LSIG Settings - %N??

[adamscb]

I was looking at some of our newer Allen Bradley thermal mag breakers, and saw adjustable dip switches for L, S, I, and G. In my mind you adjust L for the motor's full load amps (not exact, but close), S for the motor's inrush, I for the instantaneous trip, and G for the ground fault current.

However, I saw another dip switch that said %N, and you could adjust it for On or Off, and for 0%, 50%, or 100%. Has anyone encountered this setting before? Thanks

 

[Jraef]

I was looking at some of our newer Allen Bradley thermal mag breakers, and saw adjustable dip switches for L, S, I, and G. In my mind you adjust L for the motor's full load amps (not exact, but close), S for the motor's inrush, I for the instantaneous trip, and G for the ground fault current.

However, I saw another dip switch that said %N, and you could adjust it for On or Off, and for 0%, 50%, or 100%. Has anyone encountered this setting before? Thanks

I think you are a bit confused about what you have and what you are using it for.

LSIG would imply this is an ELECTRONIC Trip Unit (ETU) circuit breaker, NOT a "Thermal-Mag" circuit breaker.
L = Long Time trip, the equivalent of the "thermal" in a Thermal-Mag breaker.
S = Short Time trip, no equivalent in a T-M breaker, used for coordinating with other breakers up and down stream
I = Instantaneous trip, the same as a magnetic trip in a T-M breaker
G = Ground trip, again, no equivalent in a basic T-M breaker and if GF is added to one, it's generally a separate module.
%N = Neutral current, you would only see that adjustment on a 4 pole breaker, not commonly used in North America, but the %N = the neutral current as a % of the L current in that 4th pole that you want it to trip on.

Then you go on to mention Motor FLA? You don't use ETUs of a circuit breaker to protect a motor directly, it is branch or feeder circuit protection. There ARE versions of these breakers referred to as "Motor Protection Circuit Breakers" (MPCBs) that have adjustable thermal trips and are listed as "Manual Motor Starters" for that purpose, but they will not have LSIG (or N) trip settings, so if you have those settings, it is not an MPCB. If you want an MPCB, you have to buy an MPCB, different part number.

So what is it you plan on doing with this breaker? If you have a part number on the breaker, that would be helpful in that endeavor.

 

[adamscb]

Sorry I made a huuge mistake when typing this up, this is a magnetic breaker only, so there's only an instantaneous setting. However, there's still the %N as a choice with 0%, 50%, or 100%.

Using this to protect a 125hp motor, and using electronic overload relays with IntelliCenter software. This is the first time my plant is using IntelliCenter so obviously I'm getting a lot of kick back from the more experienced electricians.

Just to make sure I have my terminology right, a 'thermal mag' breaker is the type you see in panel boards right?

 

[GoldDigger]

Sorry I made a huuge mistake when typing this up, this is a magnetic breaker only, so there's only an instantaneous setting. However, there's still the %N as a choice with 0%, 50%, or 100%.

Using this to protect a 125hp motor, and using electronic overload relays with IntelliCenter software. This is the first time my plant is using IntelliCenter so obviously I'm getting a lot of kick back from the more experienced electricians.

Just to make sure I have my terminology right, a 'thermal mag' breaker is the type you see in panel boards right?

If you are feeding a motor, it is very unlikely that the neutral is even connected to the motor.

 

[adamscb]

I agree with that, I was just wondering what it would be used for

 

[GoldDigger]

I agree with that, I was just wondering what it would be used for

A wye load that uses the neutral.
Maybe a wye transformer primary, maybe a wye heating load that is supposed to be balanced.
If it is an unbalanced wye load set you do not set a low neutral current threshold. Among other things if the legs of the wye are individually switched.

 

[Jraef]

In an MCC made for North America you will not have a 4 pole breaker. If you do not have a 4 pole breaker, the %N adjustment is not connected to anything. Ignore it.

