# Electronic overload relay



## Heymanisth (Apr 20, 2010)

Can somebody explain electronic overload relay on motor starters. I know that they are there to protect the motor from cooking itself during overloads but how exactly does it do that. Does it disconnect the control circuit which then de energizes the coil disconnecting the line contacts or does it have its own separate set of contacts, or is it just PFM (pure f**king magic).

What is the difference between an older non electronic overload relay and a electronic overload relay? On a motor starter does the control circuit have to pass threw overload contacts on a electronic overload relay just like the non electronic ones?

Go ahead and throw me a frigging bone!!!


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## HARRY304E (Sep 15, 2010)

Heymanisth said:


> Can somebody explain electronic overload relay on motor starters. I know that they are there to protect the motor from cooking itself during overloads but how exactly does it do that. Does it disconnect the control circuit which then de energizes the coil disconnecting the line contacts or does it have its own separate set of contacts, or is it just PFM (pure f**king magic).
> 
> What is the difference between an older non electronic overload relay and a electronic overload relay? On a motor starter does the control circuit have to pass threw overload contacts on a electronic overload relay just like the non electronic ones?
> 
> Go ahead and throw me a frigging bone!!!


An Overload relay will open from the heat the amperage creates that's why they call them heaters


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## nitro71 (Sep 17, 2009)

The function just like any set of over loads. Have some kinda set of contacts in them that opens on overload. I don't know if they are electronic or mechanical. Really doesn't matter. NC set of contacts for the overloads. Usually is downstream from the coil.


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## Jlarson (Jun 28, 2009)

Just like with melting alloy and bi metal OL's all the electronic IEC OL's do is open the control circuit on overload, dropping the starter out shutting the motor down.


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## oliquir (Jan 13, 2011)

electronic o/l are much more faster to detect overloads and can be configurated for specific application (it can be used to prevent overtorque on some machinery so the gearbox doesnt break), some of them also detect voltage variation and can shut down motor if not ok. 
Mechanic o/l are slow to detect overloads (like a normal breaker) they really just protect motor from long overloads.


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## xswatts (Aug 26, 2011)

A motor starter relay will have some sort of protection for the motor, a normal relay does not. The motor current goes through the contacts so the current can be cut off at any time. The none electronic types use heat to determine the cut-off point, a bimetallic or solder that melts at a given temp. Electronic motor starters use a circuit to monitor the current and can often change the trip point of the current overload. They come in ranges, ie, 3 to 7 amps, .5 to 3, etc. When that point is reached, the armature current is interrupted by the relay contacts. There are more types, but that is the basics.


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## John Valdes (May 17, 2007)

HARRY304E said:


> An Overload relay will open from the heat the amperage creates that's why they call them heaters


Basically you are correct. But there is more to this. Heaters are usually used in NEMA OLR's and can be removed replaced or changed out. Bimetallic OLRs are usually ajustable and used mainly by IEC manufacturers.
Electronic overloads are just fancy bimetallic overloads that have more than one programmable setting.
But all work on current produces heat concept.



oliquir said:


> electronic o/l are much more faster to detect overloads and can be configurated for specific application (it can be used to prevent overtorque on some machinery so the gearbox doesnt break), some of them also detect voltage variation and can shut down motor if not ok.
> Mechanic o/l are slow to detect overloads (like a normal breaker) they really just protect motor from long overloads.


While trip times may be adjusted on an electronic overload, the overload must have some time built in or available for adjustment for starting the motor.
I see very little advantage to electronic overloads other than they can be used to do more things that a standard overload can do.
Electronic overloads cannot save a broken shaft any better than a standard overload.
Voltage regulation while important really is not the job of the overload protection. Voltage is proportional to current so how would an electronic overload be any better at protecting machinery?



xswatts said:


> A motor starter relay will have some sort of protection for the motor, a normal relay does not. The motor current goes through the contacts so the current can be cut off at any time. The none electronic types use heat to determine the cut-off point, a bimetallic or solder that melts at a given temp. Electronic motor starters use a circuit to monitor the current and can often change the trip point of the current overload. They come in ranges, ie, 3 to 7 amps, .5 to 3, etc. When that point is reached, the armature current is interrupted by the relay contacts. There are more types, but that is the basics.


Most contactors come without overload relays installed. They must be ordered separately.
Your description is that of an adjustable bimetallic IEC OLR. And AC motors do not have armatures, they have rotors.

