Technical information

For the drawing and the dimension of the motor start, we will proceed from the

motor up to the branch protection by sizing the field insulator,the thermal

protection, the meter for the protection against short-circuits (fuses, automatic

switch or motor protector).

1.3.1.1 Motor

First of all it is necessary to clearly identify the rated current of the motor that

must be used for the scaling. In North America two values must be distinguished:

a) nameplate current: the current rating plate

b) Full Load Ampacity (FLA): the full load current indicated in special tables

–DC motor

(direct current): tab. 430.147 of the NEC (0.25<hp<200), tab. D2

of the CEC (0.25<hp<200), tab. 50.2 of the UL508A (0.1<hp<200);the

UL508A table is the same as that of the NEC, while the CEC tables brings

values that are generally inferior.

–single-phase (alternate current): tab. 430.148 of the NEC (0.167<hp<10),

tab. 45 of the CEC (0.167<hp<10), tab. 50.1 of the UL508A (0.1<hp<50);

the tables present the same values.

–tw o-phase (alternate current): tab. 430.149 of the NEC (0.167<hp<10), tab.

50.1 of UL508A (0.1<hp<200), no table in the CEC; the tables present the

same values, but UL508A table is more complete.

–three-phase (alternate current): tab. 430.150 of the NEC (0.5<hp<500), tab.

44 of the CEC (0.5<hp<500), tab. 50.1 of the UL508A (0.1<hp<500); above

3 hp all the tables have the same values, under 3 hp the CEC table has

slightly higher values.

The FLA value in the table is obtained from tests done on reference motors (in

accordance with the NEMA standard) under normal conditions of use: it is known

that the reference motors have low level electrical characteristics so the FLA is

alw a ys higher than the curr ent on the r ating plate of a normal motor of open

power.

The current nameplate must always be used for the sizing of the overload

protection.

For all the other NEC and UL dimensions the use of the highest value between

the FLA table and the current on the rating plate (generally the FLA) is required;

the CEC always recommends the use of the rating plate value, while admitting the

FLA if it is unknown.

EXAMPLE

In the example being examined it is supposed that the rating value is unknown: in

this case reference is made to the FLA table.With reference to UL508A, table 50.1

shows

BRANCH CIRCUIT