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Re: Grounding Schemes

>  E-mail from: Neoman, 06-Jan-1996

>>>  it works (might be useful in the sound biz, also...). Telford Dorr <<
>
>Been there, done that. Yea, it is a usual technique for audio systems.
>It starts to get very complicated when you have a house console with a monitor
>console 300ft. or so away and also have a TV Production truck another 500ft.
>away which is tied to the satellite truck, etc, etc. You have to have a good
>grounding scheme to reference it all to and pick ONLY one. Hopefully, the right
>one. And then there are those moving lights.....
>
>

>From the 1996 NFPA 70 - National Electrical Code  (Registered Trade Mark)

ARTICLE 530 -- MOTION PICTURE AND TELEVISION STUDIOS AND SIMILAR LOCATIONS


530-70. General.
  Use of a separately derived 120-volt, single-phase, 3-wire system with 60
volts on each of two ungrounded conductors to a grounded neutral conductor
shall be permitted for the purpose of reducing objectionable noise in
audio/video production or other similar sensitive electronic equipment
locations provided that its use is restricted to electronic equipment only
and that all of the requirements in Sections 530-71 through 530-73 are met.

  530-71. Wiring Methods.
  (a) Panelboards and Overcurrent Protection. Use of standard single-phase
panelboards and distribution equipment with a higher voltage rating shall
be permitted. The system shall be clearly marked on the face of the panel
or on the inside of the panel doors. Common-trip, two-pole circuit breakers
that are identified for operation at the system voltage shall be provided
for both ungrounded conductors in all feeders and branch circuits.
  (b) Junction Boxes. All junction box covers shall be clearly marked to
indicate the distribution panel and the system voltage.
  (c) Color Coding. All feeders and branch-circuit conductors installed
under this section shall be identified as to system at all splices and
terminations by color, marking, tagging, or equally effective means. The
means of identification shall be posted at each branch-circuit panelboard
and at the disconnecting means for the building.
  (d) Voltage Drop. The voltage drop on any branch circuit shall not exceed
1.5 percent. The combined voltage drop of feeder and branch circuit
conductors shall not exceed 2.5 percent.
  530-72. Grounding.
  (a) General. The system shall be grounded as provided in Section 250-26
as a separately derived single-phase 3-wire system.
  (b) Grounding Conductors Required. Permanently wired utilization
equipment and receptacles shall be grounded by means of an equipment
grounding conductor run with the circuit conductors to an equipment
grounding bus prominently marked "Technical Equipment Ground" in the
originating branch-circuit panelboard. The grounding bus shall be connected
to the grounded conductor on the line side of the separately derived
system's disconnecting means. The grounding conductor shall not be smaller
than that specified in Table 250-95 and run with the feeder conductors. The
technical equipment grounding bus need not be bonded to the panelboard
enclosure.
  Exception: Other grounding methods authorized elsewhere in this Code
shall be permitted where the impedance of the grounding return path does
not exceed the impedance of equipment grounding conductors sized and
installed in accordance with Part G of this article.
  (FPN No. 1):  See Section 250-95 for equipment grounding conductor sizing
requirements where circuit conductors are adjusted in size to compensate
for voltage drop.
  (FPN No. 2):  These requirements limit the impedance of the ground fault
path where only 60 volts applies to a fault condition instead of the usual
120 volts.
  530-73. Receptacles.
  (a) General. Where receptacles are used as a means of connecting
equipment, the following conditions shall be met:
    (1) All 15- and 20-ampere receptacle outlets shall be ground-fault
circuit-interrupter protected.
    (2) All outlet strips, adapters, receptacle covers, and faceplates
shall be marked as follows:
  WARNING - TECHNICAL POWER.
  Do not connect to lighting equipment.
  For electronic equipment use only.
  60/120 volt 1f ac.
  GFCI protected.
    (3) A 125-volt, single-phase, 15- or 20-ampere rated receptacle having
one of its current-carrying poles connected to a grounded circuit conductor
shall be located within 6 ft (1.83 m) of all permanently installed 15- or
20-ampere rated 60/120-volt technical power-system receptacles.
    (4) All 125-volt receptacles used for 60/120-volt technical power shall
be uniquely configured and identified for use with this class of system.
  Exception: 125-volt, single-phase, 15- or 20-ampere rated receptacle
outlets and attachment plugs that are identified for use with grounded
circuit conductors shall be permitted in machine rooms, control rooms,
equipment rooms, equipment racks, and other similar locations that are
restricted to use by qualified personnel.
  (b) Isolated Ground Receptacles. Isolated ground receptacles shall be
permitted as described in Section 250-74, Exception No. 4, however, the
branch-circuit equipment grounding conductor shall be terminated as
required in Section 530-72(b).

This is for use in audio/video production in MOTION PICTURE AND TELEVISION
STUDIOS AND SIMILAR LOCATIONS Only!!!!

It works well BUT please use it only use it on stage (also -The NEC is Not
used in New York City so this is not OK here)

--------------------
Eddie Kramer    IATSE #1        Electrician     Radio City Music Hall