Kaic rating

[Dmanning25]

Hello. I am sizing a panel a 800 amp 277/480 service. My question is how do I rate the panel for kaic. My largest breaker the main is rated for 65kaic or aic for SD breakers. Do I rate it the same as the breaker kaic rating.

 

[tom baker]

How did you determine 65 kaic.? The following is how its generally done..
You first contact the POCO, get the transformer available fault current. Then calculate the fault current at your service, based on wire type, size, length, and conduit type. Then select a service disconnect breaker for that value Next determine the let thru current for downstream breakers.
You may end up with series rated gear, there are labeling requirements in the. NEC for that.
Bussman has software for fault current calcs.

 

[tom baker]

Here are some code sections to review
110.9 interrupting rating
110.16 Arc Flash B service equipment, you will need to label with AFC
110.22 B Series combo systems
110.22 C Tested series systems
110.24 AFC A Field marking

Note when you get your inspection, the AHJ will see the AFC (from the required field labeling) and can determine if yours could be considered a series rated system. It all depends on the AFC at your service.
I have done many 277/480 services but all with fused service disconnects with 100,000 AIC fuse, others here will have much more appropriate experience.

 

[electrofelon]

Hello. I am sizing a panel a 800 amp 277/480 service. My question is how do I rate the panel for kaic. My largest breaker the main is rated for 65kaic or aic for SD breakers. Do I rate it the same as the breaker kaic rating.

A panel board does not have an AIC, it has. SCCR (short circuit current rating). The SCCR of the panel will be at least that of the breakers so you don't have to worry about it.

Is the breaker AIC calculated correctly or is that just a guess?

 

[don_resqcapt19]

A panel board does not have an AIC, it has. SCCR (short circuit current rating). The SCCR of the panel will be at least that of the breakers so you don't have to worry about it.

Is the breaker AIC calculated correctly or is that just a guess?

That is not always true. The SCCR is a mechanical bus bracing issue and the bus supports must be designed to resist those mechanical forces. Putting a 65 kAIC breaker in a panel with a bus rated at 42kA does not give you a panel with a SCCR of 65kA.

 

[electrofelon]

That is not always true. The SCCR is a mechanical bus bracing issue and the bus supports must be designed to resist those mechanical forces. Putting a 65 kAIC breaker in a panel with a bus rated at 42kA does not give you a panel with a SCCR of 65kA.

Yes I am aware that may not be 100% true, I was trying to keep it simple. You may be able to piece together a panelboard from components and have this not hold. 99% of the time these will be factory ordered and parts will be coordinated. Also I have a hard time believing any modern panelboard wont always be rated at least 65k SCCR. Im looking at a siemens P1, their smallest, right now and it rated 200,000 SCCR

 

[Carultch]

Hello. I am sizing a panel a 800 amp 277/480 service. My question is how do I rate the panel for kaic. My largest breaker the main is rated for 65kaic or aic for SD breakers. Do I rate it the same as the breaker kaic rating.

The short answer is that the transformer's KVA, impedance, and secondary voltage are the main factors determine the available fault current (AFC), which the KAIC needs to meet or exceed. The upper limit for AFC from a transformer is (amps associated with KVA) divided by the impedance as a decimal.

The long answer is that available fault current on the primary side of the transformer can influence this value as well, and mean that the AFC on the secondary is less than that. Also, the impedance of conductor routes can also reduce this. Also, motor loads can contribute their own fault current to the total. It is recommended to get the available fault current at the service point, and then add in any motor contribution fault current, to get what the total AFC is at any given point in the system. There are fault current calculators (aka short circuit current calculators) that allow you to model all the factors that come in to play.

Terminology:
AFC = Available fault current is the maximum current that could realistically occur at a given position in your service.
KAIC is kilo amps interrupting capacity, which is the maximum amps that a breaker can withstand and trip safely without catastrophically failing.
KAIR is the equivalent term for fuses.
SCCR is short circuit current rating, which is the maximum amps that any other device in the system could withstand, and usually applies to equipment that isn't an OCPD, such as panelboards, disconnects, and meter sockets.

Ultimately, the values of KAIC, KAIR, and SCCR must meet or exceed the available fault current, unless combinations of devices with listed series ratings allow you to take credit for upstream devices protecting downstream devices.