Sizing a distribution panel

[CuriousElectron]

Hi folks,

Should a low voltage distribution panel be sized based on total connected load plus a safety margin or based on evaluation of coincident loads ?I would think if the panel is filled out with the loads and the ratings are available, the panel bus should be sized based on 125% of maximum coincident continuous loads. Would this evaluation be considered engineering evaluation and not necessarily based on code? I know NEC has a sample guide based on residential loads, which I don't think is applicable to industrial panel sizing calculations.

Regards,
EE

 

[7anoter4]

I don't think such a standard exists. You may consult IEEE 141 chapter 10.3.4 Ratings.
In my opinion, this part could be interesting:
The continuous-current rating of the switchgear main bus must be no less than that of the
highest rated overcurrent device or through current to which it must be subjected. The rated
continuous current of a switchgear assembly is the maximum current in rms amperes, at rated
frequency, that can be carried continuously by the primary circuit components without causing
temperatures in excess of the limits specified in IEEE Std 37.20.1-1987 [B26]. The standard
ratings of the main bus in ac low-voltage switchgear are 600 A, 800 A, 1200 A, 1600 A,
2000 A, 3000 A, 3200 A, or 4000 A, and in dc low-voltage switchgear are 1600 A, 2000 A,
2500 A, 4000 A, 5000 A, 6000 A, 8000 A, 10 000 A, and 12 000 A (IEEE Std C37.20.1-1987).

 

[waross]

The maximum motor load which may be connected at one time plus 25% of the largest motor.
or
The maximum load which may be connected when the largest motor starts plus 25% of the largest motor.
Two motors starting simultaneously shall be added together and considered a single motor for the +25% rule.
The NEC assumes that all motors are 100% loaded.

Bill
--------------------
"Why not the best?"
Jimmy Carter