[conspire] Fade and open Neutrals

[Texx]

When ATT stitched the country together with microwave, (1940s) the term
"fade" came up.
During inclement weather, rain & fog can dissipate, refract or absorb RF
energy.

I dont know if the term was used in the 30s with the first successful UHF
systems came online.

One of the reasons that ham radio has so much microwave spectrum, is that
the experts in
the early 1930s knew for a fact that radio frequencies above 30mhz were
useless.
By the late 30s, the hams had proven them wrong.  They even made a liar out
of Davy Sarnoff!

I dont know when the military started using the term.
I believe the military was the first to use the term "snow fade", however.

Later on, the satellite tv trade picked up the term.

Before the ATT microwave net was built, significant long distance
traffis was send via
bundles of coaxial cables, each one carrying multiple frequency RF channels.
They started with "A carrier" and Im sure you all heard of "T" carrier.
T carrier travveled across copper long before it went over fibre.
The coax network actually lived longer than the microwave net.

There was a problem with picks & shovels digging up coax bundles back in
the 30s & 40s.
The term "Backhoe fade" began not with fibre, but with the advent of the
backhoe itself.

This is hard to explain without a marker board, but here goes:


The top of the pole is the "primary" and could be anywhere from 4kv (4000)
to 22kv.
The potential is wire to wire, and not against the earth, but you could
still read a voltage.
The proper path is wire to wire.

Primary feeds a step down transformer, so we take 4000 and step it down to
240 volt wire to wire.

This secondary winding has a tap at the centre point.
At the pole this "neutral" tap is bonded to earth.
This is why you have 3 wires coming to your house.

In the US, "3 phase" in residential is rare, although more common in Europe.

Im talking US single phase here.

By the time the service line gets to your fuse box, the Neutral is probably
about 15 volts above earth.

The 2 hot wires are 180 of of phase from each other.  They are opposites.
When the first hot is at maximum + the other is at maximum - and vice versa.
Do NOT call these 2 hots "phases"!  This is NOT TRUE!
This is a common mistake and a great way to fail your AC theory exam or
your electrical license.

Most of the plugs in your home are wired between Neutral and one or the
other of the hots via a fuse or breaker in between.

Heavy duty loads might be 240v wired between both hots, sometimes with a
Neutral as well (stove or dryer)

Because Neutral is THEORETICALLY at earth, many appliances had their
chassis wired to Neutral.
Of course, if someone put the plug in backwards, you now had a HOT CHASSIS!

Heres where AC gets weird.
With DC you need a complete path, source, load and return.

AC can pass thorough a path that DC wont, because AC will pass over a
capacitive region.
This means that in DC holding the hot, without a return, no current will
flow.
In AC, contacting the hot, there is a capacitive path to Neutral/earth
through the air.

The ultimate solution was to install a separate ground rod at the panel and
run a ground to each outlet.
Appliances now tie chassis to the earth lead rather than the N and this
shocks fewer people.

If you lose the Neutral service to the house but still have 2 hots, current
flows through1 hot
through the leads on that hot to neutral.
With no way back to the transformer due to the broken N lead, the current
then flows through
the loads that are wired to the other hot to make the path back to the
transformer.
While this does put 2 120 volt loads in series across 240 volts, weird
things happen.
Appliances that are on at this point in time can be damaged and the pole
transformer can also be damaged.

Again, I can explain this on paper or a drawing board better than I can on
here.

An example of this was when working on Sullys place, I was reading 2 volts
across outlets.
Part of the problem was an open neutral between the breaker panel ad the
oiverhead light.
The other problem was that most of the outlets were slaved off the lighting
circuit.

Sharon was quite surprised to walk in and find the lights working for the
first time in 10 years.


-- 

R "Texx" Woodworth
Sysadmin, E-Postmaster, IT Molewhacker
"Face down, 9 edge 1st, roadkill on the information superdata highway..."
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