Canon EOS 7D Instruction Manual page 130

External Speedlites
Using Non-Canon Flash Units
Sync Speed
The camera can synchronize with non-Canon compact flash units at
1/250 sec. and slower speeds. With large studio flash units, since the
flash duration is longer than compact flash units, set the sync speed
within 1/60 sec. to 1/30 sec. Be sure to test the flash synchronization
before shooting.
PC Terminal
Cautions for Live View shooting
If you use a non-Canon flash with Live View shooting, set [z Silent
shoot.] to [Disable] (p.137). The flash will not fire if it is set to [Mode 1]
or [Mode 2].
If the camera is used with a flash unit or flash accessory dedicated to
another camera brand, the camera may not operate properly and
malfunction may result.
Do not connect to the camera's PC terminal any flash unit requiring 250
V or more.
Do not attach a high-voltage flash unit on the camera's hot shoe. It might
not fire.
A flash unit attached to the camera's hot shoe and a flash unit connected to
the PC terminal can both be used at the same time.
130
The camera's PC terminal can be
used with flash units having a sync
cord. The PC terminal is threaded to
prevent inadvertent disconnection.
The camera's PC terminal has no
polarity. You can connect any sync
cord regardless of its polarity.