Interupter rating

[wi-elec]

I'm bidding a new building up here and passed my service design specs to my pricing guy at my supply house. On my design guide from the architect he lists the main breakers in a MDP Panel all rated at 50kA/C, and all the electrical breakers in the subs at 18kA/C. My question is why would he have speced these? I've installed standard 10's in buildings like this, and the 18's drasticly increase my costs. This is a car repair shop with mainly all lighting loads and 4 -60A 3 phase circuits for machines.

Thanks for any insight on this

 

[wireguru]

what brand are they? does the series rating with the 50k require the 18k branch breakers?

 

[zog]

I'm bidding a new building up here and passed my service design specs to my pricing guy at my supply house. On my design guide from the architect he lists the main breakers in a MDP Panel all rated at 50kA/C, and all the electrical breakers in the subs at 18kA/C. My question is why would he have speced these? I've installed standard 10's in buildings like this, and the 18's drasticly increase my costs. This is a car repair shop with mainly all lighting loads and 4 -60A 3 phase circuits for machines.

Thanks for any insight on this

What is the available fault current? Simple as that.

 

[jim dungar]

This is a car repair shop with mainly all lighting loads and 4 -60A 3 phase circuits for machines.

The type of facility and the size of the loads does not impact the selection of a device's AIC rating.

As Zog said, what is the available fault current from the utility?

 

[wireguru]

What is the available fault current? Simple as that.

thats probably what called for the 50ka main, then the series rating of that main with that mfgr's branch breakers called for the 18k breakers no?

as seen on page 2 of this http://static.schneider-electric.us/assets/DIGEST/panelboards.pdf square D has series ratings of 65ka for NQ panelboards with regular QO breakers when using the proper main.
(i am not an engineer, this is not advice, just a personal observation)

 

[hurk27]

I was tagged on this long time ago by an inspector, the utility transformer was right out side the electric room with less then a 10 foot run between a 150kva 120/208 transformer and MDP, AFC was over 45ka had 25kaic breakers, costly mistake.