Technical information

1.3.2 External Wire

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

conductors, except that for the calculation of the section.

For the control circuits it is sufficient for the cable capacity not to be less than the

rating of the Overcurrent Protection either up line or in the case of control

transformers with protection on just the primary, less than the rated current of

the transformer's secondary.

or the capacities of the e xternal conductors it is advisab le to take tab le 28.1 of

UL508A as a r eference. For the control conductors the use of correction factors is

not required.

The minimum cross-section is not clearly defined in UL508A, even though AWG

14 "is suggested". Nonetheless both the NEC and the CEC haveAWG 18 as

minimum values for "laid" conductors (as usually happens on the machine) and

AWG 16 for conductors in raceways.

The power conductors inside the same raceway or tube (conduit) should be

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

insulated or is insulated for a lower voltage,it is necessary to distance it (at least

6.4 mm) or isolate it.

1.3.3 Terminal Block

1492 1492C NEMA

The terminal block for field wiring should be approved for use in an industrial

environment and should be compatible with both external and internal

conductors.

UL508A requires the terminal blocks installed to accept wire size of at least AWG

14, but in reality terminal blocks are also accepted for smaller wire size as long as

one of the following conditions are accepted.

•the terminal block accepts AWG 14 conductors and smaller cross/sections: no

particular prescriptions;

•the terminal block accepts only wire size smaller than AWG 14: it is necessary

to indicate on the electrical diagrams or with a tag at the side of the terminal

block, the maximum cross-section that it can accept.This is to avoid that, at a

later date, the conductors of the control circuit being replaced with others, not

compatible with the terminal block.

CONTROL CIRCUITS