On Fri, 25 Dec 2015 19:31:17 -0800 (PST), John G
wrote:

But how common is it for there to be no "main switch," as is the case
with this installation: feed directly from the meter to the bus bars
with no switch or main breaker to enable safer working in the panel?

Not common at all. It's a code violation, unless there are only 6
breakers in that panel, in which case they can serve as the disconnect.
Are you sure there was no disconnect near the meter?

There were 10 or 12 breakers. I saw no sign of any other breaker. And
there was only one combined ground/neutral bar in the panel -- white and
bare wires to the same bar -- so it couldn't count as a sub-panel.

Is it possible that it was OK when the house was wired originally --
long ago -- (or rewired on an earlier occasion) and the only rewiring
that was done in 2011 was from the panel on -- retaining the original panel?

There is no legal scenario where you will have a panelboard without a
service disconnect. Even in those rare cases where you can have the
1-6 disconnects, they all need to be "service rated". Until very
recently a "lighting and appliance" panelboard required no more than
2. (That was to accommodate "split bus" panels).
A couple cycles ago they removed the distinction about the types of
panels.

BTW are you sure there isn't a back fed breaker in that panel that is
acting as the disconnect? (probably not legal but happens sometime)

I could see the conduit coming down the outside wall from the meter and
going through the wall, and in the basement heavy-gauge conductors
coming through conduit into the top of the panel and connected directly
to the bus bars. There were two pairs of ganged breakers: a 30A pair and
a 40A pair; one for the range and one for the dryer, I think.

If there's a Service Disconnect anywhere, it's well hidden.

I didn't see an inspector's label on the panel, but ours didn't have one
either (but it's a different jurisdiction, so that may not mean anything).

Perce

There is such a thing as a split buss panel. The upper part would have the multi-gang breakers and a main breaker for the lower part. The upper part is not required to have a main breaker because it has six circuits or less.
Might be the case some places, but would never pass here.

Used to have some "flat rate water heater" systems where the water
heater bypassed the meter, sometimes also with a remote switching
system that let the power company shut off the water heater under high
demand periods - and even it had to have a fused disconnect. (which
could be a "split buss" panel of sorts)