Series rated panelboards vs fully rated panelboards

[shoaib10]

Hello,

I always had this question in my head...What is the difference between series rated panel boards and fully rated panel boards?

I know that series rated devices are those where you have a breaker/fuse combination tested for higher AIC ratings than the individual device itself on the line side of the low rated AIC device...

Thanks in advance for answering.....

 

[steve66]

I'll answer the easy part:

Series rated panels can be cheaper, and save money.

 

[shoaib10]

I'll answer the easy part:

Series rated panels can be cheaper, and save money.

Can you explain me why they are cheaper?

 

[GoldDigger]

Can you explain me why they are cheaper?

Here are a few reasons:
1. The contact opening speed and geometry need to extinguish a higher current arc without damage.
2. Parts need to say, if briefly, carry higher current and withstand higher magnetic and plasma pressure forces.
3. It may not be possible to achieve high AIC in space and cost saving half-width or tandem configurations.

I am sure other members can add more.


mobile

 

[shoaib10]

Here are a few reasons:
1. The contact opening speed and geometry need to extinguish a higher current arc without damage.
2. Parts need to say, if briefly, carry higher current and withstand higher magnetic and plasma pressure forces.
3. It may not be possible to achieve high AIC in space and cost saving half-width or tandem configurations.

I am sure other members can add more.


mobile

Just curious if you design any equipment to withstand higher AIC doesnt it make your equipment more expensive?

 

[GoldDigger]

Just curious if you design any equipment to withstand higher AIC doesnt it make your equipment more expensive?

As a general rule, yes.
But in answer to your question, designing it to test to withstand higher available fault current conditions only if in series (upstream) with a high AIC rated device will often be less expensive than designing it to pass the same tests when connected directly to the high current source.

A similar example would be requiring the use of two contacts in series in a switch or relay to obtain a higher withstand or interrupting voltage rating.

 

[shoaib10]

As a general rule, yes.
But in answer to your question, designing it to test to withstand higher available fault current conditions only if in series (upstream) with a high AIC rated device will often be less expensive than designing it to pass the same tests when connected directly to the high current source.

A similar example would be requiring the use of two contacts in series in a switch or relay to obtain a higher withstand or interrupting voltage rating.

Got it...I am looking for more technical answer...Hopefully other members will contribute...

 

[jim dungar]

Got it...I am looking for more technical answer...Hopefully other members will contribute...

I am not going to guess at what you want to hear. Give us some direction.
What do you really want to know? The test procedures required to pass UL testing before a series rating can be applied? The methodology under which an AIC rating is established? How about series ratings from the point of view of a fuse manufacturer?

 

[Carultch]

Hello,

I always had this question in my head...What is the difference between series rated panel boards and fully rated panel boards?

I know that series rated devices are those where you have a breaker/fuse combination tested for higher AIC ratings than the individual device itself on the line side of the low rated AIC device...

Thanks in advance for answering.....

It has to do with the available fault current, and the way the breakers in the panelboard respond to it.

In a fully rated panelboard, all breakers must have a KAIC rating that meets or exceeds the available fault current at the main breaker or main lugs. Given 20 kA of available fault current, all breakers in the panelboard have to have 22KAIC rating (that's what is usually available above 20kA).

In a series rated panelboard, the combination of a main breaker and a branch breaker that is effectively in series with it, is a listed combination that allows the higher KAIC rating of the main breaker to protect the branch breaker as well. Given 20 kA of available fault current and 22KAIC for the main breaker, you could in concept have a 10KAIC branch breaker, if it is series rated with the main.

The reason why series ratings exist, is that the timing of the breaker trips is such that the main breaker with a larger KAIC has been tested to trip before the branch breaker could catastrophically fail. For any fault originating on the branch circuit, for any amps up to the main breaker's KAIC rating. You can also have breakers that are series-rated with certain classes of fuses. This is brand/product-specific on the breakers to be series rated as such. And this is strategic to design this way, as fuses with high KAIC ratings are cheaper than breakers with high KAIC ratings. This allows you to take credit for 200KA, even with a breaker that is 22KA, provided that the combination is series rated, and the fuse is upstream of the breaker.

