Breaker types allowed by NEC????

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skiff

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Please help. I need some clarification on breaker types and what the NEC requires with regard to breakers. Specifically, I'm working with lighting circuits, so they are simply 120v or 277v applications at 20 amps.

Manufacturers of lighting control equipment (relay and dimming panels) can provide equipment that is configured as a Main breaker or MLO with branch circuit breakers to provide protection of the branch circuits. Some manufacturers provide breakers that are "fully magnetic" and other manufacturers provide circuit breakers that are "thermal magnetic". These panels are being used as distribution panels and there is no other protective devices on the branch circuits.

My understanding is that thermal magnetic breakers provide instantaneous as well as over current protection. It is also my understanding that the fully magnetic breakers do not provide overcurrent protection. Please correct me if this is not accurate. I would think that the NEC would require branch circuits to be protected for both instantaneous and overcurrent conditions. I'm having difficulty determining the code's requirements in regard to this.

In a nutshell, my question is this.... If a distribution panel uses fully magnetic breakers, does it meet the minimum requirements of the NEC for branch circuit protection???

Many thanks for your thoughts and input.

Regards,

Skiff
 

charlie b

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The purpose of a breaker is to protect the conductor, not the load. That requires the breaker to trip on overload. You can't use "magnetic only" breakers for lighting circuits.
 

skiff

Member
At this point, I'd rather not call out a specific manufacturer, although I think you would be surprised at how many manufacturers do provide fully magnetic breakers in their equipment. It's provided as an OEM item as part of a larger assembly so you have to really investigate it closely in the equipment's spec sheets.

There are quality lighting control manufacturers that do provide thermal magnetic breakers as standard equipment. However, it is a critical component that is often not given sufficient consideration.

My belief is that these manufacturers use the fully magnetic breakers to compensate for high heat issues that exist within the panels. This is done to eliminate nuisance tripping by the thermal component of the breaker. The risk is that it does not protect the conductor from an overcurrent condition.

I find that this is particularly concerning on lighting circuits... think about track lighting and owners that want to add track heads to increase light levels. It's a fire waiting to happen.
 

rbalex

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By definition overcurrent is "...overload, short circuit or ground fault." [See Article 100] So - "Magnetic Only" circuit breakers do provide ?overcurrent? protection.

However, Magnetic Only (Instantaneous Trip) circuit breakers are not "listed" for any purpose. They are marked as "recognized components" suitable only for use in a listed motor starter. See the Definition of Circuit Breaker in Article 100 and Section 430.52(C)(3).

Note "Magnetic Only" is undefined and "Instantaneous Trip" is only described in terms of motor protection in the NEC.
 

rbalex

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As part of a "listed assembly" Instantaneous Trip (Magnetic Only) circuit breakers are acceptable. They still are only permitted to provide Short Circuit or Ground Fault protection. Overload protection must be provided with some other recognized means.
 

skiff

Member
Thanks Bob. So in your opinion...

Thanks Bob. So in your opinion...

In your opinion, are you saying that as far as the code is concerned, that it would be a mis-application to use a "Fully Magnetic" breaker on a lighting branch circuit where no other circuit protection exists?

Thanks,

Skiff
 

iwire

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Just guessing here.

Perhaps the the Mag only breakers are indeed there only to provide short circuit and ground fault protection.

The overload protection may provided elsewhere on the unit.

They may be watching for temperature rise on switching / dimming components. If the temp rise is to great that circuit may get shut down.
 

templdl

Senior Member
Location
Wisconsin
In general, molded case circuit breakers are UL489 listed which includes both breakers that have inverse time and magnetic elements (thermal magnetic or TM) as well as those with magenetic only elements.
However, the TM breaker will include the 'UL' label that we all have become familiar with and the Mag only will have a 'UR' markingfor "recognized" component. Molded case switches that look like the common molded case circuit breaker which has neither thermal nor magnetic elements are built and tested in accordance to UL 1087.
Then there are breakers that are recognized under UL1077. These breakers are used to provide overcurrent protection where branch protection (for example, UL 489 MCCB) is already provided or not required. These breakers can be installed as a component within or part of an appliance or a piece of electrical equipment. This UL1077 recognized breaker is an ideal replacement for fuses that are applied as a supplementary protector, i.e. in addition to branch protection (if required).
Dave
 

charlie b

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In my current field of employment, Naval Architecture and Marine Engineering, there is indeed a valid use for breakers with instantaneous trips and without overcurrent trips. In fact, there is a Coast Guard regulation that requires that type of breaker. The application is for the motor that drives the hydraulic pump that moves the steering gear. I suspect that the idea is that steering is so important to the safety of a vessel that it will be run to its destruction rather than be tripped out during a critical maneuver. The bridge will get an alarm, and will have time to manually trip the motor, if the immediate safety needs of the vessel permit.
 

skiff

Member
General Construction -vs- special applications

General Construction -vs- special applications

Charlie,

Thanks for your response. I agree, there certainly are specific needs and applications for the magnetic only breaker. However, in my application, I am looking at general, commercial construction... college/university, healthcare, K-12 & office building lighting distribution systems. Areas where adds, moves and changes within a facility are frequent.

I'm really trying to determine if the NEC REQUIRES a thermal magnetic breaker (ie UL489) breaker for branch lighting circuits. If not, does the NEC require both instantaneous and overcurrent protection for that circuit? Some manufacturer's equipment provides the instantaneous protection only. I am concerned about what protection the owner is really getting and if we are not protecting them with overcurrent protection at the branch circuit level, then the conductor potentially becomes a fuse (bad results).

There are some folks who believe that a fully magnetic breaker is sufficient for this application. I'm looking for help determing the minimum code requirements.

Many thanks for your time & insight.

Regards,

Skiff
 

rbalex

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Everyone ? in this discussion at least, please use the term overcurrent correctly. It is inclusive of "overloads" as well as "short circuits" and "ground faults;" i.e., overload and overcurrent are NOT synonymous.

Some loads, such as fire pumps, are specifically prohibited from having overload protection.

The various tap rules also imply that there other potential means of providing conductors with overload protection. The overcurrent protective device for conductors for short circuits and ground faults MUST between the source and the conductors. The overcurrent protective device for overloads only needs to be in series with the conductors.

Theoretically, conductors for some loads, such as heaters, that are inherently ?overload? resistant, only need short circuit and ground fault protection.

It is possible a listed manufactured assembly may use instantaneous trip circuit breakers. We, ?the public? cannot.
 
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