP AC Motor, 460V, 825rpm, 6 FLA 1.15SF. Motor has been in service for 20+ yrs. Avg current draw is 10-12 amps, but the motor only runs about 15 seconds every 15 minutes.
Thanks again.

1. Yes, of course excessive current draw can be related to a motor problem, but it can also be a load problem and more often that not, it is.

2. OL relays act on an i²t trip curve, designed to approximate the thermal damage curve of an average motor. The i²t factor means that the higher the current, the faster they trip. You didn't indicate the setting of the OL but assuming it is 6A based upon the motor FLA, you have an over load of between 166 and 200% of FLA. On an average Class 10 OL trip curve, it should trip in approximately 25 seconds at 200% (see attached). So technically you have been getting away with it for so long because the short duration of the overload condition is not thermally significant.

Side note; I know the picture is bad, it's the best I could muster on short notice.