65k aic rating main gear

[27hillcrest]

I have a 480v 4000amp 65k AIC rated gear. I need to install 2 400amp panel boards. Does the Aic rating of the new panel boards need to be 65k or can I use 22k?

 

[bob]

You need a panel that is rated for the AIC at the location. If the new panels are some long distance
away then the fault current will be less. If the panels are close the the present panel then the fault
current will likely be the same. You need to check the actual fault current available. It might not be 65K.

 

[maghazadeh]

I have a 480v 4000amp 65k AIC rated gear. I need to install 2 400amp panel boards. Does the Aic rating of the new panel boards need to be 65k or can I use 22k?

It depends on the distance from new panel location to the gear, The longer the distance is the higher resistance will be, higher resistance results in lesser AIC required.

post more informations and someone here will help you to figure it out.
Gear is 65K AIC, but that does not mean the available short circuit rating is the same. It is much less than that.
If you know the value for available short circuit rating, then if you tell us the size of feeder wire (cu or Alum.) for each panel and the distance or lenght of feeder wire, that's all needed to know what AIC rating should be.
AIC ratings are marked on CBs.

 

[augie47]

In addition to distance helping your situation check to see if the main panel and your added panels are the same manufacturer then check to see if your panels can be "series rated" with the 4000 amp panel.
It is not uncommon for 22k panels to series rate with a 65k upstream panel. A distributor should be able to assist in making that determination.

 

[maghazadeh]

You need a panel that is rated for the AIC at the location. If the new panels are some long distance
away then the fault current will be less. If the panels are close the the present panel then the fault
current will likely be the same. You need to check the actual fault current available. It might not be 65K.

Bob you just beat me to this!!:lol:

 

[GearMan]

That depends on the available fault current at the 400A panels or the UL listed series ratings between the 400A breaker/fusible device and the branch breakers in the the 400A panels.

 

[GearMan]

Bob you just beat me to this!!:lol:

You all beat me....I quit.

 

[kingpb]

The longer the distance is the higher resistance will be, higher resistance results in lesser AIC required.

Close, but that would be reactance that limits fault current not resistance :slaphead:

I'm sure that was just a typo, right?

 

[templdl]

Often times a qualified person such as a PE would do a short circuit study to determining the available fault current available at each point in the distribution system.
Keep in mind that the fault current available at the 65kaic rated main DP main not even be 65kaic to begin with. As such the study would begin there and proceed down stream taking into consideration the cable sizes and length etc.
Otherswise the devices must be as the other guys of stated.

 

[bob]

Close, but that would be reactance that limits fault current not resistance :slaphead:

I'm sure that was just a typo, right?

Actually that would be incorrect. So no typo. If we depended on only reactance to reduce fault
current, that 65 ka panel would be blown off the wall in a bolted fault. Reactance does not really come into effect until the conductor
size reaches to about 1/0. After that reactance begins to be a part of the cable impedance and increases with
the size and length of the conductor. Even then is it a small part. Reactance increases when it is installed in metal conduit. The impedance is a combination of resistance and reactance.

http://aetech.com/images/pdf/05clv4sample.pdf

 

[kingpb]

I haven't seen too many air core resistors installed in substation and circuits to reduce fault current levels. Seems we always use air core reactors. Guess we must have been wrong all these years:?

I would agree though that the proper term would be impedance. But, because the resistance in generators is so low, the values used in determining fault current is X'd, X"d, Xd, Xo, and X2. Resistance is ignored. Typical for motor contribution, transformer let through, etc.

When I change the impedance from 3% to 5% on a transformer, the change is almost all reactance. This will allow less fault current (higher impedance) but the component doing the work is almost all reactance.

 

[bob]

That is true in every case you state. Air core reactors are wound so that they have a high reactance. Much higher that 600 volt cable. Thats not true with cable.
I was speaking of the reactance of the cable mentioned in the post.

 

[templdl]

I've provided air core reactors for both low and medium voltage to reduce fault currents. The low voltage (480V) commonly were used in Eaton Electrical MCCs and the medium voltage were anywhere from 4160 to 13,800. The medium voltage reactors can be huge and commonly cost 10s of thousands of dollars.

 

[kingpb]

That is true in every case you state. Air core reactors are wound so that they have a high reactance. Much higher that 600 volt cable. Thats not true with cable.
I was speaking of the reactance of the cable mentioned in the post.

Yes, I would have to agree, for cable, it should be the impedance "Z" not just R or X.:thumbsup: