Overcurrent protection, and breaker rating

[jado85]

I was told that we need to change the breaker ratings in "2BPP6" to match the Isc(31000A), and I'm having trouble understanding why? what would happen if they stay at the current 18KA rating.

Anything I could do to reduce Isc beside using fuses?

 

[templdl]

I was told that we need to change the breaker ratings in "2BPP6" to match the Isc(31000A), and I'm having trouble understanding why? what would happen if they stay at the current 18KA rating.

Anything I could do to reduce Isc beside using fuses?

What???? What in the world is 2BPP6. And (Isc)31000A. The 18kaic is the only thing that makes sense. Who made the request? Have you asked them what they meant? In my 21 years I haven't ran across these terms.

 

[Jraef]

What???? What in the world is 2BPP6. And (Isc)31000A. The 18kaic is the only thing that makes sense. Who made the request? Have you asked them what they meant? In my 21 years I haven't ran across these terms.

You have to look at his attachment. 2BPP6 is his panelboard number. Isc is Short Corcuit current. What he is being told, correctly, is that his short circuit current is 31kA and he is using breakers in that panelboard that are only rated 18kAIC. No Bueno.

Jado85
"They" are correct. Your breakers could, in theory, explode under fault conditions.

 

[templdl]

You have to look at his attachment. 2BPP6 is his panelboard number. Isc is Short Corcuit current. What he is being told, correctly, is that his short circuit current is 31kA and he is using breakers in that panelboard that are only rated 18kAIC. No Bueno.

Jado85
"They" are correct. Your breakers could, in theory, explode under fault conditions.

Got it. I would have suggested looking into a series rating with the main breaker and seeing the 1200a main breaker and he may be SOL.

 

[LMAO]

I was told that we need to change the breaker ratings in "2BPP6" to match the Isc(31000A), and I'm having trouble understanding why? what would happen if they stay at the current 18KA rating.

Anything I could do to reduce Isc beside using fuses?

hmm, according to my calculations Isc is actually 65kA, and that's not even considering the motors contribution...

Higher rated breaker or current limiting fuses.

 

[Pharon]

hmm, according to my calculations Isc is actually 65kA, and that's not even considering the motors contribution...

Higher rated breaker or current limiting fuses.

It's 65kA at the transformer, and only with infinite contribution on the primary side.

I'm guessing the 31kA was calculated taking into account the resistance and length of the feeder, but who knows. Still a problem if the breakers are only rated for 18kA at 480V.

But according to this, the Square D LA36400 breakers are rated for 30kA at 480V, so I'm not sure where the 18kA assumption comes from:

http://www.cesco.com/b2c/product/Schneider-Electric-Square-D-LA36400-I-Line-Molded/74164

 

[jim dungar]

...not sure where the 18kA assumption comes from

I have no idea either.

There is also a 100A type KA breaker, on the far right of the panel, rated 25kA.
Should we point out that the 1200A main breaker does not have GF protection required by 215.10?

 

[petersonra]

hmm, according to my calculations Isc is actually 65kA, and that's not even considering the motors contribution...

Higher rated breaker or current limiting fuses.

unless the CL fuses are series rated with the breakers it does not help, and it does nothing to help with the motor contribution.

 

[kingpb]

It's 65kA at the transformer, and only with infinite contribution on the primary side.

I'm guessing the 31kA was calculated taking into account the resistance and length of the feeder, but who knows. Still a problem if the breakers are only rated for 18kA at 480V.

And what about the potential contribution from the other two tapped feeders off the transformer? That could also be adding to the fault level; who knows.

 

[Bugman1400]

There may be a variety of reasons why the Isc has jumped up. Perhaps distributed generation (PV) has been recently added or the local POCO has upgraded the substation xfmr to a larger size and your service point is close to the sub. There are also ways to reduce the Isc. Many companies will install series reactors at the xfmr. This is often a cheaper alternative since it avoids having to replace all the panels and MCCBs.

 

[jado85]

jim dungar

Originally Posted by Pharon
...not sure where the 18kA assumption comes from



I have no idea either.

There is also a 100A type KA breaker, on the far right of the panel, rated 25kA.
Should we point out that the 1200A main breaker does not have GF protection required by 215.10?​

this is done by design according to

Exception No. 1: The provisions of this section shall not apply to a disconnecting means for a continuous industrial process where a nonorderly shutdown will introduce additional or increased hazards

And what about the potential contribution from the other two tapped feeders off the transformer? That could also be adding to the fault level; who knows.

those two feeders are also power panels with similar underrated breakers.

