Introduction—ASC and N2 Bus Networking and Troubleshooting Guide 33
Metasys Installation Practices
This document uses the terms “quiet” wiring and “noisy” wiring. With
wiring gas ignition devices especially, it is important to know the
difference between the two.
Quiet Wiring--Wiring that is free of transients. This wiring includes
binary inputs, analog inputs and outputs, 24 VAC power, and
communication buses.
Noisy Wiring--Wiring that is subjected to transients because of its
proximity to sources of electrical noise, or because of the loads to which
the wiring is connected (e.g., switched low-voltage loads, switched line-
voltage loads, gas ignition, and line-voltage distribution). Routing quiet
wiring near noisy wiring requires that the quiet wiring is shielded.
Low voltage is defined as 24 VAC. Line voltage is 120 VAC or higher.
We recommend that all ASCs are installed in enclosures, especially in
noisy areas. The ENC100 or BZ1000-7 works well. We also recommend
that the enclosures are earth grounded.
Placing ASCs inside another piece of equipment which contains a metal
housing (e.g., a rooftop unit or a motor control center) does not constitute
locating the control device inside a quiet metal enclosure. While the
location may provide physical protection for the control device, the
presence of electrical noise makes it a noisy box. Therefore, always use a
separate grounded metal enclosure for noisy environments.
Wiring the ASCs and other devices involves some type of grounding. It is
important to know the difference between the two types: hard ground and
soft ground.
Hard Ground--an electrical connection to earth through a conductor, such
as steel or other metal. A hard ground is usually necessary for safety
reasons. Hard ground is also referred to as earth ground, chassis ground,
building steel, building counterpoise, and green-wire ground.
Soft Ground--an electrical connection to earth ground through a capacitor,
such as a 560 pF capacitor. A soft ground provides high frequency
signals, such as 10 MHz, a low impedance path to earth. Power line
frequencies, such as 50/60 Hz, provide a high impedance to the earth.
Quiet Wiring vs.
Noisy Wiring
Using
Enclosures for
ASCs
Hard and Soft
Grounding
Summary of Contents for METASYS ASC
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