 

[electrofelon]

Forgive me for perhaps being a little nitpicky, but Its the OCPD's not the panelboard that have a series rating.

 

[jim dungar]

The reason why series ratings exist, is that the timing of the breaker trips is such that the main breaker with a larger KAIC has been tested to trip before the branch breaker could catastrophically fail.

Not quite.
There is nothing in the test procedures that requires the upstream device operate before the downstream device. It is possible that the upstream device may not even operate. The series rating comes from the two devices being connected and tested in series, that is all.

Say that you have a circuit breaker capable of interrupting 19kA@240V, however this is not a standard rating so you label it as 10kA instead. Then you put a 22kA device in front of your breaker, now you can test and list it at 19kA without worrying about the performance of the upstream device at all.

Series ratings may not always be about cost. It may be about preventing future mis-applications.
Very few distributors stock high interrupting branch breakers. This means that someone is likely to purchase a standard low rated breaker breaker rather than special ordering something. If the panel was series rated this over the counter sale might not be a concern.

 

[Jraef]

In the world of 22kA and below it only makes a slight difference in cost, but at high volume, it can add up. The BIG difference is when you get into systems greater than 22kA.

Let's say you have a system with 35kA available fault current. You have a 600A main, and even the smallest cheapest one is still rated 50kAIC, so no problem there. But in this situation, a "fully rated panel" would mean that EVERY feeder breaker inside of it would ALSO need to be rated 35kA or higher, even the 1 pole 20A feeders. That's going to make them the big long breakers that need bus tap connectors, the box gets bigger and the cost goes way up,etc. etc. So to pick on Sq. D, that might end up being an I-Line panel with the associated big 1 pole breakers.



But if I have a Series Rated panel, I use the same Main breaker, but the feeders down stream have been "Series Listed" with that main, so I can use something like an NQO panel where the smaller QO feeders are individually only rated 22kA, as long as I use that SPECIFIC main CB.

 

[Carultch]

Not quite.
There is nothing in the test procedures that requires the upstream device operate before the downstream device. It is possible that the upstream device may not even operate. The series rating comes from the two devices being connected and tested in series, that is all.

In any case, one of the two devices needs to operate before either of them catastrophically fails. By catastrophically fail, I don't mean an ordinary breaker trip, but rather that the breaker will cease to maintain its mechanical integrity and no longer work as a breaker.

Series ratings may not always be about cost. It may be about preventing future mis-applications.

True. Sometimes it is desired for one breaker to selectively trip before another. Selective coordination as it is called. Such that low amounts of fault current cause the branch breaker to trip first, and high amounts of fault current cause the main to trip first. You don't want the whole building going dark just because of a fault on one branch circuit, you want only that branch circuit to turn off.

 

[jim dungar]

True. Sometimes it is desired for one breaker to selectively trip before another.

Yes, selective coordination and series rating are two issues, which need to be considered.

My point about possible mis-application, was in regards to future branch circuit additions to the panel. My personal experience is that many, if not most, <100A branch circuit additions are made without regards to selecting the appropriate AIC. Because main devices are not changed very often, a series rating with 'standard rated' branch breakers is may be advantageous and less expensive in the long run.

 

[shoaib10]

It has to do with the available fault current, and the way the breakers in the panelboard respond to it.

In a fully rated panelboard, all breakers must have a KAIC rating that meets or exceeds the available fault current at the main breaker or main lugs. Given 20 kA of available fault current, all breakers in the panelboard have to have 22KAIC rating (that's what is usually available above 20kA).

In a series rated panelboard, the combination of a main breaker and a branch breaker that is effectively in series with it, is a listed combination that allows the higher KAIC rating of the main breaker to protect the branch breaker as well. Given 20 kA of available fault current and 22KAIC for the main breaker, you could in concept have a 10KAIC branch breaker, if it is series rated with the main.