There may be a variety of reasons why the Isc has jumped up. Perhaps distributed generation (PV) has been recently added or the local POCO has upgraded the substation xfmr to a larger size and your service point is close to the sub. There are also ways to reduce the Isc. Many companies will install series reactors at the xfmr. This is often a cheaper alternative since it avoids having to replace all the panels and MCCBs.

does the serier transformer affect anything beside the short circuit current?

You have to look at his attachment. 2BPP6 is his panelboard number. Isc is Short Corcuit current. What he is being told, correctly, is that his short circuit current is 31kA and he is using breakers in that panelboard that are only rated 18kAIC. No Bueno.

Jado85
"They" are correct. Your breakers could, in theory, explode under fault conditions.[/QUOT
Got it. I would have suggested looking into a series rating with the main breaker and seeing the 1200a main breaker and he may be SOL.

Thank you all,

The 18KA was indeed the wrong value, it is 30KA but that is still under the Isc of 31KA. this plant prefers using Circuit breakers over fuses(reducing downtime).

So my understanding is that I can:

1. use a main breakers that are rated higher than Isc and become fully rated
2. or have a main breaker series rated with series connected breakers/fuses , the combination of those two should be higher than the Isc? the combination of those will provide the proper protection?

 

[Bugman1400]

Series reactors typically only affect the short circuit values.

 

[jim dungar]

this is done by design according to

So my understanding is that I can:

1. use a main breakers that are rated higher than Isc and become fully rated
2. or have a main breaker series rated with series connected breakers/fuses , the combination of those two should be higher than the Isc? the combination of those will provide the proper protection?

Very few circuits actually meet the intent of the exception, for GF, that you mentioned. If hospital life safety circuits are not exempt, I am pretty sure that a simple manufacturing line isn't either. It is up to your AHJ, but I have designed and had them installed into paper mills, steel mills, and chemical plants.

1. yes.
2. yes, remember that the combination needs to be listed and the motor contribution, between the series rated devices, cannot exceed 1% of the lower device AIC rating (the KA breaker would limit you to 250A of motor load at the panelboard bus )

 

[Jraef]

...

So my understanding is that I can:

1. use a main breakers that are rated higher than Isc and become fully rated
2. or have a main breaker series rated with series connected breakers/fuses , the combination of those two should be higher than the Isc? the combination of those will provide the proper protection?

As to the first point, no, that's not good enough alone. That main breaker IS already listed for 35kAIC, but not the breakers down stream.

To the second point, YOU can't "have" a main breaker series rated after the fact; it either IS series rated with the downstream breakers, or not. That is done by the manufacturer, who submitted the specific combinations to UL for testing that way. What you CAN do is take your info to your local Square D office and ask them if that main and down stream breaker combination in an I-Line panel IS already series rated for a higher value than the individual branch breakers alone. I suspect you may find out they are not, I looked at a document I have and it does NOT show that specific main and branches listed as a series combo. But my data may be old, you should check into it for yourself. But again, it's not something YOU or anyone else determines, it has to come from THEM in the form of documented listing information. Then you take that information to whomever is asking for this.

I should mention though, many of the I-Line panels and breaker combos CAN be series listed with specific up-stream fuses. There are just fewer series combos of breaker-to-breaker.

 

[jim dungar]

There are just fewer series combos of breaker-to-breaker.

They have lots of ratings, you just need to use the on-line resources rather than relying on printed material.
Yes, there is a series combination using the installed breakers, however it cannot be used because of the amount of motor load connect in the panel, NEC 240.86(C).

 

[templdl]

Series reactors typically only affect the short circuit values.

I has provided many air core current limiting rresactors to MCC OEMs. They were commonly made up of (3) 1ph aircore reactyores stacked oh top of one another. I supplied them to be installed to the OEM's enclosure. If I supplied the enclosure it would have consisted of non magnetic material such as aluminum.
But, depending upon the existing arrangement and cost consideration, yes. A CLR is a relevant option.
I've supplied enclosed MV CLRs that were so large that each reactor and its enclosure that when shipped on 3 separate flat bed trailers that a special clearance had to be requested from the states for the authority to transport the reactors using specific roadways during specific time of day. They were big.

