The 30M-50F adapter allows you to plug your 50 amp power cord into a 30 amp RV power source. It adds versatility to your electrical hookups. If RV is wired normally it prevents the use of the 20 amp side of RV panel but allows use of the 30 amp side which helps prevent tripping of the 30 amp outlet service breaker at the post.. They are Heavy-duty 10/3 ST power cords with 3-wires plus ground.