Honda EU20i Owner's Manual page 34

Connect the cable connectors and ground terminals of the
2.
receptacle box for parallel operation to the generators and secure
the cord clamp to handle.
Place two generators at least 1 meter (3 feet) away from each
other during parallel operation.
Route the wire through the handle and clamp it to the handle
using the band.
Take care not to slacken the wire toward the starter grip side.
Connect the longer wire to the generator on which the receptacle
box for parallel operation is not installed.
Do not set the generators with the exhaust side face to face each
other.
CABLE
CONNECTORS
GROUND
TERMINAL
BAND
3. Connect the ground terminal of one generator to the ground.
When an appliance is connected to the ground, connect the
generator to the ground as well.
32
At least 1 m (3 feet)