Small power tools and special motors will have wound rotors. These are correctly called armatures. Just to clarify.

Tell us more about the circuitry that monitors current and makes changes to it and the operation of the electronic overload.

Relays are not motor starters even though they do the same action. Relays are designed to work on small currents where motor starters are designed and used as indicated for motors.


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## Handasee (Dec 18, 2009)

Be vary carefull when selecting electronic overloads. 
My experience is when they first came to market.
Two machines that I was called to repair had burned out starters.
Replaced the starters with Furnas Contactors and ESP100 electronic overloads. One week later, I was called back, one motor had burned out.
The motor had single phased and the overload did not trip. Never had this problem with Nema melting alloy overloads. 
Background information: The motor was 7.5Hp 600 volts, 7.5 amps protected with FRSR15 fuses,(and the Furnas ESP100 overload). The machine is a screw machine, where the operator must jog the machine for setups. The jogging can be very fast depending on the operator. 
When I checked the machine, I found one fuse blown.
Started to investigate this problem. Sent the ESP100 back to furnas (Siemens) for evaluation.
The response I received was that under these conditions the electronic overload might not see the single phasing. The ESP100 utilizes a capacitor to charge up to power the electronics in the overload.
On this machine, the fuse had blown, the operator just kept on jogging and the motor finally cooked. Square D was also introducing their electronic overloads, so I asked the rep what would happen under these circumstances. His reply was that theirs worked almost the same.
A few months later the second machine also blew the motor. Same problem. (I should have replaced that second ESP100) 
I have never used an electronic overload for this application after that.
Maybe the newer ones are better, I don't know.


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## Motorwinder (Dec 30, 2010)

John Valdes said:


> Basically you are correct. But there is more to this. Heaters are usually used in NEMA OLR's and can be removed replaced or changed out. Bimetallic OLRs are usually ajustable and used mainly by IEC manufacturers.
> Electronic overloads are just fancy bimetallic overloads that have more than one programmable setting.
> But all work on current produces heat concept.
> 
> ...


Technically the stator in an ac motor _is_ the armature.


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## John Valdes (May 17, 2007)

Motorwinder said:


> Technically the stator in an ac motor _is_ the armature.


Then what spins inside a dc motor?


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## oliquir (Jan 13, 2011)

John Valdes said:


> Then what spins inside a dc motor?


it is called the rotor but it is also the armature


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## mrmike (Dec 10, 2010)

Handasee said:


> Be vary carefull when selecting electronic overloads.
> My experience is when they first came to market.
> Two machines that I was called to repair had burned out starters.
> Replaced the starters with Furnas Contactors and ESP100 electronic overloads. One week later, I was called back, one motor had burned out.
> ...


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## John Valdes (May 17, 2007)

oliquir said:


> it is called the rotor but it is also the armature


Both of you are wrong. If it does not have a commutator its a rotor. If it has a commutator it's an armature. I am surprised a motor shop guy would not know the difference. 

I see one of you is outside the US so maybe you have it backwards and that is understandable.


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## piperunner (Aug 22, 2009)

Well if your asking how they work internally ill give it a try but since i cant spell or use words correctly please understand .

If you need more about the circuits meaning how they work ask !


The ones you slide your wire up through the 3 donuts are current sensors these sense the current in your motor leads ABC there electrically connected to a circuit which is kinda like a amplifier like the old OP amp which is adjusted to the settings of your motor current with the dials in percent of amps on the front of the unit which any increase in that set point will now set off the trigger circuit and trips the coil if it exceeds that point .

If you need more details just ask theres about five or six different circuits inside that motor electronic trip unit .

They do not work on heat they work on current flow when its past the set point it trips out the coil .


I notice some folks had a issue with them yes you can have a problem there actually dc powered at 5 volts if theres a voltage dip or voltage issue in the starter your going to have issues .

Like its not going to trip or its not working at all .

I dont like them personally when that can happen. 

5 volts well at times micro chips and high tech stuff just does not impress me .

Good point is there adjustable which is nice .

They reset and theres a delay on reset lets the motor cool .


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## John Valdes (May 17, 2007)

piperunner said:


> Well if your asking how they work internally ill give it a try but since i cant spell or use words correctly please understand .
> 
> If you need more about the circuits meaning how they work ask !
> 
> ...


Piperunner.

We are not discussing current transformers. CT's are usually used for instrumentation purposes and sometimes used as supplementary over current protection. But CT's are never ever used as the sole overload protection. Never.


