Technical information

The North American standards require the protection of all the conductors that

are not connected to the equipotent circuit.

EXAMPLE

A general control circuit is

assumed to be derived of a

special branch circuit Q2

protection down line, for example

a circuit breaker (UL489) 140U-

H2C3-C15 of 15 A or 1489-A2C-

150,that protects a solenoid valve

assembly (Y1,Y2,Y3) and an

electronic component (U1).

From table 29.1 the protected

BCP cross-section, or AWG 14 (20

A) is obtained.

If the wiring is all made with

AWG 14 and no component

imposes particular restrictions,

the circuit represented is correct

and does not require anything

else.

It is now assumed that the U1 component imposes the use of a 4A protection, in

the marking, or in the instructions.

There are two solutions:

•to limit the entire circuit by

replacing the BCP Q2 15 A with

another of 4 A

•to insert a further Q3 4 A

supplementary protection that

protects just the conductor

supplying U1. For example a

1492-SP1C040, supplementary

protection (UL1077 approved)

can be used. Furthermore, down

line from the Q3 protection it is

possible to wire with a AWG 18

and 7A capacity conductor.

The first solution makes it possible to save a component, but limits the

possibilities of the control circuit.The second solution cuts in locally respecting

the requirements of component U1.

CONTROL CIRCUITS