Technical information

EXAMPLE

A derivation of a control circuit down line from a BCP is assumed for a

woodworking machine, Industrial Machinery .The circuit is confined within the

panel and the BCP has a size of 25 A.

The circuit is made with a AWG 16 cable that, in accordance with tab. 28.1 of

UL508A, carries 10 A.

The control circuit protection should not be greater than 10 A, but in the

hypotheses advance it is possible for it not to be more than 20 A (and not 10 A).

If in the same conditions the control circuit were extended beyond the control

panel the conditions in table 66.4 would no longer be respected.Two solutions

are given:

•using a BCP of 20 A and refer to the conditions in which the table is being

applied;

•using a 10 A protection and respecting the general rule (without applying table.

66.4).

1.5 Power Supply

The power supply of a control circuit can be a transformer for the circuits in

alternating current or a rectifier for direct current circuits.

The components should be appr

o v ed b y an NRTL f or the envisag e use.

a) Switching Mode power supply

units: should be approved for use in

the industrial field.

UL508A also allows the use of power

units for Information Technology that

have passed a special over-

temperature test.There will be a

double marking: UR as Information

Technology Equipment (I.T.E.) and

UL as Industrial Control Equipment

(Ind. Cont. Eq.).

CONTROL CIRCUITS