GE Mark VIe System Manual page 139

6.5.3.1 Grounding Notes
Bonding to building structure - The cable tray support system typically provides many bonding connections to building
structural steel. If this is not the case, supplemental bonding connections must be made at frequent intervals from the cable
tray system to building steel.
Connected equipment - Cable tray installations for connected equipment should pay special attention to good
high-frequency bonding between the cable tray and the equipment.
Cable spacing - Maintain cable spacing between signal levels in cable drops, as recommended in the section
Separation and Routing.
Conduit sleeves - Where conduit sleeves are used for bottom-entry cables, the sleeves should be bonded to the floor decking
and equipment enclosure with short bonding jumpers.
Embedded conduits - Bond all embedded conduits to the enclosure with multiple bonding jumper connections following the
shortest possible path.
Galvanized steel sheet floor decking - Floor decking can serve as a high-frequency signal reference plane for equipment
located on upper floors. With typical building construction, there will be a large number of structural connections between the
floor decking and building steel. If this is not the case, then an electrical bonding connection must be added between the floor
decking and building steel. The added connections need to be as short as possible and of sufficient surface area to be low
impedance at high frequencies.
High-frequency bonding jumpers - Jumpers must be short, less than 500 mm (20 in) and good high-frequency conductors.
Thin, wide metal strips are best with length not more than three times width for best performance. Jumpers can be copper,
aluminum, or steel. Steel has the advantage of not creating galvanic half-cells when bonded to other steel parts.
Jumpers must make good electrical contact with both the enclosure and the signal reference structure. Welding is best. If a
mechanical connection is used, each end should be fastened with two bolts or screws with star washers backed up by large
diameter flat washers.
Each enclosure must have two bonding jumpers of short, random lengths. Random lengths are used so that parallel bonding
paths are of different quarter wavelength multiples. Do not fold bonding jumpers or make sharp bends.
Metallic cable tray - System must be installed per NEC Article 318 with signal level spacing per the section,
Separation and Routing. This serves as a signal reference structure between remotely connected pieces of equipment. The
large surface area of cable trays provides a low impedance path at high frequencies.
Metal framing channel - Metal framing channel cable support systems also serve as parts of the SRS. Make certain that
channels are well bonded to the equipment enclosure, cable tray, and each other, with large surface area connections to
provide low impedance at high frequencies.
Noise-sensitive cables - Try to run noise-sensitive cables tight against a vertical support to allow this support to serve as a
reference plane. Cables that are extremely susceptible to noise should be run in a metallic conduit, preferably ferrous. Keep
these cables tight against the inside walls of the metallic enclosure, and well away from higher-level cables.
Power cables - Keep single-conductor power cables from the same circuit tightly bundled together to minimize interference
with nearby signal cables. Keep 3-phase ac cables in a tight triangular configuration.
Woven wire mesh - Woven wire mesh can serve as a high-frequency signal reference grid for enclosures located on floors not
accessible from below. Each adjoining section of mesh must be welded together at intervals not exceeding 500 mm (20 in) to
create a continuous reference grid. The woven wire mesh must be bonded at frequent intervals to building structural members
along the floor perimeter.
Conduit terminal at cable trays - To provide the best shielding, conduits containing level L cables (see Leveling channels)
should be terminated to the tray's side rails (steel solid bottom) with two locknuts and a bushing. Conduit should be
terminated to ladder tray side rails with approved clamps.
Where it is not possible to connect conduit directly to tray (such as with large conduit banks), conduit must be terminated with
bonding bushings and bonded to tray with short bonding jumpers.
Installation Guidelines
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GEH-6721_Vol_I_BP System Guide 139