"Puddin' Man" wrote in message
...
On Thu, 21 Dec 2006 13:31:22 -0600, CJT wrote:

Puddin' Man wrote:
On Thu, 21 Dec 2006 09:48:39 -0500, "The Streets"
wrote:


"terry" wrote in message
egroups.com...

HeyBub wrote:

There are two phases dropped to the house, 120 each. If you lose one,
you
still have the other. ....................... snip ...................

Also: While agreeing that the term 'phase' is sometimes used
........................

More correctly there are two 'legs' which are the opposite ends of the
same centre tapped 230 volt single phase!

Thus one can be considered (sort of, although incorrectly as far as AC
is concerned) as being plus 120 volts and the other as neg. 120 volts
and therefore about 240 volts between the two of them; which is used to
power heavy y items such as water heaters, electric cooking stoves
etc.

If the the two wires were really different phases they would have
voltages 120 degrees apart and there would be a peculiar voltage
between the two. Not the 230/240 volts (180 degrees with the two ends
always of opposite polarity) expected.

Same thing happened to my neighbours garage; they lost one side (or
leg) of the 230 volt supply. The 'electrician' they hired came over to
my house to borrow a multimeter and I went over and checked it for
them! Utility company fixed a defective over head drop later that day.

Losing one leg is not all that uncommon, at least around here. I've
seen
this at least three time in the past year -- all problems that the local
utility
had to fix. As another poster has mentioned - the tip off is if every
other
circuit is off. Also, be careful of back feeds through 220v appliances
like
ranges, water heaters and dryers.


I'll bite.

Suppose I've got a (residential) 200A main breaker panel, and the
street power fails.

I switch off the main breaker and use a gas powered 40A generator
to backfeed the 30A (220v) circuit for the elec. dryer.

What can I expect? Live circuits, dead circuits? Overload
conditions??

That depends where you connect, and which breakers are "on."

There's a good chance you'll energize the whole house unless
you're careful, which might very well overload your generator.

What you suggest is _very_ dangerous. You should have a
proper transfer box.

Suppose, in an emergency scenario, I pick a couple 15A circuits
and switch all the other breakers off? Safe?

If you do it properly, and your circuit breakers work properly, it is safe.
If someone gets hurt while you are doing something illegal you are in very
deep trouble. Since a transfer switch costs maybe $150 and takes a couple
hours to install, it is not a risk I am willing to take.

Its sort of like driving without your seat belt on. It is safe (after all,
how often do you have a collision?) but it is just not smart.