How many times can a breaker trip before it should be replaced?

[jim dungar]

As always we have people talking about 15 amp SP breakers at a home and some talking about large commercial / industrial breakers. Now there is nothing wrong with that except it makes the thread hard to follow and tough to know what the answer is.

The difference is not between residential and commercial/industrial as far as the breaker is concerned. UL489 and NEMA AB1 tests apply to all molded case breaker regardless of their application. The Square D Homeline breaker quoted by the OP is tested to the same standards as the one in the picture posted by Brian John.

The difference comes in when we consider how much current may have been interrupted and then how much current will need to be interrupted if the breaker is closed onto a fault. It is unlikely that a single family residential breaker will ever see a "short circuit" in its branch wiring that will come close to the maximum ampere interrupting capacity of the breaker, however the same cannot be said of commercial and industrial applications.

The OSHA proscrition against resetting a breaker effectively says you must figure out why the breaker tripped before it is reset. If you have a breaker feeding a counter top that trips whenever the microwave and the toaster oven are operated at the same time you may simply turn off a device and reset the breaker. If a breaker has tripped with no explanation then troubleshooting should be performed prior to resetting the breaker.

 

[iwire]

The difference is not between residential and commercial/industrial as far as the breaker is concerned.

Jim, We are saying the same thing in different ways.

I imagine that the fault current that a single pole 20 amp breaker is exposed to even in a commercial installation is likely to be fairly low with circuit impedance considered.

 

[zog]

If a breaker has tripped with no explanation then troubleshooting should be performed prior to resetting the breaker.

And, that is one of the advantages to upgrading older power circuit breakers to electronic trip units that has indications of why the breaker tripped.

This would be a waste of money (but sort of cool) to put a $2,500 trip unit on a $5 resi breaker, that would be like putting a Nissan 350Z engine and powetrain in a 1972 Super Bee. (They did that one on "monster garage".)

 

[G & G Electric]

I would NEVER close a CB until the fault was located and the CB tested.

I agree. The breaker has opened to let you know there is a problem. Find and fix it and the breaker shouldn't open again. However, I would like to know if the OP's question relates to shunt trip breakers also?

 

[jim dungar]

I would like to know if the OP's question relates to shunt trip breakers also?

A "shunt trip breaker" is no different than a standard breaker except for the addition of an additional piece of hardware. The shunt trip mechanism is simply a plunger that pushes the internal latch of the breaker causing it to turn off, it really is not much different than manually turning the breaker off using the handle.

 

[G & G Electric]

A "shunt trip breaker" is no different than a standard breaker except for the addition of an additional piece of hardware. The shunt trip mechanism is simply a plunger that pushes the internal latch of the breaker causing it to turn off, it really is not much different than manually turning the breaker off using the handle.

At my last fire marshall inspection the supression guys couldn't get their gas valve to close when the system was tripped. And each time the system was tripped, my shunt breaker opened like it was supposed to. These guys must have tried at least 20 times to get their gas valves right. I got to thinking about how many times that shunt breaker could open without some sort of damage or at least weaken the breaker. After reading this post, I may recommend to the owner that a new shunt breaker may not be a bad idea.

 

[zog]

At my last fire marshall inspection the supression guys couldn't get their gas valve to close when the system was tripped. And each time the system was tripped, my shunt breaker opened like it was supposed to. These guys must have tried at least 20 times to get their gas valves right. I got to thinking about how many times that shunt breaker could open without some sort of damage or at least weaken the breaker. After reading this post, I may recommend to the owner that a new shunt breaker may not be a bad idea.

Again, the shunt trip is irrevelant.

 

[jim dungar]

After reading this post, I may recommend to the owner that a new shunt breaker may not be a bad idea.

Why, the breaker is tested to a standard that requires 6,000 full current rating non-fault operations?

 

[RHJohnson]

I know we all get out of the way when we close a breaker. I know we do not look at the breaker to see what happens! I don't want to burn my eyes, face, hair, etc....I may be pretty ugly, but I like me the way I am!

I think the environment has a lot to do with how long the breaker lasts. I have worked in some really harsh environments, and have seen some contacts and arc suppressors in really bad condition. I don't think CB's in an outside panel would fare nearly as well as one indoors.

 

[Kdog76]

To do otherwise is an OSHA violation.

10 CFR 1910.334(b)(2)"Reclosing circuits after protective device operation."

After a circuit is deenergized by a circuit protective device, the circuit protective device, the circuit may not be manually reenergized until it has been determined that the equipment and circuit can be safely energized. The repetitive manual reclosing of circuit breakers or reenergizing circuits through replaced fuses is prohibited.

This may be a serious shortcoming on my behalf, so any guidance would be appreciated. In all my years in the trade, I have yet to use a megger. I understand not resetting a breaker until you can determine it is safe to do so, but in all my training, micro-meggering was not part of it.
Typically, my approach would be to check continuity from load side of the breaker, to the grounded conductor, or ungrounded conductor. If I see continiuty then I know there is a dead short to ground or neutral. Then to check phase-to-phase with a wiggy to unsure it's not a line-to-line fault. If don't see a short in either case I would typically feel safe about resetting the breaker. (i.e. figure maybe an overload). And yes , to turn my head & not stand in front is always my practice. I would like some extra info on this 10 CFR reg, and the best place to review the OSHA regs. I know we all need safety to be #1, ALL the time.

