Manual Overload Relay Resetting

[kwame]

Hi folks! Most thermal overload relays have test buttons and reset buttons. What happens when the overload relay trips due to excessive current ? I have read,its needs to cool down before resetting. How is the resetting done.Do you turn the resetting knob right or left. How does one know the motor has cooled enough ? Is reset needed when you use the 'test ' buttons? Kwame

 

[Reloadron]

What you are asking depends on the type of overload used. Thermal overload is but one type of protection used on motors. The simplest form of thermal overload uses a switch that is N/C (Normally closed) and wired into the motors start/run latching relay system. Most are wired to require a manual reset once the thermal overload trips and will not allow reset as long as the circuit is tripped.

Is reset needed when you use the 'test ' buttons?

That all depends on how the circuit is wired at design time. In the case of many small motors they use a single small button mounted on the motor frame, large motors use large high current contactors that are latched for normal operation. You don't specify a specific motor so a generic response is all that can be provided. **broken link removed**. Again without specifics your question is hard to answer. A simple thermal overload passes the motor current through an element. When the motor is overloaded the motor current increases and thermal expansion is used to open the contacts.

Ron

 

[KeepItSimpleStupid]

here's a whole PDF on overloads. https://www.google.com/url?sa=t&rct...=NjGY5MxhNuTc_AGTgba7lg&bvm=bv.80642063,d.cWc

In the motor-starters, the alloy has to melt and then the overloads are replaced like fuses. Solid state motor overloads are much nicer. I did replace a standard overload system with a solid state one. I added 3 phase protection to a few motor starters. One motor had an internal "pilot duty" mounted thermal sensor but it needed external controls. These were all 3-phase motors. The amount of protection was based on how much it would cost to replace.

Some $50,000 liquid nitrogen replacement systems got more protection because a new compressor is like $8,000 and a "roots" blower was like $10K to replace and difficult. You don't just plug 5 HP 3 phase motors into the wall.

The "building" had it's own motor overloads based design with it's infrastructure.

Then there are the simple "red buttons" on a motor.

 

[kwame]

I am alluding to general purpose the three phase overload relays used for motor protection. The circuit used in my country is exactly what Reloadron described. Ron,you claim sometimes a button is used in small m

 

[kwame]

I am alluding to general purpose the three phase overload relays used for motor protection. The circuit used in my country is exactly what Reloadron described. Ron,you claim sometimes a button is used in 'small motors' how is the reset wired?

 

[Wade Hassler]

Some small motors have a line-level thermal switch mounted directly on the motor. After tripping, it will cool down and can be restored to the run-position by pressing a (often red-colored) button: https://gearmotorblog.files.wordpress.com/2009/09/manual-reset_ovlp_50.jpg?w=500

Really, though, Google is full of information on this: search for "thermal overload mechanism" and be prepared to waste an afternoon.

 

[Reloadron]

I am alluding to general purpose the three phase overload relays used for motor protection. The circuit used in my country is exactly what Reloadron described. Ron,you claim sometimes a button is used in 'small motors' how is the reset wired?

Yes, small fractional horsepower single phase motors often just have a small button mounted on the motor frame. There is a small thermal element inside the motor frame. The button will "pop" out under overload conditions and remove power from the motor. Generally overloads like this can not be reset until the motor cools down enough. I say "generally" because designs can vary. Larger motors which are frequently powered by 3 phase power typically use circuits like those shown in the link I provided.

The thermal overloads can vary and some are adjustable. Then we also can have motor overloads which as KISS mentions are solid state where the load current is sensed and if the load current exceeds a set (adjusted) trip point the circuit opens and the motor shuts down. Just about all of these systems require a manual reset. Burning up a small fractional horsepower motor is no big deal but burning up a large multi-horsepower motor can be a very big deal when motors can cost big money like a $75,000 pump motor.

In conclusion overload protection for motors comes in a variety of designs. The idea being to preserve the motor from damage. The exact protection scheme or method is normally chosen for the motors intended application.

Wade covers it quite well:

Some small motors have a line-level thermal switch mounted directly on the motor. After tripping, it will cool down and can be restored to the run-position by pressing a (often red-colored) button: https://gearmotorblog.files.wordpress.com/2009/09/manual-reset_ovlp_50.jpg?w=500

Really, though, Google is full of information on this: search for "thermal overload mechanism" and be prepared to waste an afternoon.

Ron

 

[nsaspook]

I am alluding to general purpose the three phase overload relays used for motor protection. The circuit used in my country is exactly what Reloadron described. Ron,you claim sometimes a button is used in 'small motors' how is the reset wired?

