Technical information

1.6.1 Power supplies

The control circuits Class 2 are fed by sources intrinsically limited. In particular

UL508A imposes

1. transformers: CCN XOKV,XOKV2 (UL 1585 ”Class 2 transformer”);

2. transformers:CCN NWGQ, QQGQ2 (UL 1950 “Information Technology

Equipment”) only if use in Class 2 circuits is expressly indicated in the

marking.

All the derived circuits down line of a Class 2 supply are to be considered Class 2

circuits if properly wired.

1.6.2 Overcurrent Protection

Protections are not needed down line from the power source because the circuit

is self/protected (there might be some few rare exceptions in the case of the use

of conductors or components with particular characteristic).

Up line from the supply, the protection should be suitable for the point of

installation (only BCPs are derived directly from the general feeder,overcurrent

protection if we derive from a pre-existing BCP,down lines) and it should respect

all restrictions imposed on the marking or instructions.

1.6.3 External Wiring and Terminal

The conductors on the machine of Class 2 circuits should be appr

o v ed; in

addition they should be separated (with the use of special accessories) or isolated

(minimum distance 50.8 mm) from the conductors of all the other non Class 2

circuits.

The panel-on machine interface should follow the same provisions valid for the

terminal blocks of a general control circuit (for example the limits on the cross-

section that can be connected): in opposite cases the terminal blocks should be

separated from of all the other circuits (not Class 2).

The Class 2 circuit terminal block should be clearly indicated with a marking.

If this instruction is not respected the circuit goes automatically to Class 1, losing

all the relative advantages.

1.6.4 Internal Wiring

The Class 2 approved conductors should be separated or isolated from the

conductors of the other circuits (not Class 2) unless they are insulated f or the

maximum v oltag e present.

CONTROL CIRCUITS