 

[templdl]

Sorry I made a huuge mistake when typing this up, this is a magnetic breaker only, so there's only an instantaneous setting. However, there's still the %N as a choice with 0%, 50%, or 100%.

Using this to protect a 125hp motor, and using electronic overload relays with IntelliCenter software. This is the first time my plant is using IntelliCenter so obviously I'm getting a lot of kick back from the more experienced electricians.

Just to make sure I have my terminology right, a 'thermal mag' breaker is the type you see in panel boards right?

Am I to assume that you have a starter with an overload to control the motor? If so the starter normally provides motor protection from overload.
If so you look at the breaker differently as it's job is to take the motor off line should the motor fail protecting the motor circuit and isolating the motor f RT on the upstream distribution system.
Then look at the setting of your breaker if when it trips the motor has failed and your goal is to limit the damage to the motor.
I always advise to set the breaker adjustments as low as practical to o a point just above nuisance tripping. When adjusted as such should the breaker trip then yu you should consider that the motor has failed.
Make sense?
A picture of the breaker would help varify my thoughts.

 

[adamscb]

Am I to assume that you have a starter with an overload to control the motor? If so the starter normally provides motor protection from overload.
If so you look at the breaker differently as it's job is to take the motor off line should the motor fail protecting the motor circuit and isolating the motor f RT on the upstream distribution system.
Then look at the setting of your breaker if when it trips the motor has failed and your goal is to limit the damage to the motor.
I always advise to set the breaker adjustments as low as practical to o a point just above nuisance tripping. When adjusted as such should the breaker trip then yu you should consider that the motor has failed.
Make sense?
A picture of the breaker would help varify my thoughts.

I am not following you. What I have is an instantaneous MCP breaker with electronic overloads to protect the motor from both short circuits and overloads, respectively.

 

[templdl]

I am not following you. What I have is an instantaneous MCP breaker with electronic overloads to protect the motor from both short circuits and overloads, respectively.

OK, the MCP does not provide motor protection, the electronic overload does. The electronic overload controls the contactor, the contactor is designed to be able to start and stop the motor incuding the locked motor amps. The electronic overload may include other protective features but the contactor is not designed with the capability to clear faults where the MCP being a breaker is.
The MCP, mag only breaker, is a motor circuit protector which is intended to protect the motor circuit should there be a motor failure. In NEC art 430 I believe that the NEC may refer to it as providing ground fault protection. If the MCP trips it isolates the motor from affecting the distribution system. As an example if the windings of a motor start to fail it is not unusual that one phase will start to go to ground. You want the MCP to trip as soon as possible to limit motor damage and before there is a phase to phase winding fault. I always have recommended that the mag pickup setting of an MCP be set just above the inrush current as the motor starts just high enough not to nuisance trip. When adjusted as such should the MCP trip it is a strong indication that there is a motor winding issue. NEC art 430 -52 does however, state what the allowable limitations of the mag pickup settings are. For convenience it is common that the pickup setting be set as high as the NEC allows.
Remember the instantaneous is just that. The is no ramp or time delay. When a fault occurs it will be an instantaneous spike of current the magnetude of which can be extremely high.

 

[adamscb]

OK, the MCP does not provide motor protection, the electronic overload does.

I disagree. It is a commonly accepted fact that a circuit breaker provides motor protection from a short circuit and ground fault perspective, while overloads provide protection from just that, overloads. I believe this is in the code book. You can argue linguistics all you want, but the statements I just made can be agreed upon by almost everyone on this forum.

You say that MCP's dont provide motor protection, but then you go on to say that if there's a problem with the motor, then it should trip as soon as possible. Is that not a form of protection?

 

[GoldDigger]

I disagree. It is a commonly accepted fact that a circuit breaker provides motor protection from a short circuit and ground fault perspective, while overloads provide protection from just that, overloads. I believe this is in the code book. You can argue linguistics all you want, but the statements I just made can be agreed upon by almost everyone on this forum.

