On 12/12/2013 7:13 PM, The Daring Dufas wrote:
On 12/12/2013 5:10 PM, Pete C. wrote:

Nate Nagel wrote:

On 12/12/2013 05:49 PM, Pete C. wrote:

The Daring Dufas wrote:

On 12/12/2013 3:12 PM, Pavel314 wrote:
I recently hooked my generator into the main box, with a lock-out
device of course. If the power goes out, I'll turn off the main
switch to the street manually and flip to generator power.

The problem is how to know when the street power is back on, other
than looking down the street to see if the neighbors have lights on
again. When I just ran extension cords from the generator to the
well, refrigerators, etc., during an outage, when the power started
up again various lights would light up around the house as they had
been on and were still street-connected. Now, everything is
disconnected from the street.

It would be nice if there were some sort of induction device I could
clamp on the main line coming in from the street which would light up
an LED if there were power in the line, but if there's no current
actually flowing I don't see how it would pick up the potential
voltage in the line. Is there such a thing available or will I have
to invent one?

Paul

Some utility meters have LEDs that indicate there is power. A
'non-contact' voltage tester might indicate if held next to the meter in
the right spot. I don't know of a simple method other than that I would
use to show the power is back on.



Years ago, I installed some taps for roadies to hook up lights for the
stage in a night club. To let them know that the power was on the box
at the end of the conduit, I installed a neon pilot light for each
phase. In your case, you can get voltage sensors that can be wired to
an alarm or flashing indicator light to let you know when your main
power comes back on or just wire up a standard wall light or an exit
sign with your own panel reading "POWER". ^_^

TDD

Along those lines I installed a pair of neon indicators mounted to a
metal box cover, installed in a metal electrical box and connected
to my
panel with a metal offset nipple. They are connected to the input side
of the main breaker directly, being ~18ga wire and enclosed in metal
enclosures if something fails they are self fusing and can't start
anything on fire. I use an interlock kit for the generator connection
(Square D kit in a Square D panel).

So what happens if the #18 wire acts as a fuse? There are a few thousand
amps fault current available at the service. A fault of a few thousand
amps through #18 wire will continue an arc over a rather long distance.
And what will happen with the 'spring' in the wire - where will the
wires go when they are broken at the arc?


That sounds like a good idea, and probably what I would do were I trying
to do something like this myself, I just wonder if it's code compliant?

Nope.


I'm not sure on that, code mostly is concerned with fire risk, and when
enclosed in all metal conduit and box the heat produced in the mS it
takes to vaporize an 18ga wire at fault currents couldn't possibly set
anything outside the enclosure on fire.

It is a rather different case. But downtown there was a maybe 8 story
building that had a fire. They tore it down to the first floor and
basement, installed a ramp, and used what was left as a parking lot. The
original service remained (208/120V), far larger than needed, with 6
parallel sets of service wires. They cleverly stored salt for the ramp
on top of the service switchgear. The service wound up with an arc-fault
and burned down. Some of the service wires burned back into the supply
conduits. Some of them were live in the conduit. Some wires welded to
the conduit and the utility couldn't pull them out with a comealong.
(The wires were protected by "cable limiters" at the utility transformer
vault.


I always put an inline fuse holder on the power feeding the indicators
and install a 1 amp or smaller fuse.

So what happens if there is a large fault current through the fuse? Like
the wire, with high current the arc continues and the fuse and fuse
holder blow up. Fuses have a rating for available fault current. In most
applications on a branch circuit you don't think about it. When you have
high fault currents available you have to (and are required to by the NEC).

[The fuses included in some Fluke meters are rated for high fault
currents and the meters have a "category" rating for use where there are
high available fault currents.]

Is a problem likely? Don't know. But I wouldn't connect anything to the
service wire terminals.



Also, at what voltage do the neon indicators light up? e.g. will they
glow if there's say 10V on the line?

A quick look on Digi-Key seems to indicate a 105-125VAC rating on many
indicators. I don't see a clear indication that 105VAC is the threshold,
but I expect it's not too far below that. For more $ you could install
basic panel meters, and probably inline fuses on them, though I'd still
use the indicators as well since you can check them from a distance to
see if utility power is back.


I seem to recall 90vac as the lowest voltage that will light one of
those small neon pilot lights. ^_^

TDD

NE-51 (bayonet base) and NE-2 (wire lead) are common neon pilot lights.
They trigger on at about 65V (and would be used at a higher voltage).
Neon lamps must have a series resistor which is built into the
assemblies above.