Do you mean like this? https://electrical-engineering-portal.com/working-principle-of-thermal-motor-protection-relay

 

[4pyros]

What happens when the overload relay trips due to excessive current ? I have read,its needs to cool down before resetting.

How does one know the motor has cooled enough ?

At will not reset until it has cooled down enough, it will just keep going back to the overload positioning.

How is the resetting done.Do you turn the resetting knob right or left.

That depends on who made it, Do you have an owners manual?

 

[kwame]

Friends i am making reference to abb overload relay.The reset button comes on the form of a screw.The pro spec:TA CLASS 10 follow link :www.nema7.com
How is resetting going to be like? relay is found on page 4 of the pdf file.
.

 

[4pyros]

That link is for the enclosure only.
Not who made the motor contactor.
Do you know who made the controler and put it in that box?

 

[Reloadron]

That link is for the enclosure only.
Not who made the motor contactor.
Do you know who made the controler and put it in that box?

He mentions it as ABB. IN the link if we dig enough we find **broken link removed** for ABB. I believe when he mentions Page 4 I believe he means page 2.2 of the .pdf document. Ain't this fun? Actually I forgot how I ended up here:
**broken link removed**

There is the Amp Setting Range control which is adjustable for the current trip limit and beside that we can select Manual or Automatic Reset which is self explanatory. Manual requires a Manual Reset and Automatic will Automatically Reset once the unit cools down following an overload trip. There is also a Manual Test which allows manually tripping the thermal overload contacts. Manually Trip the overload contacts and then using the Blue Button to the far right in the picture turn in CCW (Counter Clockwise) and see if the thing resets. Most of these things work in a similar fashion. You should be able to manually trip and reset the thing. Rotate that screw CW and CCW to see what it does and how it works.

Kwame, you really need to do better with links and manufacturer part numbers so people know what you want as to information. Otherwise things get hard to follow.

Ron

 

[KeepItSimpleStupid]

I ran into an issue with someone over page numbers. I now always say PDF page x, not things like Section 5, sub-section C, Figure 6.

It's best said as "Figure 6" on PDF page 7.

 

[Reloadron]

I ran into an issue with someone over page numbers. I now always say PDF page x, not things like Section 5, sub-section C, Figure 6.

It's best said as "Figure 6" on PDF page 7.

So what would I say? Should I say **broken link removed** page 4 or should I say page 2-2? I would generally use the latter as page 4 is no big deal but if the thing has hundreds of pages and I say page 100 (the 100th page in) then someone has to count and scroll through 100 pages to get where I want them to be? Then too, I am still not sure I am on the page that Kwame was referencing?

Ron

 

[KeepItSimpleStupid]

You can sometimes have a title page, then a-f or whatever, and then real page numbers. By specifying a PDF page, you avoid the ambiquity and just type it in and Bamm, your there.

If, it were a book, you have a cover page and then that page with the ISBN number on it and the table of contents. Sometimes all of those pages aren't numbered in a real book. i.e the PDF page and the page at the bottom don't match.

 

[Reloadron]

You can sometimes have a title page, then a-f or whatever, and then real page numbers. By specifying a PDF page, you avoid the ambiquity and just type it in and Bamm, your there.

If, it were a book, you have a cover page and then that page with the ISBN number on it and the table of contents. Sometimes all of those pages aren't numbered in a real book. i.e the PDF page and the page at the bottom don't match.

Works good on that one.

Ron

 

[BobW]

In the motor-starters, the alloy has to melt and then the overloads are replaced like fuses.

That is not correct. However the term "melting alloy overload" tends to lead people to believe that they behave like a fusible link. But they are indeed resettable. It's explained in the the document that you linked to.

In melting alloy thermal overload relays, the motor current passes through a small heater winding. Under overload conditions, the heat causes a special solder to melt allowing a ratchet wheel to spin free thus opening the control circuit contacts. When this occurs, the relay is said to “trip”. To obtain appropriate tripping current for motors of different sizes, or different full load currents, a range of thermal units (heaters) is available. The heater coil andsolder pot are combined in a one piece, nontamperable unit. Melting alloy thermal overload relays must be reset by a deliberate hand operation after they trip. A reset button is usually mounted on the cover of enclosed starters.

These are designed to have a thermal time constant similar to that of the motor, so that, by the time the overload has cooled sufficiently to allow it to be reset, then the motor has also cooled sufficiently to be safely restarted.

 

[kwame]

It is actually page 2.2 not page 4.Ron you are right

 

[Reloadron]

It is actually page 2.2 not page 4.Ron you are right

OK, so does it all make sense now? Do you understand how it works. and can be manually operated etc.

Ron

 

[kwame]

Yep Ron.Does make picture much clear. Happy Thanksgiving Day.