You say that MCP's dont provide motor protection, but then you go on to say that if there's a problem with the motor, then it should trip as soon as possible. Is that not a form of protection?

To say that MCPs do not provide motor protection is equivalent to saying that they do not provide all of the motor protection, not that they do not provide any part of motor protection.
If the motor does not have impedance protection or built-in thermal protection against overloads, then an MCP by itself will not provide motor protection.
On the other hand, a motor starter, which is understood to provide overload protection, in combination with almost any breaker or including an MCP inside, will provide complete motor protection.

 

[templdl]

I disagree. It is a commonly accepted fact that a circuit breaker provides motor protection from a short circuit and ground fault perspective, while overloads provide protection from just that, overloads. I believe this is in the code book. You can argue linguistics all you want, but the statements I just made can be agreed upon by almost everyone on this forum.

Yes, please reread NEC art 430.52. As I refered to regarding the setting of an instantaneous breaker and ground foult. You say that MCP's don
t provide motor protection, but then you go on to say that if there's a problem with the motor, then it should trip as soon as possible. Is that not a form of protection?

Motor protection? A circuit breaker does not protect the motor. If so from what? The motor has already failed. You would like the MCP limit damage. I didn't want to go this far but it was Westinghouse that invented the MCP to reduce if not eliminate fires due to motor failures. It was found that commonly used fuses were not capable of detecting and clearing faults fast enough to blow due to a motor failure where mag. trip breakers do. The breaker's job is to remove the failed motor from the circuit preventing the failed motor from affecting the power distribution supplying power to it. Trip a breaker upstream from the motor most likely will take out other items in the power grid. It is best ft or the MCP to trip.
The contactor controls the motor and the overload relay is sized and configured to monitor the motor dropping the contactor should the motor be overloaded.

 

[templdl]

I disagree. It is a commonly accepted fact that a circuit breaker provides motor protection from a short circuit and ground fault perspective, while overloads provide protection from just that, overloads. I believe this is in the code book. You can argue linguistics all you want, but the statements I just made can be agreed upon by almost everyone on this forum.

Yes, please reread NEC art 430.52. it is called a motor circuit protector and not s motor protector. As I refered to regarding the setting of an instantaneous breaker and ground foult. You say that MCP's don
t provide motor protection, but then you go on to say that if there's a problem with the motor, then it should trip as soon as possible. Is that not a form of protection?

Motor protection? A circuit breaker does not protect the motor. If so from what? The motor has already failed. You would like the MCP limit damage. I didn't want to go this far but it was Westinghouse that invented the MCP to reduce if not eliminate fires due to motor failures. It was found that commonly used fuses were not capable of detecting and clearing faults fast enough to blow due to a motor failure where mag. trip breakers do. The breaker's job is to remove the failed motor from the circuit preventing the failed motor from affecting the power distribution supplying power to it. Trip a breaker upstream from the motor most likely will take out other items in the power grid. It is best for the MCP to trip.
The contactor controls the motor and the overload relay is sized and configured to monitor the motor dropping the contactor should the motor be overloaded.

 

[adamscb]

Motor protection? A circuit breaker does not protect the motor. If so from what? The motor has already failed. You would like the MCP limit damage. I didn't want to go this far but it was Westinghouse that invented the MCP to reduce if not eliminate fires due to motor failures. It was found that commonly used fuses were not capable of detecting and clearing faults fast enough to blow due to a motor failure where mag. trip breakers do. The breaker's job is to remove the failed motor from the circuit preventing the failed motor from affecting the power distribution supplying power to it. Trip a breaker upstream from the motor most likely will take out other items in the power grid. It is best for the MCP to trip.
The contactor controls the motor and the overload relay is sized and configured to monitor the motor dropping the contactor should the motor be overloaded.

