Technical information

CONTROL CIRCUITS

The Class 1 circuit terminal block should be clearly indicated with a marking.

EXAMPLE

A control circuit made of AWG 18 cross section conductors is assumed.

If the interface terminal block accepts a AWG 18 – AWG 14 cross-section interval,

one can go ahead regularly; if on the other hand the terminal block only accepts

sections AWG 18 – AWG 16 then the maximum cross-section to be used should be

indicated, for example on the schematics.

1.3.4 Internal Wire

The conductors inside the panel follow the same rules given for power

conductors, except for the calculation of the section.

For the control circuits it is enough for the cable capacity not to be smaller than

the rating of the protection upline or in its absence to the nominal current to the

secondary of the control transformer.

or the capacities of the e xter

nal conductors it is advisab le to take tab le 28.1 of

UL508A as a r eference.

The operating temperature of the conductors is 90°C for wire size above AWG 16

and 60°C for conductors with cross sections the same as or lower than AWG 16

(it should be remembered however that a AWG 16 to 60°C conductor cannot be

used for power circuits).

The minim

um cross-section to be used for the internal control circuits is in both

xts A WG 18, but only wire size lower than AWG 30 are allowed for wiring for

PLC or static components (semi conductors and/or electronic). In UL508A table

38.1 shows the capacities allowed for conductors lower than AWG 18.

All the control circuit conductors inside the same raceway should be insulated for

the maximum voltage present if one of the conductors is not insulated for a lower

voltage,it is necessary to distance or isolate it.