LSIG Settings - %N??

[don_resqcapt19]

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>

If the MCP trips because of a short circuit or ground fault at the motor, the motor is already damaged and the MCP prevents a fire that would cause damage beyond the motor. It is commonly accepted that the breaker provides ground fault and short circuit protection for the motor circuit and the overloads provide protection for the motor.

 

[templdl]

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>

So, the motor protection circuit breaker is what you are referring to and not a traditional MCP. I guess you found an exception to an MCP as is commonly used in combination motor starters since their inception back in the 1940's as I can recall. And you are referring to an entirely different product rather than an MCP. With your less than 5years experience good for you. Being new to his forum you are to be commended. ?

 

[iwire]

I disagree. It is a commonly accepted fact that a circuit breaker provides motor protection from a short circuit and ground fault perspective,

If the motor has an internal short or ground fault there is no motor to protect, it is already damaged. The breaker is protecting the conductors supplying the motor from damaging currents due to the faulted motor. That being the case the breaker does not 'protect' the motor.

On the other hand motor OLs open before motor damage so they do in fact protect the motor.

 

[Jraef]

MCP = Motor CIRCUIT Protector, not "Motor Protector", it is protecting the circuit, not the motor. If there is a GF or phase to phase fault in the cables ahead of the motor, that would not immediately damage the motor and the OL relay should react in time to protect it (if allowed to). The issue, as stated many times now, it that the MCP prevents the SC or GF event in the CIRCUIT from causing a fire before other devices can react.

MPCB is a different animal, it is a THERMAL-Magnetic circuit breaker that has ADJUSTABLE thermal trips that can be set just like a bi-metal overliad relay. It IS the overload relay, in fact its UL listing is often that of a Manual Motor Starter. In countries outside of North America, adjustable thermal trips on circuit breakers are not unusual so there is no separate term for them. Here they were illegal in terms of calling them "Circuit Breakers" for a long time, because the concept of adjustable thermal trips was unacceptable for safety. So the only way to get them UL listed was as a Manual Motor Starter. More recently though, UL489, the standard for Circuit Breakers, was amended to include MPCBs, but for use ONLY on motor circuits. That's because UL508, which covers Manual Motor Starters, did not have the necessary testing requirements for interrupting capacity as UL489. So they added MPCBs to UL489 to require that added testing.

So there are now both versions available, different uses. Many people who do not build OEM motor control systems on a regular basis however are still unfamiliar with MPCBs yet because they are just now filtering down into the workplace.

 

[steve66]

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.

Isn't it possible the %N measures the 3 line currents, and determines the neutral current by the vector sum of those three currents?

Granted, most motors wouldn't have a neutral anyway, so it wouldn't matter then, but is it possible there is some oddball motor that uses a neutral?

 

[Jraef]

Isn't it possible the %N measures the 3 line currents, and determines the neutral current by the vector sum of those three currents?

Granted, most motors wouldn't have a neutral anyway, so it wouldn't matter then, but is it possible there is some oddball motor that uses a neutral?

Maybe, but that's not what's going on here. These SPECIFIC breakers have an option for using a 4 pole breaker because in some systems outside of North America, you are required to switch the neutral. WHEN you have a 4 pole breaker with an ETU (Electronic Trip Unit), there is a setting for tripping on the Neutral current as a percentage of phase current: 100%, 50% or 0%. On larger frames of this series of breaker, they only make one ETU that is used on 3 pole or 4 pole breakers. If you have a 3 pole breaker, the %N adjustment DIP switches are superfluous, they are not connected to anything, you ignore them.