How To Obtain A Safety Ground When Using A 2-Wire Outlet - Yamaha PM4000 Operating Manual

voltmeter. It is also a good idea to use a
special outlet tester that will also indicate
reversed polarity, weak or missing neu-
tral, and weak or missing ground connec-
tions in the outlet. Test the power supply
before connecting the umbilical cable to
the console.
Severe over voltage or under voltage in
the power mains can damage your equip-
ment. For U.S.A. and Canadian models,
the power line must measure more than
105V and less than 130V RMS. The toler-
ance for General Export models is plus or
minus 10%. Some lines are "soft" meaning
that the voltage drops when the line is
loaded due to excessive resistance in the
power line, or too high a current load on
the circuit. To be certain the voltage is
adequate, check it again after turning on
the PW4000 with the PM4000 connected,
and with any power amplifiers turned on
if they are connected to the same power
mains.
If the power line voltages do not fall
within the allowable range, do not con-
nect the PW4000 to the mains. Instead,
have a qualified electrician inspect and
correct the condition. Failure to observe
this precaution may damage the power
supply and console, and will void the
warranty.
NOTE: The following discussions of AC outlet wiring are
written for U.S.A. and Canadian power systems, al-
though the principles generally apply worldwide. In
other areas, however, be sure to check local codes for
specific wiring standards.
4.2.3 How To Obtain a Safety Ground
When Using a 2-wire Outlet
Two-wire AC outlets do not have a hole for the
"safety ground" prong of a 3-wire power cord. A two-
wire to three-wire AC adaptor is required if you want to
use one of these two-wire outlets with the three-wire AC
plug on your sound equipment. These adaptors can
maintain a safe ground for the sound system if you
connect the loose green wire on the adaptor to a
grounded screw on the two-wire outlet. How do you
know whether or not the screw is grounded?
1. Connect the adaptor's green wire to the screw on
the two-wire outlet.
2. Plug the adaptor into the outlet.
3. Plug in your three-wire AC outlet tester into the
adaptor. The AC outlet tester will indicate whether
the screw is grounded.
If the screw is not grounded, connect the adaptor's
green wire to some other ground point in order to
maintain a safe ground for your system. If the
outlet tester indicates a good ground but reversed
polarity on your two-wire to three-wire adaptor,
sometimes you can reverse the adaptor in the outlet
by pulling it out, twisting it a half-turn and recon-
necting it; this may not be possible if the outlet or
adaptor is "polarized" with one prong larger than
the other.
Figure 4-1. Testing a 2-wire AC Outlet
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