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## Handasee (Dec 18, 2009)

mrmike said:


> The problem here was not the overload protection, as they "see" heat over time. Electronic or manual would not trip in this case. The problem is the "setup" having in-line fuses which do nothing but cause a single phase. I saw this time & time again in industry & most of these setups have been done away with........


I can assure you that for the machines I work on, the melting alloy thermal overloads will trip out before the motor burns. The problem is that the ESP100 solid state relays specified in their literature that they had "true phase loss protection;trips within 3 seconds". The letter I received back from the testing on the overload stated that under the conditions I described it took longer than 20 seconds to trip. The electronic overloads have to get power from the current going through the motor leads. That time under a normal start is less than 3 seconds, but when jogging, the overload may not operate properly. 
As to the fuses, properly sized fuses for overcurrent protection are not a problem. I consider fuses better than circuit breakers in an industry where oil is the major reason for motor control failure.


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## Motorwinder (Dec 30, 2010)

John Valdes said:


> Both of you are wrong. If it does not have a commutator its a rotor. If it has a commutator it's an armature. I am surprised a motor shop guy would not know the difference.
> 
> I see one of you is outside the US so maybe you have it backwards and that is understandable.


Not wrong..

http://en.wikipedia.org/wiki/Armature_%28electrical_engineering%29



> In alternating current machines, the armature is usually stationary, and is known as the stator winding. In DC rotating machines other than brushless DC machines, it is usually rotating, and is known as the rotor. The pole piece of a permanent magnet or electromagnet and the moving, iron part of a solenoid, especially if the latter acts as a switch or relay, may also be referred to as armatures.
> _*Mechanical*_
> *Rotor:* The rotating part of an alternator, generator, dynamo or motor.
> *Stator:* The stationary part of an alternator, generator, dynamo or motor
> ...



Didn't think I'd have to prove it to you, John.


I call DC armatures, huh,, armatures. Though they are called rotors too. I can also call a stator an armature, but generally call them stators. :laughing:


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## piperunner (Aug 22, 2009)

John Valdes said:


> Piperunner.
> 
> We are not discussing current transformers. CT's are usually used for instrumentation purposes and sometimes used as supplementary over current protection. But CT's are never ever used as the sole overload protection. Never.


Well thats how the trip units work current sensors work inside the ABB there starters .
A current sensor is a ct my friend .

I guess ill have to put up a circuit drawn of a ABB electronic overload unit .

Wait till after i get home today John


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## mrmike (Dec 10, 2010)

Handasee said:


> I can assure you that for the machines I work on, the melting alloy thermal overloads will trip out before the motor burns. The problem is that the ESP100 solid state relays specified in their literature that they had "true phase loss protection;trips within 3 seconds". The letter I received back from the testing on the overload stated that under the conditions I described it took longer than 20 seconds to trip. The electronic overloads have to get power from the current going through the motor leads. That time under a normal start is less than 3 seconds, but when jogging, the overload may not operate properly.
> As to the fuses, properly sized fuses for overcurrent protection are not a problem. I consider fuses better than circuit breakers in an industry where oil is the major reason for motor control failure.


First, I have to tell you that the O/L's will not always trip out like you stated. I have see them blow up before they tripped. The heater can burn open , but the mechanical part of the O/L may not trip out to shut down the control circuit, which is usually wired in to a contact on that O/L.
Secondly, Sure the fuses are sized Properly, but what happens when only one burns open ? My experience is that the motor keeps on chugging without that Phase-leading to it burning out. 
The circuit breaker will trip & kill the power to the motor, thus saving it.


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## JRaef (Mar 23, 2009)

Lots of slight misconceptions here, but it's not surprising and I don't mean to sound condescending . When I came in out of the field, I was shocked at how little I was taught about the inner workings of things that I had used every day. I just don't think there is enough time to do field work and learn all this stuff, I know I never had it. Thankfully, newer generations will have places like this to learn more than "other people" think you need to know.

First, an OLR is NOT intended to be the primary means of protecting agains a phase loss in a 3 phase system. Here is why. 

