Here you will find Dryer and Range pigtails and 30 and 50 amp cords.
The National Electric Code requires 4-wire cords and plugs in all new installations and every mobile home [trailer] and recreational vehicle [RV].
For maximum safety, use a four-wire cord and do not bond the grounded
conductor ["neutral"] to the frame ground in the appliance.
But if you are using an existing three-wire circuit that you cannot
upgrade to the current standard, then verify that the frame ground (sometimes
a green screw or wire, or bare jumper) is bonded to the "neutral" (white wire,
silver screw) in the appliance.
Test appliance and circuit to verify proper installation and effective grounding.
NEC 2002-2005 Article 250.142(B) prohibits grounding via the grounded
conductor ["neutral"] of load-side equipment frames except as
permitted for existing installations only per Article 250.140
and only if that branch circuit originates from the service equipment.
A new installation must have an equipment grounding conductor in
addition to the grounded conductor, i.e., four wires.