Technical information

1Control Circuits

1.1 Definition of Remote control Circuit

In the National Electrical Code (art. 100 Part I) and in the Canadian Electrical

Code (section 0) the following definition is given:

• Remote control circuit: any electric circuit that controls any other circuit

through a relay or an equivalent device.

In the UL508A standard, Part 2 Glossary, the definition is: simplified and applied

to the electrical panel:

• Remote control circuit: an electrical circuit that commands a control element

(e.g. a contactor) and that does not supply power loads.

Single norms do admit different types of control circuits characterised by voltage,

current and functions.

1.1.1 Classification of the circuits

The National Electric Code (NEC) distinguishes between three different types of

control circuit:

• Class 1: general control circuit (up to 600 V, no limit in power VA); in some

applications there is a requirement that the voltage and power be limited (30 V,

1000 VA).

• Class 2: control circuit powered by sources of limited power upon special

approval: it is considered safe from the points of view of both direct contact

and the risk of fire.

• Class 3: control circuit powered by limited power sources upon special

approval, but with more power than it allowed for Class 2: it is considered safe

from the risk of fire but not for the risk of direct contact.

Voltage and power limits for class 2 and 3 circuits are not given in the NEC

because these are inherent to the limitations imposed on power sources in the

relative construction standards.

The Canadien Electric Code (CEC) distinguishes between two different types of

control circuit:

• Class 1: general control circuit: this can be limit in voltage and in power (30 V,

1000 VAC) or not (600 V, no limit for VA).

• Class 2: control circuit powered by limited power sources with special

approval; distinctions are made on the base of the power voltage:up to 20 V,

above 20 V up to 30 V, above 30 V up to 60 V and above 60 V up to 150 V.

It should be noted that the instructions for Class 1 circuits are similar in both NEC

and CEC.Also these are very similar for Class 2 circuits: the CEC limits itself to

giving a few additional instructions regarding the protections to adopt, while the

NEC limits itself to referring to the approved components.

CONTROL CIRCUITS