In article , " wrote:
About 10 years ago I bought a Square D 100 amp electrical panel and
some breakers at Home Depot and had an electrician replace my old
box. I suspect that one bus is not energized because last night, a
number of lights and outlets throughout the house stopped working.
After I flip the main breaker, remove the cover, and verify that both
incoming hot wires are tight, what else can I check for?

Danger Danger Will Robinson!

Even after you flip the main breaker, the incoming hot wires are STILL HOT,
and you can be fatally shocked from touching them. Some main breakers use
standard screws to hold down the wires; the plastic handle of a screwdriver
affords adequate insulation. Other main breakers use socket-head screws; if
you stick a hex key (aka Allen wrench) into one of those, you may turn
yourself into a crispy critter.

The very first thing you should do, even before flipping the main breaker, is
check the voltage between the two incoming hot wires. If it's not somewhere
between 220 and 250, then call your utility company -- it's their problem.

If it *is* between 220 and 250, then the problem is in your house somewhere.
With the main breaker *on*, measure the voltages between the two buses (should
be approximately 240) and between each bus and ground (should be approximately
120 each time). If not, the main breaker needs to be replaced -- and you
*still* need to call the utility company. As noted above, those incoming wires
are hot. You want the utility company to pull the meter before you change the
breaker, and reinstall it after you're done.