Grounding Procedure; General; Conductive Pipeline - ABB COPA-XM 3000 Series Instruction Manual

Series 10DX3000 Magnetic Flowmeter Instruction Manual

2.5 Grounding Procedure

2.5.1 General

Satisfactory operation of Magnetic Flowmeter Systems requires that careful attention be paid to
proper grounding techniques. A good ground is one that is in contact with the earth over a large
conductive area. An excellent example of this is a cold water pipe which is buried in the earth and
travels many miles in its distribution system. A great number of pipe branches form a large conduc-
tive area of contact which provides a low resistance connection to earth. A hot water or steam pipe
must first return to a boiler before it becomes a cold water pipe, and therefore, its greater length of
ungrounded path offers a less desirable ground bus. A metallic structural member of a building, such
as a supporting " I " beam, may be a good earth ground, but it is a second choice to a cold water pipe.
Meter grounding requirements are really a combination of standard grounding methods and a
bonding of the meter body to the process liquid. The most important of these is the process bonding,
which is nothing more than ensuring that the meter body is in contact with the process liquid at both
ends of the meter body. Basically, the bonding procedure places an electrical short circuit across the
meter, thereby routing any stray current around the liquid in the meter (rather than through it).
From the point of view of grounding there are two basic types of piping systems:
• electrically conductive pipeline: the process liquid comes in contact with
conductive pipe. This piping requires that each meter flange be connected
with a bonding wire to the adjacent pipeline flange. The grounding procedure
to use with conductive pipeline is described in 2.5.2.
• non-conductive or electrically insulated pipeline: the pipeline may be made of
an electrically non-conductive material (plastic, concrete, etc.) or lined with a
non-conductive material (rubber, TEFLON, etc). These non-conductive
pipelines require the use of metal grounding rings to bond the process liquid
to ground. The grounding procedure to use with nonconductive pipeline is
described in 2.5.3.
Proper grounding of the Magnetic Flowmeter is required for optimum system performance.

2.5.2 Conductive Pipeline

If the flowmeter is included as part of a conductive pipeline that is not electrically insulated from the
liquid to be metered, the following grounding procedure should be followed. Refer to Figure 2-20 to
supplement the following text.
1) Drill and tap both pipeline flanges adjacent to the bonding connections on the
flowmeter. The lugs on the bonding cables are sized for metric M6 fasteners (a 1/4"
bolt).
2) Obtain a bright metal surface around the edges of the tapped hole with a file or
burnishing tool.
3) Attach the bonding wire and another length of ground wire to the flanges as shown.
Use internal tooth lockwashers as shown in the detail. The wire to the good external
ground should be #12 AWG, or heavier, copper wire.
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