IBM 3270 Hardware User's Manual page 48

3. CAUTION
Do not make this connection during an
electrical storm.
Attach the coaxial cable from your hosts'
3274 Control Unit to slot 1 on the back of
your system unit. Slot
1
is the rightmost slot.
4. CAUTION
Use a properly grounded outlet to avoid
electrical shock.
Plug the system unit into a grounded wall
outlet.
Chapter 2. Setting Up and Checking Your 3270 PC 2-31