THESE NEWS ITEMS MOTIVATED CHUCK KRALY, K0XM, TO WRITE THIS MESSAGE:
I just saw this one on the news, and had to write a this message to be
passed on to the ham community, especially the newer hams.
We lost another ham today, and it is a very sad event. The parties
involved, were installing a Comet FIBERGLASS antenna, that came in
contact with a single 7620V power line. Now how do I know what the
exact voltage is? I built and maintained the substation that fed this
circuit. I spent 27 yrears as a substaion technician for the Board of
Public Utilities. I am still in this field. So, I feel I have some
experience in what I am passing along.
In a nutshell, the location of the accident was a few blocks from the
substation. The wires you see going thru the residential areas are AT
MINUMUM 7200 volts from each wire to ground, and between any two of
them is 13,800 volts. This is nothing to play with at any time. I have
seen a fault TOTALLY vaporize 1" copper buss (which is solid). Imagine
what it can do to a human.
Each wire is fed from what is called a 3 phase line. From there, it
can be broken off and sent down a property line as a single wire.
Those are called "laterals" Yes, you will see a device at the break
out point, and this is a fuse. BUT the caution needs to be conveyed.
These fuses are in the 60-100 amp range. This is at 7200 volts. On top
of that, anytime a tree falls across a line, or a pole gets hit, there
is a circuit on the "feeder" at the substaion that AUTOMATICALLY
closes the fedder back in, and TRIES to restore the power to the area.
Some of these "reclosers" can operate 2-5 times, depending on how they
are set. Now from the substaion end, the protective device is set for
the full fault capabilites of the line. In the case of BPU, this can
be set at 600 AMPS, and multiples of that value. The protective
devices are set for what is called a "time" or and "instantaneous"
operation. Picture a fast blow fuse and a slow blow, and you will
understand the difference in the settings. These setting are at
multiple of the 600 amp value. So, if there is a direct short, then it
will not trip until it reaches a value at, oh lets say, 8 times that
value. So we are looking at 4800 amps. and this is at 7200 volts and
lower. So, it trips, then it energizes it AGAIN. The possiblity of
survival is slim and none.
Now remember how I said they were installing a FIBERGLASS antenna?
Well guess what. It is metal inside. Yes, fiberglass does not radiate
as we all know. Hence the metal. That is what caused the accident.
They got too close to the line (remember your 'magnetic lines of flux'
theory? If not, look it up on the web). There is a minimum approach
area that MUST be followed. This changes for ALL voltages. This
distance must NOT be broken. If it is a flashover will happen, and it
is not pretty. Electricity will find the shortest path to ground. In
this case it was a couple of men.
Folks, this is nothing to take chances with. In my almost 30 yrs as a
ham, and 27 yrs in the power utility field, I have seen way too many
"accidents." Stop, look and if it is close or SEEMS that way- DON'T.
Find another place. High voltage lines are NOT forgiving. Your life
depends on it. You always hear "it is the amps not the volts" well I
can tell you when you get at these levels, who is going to argue what
killed the person who had the accident. PLEASE ,PLEASE follow the
warnings. ANYWHERE close is too close.
Stay safe, and I hope we can enjoy many more years of hamming.
Chuck Kraly, K0XM