help with square D series rating for legacy breaker

[electrofelon]

Is anyone by chance knowledgeable in navigating/finding square D series ratings? The information seems to be scattered all over their website, its not easy. They could definitely do a better job of organizing the data.

Ive got a 1976 power style switchboard
with a PA frame 1000A main, and Q2 distribution breakers. The main is 65K (@ 240). There is a mix of Q2 (10K AIC) and Q2H (22K) distribution breakers. I think the 10K ones were added after the fact. I looked here:

https://www.schneider-electric.us/en/download/document/2700DB9901/ and the closest thing I saw was a QD. I have a hard time believing the Q2 doesnt rate with the main. Want to confirm that it does and whether it needs to be the "H" version.

 

[ron]

I think that is the right document.

The older breaker combinations were not tested as the series rated concepts and rules came about in the 90's so the QD and Q2 CB's are different and probably mean that there is no series listing.

 

[drktmplr12]

all listings for combo ratings are provided on UL's site:

https://industries.ul.com/industria...s-for-combination-motor-controller-components

edit: i misunderstood-i posted reference to motor controllers, which you do not have. apologies.

 

[electrofelon]

I think that is the right document.

The older breaker combinations were not tested as the series rated concepts and rules came about in the 90's so the QD and Q2 CB's are different and probably mean that there is no series listing.

Oh interesting, I wasn't aware series ratings were that new a concept.

 

[drktmplr12]

Oh interesting, I wasn't aware series ratings were that new a concept.

UL needed money quick

 

[ron]

UL needed money quick

Or people were haphazardly using the fuse let through curves without understanding dynamic impedance of the distribution path.

 

[electrofelon]

UL needed money quick

Lol.

So how did this typically work say around this time, mid 70's.... . Breakers still had AIC ratings. Was AFC just often ignored? I guess if there weren't series ratings, you had to either fully rate everything or ignore it.

 

[ron]

So how did this typically work say around this time, mid 70's.... . Breakers still had AIC ratings. Was AFC just often ignored? I guess if there weren't series ratings, you had to either fully rate everything or ignore it.

Correct, before it was formally accepted in the NEC (around 2005 or a cycle or two before), you fully rated equipment, and that was it.

If you ignored the SCCR, then you were wrong.

 

[electrofelon]

Correct, before it was formally accepted in the NEC (around 2005 or a cycle or two before), you fully rated equipment, and that was it.

If you ignored the SCCR, then you were wrong.

Not saying that it makes it correct, but without series ratings, it must have been "impractical" to use properly rated equipment in many situations. It must have been extensively ignored.

 

[electrofelon]

I am not aware of any 240v miniature circuit breakers that go above 22k. I guess there's always the old trick of using 480/277 gear to get high AIC ratings.

 

[ron]

I am not aware of any 240v miniature circuit breakers that go above 22k. I guess there's always the old trick of using 480/277 gear to get high AIC ratings.

No trick at all. The equipment can be rated up to 600V, as long as it also had a fully rated tested SCCR for the 120V AIC 1 pole number that is needed.

I've had 1 pole molded case CB's up to 65kA. Past that, generally had to go to fuses or insulated case CBs or power CBs if practical for feeders.

For small circuits, the impedance of the small conductors knocked the SCCRs down pretty fast below 65kA when needed or we ran the feeder long to do so.

 

[electrofelon]

No trick at all. The equipment can be rated up to 600V, as long as it also had a fully rated tested SCCR for the 120V AIC 1 pole number that is needed.

I've had 1 pole molded case CB's up to 65kA. Past that, generally had to go to fuses or insulated case CBs or power CBs if practical for feeders.

For small circuits, the impedance of the small conductors knocked the SCCRs down pretty fast below 65kA when needed or we ran the feeder long to do so.

Yeah the AIC goes up a lot from 480 to 240. A Siemens BQD which is their common 277/480 breaker is rated 14k at 480, but 65k at 240. That would sure get expensive. This one job that the OP is about has around 160 poles and most of them would be well above 22k. I'll try not to call it a "trick" anymore

 

[drktmplr12]

Or people were haphazardly using the fuse let through curves without understanding dynamic impedance of the distribution path.

as in...not accounting for asymmetrical components of fault currents depending on when in the cycle the fault occurred?

 

[ron]

as in...not accounting for asymmetrical components of fault currents depending on when in the cycle the fault occurred?

No, as in the opening of protective devices in the distribution path, such as smaller circuit breakers seeing the fault that as the contacts part, impose a changing impedance to the circuit and slowly (as related to the fault and the attempt of the current limiting of the fuse) reduce fault current below the current limiting range of the fuse, or reduce it into different parts of the up/over/down curves.

