P06 datasheet(7/64 Pages) SCHNEIDER

7 / 64 page

Manual Motor Starters, Controllers, and Protectors

General Information

10/02

FUSE AND CIRCUIT BREAKER SELECTION

Selecting the proper upstream short circuit protection for Group Motor installations can sometimes be

a confusing process. Specific National Electric Code rules must be applied for Group Motor installations.

The examples below illustrate the most common applications of GV manual starters with upstream short

circuit protection in a Group Motor installation. Refer to NEC Section 430-53 C and D for proper

conductor ampacity selection.

NOTE: Examples below show full load currents that may not be typical. Use actual motor nameplate

date for determining actual values.

Example 1:

Eight motors with the sizes shown below are installed on a conveying system. Choose the correct GV

manual starter and the proper size short circuit protection for this application. The user prefers time-

delay fuses.

One GV2M14, two GV2M10, and five GV2M08 manual starters would be selected for this group motor

installation.

Per N.E.C. section 430-52 & -53 and N.E.C. table 430-152, the time-delay fuse must be sized as follows:

175% FLA for largest motor + sum of FLAs for all other motors

==> (1.75 x 7.6) + (2 x 4.8) + (5 x 3.4) = 39.9 A

N.E.C. 430-52 allows use of the next largest standard size fuse — which in this case is 40 A. If nuisance

tripping is a problem with this fuse selection, N.E.C. does allow 225% of largest motor FLA to be used

in lieu of 175% when calculating the size. In this case, the calculation would be as follows:

(2.25 x 7.6) + (2 x 4.8) + (5 x 3.4) = 43.7 A

The next largest standard size in this case is a 45 A fuse.

Example 2:

Ten motors with the sizes shown below are installed on a packaging machine. Choose the proper size

circuit breaker for this application.

Per N.E.C. section 430-52 & -53 and N.E.C. table 430-152, the circuit breaker must be sized as follows:

250% FLA for largest motor + sum of FLAs for all other motors

==> (2.5 x 14) + 14 +7.6 + (2 x 4.8) + (5 x 3.4) = 83.2 A

The next largest standard size circuit breaker is 90 A.

If nuisance tripping is a problem, N.E.C. allows for circuit breaker sizes that “shall in no case exceed

400% for full load currents of 100 amps or less, or 300% for full load current greater than 100 amps”.

In this case:

(4.0 x 14) + 14 +7.6 + (2 x 4.8) + (5 x 3.4) = 104.2 A

The next largest standard size in this case is a 110 A circuit breaker.

Motor Qty

Voltage

FLA

460

7.6

460

4.8

460

3.4

Motor Qty

Voltage

FLA

460

7.6

460

4.8

460

3.4

Disconnect

Fuse or

Circuit Breaker

GV2 Manual Motor Starter

D-Line or K-Line Contactor

Motor

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