Installing a Technical
Grounding System
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Technical Support Information
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1.)   Drive two copper-clad 8-foot x 5/8” (or larger) ground rods, a minimum distance of 6 feet apart into the Earth.  As an option, a ring ground, plate ground or other low impedance grounding electrode such as a chemical ground may be used. Consult with a qualified electrical installer if you choose one of the alternatives. Using an alternate grounding electrode for a technical ground is usually unnecessary with balanced power unless there is poor soil conductivity or very high RF levels in your area.
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2.)   Run a #6ga. copper wire between the two ground rods passing through a UL listed brass acorn clamp on one of the rods and terminating the run at the main grounding electrode of the building's AC system.  It is essential to bond together all of the grounding electrodes in a building for safety.  NEVER use a separate grounding electrode system for the technical ground that is not bonded to the building ground.  With balanced power under normal conditions, bonding the ground rods to the building's main grounding electrode in this manner will not have an adverse effect on noise levels in the studio.
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3.)   From the technical ground buss in the studio power panel, run a #6ga. copper wire to one of the copper-clad ground rods and connect it to the ground rod with a UL listed brass acorn clamp.  Using a brass clamp will provide resistance to corrosion in damp environments and insure longevity of the termination.  Brass acorn clamps may be buried in the soil however it is recommended that they remain visible and above ground for occasional inspection.  If another type of grounding electrode is used, such as a chemical grounding electrode, a ground ring or euffer ground, a larger grounding conductor may well serve to lower the grounding impedance.  This is especially true where there is a long distance to the grounding electrode from the studio ground buss.  Larger grounding conductors will also have a wider bandwidth of RF noise attenuation because of their larger surface area of copper.  This phenomenon is called skin effect.  However, it is best to use some judgment when deciding if a wider bandwidth of RF noise attenuation is needed in your area.  Often the problem of high-frequency RF is very localized and the cost of a large copper ground wire will yeild only marginal returns.  But one area where a large conductor would yeild benefit would be high up in an office building in a large city where RF transmissions are thick like mud.  So consider your locale when making this decision.  Just for your information, the most sophisticated grounding electrodes short of chemical systems are often used at radio transmission tower sites.  The most popular method is the ground ring which consists of a 4/0 or larger bare copper wire burried in a circle around the building about 2ft. - 3ft. deep.  All "joints" and connections to the tower and electrical system are cadwelded.  Often, the grounding conductors used inside of the ring are 6 inch wide copper ribbons, or at least very large copper conductors.
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4.)   When using an Equi=Tech isolation transformer (in a permanent, hard-wired balanced power system,) the isolated ground buss in the primary tech power panel must also connect to the center tap terminal on the output of the isolation transformer.  This wire must occupy the same raceway as the main power feeder wires that feed from the isolation transformer to the tech power panel.  Minimum sizing requirements for this conductor are contained in Table 250-95 in the National Electrical Code.
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5.)   The (isolated) technical ground buss in the studio technical power panel is where all technical branch circuit ground wires are to be terminated.  The technical ground buss is the “single-point" ground source of the studio.  From the isolated ground buss in the panel, sharing the same conduit (or cable) with the branch circuit conductors, run an insulated ground wire and connect it to the grounding screw on each receptacle that is fed by that circuit.  In a balanced power system, multiple receptacles on the same circuit may share a single ground wire in daisy-chain fashion without inducing noise.  Radial or star grounding has little impact where there is no noise in the ground however there is nothing wrong with employing radial or "star" grounding.
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6.)   If metal conduit or metal clad (MC) cable and metal outlet boxes are used in construction, isolated ground (IG) receptacles must be used.  Be sure that the ground wire in the conduit or cable is insulated.  If you are using a section of flexible conduit or MC cable longer than 6 feet, a FOURTH wire called an electrical equipment ground (dirty ground) may be required in EACH CABLE to ground the metal outlet boxes.  Be very aware of this ELECTRICAL CODE REQUIREMENT if you want true isolated grounding.  The additional electrical equipment ground wire may be a bare conductor.  Another common term for this conductor is "bonding wire".  The function and purpose of this "bonding wire" is to make sure that the entire metal conduit system and all metal outlet boxes, J-boxes and panelboards are grounded.  Often this requirement is forgotton or neglected and this can spell trouble later.  Isolated ground wires should not be used to ground metal outlet boxes especially where flex, metal conduit, metal clad cable or steel wall studs are used in construction.  So remember the bonding conductor requirement.  The additional bonding wire is only necessary if the conduit system is OTHER than rigid aluminum or steel conduit, intermediate metal conduit (IMC), or electrical metal tubing (EMT).  If romex is used in construction, the bare wire in the romex cable may serve as the isolated ground.  Isolated ground receptacles are unnecessary when using romex and plastic boxes.
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Studio equipment with a 3-prong plug is grounded via its AC cord.  Equipment with a two prong cord may be grounded with a supplemental ground wire. This is accomplished by connecting the bare metal of the equipment chassis to the technical ground (isolated ground) with a #12ga. or #14ga. green copper wire. A simple means of accessing the technical ground electrically is to use a male cord plug having only a ground wire connected to it and plugged into an isolated ground receptacle.  When using an Equi=Tech rack system, use the grounding terminal on the back of the unit as a supplemental means of grounding studio equipment chassis or racks.
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NEVER use an AC ground lift adapter on equipment that has a grounded 3-prong AC cord. This is a very dangerous practice. When using unbalanced power, chassis and/or signal grounds are often lifted from the AC ground to reduce noise. When balanced power is used, all chassis and audio/video signal grounds can be referenced to the AC ground without adding interference. The only exception to this is the rare occasion when a piece of equipment has a “dirty chassis" condition.

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For more information see tech support bulletins:
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Audio Wiring & Grounding and The "Dirty Chassis" Condition
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Technical Support Index ...... Equi=Tech Index
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(c) Copyright 1996 Equi=Tech Corporation all rights reserved