Yamaha P-2200 - Manual (Page 37)

Fig. 61 - Use of Ground Lift Switch
system. This problem is usually most noticeable with
sensitive equipment such as the mixer. Lifting the AC
ground at the mixer can often solve this problem.
However, lifting the AC ground on the mixer also lifts
the AC ground on the microphone chassis, causing a
safety hazard. Try connecting the mixer and any other
sensitive equipment to other AC circuits. The only other
apparent solution to this problem is to eliminate the
noise on the AC ground, which is not an easy task. A
portable AC power distribution system with its own
ground, connected to the house service entrance, may
be the most effective way to avoid all AC noises. Such
a system can be designed and constructed by a qualified
electrician; check local electrical codes before each use.
Perhaps the best answer to portable system grounding
problems, RFI, EMI, and AC noises, is to develop a
versatile grounding scheme with ground lift switches and
adapters, and, if possible, a portable AC power distri-
bution system, so that different combinations can be
tried easily and quickly when a problem occurs.
AC: POWER, FUSES, ACCESSORY OUTLETS, WIRING,
SAFETY (Not applicable in 220/240 Voltage area.)
The P-2200 requires an AC voltage of 105V AC to
135V AC, 50 or 60Hz. If the voltage falls below 105V
AC or rises above 135V AC, the P-2200 will not operate
properly, and may be damaged. At full power with both
channels operating into 8 ohms, the P-2200 draws
approximately 960 volt-amperes, or 8 amps at 120V AC
(see Figure 12, Page FOUR 2). When a system uses
several P-2200 amplifiers, check the current capacity
of the AC line, and distribute the amplifiers among
several AC circuits, if necessary. It is extremely
important to always replace blown AC fuses in the
P-2200 with the same type and value.
The AC accessory outlets on the rear panel of the
P-2200 are provided for operation of cooling fans or
other low power equipment, not for the connection of
another P-2200, or other high power device.
The American Electrician's Handbook published by
IvlcGraw Hill is a good reference for an understanding of
proper AC wiring. Other smaller books, often available
in hardware or electrical supply stores, detail simplified
Fig. 62A - Properly Wired 110VAC Outlet
residential wiring. We do not suggest that you modify
the AC wiring in an auditorium or a club, or anywhere
else. Such work should be reserved for a qualified,
licensed electrician. But, if you understand proper AC
wiring, you will also understand the potential problems
of improper wiring, some of which are described below.
CAUTION: In any audio system installation, govern-
mental and insurance underwriters' electrical codes must
be observed. These codes are based on safety, and may
vary in different localities; in all cases, local codes take
precedence over any suggestions contained in this
manual. Yamaha International Corporation shall not
be liable for incidental or consequential damages,
including injury to persons or property, resulting from
improper, unsafe or illegal installation of the P-2200
or of any related equipment; neither shall the
Corporation be liable for any such damages arising
from defects or damage resulting from accident, neglect,
misuse, modification, mistreatment, tampering or any
act of nature.
Lifted Ground
Broken, or disconnected AC ground wires in existing
AC outlets can create shock hazards; so can older, two-
wire sockets with no ground. Note that unless metal
conduit connects the older, two-wire AC outlet to
ground (an uncommon practice except in some public
buildings), the screw on the outlet cover plate is
probably not grounded either. In this case, an AC
ground, or earth ground must be located somewhere
else.
Fig. 62B - 110VAC Outlet with Disconnected AC Ground
Wire creating potential shock hazard.
Reversed Polarity
Improper polarity connections, or polarity modifica-
tions, can cause reversal of the "hot" and "neutral" AC
wires. This can cause shock hazards, and noise in some
equipment.
Fig. 62C - 1 1 0 V A C Outlet with Polarity (Hot and Netural)
Reversed creating shock hazard and causing possible noise.
Lifted Neutral
The "neutral," or return, wire of a 1 1 0 V AC circuit
should be connected to AC ground at the building
service entrance (where the main AC power enters).
However, this neutral is usually a center tap from a 220V
AC circuit; if it becomes disconnected at the service
entrance, a varying voltage will appear at the AC outlet,
which may rise as high as 220V AC, depending on the
load on each circuit. This poses shock hazards, and can
easily cause equipment damage.