 

[bjp_ne_elec]

Primary injection and compare to trip curves.

Zog - is this something you have capability to do yourself, or do you bring it to a test house?

 

[bjp_ne_elec]

After a fault at a minimum the CB should be meggered with the CB open Line to Load, ..............

How would you do this? You're saying meg the CB - but is open - so I'm not following. With breaker open you could meg from the terminal of the CB downstream. Maybe I'm missing what your saying.

Thanks

 

[brian john]

Megger Line to load with the CB open A to A, B to B, C to C

Megger the line load or with the CB closed (assuming the CB is out of the panel (removed safely) or the panel/distribution equipment is de-energized disconnect load and if in the panel load.

A to B, B to C, C to A, A to ground, B to Ground, C to Ground With the CB

or megger the load side

A to B, B to C, C to A, A to ground, B to Ground, C to Ground With the CB

megger the line side

A to B, B to C, C to A, A to ground, B to Ground, C to Ground With the CB


You need to megger line and load as there can be carbon across the arc chutes and breaker interior and on the line side across the movable contacts and breaker interior.

Micro-ohm will tell if you have any damage to the stationary/movable contacts.

As for high current testing we prefer to take a single CB to our shop as the high current test sets weigh 600-1200 pounds and require single phase 208 at 100 amps or single phase 480 100 amps (we have several different sizes). When we do maintenance we take the test set to the project

 

[zog]

Primary injection and compare to trip curves.

Zog - is this something you have capability to do yourself, or do you bring it to a test house?

I have 5 primary injection test sets, they run from $10,000 to $50,000 and weigh around 2000 pounds, we have some that are mobile and some in our breaker shop.

http://photos.gcbsinventory.com/trailers/

 

[weressl]

Does anyone have information on the best way to test a circuit breaker to see if it is bad? How many times can a breaker trip before it should be replaced? I'm sure the manufactures have a rated duty cycle for each breaker. Does anyone know where to find this information. I have tried several places and have only found the amount when used as a switch but not if it trips.

Molded case circuit breakers can interrupt one short circuit with the magnitude of their rating. There is usually data available of both mechanical life, eg. how many times can be turned on/off without load and the contacts are rated in terms of ther full lod capacity.

Circuit breakers can be bench tested with injected current. Equipemnt is available that times the trip and it can be compared to the breakers T/C curve. Small breakers, such as in the 100/200A panels are seldom, if ever, tested.

 

[zog]

Small breakers, such as in the 100/200A panels are seldom, if ever, tested.

Cheaper to replace then to properly test, but an IR and contact resistance test would be better than nothing.

 

[brian john]

Circuit breakers can be bench tested with injected current. Equipemnt is available that times the trip and it can be compared to the breakers T/C curve. Small breakers, such as in the 100/200A panels are seldom, if ever, tested.

Test them all the time had a job for a nuke subcontractor and we had 100's in the 100-200 range for testing, many local muncipalities require testing of 100 and above in acceptance specs for some projects.

 

[bjp_ne_elec]

Megger Line to load with the CB open A to A, B to B, C to C

How do you do this if the load is 100' away. Maybe I'm not understanding what your describing. Let's take a single phase load, as I'm assuming you're describing a three phase load.

When "growing up" as an apprentice, the only meggering I was ever exposed to when the JW was meggering phase to phase and each phase to ground - say in a piece of switch gear. I'm really wanting to expand my knowledge of how and when to megger, so please bear with me, if it appears I'm asking a "stupid" question.

Thanks

 

[zog]

How do you do this if the load is 100' away. Maybe I'm not understanding what your describing. Let's take a single phase load, as I'm assuming you're describing a three phase load.

When "growing up" as an apprentice, the only meggering I was ever exposed to when the JW was meggering phase to phase and each phase to ground - say in a piece of switch gear. I'm really wanting to expand my knowledge of how and when to megger, so please bear with me, if it appears I'm asking a "stupid" question.

Thanks

He means the line side and load side of the breaker, not the actual load. This is done with the breaker removed from the system. You are just meggering across the open contacts to test the breakers open pole insulation.

 

[electricguy61]

my opinion, unmarred by any research or factual knowledge whatsoever,
is that with 10k interrupting capacity breakers of the type usually used
in home panels, when a breaker has been habitually overloaded and
repeatedly reset, it loses its spunkiness, and begins tripping at a lower
set point than the rating of the breaker. it starts feeling mechanically
unsound as well when you reset it, and sometimes won't reclose at all.

these are the symptoms of creeping breaker sickness. time to bury it,
and put another $5 breaker in.

for big breakers, rack in breakers, and such, go ask zog.

Didn't anyone get this posting?

Homeline 2 pole 50amp breaker= $8 wholesale, $40.30 retail (according to the Square D catalog)

Replace the homeowner's breaker and forget it!