Engineering Documentation

Table Of Contents
Chapter 1 Wiring Regulations and Specifications
Conduit SharingClass 1/Class 2 Separations
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Circuit Classes
Article 725 of the NEC applies to building control system installations and defines
different classes of circuits. As applied to Siemens Industry, Inc. Building Automation
Systems, these are:
Class 1 Remote Control Circuits
Class 1 Power Limited Circuits
Class 2 Power Limited Circuits
Class 3 Power Limited Circuits
Class 1 Remote Control Circuits
Circuits not exceeding 600 volts, used for controlling equipment. Typically, this covers
DO-type circuits used to control motors by energizing motor starters. These DO
circuits are also used to control lights and other items through pilot devices such as
relays or electro-pneumatic valves.
Class 1 Power Limited Circuits
Circuits not exceeding 30 volts and 1000VA. Typically, this covers power trunks.
Class 2 Power Limited Circuits
Circuits of relatively low power (such as 24 volts and up to 4 amps).
This covers the bulk of our circuits and includes the ALN communication wiring
(Ethernet TCP/IP, P2/P3 RS-485, and MS/TP RS-485), all FLN bus wiring (P1 RS-
485, LON, and MS/TP RS-485), 24 Vac power trunk wiring (with 100 VA power limit),
and DI, AI, and AO circuits.
Class 3 Power Limited Circuits
Circuits of relatively low power but of higher voltage than Class 2 (such as 120 volts
and up to 1 amp). This circuit would be achieved if 1 amp fuses were installed in a
120-volt DO-type circuit. This is not a common application.
See the Field Purchasing Guide for recommended wire. The wire listed in the Field
Purchasing Guide has been selected to meet the requirements of the APOGEE
product line.
Radio Frequency Transmitter Limitations
CAUTION
Keep devices that can generate Radio Frequency Interference (RFI), such as
Electro-pneumatic devices (EPs), relays, and walkie-talkies, at least 12 feet (3.7 m)
away from all field panels.
Conduit SharingClass 1/Class 2 Separations
NOTE:
Separate knockouts should be used for high voltage and low voltage wiring. Leave at
least 2 inches (50.8 mm) of space between the Class 2 wires and other wires in the
panel.