QA/QC Questionnaires FIELD INSTRUMENT/JUNCTION BOX/COLOR CODING Grounding (J902)

 

CONNECTIONS at FIELD INSTRUMENTS and JUNCTION BOX

a. Connections at field instruments shall be screw type terminal blocks. Wire nuts and spring

type terminals shall not be used. Instruments’ with integral terminal blocks shall be

connected directly to the field cable.

b. The outer jacket of shielded twisted single pair/triad cables shall be left intact up to the

point of termination. Drain wires and Mylar shields on shielded cables shall be cut and

insulated with heat shrink sleeve at the field instrument unless otherwise specified by the

Instrument manufacturer.

c. Twisted multi‐pair triad cables shall be cut to the appropriate length to minimize looping

and flexing of the cable within the junction box.

COLOR CODING

Power and signal wiring shall be color coded as follows:

Grounding (J902)

17.1 General

17.1.1 Electrical
systems must be connected to ground for the protection of personnel and

equipment from fault currents (AC safety ground) and to
minimize electrical

interference in signal transmission circuits (Instrument
circuit ground).

17.1.2 Two
grounding systems are required for instrumentation systems:

a) safety ground for personal safety.

b) Instrumentation Safety Ground.

17.2 Safety Ground

17.2.1 All
exposed non‐current‐carrying metallic parts that could become energized

with hazardous potentials must be reliably connected to
the equipment

grounding circuits. This assures that hazardous potential
differences do not exist

between individual instrument cases or between an
instrument case and ground.

Therefore, all metal equipment and enclosures within a
panel or series of panels

(i.e., instrument cases, hinged doors, racks, etc.) shall
be bonded with bonding

jumpers and connected to a safety ground bus with a minimum
copper wire size

of 4 mm² cross‐sectional area. Two copper conductors, 25
mm² minimum, shall

be connected from the safety ground bus to a single tie
point on the safety

ground grid in a closed loop configuration. Safety ground
connections must be

made such that when a case‐grounded instrument is removed,
the integrity of

the rest of the safety ground system is maintained.

17.2.2 Enclosure for field instruments shall be grounded as follows: (J‐902)

17.2.2.1 Instruments
Operating at greater than 50 Volts

The enclosure for Instrument devices operating at 120 V AC
or

125 VDC shall be grounded per SAES‐P‐111.

Instrument Circuit Ground (J902)

17.3.1 The
purpose of instrument circuit grounding is to reduce the effect of electrical

interference upon the signal being transmitted. An
instrument circuit ground

bus shall be provided for consolidating instrument signal
commons and cable

shield drain wires. This ground bus shall be isolated from
the safety ground

system
except at a single tie point as described below.