Theatre Design & Technology - Feb 1969 - 15

for the convenience of those afflicted with tidy minds, these
disparate functions may be grouped into three broad catagories:
Emergency Circuits which, in the event of the failure of
normal power automatically derive their feed from a secondary source.
Panic Circuits which have provisions for manually (including
remote switching) transferring their loads directly to the
normal main bus.
Bypass Circuits which merely circumvent a dimmer function
to obtain switched, full intensity lighting.
Emergency lighting circuits are required by many local buiiding codes, including those for major cities. Where required
or where installed in the name of common prudence (rural
areas without codes are more subject to power failure than
the strictly regulated urban areas) this installation is governed by article 700 of the National EI ectrical Code (NEC).
These provisions are often modified, and usually tightened,
by local law. Where required (e.g. in all theatres seating
over 500 in Los Angeles) these circuits must commonly be
provided for the exit lights and sufficient circuits in the
house, lobbies, fire escapes and corridors to insure safe
passage through the normal exit routes. Sufficient luminaries must be provided to maintain adequate illumination
should any single lamp fail (NEC Art. 700.14).
The circuits may be (and in some jurisdictions, e.g. New
York City, must be) fed from an emergency source at all
time. More generally (NEC 700.15) they must automatically
transfer to the emergency source in the event of failure of
the normal feeders (NEC 700.15 (a)). Notice that emergency
transfer need not (though often does) imply the automatic
illumination of the emergency lighting, except in the case of
fixed unit ballery-operated equipment (NEC 700.22).
The emergency source may be storage balleries (700.17),
an automatically cranked emergency generator set (700.8),
a separate service from the same mains (700.9), a completely separate power source (700.1 1) or even, if no other
source is practicable, a separate feeder tapped from the
normal main service ahead of the building main disconnect
(700.10). The more completely separated, and hence likely
to remain available, the more serviceable the supply will be:
provisions to insure maximum feasable separation are built
into the code.
The same separation is required of branch circuit wiring.
Complete isolation from the normal lighting branch circuit is
required (700.17). This mandates separate wire runs, breaker
magazines, fixtures and boxes; mechanical isolation of emergency sections in lighting switchboards and panelboards,
and separate or barriered control stations where manual controls are permilled. The only common points between the
normal and emergency systems permilled are in the transfer
switch compartment itself and in exit signs which have dual
lamp circuits. (700.17 exceptions 1 and 2).
Where permitted these branch circuits may be used as part
of the normal illumination system: however when required
they must completely and automatically transfer to the
emergency system. This transfer must include the neutral
conductor. Because of the required isolation, and because
of the limitation placed on manual control of emergency circuits, it is ordinarily desirable to place the major lighting
system control elements ahead of thiS transfer and on the
normal side. Where transfer is not permitted it will often be
more economical to provide completely functionally and
mechanically separate emergency circuits.
Flexibil ity of manual controls for emergency circuits is
severely limited by code, this circumscription serving again
to increase the reliability by decreasing the possibilities for
. This does not necessarily imply an "automatic transfer switch," but
that is another discussion.



error. Essentially only a limited ON-OFF control is permilled,
principally to
cover the panic function. Only single throw
switches are allowed (700.18). This provision is usually
interpreted to allow single acting &up is always on, down is
always off) switches or the equivalent in pushbullons. Three
and four way switches are proscribed to preclude confusion
as to which throw turns the light on. All switches are
preferably accessible only to authorized personnel (700.19).
At least one switch, located in or near the lobby, must be
under the exclusive control of authorized persons. No
switches except those which serve only to energize the
lights may be located in a motion picture projection booth
or on stage. This last prevents a local emergency from fouling the circuit so as to prevent the light from being energized. Time clocks are permilled on exterior lights where
no lighting is required for public passage during daylight
hours (700.20). Again, to provide maximum security against
errors and failure only one overcurrent protection device is
permilled in an emergency breaker circuit, and that may only
be accessible to authorized persons (700.21). In all of these
provisions the common denominator is the restriction of control functions to the absolute minimum consistent with the
primary emergency lighting function.
It is worthwhile to reemphasize here once again that local
codes may drastically alter any or all of the above. New
York, for example, prohibits all but one manual switch which
must be in the lobby area. Only licensed professionals
should attempt to design these systems.
Stangely enough panic circuits, where not simply the manual
functions of an emergency system, are not specifically
treated in the NEC. Nevertheless they perform the same public safety service as do emergency circuits and, following
the same design philosophy should be installed to the same
standards. The principle difference in installation will be,
naturally, the absence of any requirement for isolation at the
feeder as by definition these circuits are derived directly
from the normal main house feeder, and the use of a common neutral for the same reason. Usually strict isolation of
the control elements is not observed either, on the grounds
that the isolation accorded the dual service above is not
here justified.
The panic contactors must provide a direct high current path
between the panic circuit overcurrent device and the normal
subfeeder overcurrent devices. This will usually imply interruption of the normal panic branch feed and transfer to
the direct feed. If the entire output of an SCR dimmer constitutes the panic circuit, a direct shunt bypass will provide
the required path.
Bypass circuits, which do not primarily serve a public safety
function, need observe no requirements other than those imposed upon normal feeder and branch circuits. This type of
circuit lends itself to all forms of special purpose lighting
control providing classroom I ighting, janitorial service I ighting, night lights, etc. Of course it may be possible to have
the emergency or panic circuits double in these functions
but where this is not practical a simple circuit is usually
sufficient. Often the bypass merely brings a dimmer to full
All three types of "on-direct" lighting circuits fill their own
niche in theatre practice. It is necessary that the distinction
between them be understood before they can be properly
specified or applied. Emergency currents are covered by
codes and the designer must follow these regulations. Panic
circuits are not codified but probably should be as they directly affect public safety. In the absence of specific regulations it is necessary to regard these as special classes of
emergency circuits. Bypass circuits, serving only utilitarian
or cosmetic requirements, need meet only those installation
requirements imposed on ordinary branch circuits .



Table of Contents for the Digital Edition of Theatre Design & Technology - Feb 1969

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