480V 3ph power Panelboards - bracing

[Isaiah]

We have several 3 Phase 480V Panelboards, MLO with 800A bus and 3 phase branch circuits to various loads such as welding receptacles lighting transformers etc being fed from an feeder 800AT CB in the adjacent switchgear.
The switchgear bus is 480V 4000A, 3P, 3W 85kAIC RMS SYM, 60 Hz.
The client wants “fully rated” Panelboards. Does this mean the Panelboard must also be rated 85kAIC to match the bus in the switchgear? What about the branch circuit breakers?
Would a “series rated” panelboard be more practical here?


Sent from my iPhone using Tapatalk

 

[jim dungar]

We have several 3 Phase 480V Panelboards, MLO with 800A bus and 3 phase branch circuits to various loads such as welding receptacles lighting transformers etc being fed from an feeder 800AT CB in the adjacent switchgear.
The switchgear bus is 480V 4000A, 3P, 3W 85kAIC RMS SYM, 60 Hz.
The client wants “fully rated” Panelboards. Does this mean the Panelboard must also be rated 85kAIC to match the bus in the switchgear? What about the branch circuit breakers?
Would a “series rated” panelboard be more practical here?


Sent from my iPhone using Tapatalk

The AIC rating of existing equipment may have absolutely nothing do do with what is required on down stream equipment.

You need to know the available fault current at you new panel locations. Then for a fully rated system you select equipment, panels and breakers, with an AIC that is higher.

The practicality of series ratings is often open to debate. Personally I like them for branch circuits in panel boards up to 250A, because these are locations most likely to have breakers added in the future on a onsie-twosie basis.

 

[electrofelon]

Some additional thoughts:.


Higher AIC breakers are not that much more expensive on factory ordered gear. For example I got a quote on a Siemens panelboard with both standard 10k branches and higher 22k branches. The 22k worked out to about $3 more per pole. Buying/ Ordering them from the supply house Is often pricey. You are better off getting them from one of the online breaker suppliers such as superbreakers or pacific coast breaker to name a few . So in short, grabbing a other than 10k branch is going to take time and/or be expensive.

And just to be clear, the panel board will have an SCCR rating and the breakers will have an AIC rating. In practice however, I believe most/all panelboards (at least with Siemens) have an SCCR of 200k so you don't have to worry about that.

One other consideration: you should check the series rating charts and see what sort of advantage you will get. With an 800A feeder OCPD, you will likely be looking at 22k branches even with series ratings.

 

[Isaiah]

Some additional thoughts:.


Higher AIC breakers are not that much more expensive on factory ordered gear. For example I got a quote on a Siemens panelboard with both standard 10k branches and higher 22k branches. The 22k worked out to about $3 more per pole. Buying/ Ordering them from the supply house Is often pricey. You are better off getting them from one of the online breaker suppliers such as superbreakers or pacific coast breaker to name a few . So in short, grabbing a other than 10k branch is going to take time and/or be expensive.

And just to be clear, the panel board will have an SCCR rating and the breakers will have an AIC rating. In practice however, I believe most/all panelboards (at least with Siemens) have an SCCR of 200k so you don't have to worry about that.

One other consideration: you should check the series rating charts and see what sort of advantage you will get. With an 800A feeder OCPD, you will likely be looking at 22k branches even with series ratings.

Thanks to both of you gentlemen for your excellent feedback


Sent from my iPhone using Tapatalk

 

[kwired]

Some additional thoughts:.


Higher AIC breakers are not that much more expensive on factory ordered gear. For example I got a quote on a Siemens panelboard with both standard 10k branches and higher 22k branches. The 22k worked out to about $3 more per pole. Buying/ Ordering them from the supply house Is often pricey. You are better off getting them from one of the online breaker suppliers such as superbreakers or pacific coast breaker to name a few . So in short, grabbing a other than 10k branch is going to take time and/or be expensive.

And just to be clear, the panel board will have an SCCR rating and the breakers will have an AIC rating. In practice however, I believe most/all panelboards (at least with Siemens) have an SCCR of 200k so you don't have to worry about that.

One other consideration: you should check the series rating charts and see what sort of advantage you will get. With an 800A feeder OCPD, you will likely be looking at 22k branches even with series ratings.

