MCCB Selection

Check EC&M and Mike Holt websites.

Trial and error testing may not be the way to go.

I'd consult NFPA-70 or NEC and not guess.

Of course, a class in electricity would be helpful, too.

Hi Nald:

Hope below basic data will assist in some way.

Example: This example is only to illustrate the basic requirements to install the motor. Assuming it is a 45kW or 60.32HP motor at 415V, 80A.

Motor Details:

Kw = 45kW = 60.32HP

FLC = 80A

LRC=263.73

Voltage = 415V

P.F = 0.80

Cable:

Say cable route = 20m

Method of installation = spaced on cable ladder.

Cable Size for short run = 50sqrmm, 3C + E. Cable amps rated at 146A, Ics 7.77kA/s.

35sqmm 3C + E will also be good for the installation, just got protections right.

Motor Starter:

DOL-Direct On Line Starter

Look up NHP Motor Starters and MCCB Catalogues or others for DOLs and MCCBs that will suit your motor.

Voltage Drop:

At 100m, 50sqrmm, 3C + E. Cable amps rated at 120A

Voltage drop is 2.1%, with an allowable voltage drop of 8.7V.

MCCB:

Terasaki MCCB TemBreak 2. Type is S125GJ. (Standard-125A-Meduim-Voltage-Adjustable Settings)

The breaker has adjustable settings which allow you to adjust the MCCB rated amps as required to suit the cable, motor FLC rating, and magnetic trip current settings to be below the cable short circuit rating-so as to protect the cable as well.

For basic motor formulas & calculations, refer to;

http://www.reliance.com/mtr/flaclcmn.htm

http://electriccalcs.com/calculators/view/166/

Refer to previous CR4 links below for more information:

http://www.engineeringtoolbox.com/electrical-motor-calculator-d_832.html

http://cr4.globalspec.com/thread/19925/Motor-Inrush-Current

http://cr4.globalspec.com/thread/34313/How-to-Calculate-Motor-Full-Load-Current

http://cr4.globalspec.com/thread/58774/starting-current-calculation

Try this

1. cable size calculator
2. Feeder Sizing

For over-current protection of a conductor, the Design Current (Ib), should be equal to or less than the MCCB nominal or rated current (In) and In should be equal to or less than the current carrying capacity of the cable (Iz) i.e

Ib </= In

In </=Iz

For short circuit protection, the MCCB breaking capacity should be more than the Prospective Short Circuit Current (PSCC).

However, for motor protection as in your case, the MCCB may be rated at 1.5 to 2.0 times the FL current since the conductor protection is provided by the Over Load protection of the motor. In such a case the MCCB must provide short circuit protection.

British Standard 7671.