This is related to series rating but also talks about dynamic impedance.
https://www.nema.org/Products/Documents/eng+series+rating+paper.pdf

 

[drktmplr12]

No, as in the opening of protective devices in the distribution path, such as smaller circuit breakers seeing the fault that as the contacts part, impose a changing impedance to the circuit and slowly (as related to the fault and the attempt of the current limiting of the fuse) reduce fault current below the current limiting range of the fuse, or reduce it into different parts of the up/over/down curves.

This is related to series rating but also talks about dynamic impedance.
https://www.nema.org/Products/Documents/eng+series+rating+paper.pdf

This is an excellent explanation. Thank you for your feedback and link to extra reading!

Sent from my Pixel 2 using Tapatalk

 

[kwired]

I am not aware of any 240v miniature circuit breakers that go above 22k. I guess there's always the old trick of using 480/277 gear to get high AIC ratings.

Square D digest has 42 and 65k QO breakers. They are not available in all standard sizes, even the 22k skips some standard sizes in the catalog.

You probably don't want to know the price and probably need to wait for many of them to be manufactured after you order them.

 

[wvengineer]

No, as in the opening of protective devices in the distribution path, such as smaller circuit breakers seeing the fault that as the contacts part, impose a changing impedance to the circuit and slowly (as related to the fault and the attempt of the current limiting of the fuse) reduce fault current below the current limiting range of the fuse, or reduce it into different parts of the up/over/down curves.

This is related to series rating but also talks about dynamic impedance.
https://www.nema.org/Products/Documents/eng+series+rating+paper.pdf

Nice! Thanks for the info.

 

[jim dungar]

Ive got a 1976 power style switchboard
with a PA frame 1000A main, and Q2 distribution breakers. The main is 65K (@ 240). There is a mix of Q2 (10K AIC) and Q2H (22K) distribution breakers.

The earliest Square D series rating data I have is from 1988. At that time the Q2 circuit breaker was not rated with any upstream device. There were a few series ratings for the Q2-H breakers, but they were primarily 2-pole applications.

Back in the old days, many electricians and engineers basically ignored AIC ratings except at the service entrance device. The began to change in the late 70's and early 80's, but a lot of bad habits are hard to break and therefore last a long time.

In my experience very few distributors stock any breaker that is not the base model. It also seems some contractors rarely take the time to go to a job first to find out what devices are actually installed. Finally customers do not like having to pay several hundreds of dollars for a breaker, much less having to special order a really expensive one.

In your case, do you know what the available fault current really is?

 

[electrofelon]

The earliest Square D series rating data I have is from 1988. At that time the Q2 circuit breaker was not rated with any upstream device. There were a few series ratings for the Q2-H breakers, but they were primarily 2-pole applications.

Back in the old days, many electricians and engineers basically ignored AIC ratings except at the service entrance device. The began to change in the late 70's and early 80's, but a lot of bad habits are hard to break and therefore last a long time.

In my experience very few distributors stock any breaker that is not the base model. It also seems some contractors rarely take the time to go to a job first to find out what devices are actually installed. Finally customers do not like having to pay several hundreds of dollars for a breaker, much less having to special order a really expensive one.

In your case, do you know what the available fault current really is?

Jim,

I admit to at first assuming fault current based on what was in there, yeah that happens a lot no doubt. As I said, there were a bunch of 10k Q2's in there that must have been added later. The original 22k ones i didnt even know were rated higher at first because its not marked on the front.

Utility quoted me 110k. I was skeptical, so i went into the vault and got the actual transformer size and impedance data. 3x167 @ 1.8% is about 77k, and 55k at the main. Note the transformers are oddly large (its a 1000 amp service) and were changed sometime around 1998 based on the date on the data plate, so who know what was there before but maybe the Q2H's were ok when first installed.

 

[jim dungar]

Jim,

I admit to at first assuming fault current based on what was in there, yeah that happens a lot no doubt. As I said, there were a bunch of 10k Q2's in there that must have been added later. The original 22k ones i didnt even know were rated higher at first because its not marked on the front.

Utility quoted me 110k. I was skeptical, so i went into the vault and got the actual transformer size and impedance data. 3x167 @ 1.8% is about 77k, and 55k at the main. Note the transformers are oddly large (its a 1000 amp service) and were changed sometime around 1998 based on the date on the data plate, so who know what was there before but maybe the Q2H's were ok when first installed.

Yep, you have some overdutied equipment that should be replaced.
Square D started putting labels on the front of their I-Line breakers around 1985. Prior to that the higher AIC 480V devices often had colored handles.

Your main breaker is more than 40 years old, has it ever been tested?