[Amps] 3 or 4 wire 240v for amp

[RadioMB@aol.com]

Hello,
  I have just moved to a new house in FL. I had a 240v line run to the ham 
shack. The box contains 4 wires. The normal red and black hot wires, a copper 
ground wire, and a fourth white wire. Is the white wire a neutral wire? Since my 
Drake L-7 has 3 wire cord (two hot and the ground wire). Do I now use the 
white neutral wire or the copper ground wire as the third wire in the line cord? 
When adding the new plug to the three wires from the Drake do I just not use 
the fourth wire? Does this meet code for a 4 wire system? Thanks for your 
replies, looking forward to using the L-7 again.

73  Mike  WD5GLW