The reason why series ratings exist, is that the timing of the breaker trips is such that the main breaker with a larger KAIC has been tested to trip before the branch breaker could catastrophically fail. For any fault originating on the branch circuit, for any amps up to the main breaker's KAIC rating. You can also have breakers that are series-rated with certain classes of fuses. This is brand/product-specific on the breakers to be series rated as such. And this is strategic to design this way, as fuses with high KAIC ratings are cheaper than breakers with high KAIC ratings. This allows you to take credit for 200KA, even with a breaker that is 22KA, provided that the combination is series rated, and the fuse is upstream of the breaker.

Thanks for the explanation...But i have one question..Lets say you have fuse/breaker combination as series listed for up to 200kA. And the breaker has an AIC rating of 35kA. Now if the amount of the fault current on the load side of the breaker is >35kA,then will the fuse trip before the breaker?Thats what i understood from your explanation...Am i right?

 

[jim dungar]

Thanks for the explanation...But i have one question..Lets say you have fuse/breaker combination as series listed for up to 200kA. And the breaker has an AIC rating of 35kA. Now if the amount of the fault current on the load side of the breaker is >35kA,then will the fuse trip before the breaker?Thats what i understood from your explanation...Am i right?

I will say it again.

This is no requirement that the upstream device clears the fault before the downstream device operates. Even with fuse-breaker combinations the breaker may operate first.

Overcurrent devices begin to react before current gets to the maximum available amount. A test circuit that allows a possible 200kA of fault current to flow may result in the breaker might operate fast enough so that the current actually never climbs past 30kA. The standards talk about the devices being applied on a circuit capable of delivering an amount of current. The Listing tests do not require the device to actually clear the maximum available amps. It would not be strange to see a 20A 35kA breaker clear the fault before a 1200A 200kAIC fuse even notices the fault exists.

 

[Carultch]

Thanks for the explanation...But i have one question..Lets say you have fuse/breaker combination as series listed for up to 200kA. And the breaker has an AIC rating of 35kA. Now if the amount of the fault current on the load side of the breaker is >35kA,then will the fuse trip before the breaker?Thats what i understood from your explanation...Am i right?

Series rating in general, just means that the larger KAIC device will trip before either catastrophically fails. Or that the larger KAIC device prevents that fault current from getting to the smaller device in the first place. Which device trips first, is a different issue called selective coordination.

In concept, since the 35KAIC breaker is not officially rated for 36kA, you would expect the fuse to trip first for 35 kA to 200KA, and if they selectively coordinate, you'd want the breaker to trip first from its trip rating to 35KA. But there is the possibility that the breaker is capable of safe operation all the way up to 41kAIC, and just isn't marked as such, but rather for the previous standard rating. In such a case, it could still be possible that the breaker trips first at 36kA.

 

[shoaib10]

But there is the possibility that the breaker is capable of safe operation all the way up to 41kAIC, and just isn't marked as such, but rather for the previous standard rating. In such a case, it could still be possible that the breaker trips first at 36kA.

Just curious...How can a breaker rated for safely interrupting up to 35kA is capable of safe operation till 41kA?

 

[iwire]

Series rating in general, just means that the larger KAIC device will trip before either catastrophically fails. Or that the larger KAIC device prevents that fault current from getting to the smaller device in the first place. Which device trips first, is a different issue called selective coordination.

Is that true?

I am not sure it has to be the larger KAIC device that opens.

 

[jim dungar]

Just curious...How can a breaker rated for safely interrupting up to 35kA is capable of safe operation till 41kA?

There are standard AIC values, breakpoints, used for fully rated devices regardless of what they can really handle. Common values are 10kA and 22kA @240Vmax, 14kA and 18kA @480V max, and 35kA regardless of the voltage.

Listed series-ratings simply say the devices have actually been tested and the fault was cleared per the standard. Which device cleared the fault and what current level was cleared is immaterial to the series-rating.