When you lose a phase on a circuit where the motor is already spinning, it will CONTINUE to spin in that direction. Under the same load, it will draw 1.732X more current on the other two phases. This SHOULD cause a trip eventually, but the catch is, ONLY if that 1.732 value is ABOVE the trip point of the relay. Here's an example to illustrate: Say you have a motor with a FLC of 10A so that's what the OLR is set to pick up on. But because the load is light, when it's running it's only drawing 5A. Then let's say a fuse blows somewhere up stream and now that motor is getting single phase power. The current it will draw UNDER THAT SAME LOAD THAT WAS DRAWING 5A, will increase to 8.66A. But guess what? 8.66A is STILL less than the 10A that the OLR is set to start protecting at. So, no harm no foul you think? I mean, what's the problem if the motor is still drawing less than FLC? The problem is called "Negative Sequence Currents" that are created INSIDE the motor as a result of only 2 pf the 3 phases having power on them. The ROTOR is inducing counter EMF (voltage for short) BACK onto the stator, but if one set of windings is dead part of the time, the induced currents are at 90 degrees to the others (making a long story short here). That creates wasted energy in the form of heat in both the stator and then the rotor. So that means for a given amount of current that the motor is pulling, the HEAT in the windings is increasing FASTER than it should. The tripping curve of any type of OLR is based on NORMAL current heating effects. If the heating effect is increased BEYOND that, as it is with Negative Sequence Currents, the *motor may actually "burn up" without ever exceeding the FLC rating.* 

THAT is why phase loss protection is VERY important. IEC bimetal OLRs claim to provide single phasing protection. How they do it is too long to go into here, but it is not as good as they want you to believe. It is better than NEMA bimetal OLRs and melting alloy OLRs, but by no means perfect. You should STILL have a Phase Loss Relay in the system.

The first version of the ESP100s did not factor this in, it emulated a bimetal OLR. Subsequent versions did fix it, and many of the competitors actually learned from Furnas' mistake and incorporated better phase loss protection in future SSOLs.

But not all SSOLs are created equal. There are still quite a few that think that the job of an SSOL is to just emulate a bimetal OLR, which does not do a good job of single phasing protection. Many, but not all, will take it to a higher plane and add in better protection. You really have to read the specs. The best policy is, if you want a feature and it doesn't SPECIFICALLY say it has it, assume it does not.

The best SSOLs will sense a phase loss by looking for less than 20% of the set current on any one phase. So they do NOT wait for the heating effect to call for a trip, it ASSUMES the worst. The problem is, sometimes a load is so light that the motor does not pull 20% current on ALL THREE phases and you get a nuisamnce trip. So in those situations you need to be able to disable the phase loss function, but then you want to be able to add in a phase current IMBALANCE protection, which will regain protection from the effects of a phase loss. Sq. D's Motor Logic SSOLs have that nuisance tripping problem and it bites people in the rear on pump panels if they don't ask for the special version that has that issue disabled and the current imbalance added in.

Some mfrs add in protection features based on voltage as well, i.e. kW, kVAR, PF, etc. etc. But that adds quite a bit of cost and extra wiring. I prefer to have ONE power protection realy in a system, then just current based SSOLs on the motors.

The major benefit of SSOLs in my opinion is the repeatability. They are 100% consistant over time. You cannot say that about bimetal OLRs and especially metling alloy. They build up what's called "thermal memory" over time and begin to nuisance trip on you. SSOLs never do that, they are not based on sensing heat, they are based on sensing current, and KNOWING how that current will affect heat in the motor.

I happen to believe that SSOLs are the only way to go now, I have seen too many failures in electro mechanical OLRs over the years. The only time I experienced a motor failure on an SSOL turned out to be on a Sq. D Motor Logic unit, which is how I learned that it was a common problem and that they have a "fix" that they rarely let anyone know about (probably out of embarassment).


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## Motorwinder (Dec 30, 2010)

I like cheap, non-functioning overloads. Keeps me in a job.:thumbsup:


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## Hippie (May 12, 2011)

Motorwinder said:


> I like cheap, non-functioning overloads. Keeps me in a job.:thumbsup:


I hear that haha


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## piperunner (Aug 22, 2009)

John Valdes said:


> Piperunner.
> 
> We are not discussing current transformers. CT's are usually used for instrumentation purposes and sometimes used as supplementary over current protection. But CT's are never ever used as the sole overload protection. Never.


Well we kinda are thats what makes them work inside read the pages 
http://www.a-aelectric.com/pdfs/ss_motor-protection.pdf Check out page B9 its about the different CT,s that sense the current flow .


You can pick what CT is the correct size for you electronic overload .


Now there is also a voltage sensing circuit which measures the voltage of load legs and converts that to current flow they used that on mostly DC motors but thats another topic not to many work with DC in our trade .Just them old Navy electricians


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