According to Chris Lewis :
According to zxcvbob :

But from the outbuilding's perspective, the box is a service entrance
and must be listed as such if it is fed without a separate grounding
conductor (which is what I think you were proposing.)

Maybe the rules are different up there in Canada, but I installed a
3-wire 240/120V feeder to an outbuilding 1.5 year ago and had it
inspected. The incoming grounded neutral wire is bonded to the panel,
and I had to add a grounding electrode.

Think logically about it for a moment - pull full amps on one side
of the subpanel. You'll pull the neutral 3V or so way from ground
potential. Yet, you have a grounding electrode at either end of it.
Means current flow between grounding electrode - in some cases
several amps in normal operation. Corrosion of grounding electrodes.

Worse, sever the subpanel neutral. Now the neutral return from the
whole subpanel is trying to go through the grounding electrodes, and
depending on electrode-to-dirt resistances, every grounded device
connected to the subpanel could present frame voltages relative to
ground as much as 120V.

Then I realized, if you _don't_ bond the grounding electrode to the neutral
in the outbuilding with a three wire feed, a hot ground short in the outbuilding
has to push the fault current thru the dirt. Which in most cases would NOT trip
a breaker.

Which is probably the worse of the above evils.
--
Chris Lewis, Una confibula non set est
It's not just anyone who gets a Starship Cruiser class named after them.