Industrial Control Panels for North America

Applications Examples

Branch/Feeder Circuit

Branch/Feeder Circuit

Branch Circuit

  • The conductors and components following the last overcurrent protective device protecting the load.

Feeder Circuit

  • The conductors and circuitry on the supply side of the branch circuit overcurrent protective device.

  • Employed devices:
    - Listed circuit breakers according to UL 489, or
    - Disconnect switches according to UL 98 and fuses with holder according to UL 248
    - Industrial control equipment according to UL 508 with additional field wiring terminals

  • Devices in the feeder circuit and line terminals of the branch circuit protective device shall have bigger distances through air and over surface

  • Depending on the voltage up to
    - 1 inch – through air
    - 2 inches – over surface

feeder Circuit

Combination Motor Starters

The assembly options of combination motor starters within the IEC greatly differ from those for the UL market. Various assembly and combination options are permitted by UL. However, disconnect, short-circuit protection, motor control, and motor overload protection must always be implemented (see branch example).

Standard tables exist at Siemens for motor branches, with standardized devices and wiring from 0.5 HP to 500 HP and SCCR values up to 65 kA.

For more extensive technical documentation, please "contact" the responsible office in your local region.

SCCR (Short Circuit Current Rating)

Short Circuit Current Rating of the Control Panel Power Circuit

An industrial control panel must be marked with a so-called SCCR - Short Circuit Current Rating. In the IEC, this approximately corresponds to the Icw value of the switchboard. The NEC 2008 Art. 409 describes the specifications of short circuit current rating mark on industrial control panels (with reference to the UL 508A, SB4). For short circuit rating, not only the short circuit breaking capacity, e.g. of the circuit breaker, but also the short circuit rating of every individual device in the power circuit is relevant. The SCCR-relevant components in the power circuit include circuit breakers, contactors, overload relays, solid-state switching devices, terminals, busbars, the line side of control transformers and frequency converters, however, no internal wiring of the industrial control panel.

The lowest value is applicable to the entire industrial control panel. No higher short circuit current shall occur on the industrial control panel’s supply terminals.

Low-Voltage Networks in the USA

The network types used in the USA significantly differ from European networks. Other than in the IEC, also corner-grounded delta networks as well as solidly grounded wyes, which closely resemble the TN-S network, are employed. In the United State of America/UL/NEC, all voltages used in the respective network type are stated (see table). As regards device selection, close attention must be paid to checking the network type used at the application site and the network types for which the individual devices are approved. The common network types used in industrial and functional building applications are 3-phase networks with 240 V and 480 V as well as 3- and 4-wire systems with 480Y/277 V. Furthermore, the single-phase system with 120/240 V can be frequently found particularly in residential buildings, but also in offices in industrial and functional buildings.

05/26/2013 | Author: Danish Bhimani

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