Section 5: Wiring Techniques; Overview; Device Wiring; Avoid Common Returns - Emerson ControlWave Series Site Considerations For Equipment Installation, Grounding, And Wiring Manual

Section 5: Wiring Techniques

This section covers the following topics:
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5.1

Overview

This section provides information on good wiring practices, including good wire preparation and
connection techniques. It also discusses the installation of power and "measurement & control"
wiring; circulating and ground power loops; bad relays; and resolutions for common and
uncommon problems.
5.2

Device Wiring

This section briefly discusses each of the following rules, placing emphasis on avoiding problems
and assuring equipment safety.
Rule 1 – Never use common returns.
Rule 2 – Use twisted shielded pairs (with overall insulation) on all signal/control circuits.
Rule 3 – Ground cable shields at one end only.
Rule 4 – Use known good earth grounds (rod, bed, system) and test them periodically,
Rule 5 – Earth connections must use smoothly dressed large wire.
Rule 6 – Perform all work neatly and professionally.
Rule 7 – Route high power conductors away from signal wiring according to NEC rules.
Rule 8 – Use appropriately sized wires as required by the load.
Rule 9 – Use lightning arresters and surge protectors.
Rule 10 – Make sure all wiring connections are secure.
5.2.1

Avoid Common Returns

Using common returns on I/O wiring is one of the most common causes of obscure and difficult-to-
troubleshoot control signal problems. Since all wires and connections have distributed resistance,
inductance, and capacitance, using common returns considerably reduces the chances of
achieving a balanced circuit or a balanced system. Balanced circuits and systems only occur when
all currents and voltages developed in association with each of the common returns are equal. In a
balanced system (or circuit) prevents the introduction of noise or measurement errors due to
"sneak circuits."
Figures 5-1
sneak circuits and one that use common returns. Common sense tells us that it is tough to mix up
Wiring Techniques
Site Considerations for Equipment Installation, Grounding, and Wiring Manual
Overview
Intrument Wiring
and 5-2 show the difference between testing an I/O circuit that is discrete and has no
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