Technical information

CONTROL CIRCUITS

The UL508A links up with both NEC and CEC codes, but it gives additional

instructions on how to ease the application.

• Control circuit: this is not clearly identified but it can be traced back to a

Class 1 non

limited circuit: there are no power or voltage limits (within the 600

V that specify the low voltage).

• Class 2: control circuit powered by limited power sources (generally 100 VA )

with special UL approval (see for example the XLP 1606 Class 2)

1606

• Low-Voltage Limited Energy Circuit: is a type of control circuit limited in

voltage and energy and is envisag ed only b y UL that reunites regulations of

both Class 1 limited power and Class 2 circuits.

In the last edition of the NFPA 79 (2002) standard for Industrial Machinery ,

further restrictions were introduced for the circuits of control and command, in

particular:

• 120 V as a maximum voltage limit in alternating current and 250 V in direct

current;

• transformer with separate windings for the 120V control circuit power

derived from greater voltage power circuits.

1.2 Control circuits

The control circuits (remote control) are considered to be the circuits that power

and control loads like:

1. A pilot light shall comply with the Standard for Industrial Control Equipment,

UL 508, and a miscellaneous lamp holder shall comply with the Standard for

Edison-Base Lampholders, UL 496;

2. An electrically-operated valve shall comply with the Standard for Electrically

Operated Valves, UL 429;

3. A solenoid shall be evaluated for the intended use;

4. A time-indicating or time-recording device, including an hourmeter,or a

synchronous motor shall comply with the Standard for Time-Indicating and -

Recording Appliances, UL 863;