Grounding Procedure; General; Conductive Pipeline - ABB CK-MAG 10D1477 Instruction Manual

10D1477 MAGNETIC FLOWMETER INSTRUCTION MANUAL

2.4 Grounding Procedure

2.4.1 General

Satisfactory operation of the magnetic flowmeter system requires that careful attention be paid to
proper grounding techniques. Meter grounding requirements are a combination of standard ground-
ing methods and grounding of the meter body to the process liquid. The grounding of the process
liquid places an electrical short circuit through the meter body, thereby routing any stray current
around the process liquid rather than through it.
There are two basic types of piping systems:
• One type is an electrically conducting pipeline in which the process liquid comes in
contact with the conductive pipe. This piping requires only that the grounding wires
be attached to the adjacent pipe flanges.
• In the other case, the pipeline may be lined with a non-conductive material. These
lined pipelines require the use of metal grounding rings to ground the process liquid
and the conductive exterior of the pipe/meter to ground.
A good ground is one that is in contact with the earth over a large conductive area. An excellent
example of this is an iron cold water pipe that is buried in the earth for a considerable distance in its
distribution system. The water pipe laterals form a large conductive area of contact, that in turn
provides a low resistance connection to earth. Plastic pipe does not provide an adequate ground
system.
Select the grounding procedure applicable to the installation from Paragraph 2.4.2 or 2.4.3. Proper
grounding of the magnetic flowmeter is required for optimum system performance.
Installation of the CK-Mag magnetic flowmeter must provide a minimum of five pipe diameters of
conductive exterior pipeline (may be lined with insulating material) on each side of the meter. This
must be done to prevent stray electrical interference from coupling to the interior of the meter and
producing unacceptable zero offsets.

2.4.2 Conductive Pipeline

If the magnetic 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
2-10 to supplement the text. Note that the grounding method shown in Figure 2-10 is applicable also
for meters supplied with sanitary fittings.
1. Drill and tap a blind hole on the peripheral surface of each of the two adjacent pipeline flanges (see
Figure 2-10 Inset). These tapped holes should be placed so that they are within easy reach of the
bonding straps (2 supplied) attached to the ground lug on the meter housing.
2. Obtain a bright metal surface around the edges of both tapped holes with a file or emery cloth.
3. Clamp the lug on the end of each bonding strap to the adjacent pipe flange, using a pair of 1/4" hex
head bolts and external tooth lockwashers (supplied by user).
4. The user must supply a sufficient length of grounding wire for connecting the meter grounding post
(ring lug supplied) to a good electrical ground. (Number 12 AWG, or heavier, copper wire may be
used for this grounding wire.)
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