Technical information

FEEDER AND BRANCH CIRCUITS

2. Disconnecting means

194R 1494V

The main disconnecting means is a necessary part of all electrical equipment but

can be provided by the final user (unlike the provisions of European standards).

In this case it is necessary to clearly specify the characteristics of the device in the

attached documentation.

In this section,

the devices suitab le f or s witching and their sizing independently of

their nature will be analyzed (switch or circuit breaker ).

It is possible to use the devices suitable for disconnecting to the function of

overload protection of electrical equipment.

2.1 Sizing the switch in accordance to UL 508

First of all it is necessary to distinguish between switch and circuit breaker.

Inverse-time or instantaneous-trip circuit breaker UL489 “Molded-Case Circuit

Breakers, Molded-Case Switches and Circuit Breaker Enclosures)

The total current (obtained by adding the FLA and the rated currents of all the

branch circuits) should not be more than 80% the size of the switch. It may be

more useful to express the same rule backwards: the size of the switch should not

be less than 125% of the total current.

EXAMPLE

Motor 7.5HP,230V,3ph

Table 50.1 > FLA = 22A

The circuit breaker shall have a size of

at least 1.25 x (22 + 8+ 4) > = 42.5A

For example a 140U-H2C3-C50 can be used