That really depends on the source and it's impedance, the size and length of service conductors, size and length of feeder conductors, or even multiple feeders if that applies.

Only rule of thumb is that the higher the capacity involved the more likely it will be something you need to pay more attention to, but there also is plenty of gear out there that don't have the available current it is rated for and further downstream you go the less available current there is.

 

[electrofelon]

That really depends on the source and it's impedance, the size and length of service conductors, size and length of feeder conductors, or even multiple feeders if that applies.

Only rule of thumb is that the higher the capacity involved the more likely it will be something you need to pay more attention to, but there also is plenty of gear out there that don't have the available current it is rated for and further downstream you go the less available current there is.

I think you misunderstood what I was saying - or maybe I didn't state it clearly.

My point was that at 240V, a series rating down to 10 k branches is very dependent on the upstream breaker size. For example for Siemens you can go up to 100k upstream and still series rate down to standard 19k branches IF the upstream breaker is 250A or less. I don't believe Siemens has any series ratings at 65k down to standard 10k branches for breaker frames over 250A. But move up to 22k rated branches, and you can get series ratings with up to a 2000A main with 65k available. So my point was just that if you are trying to go with standard 10k branches, you will likely be out of luck if you upstream is larger than 250A. (Note this is for Siemens, and I know the OP said 480 not 240, but it's similar for 480 breakers - the typical 480 Siemens breaker is a BQD and doesn't have any series rating with larger frame upstream breakers).

 

[kwired]

I think you misunderstood what I was saying - or maybe I didn't state it clearly.

My point was that at 240V, a series rating down to 10 k branches is very dependent on the upstream breaker size. For example for Siemens you can go up to 100k upstream and still series rate down to standard 19k branches IF the upstream breaker is 250A or less. I don't believe Siemens has any series ratings at 65k down to standard 10k branches for breaker frames over 250A. But move up to 22k rated branches, and you can get series ratings with up to a 2000A main with 65k available. So my point was just that if you are trying to go with standard 10k branches, you will likely be out of luck if you upstream is larger than 250A. (Note this is for Siemens, and I know the OP said 480 not 240, but it's similar for 480 breakers - the typical 480 Siemens breaker is a BQD and doesn't have any series rating with larger frame upstream breakers).

What I was saying is unless your source, MDP, and branch panel are all in close proximity to one another you often have 10kA or less available at the branch breaker locations anyway. Larger feeders does give you higher available current, but it doesn't take all that much distance and available fault current drops pretty significantly.

Seen many times where having just 25-50 feet of conductor made a huge difference in whether 10 kA rated equipment would be acceptable or not regardless of what series ratings might be able to be applied, vs having only 10 feet or less of same size/type supply conductor.

Have a 2000 amp set of supply conductors? having 50 feet conductor to the MDP might need less withstand rating on the gear than if it were literally as close as practical, and of course actual numbers still depend on size and impedance of the source. Many times 2000 amp gear is installed but POCO doesn't have a transformer that is rated for 2000 amps either. Though might be good idea to design that so that if larger transformer ever becomes necessary you still have proper rating of your gear.

 

[electrofelon]

What I was saying is unless your source, MDP, and branch panel are all in close proximity to one another you often have 10kA or less available at the branch breaker locations anyway. Larger feeders does give you higher available current, but it doesn't take all that much distance and available fault current drops pretty significantly.

Seen many times where having just 25-50 feet of conductor made a huge difference in whether 10 kA rated equipment would be acceptable or not regardless of what series ratings might be able to be applied, vs having only 10 feet or less of same size/type supply conductor.

Have a 2000 amp set of supply conductors? having 50 feet conductor to the MDP might need less withstand rating on the gear than if it were literally as close as practical, and of course actual numbers still depend on size and impedance of the source. Many times 2000 amp gear is installed but POCO doesn't have a transformer that is rated for 2000 amps either. Though might be good idea to design that so that if larger transformer ever becomes necessary you still have proper rating of your gear.

Sure, I was discussing series ratings. If there is enough conductor to drop the AFC to the point that you dont need series ratings or anything over 10k devices then great.