I agree with the starter turning the motor on/off and how the overloads are wired into the control circuit. I understand all of that. I have less than 5 years in this field, so these questions are semi-serious but I believe I know the answers 1)What if there's a phase-to-phase fault in the cables? This would trip the circuit breaker thus protecting the motor am I correct? 2)What if there's a ground fault? Do overloads trip on a ground fault in the cables? These are scenarios where the motor is perfectly fine, but the circuit breaker would trip (I believe anyway), in order to prevent the motor from single-phasing thus causing damage. Circuit breakers (in my mind) don't only trip when the motor goes bad. That's why you meg both the feeder cables going to the motor, as well as the motor leads themselves.

And last but not least why does MPCB literally stand for Motor Protection Circuit Breaker? How can you argue that a circuit breaker doesn't protect a motor if it's literally in the name?

 

[GoldDigger]

And last but not least why does MPCB literally stand for Motor Protection Circuit Breaker? How can you argue that a circuit breaker doesn't protect a motor if it's literally in the name?

Probably because it is only usable for building a motor starter and not as a general purpose (with thermal) breaker?

If it were listed as a breaker rather than being a registered component, then people would be likely to try to use it stand-alone.

 

[templdl]

I agree with the starter turning the motor on/off and how the overloads are wired into the control circuit. I understand all of that. I have less than 5 years in this field, so these questions are semi-serious but I believe I know the answers 1)What if there's a phase-to-phase fault in the cables? This would trip the circuit breaker thus protecting the motor am I correct? 2)What if there's a ground fault? Do overloads trip on a ground fault in the cables? These are scenarios where the motor is perfectly fine, but the circuit breaker would trip (I believe anyway), in order to prevent the motor from single-phasing thus causing damage. Circuit breakers (in my mind) don't only trip when the motor goes bad. That's why you meg both the feeder cables going to the motor, as well as the motor leads themselves.

And last but not least why does MPCB literally stand for Motor Protection Circuit Breaker? How can you argue that a circuit breaker doesn't protect a motor if it's literally in the name?

I revert back to what I said about why Westinghouse invented the MCP ( motor CIRCUIT protector) as I had previously described. Yes, the "MCP" will trip for the reason you have described but that is not what it was intended for thst. The risk is slim to none. The risk of a motor winding failure is much greater. And it is fact a Motor Circuit Protector and not a motor protection circuit breaker.

 

[templdl]

Probably because it is only usable for building a motor starter and not as a general purpose (with thermal) breaker?

If it were listed as a breaker rather than being a registered component, then people would be likely to try to use it stand-alone.

I'm sure as seasoned as you are goldDigger you know this alresdy. As such it is a reverse UR component listed device. It will no have an interupting rating shown on it. The current rating as shown on the MCP are very critical to observe as the MCP has no thermal protection and may be destroyed should it's current rating be exceeded. It depends upon a properly applied thermal OLR as part of a listed combination motor starter.

 

[adamscb]

I revert back to what I said about why Westinghouse invented the MCP ( motor CIRCUIT protector) as I had previously described. Yes, the "MCP" will trip for the reason you have described but that is not what it was intended for thst. The risk is slim to none. The risk of a motor winding failure is much greater. And it is fact a Motor Circuit Protector and not a motor protection circuit breaker.

There are such things as Motor Protection Circuit Breakers (MPCBs), look them up. There are also MCP's as well.

So you just admitted that circuit breakers can in fact protect the motor without the motor already being bad, which is what I've been saying all along. What I said about ten posts ago is that you have all types of protection covered: 1) short circuit 2) ground fault 3) overload. Numbers 1 and 2 are supplied by the breaker, and 3 is supplied by the overloads (or what you're referring to as the starter).

But then again you have 20+ years of experience and I have less than 5, so I obviously have no clue what I'm talking about <sarcasm>

 

[Ingenieur]

Page 102 has the curve/settings
http://literature.rockwellautomation.com/idc/groups/literature/documents/td/140g-td100_-en-p.pdf