[AMPS] 240VAC Amplifier Wiring

[Eric Moore]

> It is potentially dangerous not to connect the cabinet of U. S. built
> amplifiers to the Neutral wire.  This is true for 120v as well 240v
> operation.

I have to take exception to this statement.  The cabinet has to be connected
to only an equipment ground, not the neutral, per code, since these
amplifiers are not marked  "double insulated" by UL.
The neutral is only used as a current carring conductor, and only needed if
120V control power is needed inside the amplifier, which does not include a
tap for 120V on the transformer.

The 1999 NEC states: (cut directly from the CD-ROM)

250-114. Equipment Connected by Cord and Plug

Under any of the conditions described in (1) through (4), exposed
noncurrent-carrying metal parts of cord- and plug-connected equipment likely
to become energized shall be grounded.

Exception: Listed tools, listed appliances, and listed equipment covered in
(2) through (4) shall not be required to be grounded where protected by a
system of double insulation or its equivalent. Double insulated equipment
shall be distinctively marked.

1. In hazardous (classified) locations (see Articles 500 through 517)
2. Where operated at over 150 volts to ground

Exception No. 1: Motors, where guarded, shall not be required to be
grounded.
Exception No. 2: Metal frames of electrically heated appliances, exempted by
special permission, shall not be required to be grounded, in which case the
frames shall be permanently and effectively insulated from ground.

3. In residential occupancies

a. Refrigerators, freezers, and air conditioners

b. Clothes-washing, clothes-drying, dish-washing machines; information
technology equipment; sump pumps and electrical aquarium equipment

c. Hand-held motor-operated tools, stationary and fixed motor-operated
tools, light industrial motor-operated tools

d. Motor-operated appliances of the following types: hedge clippers, lawn
mowers, snow blowers, and wet scrubbers

e. Portable handlamps

4. In other than residential occupancies

a. Refrigerators, freezers, and air conditioners

b. Clothes-washing, clothes-drying, dish-washing machines; information
technology equipment; sump pumps and electrical aquarium equipment

c. Hand-held motor-operated tools, stationary and fixed motor-operated
tools, light industrial motor-operated tools

d. Motor-operated appliances of the following types: hedge clippers, lawn
mowers, snow blowers, and wet scrubbers

e. Cord- and plug-connected appliances used in damp or wet locations or by
persons standing on the ground or on metal floors or working inside of metal
tanks or boilers

f. Tools likely to be used in wet or conductive locations

g. Portable handlamps

Exception: Tools and portable handlamps likely to be used in wet or
conductive locations shall not be required to be grounded where supplied
through an isolating transformer with an ungrounded secondary of not over 50
volts.

73,
Eric
K8CCA




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