 

[jado85]

As to the first point, no, that's not good enough alone. That main breaker IS already listed for 35kAIC, but not the breakers down stream.

To the second point, YOU can't "have" a main breaker series rated after the fact; it either IS series rated with the downstream breakers, or not. That is done by the manufacturer, who submitted the specific combinations to UL for testing that way. What you CAN do is take your info to your local Square D office and ask them if that main and down stream breaker combination in an I-Line panel IS already series rated for a higher value than the individual branch breakers alone. I suspect you may find out they are not, I looked at a document I have and it does NOT show that specific main and branches listed as a series combo. But my data may be old, you should check into it for yourself. But again, it's not something YOU or anyone else determines, it has to come from THEM in the form of documented listing information. Then you take that information to whomever is asking for this.

I should mention though, many of the I-Line panels and breaker combos CAN be series listed with specific up-stream fuses. There are just fewer series combos of breaker-to-breaker.

I should have said " replace the all the underrated breaker to become fully rated"

jim dungar

Originally Posted by jado85
this is done by design according to

So my understanding is that I can:

1. use a main breakers that are rated higher than Isc and become fully rated
2. or have a main breaker series rated with series connected breakers/fuses , the combination of those two should be higher than the Isc? the combination of those will provide the proper protection?

Very few circuits actually meet the intent of the exception, for GF, that you mentioned. If hospital life safety circuits are not exempt, I am pretty sure that a simple manufacturing line isn't either. It is up to your AHJ, but I have designed and had them installed into paper mills, steel mills, and chemical plants.​

I was told it has been used in this plant in the past(fire Hazard), but we'll still examine the situation.

templdl

Originally Posted by Bugman1400
Series reactors typically only affect the short circuit values.



I has provided many air core current limiting rresactors to MCC OEMs. They were commonly made up of (3) 1ph aircore reactyores stacked oh top of one another. I supplied them to be installed to the OEM's enclosure. If I supplied the enclosure it would have consisted of non magnetic material such as aluminum.
But, depending upon the existing arrangement and cost consideration, yes. A CLR is a relevant option.
I've supplied enclosed MV CLRs that were so large that each reactor and its enclosure that when shipped on 3 separate flat bed trailers that a special clearance had to be requested from the states for the authority to transport the reactors using specific roadways during specific time of day. They were big.​

My impression that CLR is a cheaper alternative to replacing the panels or the breakers! based on how you describe do they cost more in labor,foot print, and transportation?

 

[jim dungar]

I was told it has been used in this plant in the past(fire Hazard), but we'll still examine the situation.

The most likely fault in any system is a ground fault. I don't know why more people don't install multiple levels of GF (like is done in hospitals) instead of trying to skip having it. GF almost never clear themselves neatly.
Several years ago we implemented GF in a paper mill. They had a transformer fault to ground, and the entire facility was knocked off-line. Within 3 hours they were back into production. I was told this was the shortest recovery, from similar failures, because it did not result in the fire department needing to be called.

 

[Pharon]

The most likely fault in any system is a ground fault. I don't know why more people don't install multiple levels of GF (like is done in hospitals) instead of trying to skip having it. GF almost never clear themselves neatly.
Several years ago we implemented GF in a paper mill. They had a transformer fault to ground, and the entire facility was knocked off-line. Within 3 hours they were back into production. I was told this was the shortest recovery, from similar failures, because it did not result in the fire department needing to be called.

I agree with you -- more levels of GF is always better so that you take fewer things offline. The problem, though, is that because of the 0.1 second separation required for proper coordination, you are sort of limited to how many overall devices you can install in the first place.

I can tell you this -- the most common issue I've had from working in a hospital is a ground fault taking out some 800A main because not enough downstream protection was put in. Not a pleasant scene. All it takes is an errant screwdriver and a 277V ballast.

 

[jado85]

You have to look at his attachment. 2BPP6 is his panelboard number. Isc is Short Corcuit current. What he is being told, correctly, is that his short circuit current is 31kA and he is using breakers in that panelboard that are only rated 18kAIC. No Bueno.

Jado85
"They" are correct. Your breakers could, in theory, explode under fault conditions.

what side of the breaker is the short circuit current available? if it is at the upstream wouldn't the Main CB be sufficient ,The main panel CB (SQUARE D POWERPACT PG 1200 CAT NO. PGA36120)is rated for 35KA, we do we have to change the remaining breakers in the panel?