Motor overload tripping

[Jraef]

I get workers all the time calling electronic OL's thermal without realizing that theres no thermal in a solidstate OL, I guess its an old carryover from the days of the real thermal OL's actully many don't even know how they work using CT's instead of heaters.

Common misconception by the way.

A "thermal over load relay" is a protective device (ANSI 49) that protects a piece of connected equipment based on the thermal state of the equipment.

ANSI 49 – Thermal overload

Protection against thermal damage caused by overloads on machines (transformers, motors or generators).

It doesn't matter how it is determined. The bi-metal strips or eutectic melting alloy pots are designed to inexpensively mimic the thermal damage curve of the motor connected to it based on other ANSI standard design criteria for motors or generators. Solid State Over Load relays do the same thing, but more accurately and reliably with a few extra features thrown in, such as phase loss / imbalance and maybe GF protection. Digital "Motor Protection Relays" take it a step further and give you the ability to tweak the standard thermal curves to fit a specific motor or application to help avoid nuisance tripping or equipment damage beyond just thermal damage.

But bottom line, the "thermal" in thermal over load means the MOTOR's thermal condition, not how it works. So an SSOL is still an ANSI 49 thermal over load relay, so is a $7,000 GE/Mulitlin SR469 MPR (among other things).

 

[Jraef]

...
But, I must admit that I have been lucky enough when struggling with an issue when it just happens to start to work not knowing what in the heck I did. ...

I call that the "Microsoft" method. Turn it off, turn it back on, if it works, you fixed it!

But don't try to explain it to anyone, call it "trade secrets", it adds to your mystique. :angel:

 

[petersonra]

we have used tens (possibly 100s) of thousands of these 3RT10 series contactors. I don't recall having any unusual problems with them or the overloads.

 

[Jraef]

we have used tens (possibly 100s) of thousands of these 3RT10 series contactors. I don't recall having any unusual problems with them or the overloads.

I would venture to say that you likely buy the contactors and over load relays separately and assemble them yourselves. The problems they (Siemens USA) had were in the final assembly proceess when customers bought them as complete assembled starters.

 

[templdl]

I call that the "Microsoft" method. Turn it off, turn it back on, if it works, you fixed it!

But don't try to explain it to anyone, call it "trade secrets", it adds to your mystique. :angel:

How true this is. How many times has something not worked and it just started working. Then how can you fix something that is working? Then you leave and at some later date it stops working and you return and I this working fine. How can you fix something that is working?