(breaker) Interrupting rating explained (simply)

[jap]

Yeah, what I meant didn't come out as what I wrote. I can see I indicated the apprentices understand, what I meant was that I present it to them. They generally sit like lumps on a log and when I review it later, they can't seem to remember.

 

[kwired]

Yeah, what I meant didn't come out as what I wrote. I can see I indicated the apprentices understand, what I meant was that I present it to them. They generally sit like lumps on a log and when I review it later, they can't seem to remember.

I can probably say I didn't really fully get it until maybe at least 3-5 years of experience maybe even more. The right demonstration possibly would have worked early on though, with some good explanations of why things were the way they were.

Then throw in series ratings to complicate things. I maybe still don't quite fully understand how that really works, just know that someone tested it and it supposedly works.

 

[Strathead]

I can probably say I didn't really fully get it until maybe at least 3-5 years of experience maybe even more. The right demonstration possibly would have worked early on though, with some good explanations of why things were the way they were.

Then throw in series ratings to complicate things. I maybe still don't quite fully understand how that really works, just know that someone tested it and it supposedly works.

Fully rated I have no problem with. Over a certain amperage, the contact metal can melt more quickly than the mechanical opening can function. When that happens, the contacts fuse and the springs can't over come that. This is only one scenario. Once that happens the current will continue to flow until the entire breaker or something else between the fault and the source, melts or give way. Series rating I am not positive about, but basically a breaker or fuse upstream has been tested and proven to trip BEFORE the above described destruction of the downstream breaker and/or wiring can occur at or below the rating of the downstream breaker.

 

[kwired]

Fully rated I have no problem with. Over a certain amperage, the contact metal can melt more quickly than the mechanical opening can function. When that happens, the contacts fuse and the springs can't over come that. This is only one scenario. Once that happens the current will continue to flow until the entire breaker or something else between the fault and the source, melts or give way. Series rating I am not positive about, but basically a breaker or fuse upstream has been tested and proven to trip BEFORE the above described destruction of the downstream breaker and/or wiring can occur at or below the rating of the downstream breaker.

That is about the only thing that makes sense about it for me. That might not mean it is a good idea to use the device again after such an event, just means it will not have a catastrophic failure in said event.

 

[romex jockey]

??

Meaning the NRTL tests to 3K on resi serv gear, and claims it's good for 22K Kwired

~S~

 

[kwired]

Meaning the NRTL tests to 3K on resi serv gear, and claims it's good for 22K Kwired

~S~

Without more information that appears fairly illogical.

And what is resi serv gear? Most what you see is not restricted to residential only but some of it may not be preferred by designers/installers for other than residential.

 

[xformer]

Pretty sure everyone understands the overcurrent rating on a breaker but does anyone have a (5 grader) explanation for what the Interrupting rating (240.83(c)) is and how it meshes-up with the panel it's being used in?

My explanation is this.... Interrupting Current is the Maximum current a device can handle without exploding when a Short Circuit occurs on the circuit. I also explain that when a fault occurs, the current rises to an extremely high value. In the case of a short circuit caused by accidently cutting hot and neutral of a live circuit with your pliers, the current blows hole in your pliers, but not blow up the breaker in the panel.

 

[kwired]

My explanation is this.... Interrupting Current is the Maximum current a device can handle without exploding when a Short Circuit occurs on the circuit. I also explain that when a fault occurs, the current rises to an extremely high value. In the case of a short circuit caused by accidently cutting hot and neutral of a live circuit with your pliers, the current blows hole in your pliers, but not blow up the breaker in the panel.

Both those (breaker and your pliers) the amount of damage kind of depends on both current level and time duration.

Seen a few times where a 1 pole QO (which have low magnetic trip setting) will trip fast enough that little damage is done to your pliers.

 

[xformer]

Both those (breaker and your pliers) the amount of damage kind of depends on both current level and time duration.

Seen a few times where a 1 pole QO (which have low magnetic trip setting) will trip fast enough that little damage is done to your pliers.

True that. was just providing 5th grade explanation.

 

[augie47]

True that. was just providing 5th grade explanation.

Thank you !!! More in line with what the OP asked for without the pontificating,

 

[Strathead]

Both those (breaker and your pliers) the amount of damage kind of depends on both current level and time duration.

Seen a few times where a 1 pole QO (which have low magnetic trip setting) will trip fast enough that little damage is done to your pliers.

Since this is the anal electrician's forum, we must add voltage to that list, because the damage is really the wattage, so if we want to be REALLY anal the damage is reduced by the power factor

 

[jim dungar]

Since this is the anal electrician's forum, we must add voltage to that list, because the damage is really the wattage, so if we want to be REALLY anal the damage is reduced by the power factor

No. It is the current that causes the damage. During a true bolted fault condition the voltage across the fault approaches zero. As the current is interrupted the voltage does come into play and is a factor in the AIC rating.

 

[Strathead]

No. It is the current that causes the damage. During a true bolted fault condition the voltage across the fault approaches zero. As the current is interrupted the voltage does come into play and is a factor in the AIC rating.

The damage is caused when the breaker is opening. Any breaker is going to melt if it is carrying run away voltage for more than a few cycles.

 

[jim dungar]

The damage is caused when the breaker is opening. Any breaker is going to melt if it is carrying run away voltage for more than a few cycles.

The energy in a low impedance or bolted fault, as caused by cutting through a conductor, is primarily a function of the available fault current and length of time it flows.
The voltage of the circuit does come into play during the opening of an overcurrent protective device, because this is in effect a controlled arcing fault.

A fault on a lower voltage system, like 208V, may produce more damage than a fault at a higher voltage, like 480V.

 

[jap]

Both those (breaker and your pliers) the amount of damage kind of depends on both current level and time duration.

Seen a few times where a 1 pole QO (which have low magnetic trip setting) will trip fast enough that little damage is done to your pliers.

On the few occasions I've accidently shorted out a conductor with my "pliers" I've never seemed to be that fortunate.

JAP>

 

[GoldDigger]

Since this is the anal electrician's forum, we must add voltage to that list, because the damage is really the wattage, so if we want to be REALLY anal the damage is reduced by the power factor

The wattage is the wattage dissipated before the contacts open and in the arc itself after opening, which will almost certainly be in phase with the voltage across the breaker contacts. If the "bolted fault" is actually inductive, that will reduce the short circuit current, but will not change the phase angle between current and contact or arc voltage. So current is really the sole factor except to the extent that time to arc extinction is dependent on the supply voltage.

 

[jap]

The wattage is the wattage dissipated before the contacts open and in the arc itself after opening, which will almost certainly be in phase with the voltage across the breaker contacts. If the "bolted fault" is actually inductive, that will reduce the short circuit current, but will not change the phase angle between current and contact or arc voltage. So current is really the sole factor except to the extent that time to arc extinction is dependent on the supply voltage.

Hey Strathead,,,, I'm picturing your students while reading this.. ...

JAP>

 

[kwired]

Hey Strathead,,,, I'm picturing your students while reading this.. ...

JAP>

They probably don't look anything like what you pictured

 

[augie47]

Thread has run it's course and is far from OP original question and thus closed.