ECN Forum Forums Code Related Discussion Canadian Electrical Code Topics 3wire and GFI's

I would say that GFCI just filters current. So Line from panel to the load to the shared neutral. What happ when power travels from opposite side. Unbalanced load flows only behind GFCI. If in CEC doesn't say it clearly, well you can and can't. That right inspectors reserve for themselfs.
If you don't see something a lot in practice people are sceptical about it. GFCI should be checked every month. Not for use everywhere.
In parrallel circuits:

voltage=constant
current=variable

If you split neutral before comming to GFCI you just changed current...

...or I am just talking nonsense

A GFCI doesn't filter anything. It measures the current leaving the device on the phase wire (black) and the current returning to the device on the neutral wire (white) and then compares the two. In normal operation they should always be the same since electricity flows in a closed circuit.

If the two current measurements differ by more than a prescribed maximum amount (4-6 milliamperes), a contact inside the GFCI opens and shuts off the current flow.
So if 9 amperes is traveling through the heating elements in the toaster and 1 ampere is flowing up your arm, through your heart, down your other arm and into the faucet on the kitchen sink, that 1 ampere (1,000 milliampere) difference sensed by the GFCI will open the circuit at the device rather than stand there cooking yourself to death.