34 Introduction—ASC and N2 Bus Networking and Troubleshooting Guide
In most equipment locations, whether or not to provide a low impedance
connection to earth ground depends on the circumstances. The high
frequency components of electrical noise can render a long wire
connection to ground practically useless because of the wire’s inductance.
Wherever possible, connecting a shield to a large sheet metal enclosure,
such as a rooftop unit, is much better than trying to find a “true” earth
ground. If a metal enclosure is not available, tie the shield to one of the
following ground connections (listed in order of preference):
1.
Direct bond to building counterpoise ground system.
2.
Direct bond to main building structural steel (e.g., bolt into threaded
hole).
3.
Bond to ground rod installed a minimum of two feet below minimum
water table depth.
4.
Bond to conduit or electrical distribution box.
5.
Bond to nearby metal water pipe (preferably copper).
Note: In all cases, make the bond to ground as short as possible. Derate a
ground point by one level (in order of preference) for each 50 feet
of conductor run between the ground point and the equipment to be
grounded. For example, a water pipe bond located 10 feet away is
preferable to a structural steel bond located 150 feet away.
The recommended gauge for the ground wire is 10 or 12 AWG.
Metasys was specifically designed to use unshielded cable. In most
situations, the N2 Bus functions reliably with this type of cable.
However, some devices emit very high levels of electrical noise.
Examples include radar, magnetic resonance imaging equipment, arc
welders, and gas ignition systems. Use shielded cable for these devices.
A gas ignition system requires that you use shielded cable on the sections
of the N2 Bus that are close to the spark. This section outlines the
standard practices you must follow when using shielded N2 cable for this
or any other noisy application.
Using Shielded
Cable in Noisy
Environments
Summary of Contents for METASYS ASC
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