Technical information

CONTROL CIRCUITS

It should be noted that if internal non approved conductors are used (for example

N07V-K or H05V-K), what has been said above is no longer applicable and it is

necessary to separate or segregate these conductors.

1.7 Low-Voltage Limited Energy Circuit

The Low-Voltage Limited Energy circuit has similar characteristics to those of a

Class 2 circuit and has been introduced into the UL508A by the Underwriters

Laboratories unifying instructions for the circuits in Class 1 and limited in energy

to 100VA as in Class 2.

As also for the Class 2, in these circuits it is possible to use non-approved

components, loads and wiring down line from the limiting protection devices i.

The Low-Voltage Limited Energy circuit is easier to implement inside equipment

than a Class 2, and is therefore the most "con

v enient" method f or using

customised or self made non appro v ed components like electronic cards, pro v es.

The maximum voltages allowed are 30 V effective in alternate current and

42,4 V in direct current.

1606XL 1492-SP

1.7.1 Supply

The Low-Voltage Limited Energy circuits do not require specially approved

power sources, but only that the galvanic separation of the power circuits is

assured. In particular UL508A imposes:

1. Separate windings and transformers: CCN XPTQ, XPTQ2, XQNX and XQNX2

(UL506 ”Specialty Transformers” e UL1561 “Dry-Type General Purpose and

Power Transformers”);

2. transformers: CCN QQAQ2: a CCN collection including in particular QQGQ2

(UL60950 “Safety of Information Technology Equipment”);

3. Other sources with separate secondary: several types but in particular CCN

NMMS and NMMS2 (UL508C “Power Conversion Equipment”);