I believe the 4 wire is the "new" standard whereas in the 60's three was enough. I was told that the 4 wire convention uses two grounds instead of one (hence the 4th wire). I would just hook the black and white wires to the plug's line and neutral and hook your green wire to the green (ground lug) on the plug and leave it at that. Lots of appliances still use only 3 wires for 240VAC. I believe .... I was told ...
Know NEC, do NOT provide guesses about AC residential wiring.
The Drake L-4PS has installed a 3 wire cable. It is a Triangle cord 14-3 spt-3.
It is a grey cord with two grey 14 Gauge wire and one green ground cord.
North America AC electrical wiring is standardized by NEMA (National Electrical Manufacturers Association) Connectors for residential and light/commercial buildings.Familiarize yourself (memorize) proper usage.http://en.wikipedia.org/wiki/NEMA_connector
Your Drake L-4PS power cord (3 wires, 14 AWG) for traditional 240 VAC wiring is normally terminated in a NEMA 6-15P (15 amp) Straight Blade Plug.
The wall receptacle for that plug would be a NEMA 6-20R (T-slot, accept 15 or 20 amp plugs) Straight Blade Receptacle on a 240 VAC, 20 ampere circuit breaker on your main electrical panel.
That circuit would use 2 HOT wires L1 (black) and L2 (red) and Safety GROUND (SG, green wire).
The NEUTRAL (white) wire is NOT used in this instance, since the Drake L-4PS was manufactured before 1996 and has an AC transformer with 240 VAC primary (No line side 120 VAC components).
I have 200 amp main electrical service and have run a box over the radios.
I have 4 wire cable running from the circuit box terminating in a 4 wire receptacle.
The usage of 4 wires (conductors) is not unusual for NEW 240 VAC circuit wiring by licensed electricians.IF this is an existing outlet, is this a Dryer outlet in a laundry area ?
What is the AWG of wire used and amperage of circuit breaker for this circuit?PLEASE identify the Wall Receptacle at this location. Is it a NEMA 14-20R receptacle ?
The National Electrical Code (NEC) was changed in 1996, introducing NEW requirements for wiring of 240 VAC appliances (electric range, combination washer/dryer) that have 120 Volt and 240 Volt components.Ranges, Dryers and Ovens Now Require 4-Wire Receptacles and Cords. NEC Section 250-60
It dictated that all Dryer (laundry) and range ovens (kitchen) receptacles installed after 2000 must have a four-wire type connection (NEMA 14). Some appliance companies moved to the new connector before 2000.
Therefore, dryers and range ovens manufactured from 1996 to 2000 can have either connector.
The four-prong connector (NEMA 14) has a separate GROUND wire plus Three Poles.
Two of the poles are HOT wires, and the third is a NEUTRAL wire. They still have a 240-volt rating.
The stipulation requiring the switch to four-prong connectors appears in Article 250, Section 140 of the National Electric Code.
The NEMA 14-30 (30 amp) and 14-50 (50 amp) are Four-Prong connectors used for these appliances. They have a rating of 250 volts, and replaced the previous NEMA 10 connectors used from 1947-1996.
==Once we have some answers (above) ... specific to your situation ... a specific answer can be provided.
73 de Greg, w9gb