Dan Richardson wrote:

On Wed, 18 Jan 2006 08:24:40 -0500, Amos Keag
wrote:


The Astron RS-35 power supply connects utility power neutral to the
case. It also connects the 13.8 volt return to the case. [This is
commercial common practice but is prohibited in Military Systems
design.]


You've tweaked my curiosity what does the military do?

73
Danny, K6MHE

The general no pun intended Military design requirement is the the
equipment cases carry no intentional or credible fault currents.
[Therefore no inadvertant shocks, in MIL STD terminolgy no personnel
RISK, from a hot chassis]. [RISK is assign for personnel, HAZARD for
equipment]. Accordingly, the cases and circuit returns are isolated
typically by a 500K resistor. There is one system ground point, not a
distributed grounding system.

RF circuit design includes isolation between onbly for the output from
the low level circuits. Coax shields, shielding on shielded
circuits/wires carry no intentional currents and to the maximum extent
possible no fault currents.

Example: the output stages of a 5 GHz telemetry transmitter is on a
circuit board that is physically isolated from the low level stages and
the power source. The isolation may be either capacitive or inductive
coupled; in my last design [c.a. 1986] we used 1/4 wave stubs on the
same board, top circuit to bottom circuit, woking against two separate
returns [top surface base copper versus bottom surface base copper]

In the Nuclear safe environment for example, the primary and secondary
of power transformers MUST be 100% isolated and each winding separately
shielded with the shields connected independently to the chassis.
Therefore a transformer short circuit on the primary cannot propagate
through to the secondary. Or, a primary short to chassis cannot
propagate to the secondary. And the design MUST include 100% absolute
disconnect from primary power in the event of a transformer failure or
power out of spec condition. The requirements go on and on and on ...

Bottom line, equipment cases carry no current, share no current carrying
path [exception is RF output stages only].

So, the ASTRON RS 35 is not suitable for MIL usage. Now the ASTRON
becomes 100% MIL suitable with the removal of just one [1] jumper in the
supply [the connection from 13 volt return to chassis. The secondary of
the PS is 100% isolated from the primary and the regulator circuits are
100% isolated from chassis]. But, the ICOM radios being powered also
violate the MIL requirements and corrupt the system. Remember, HAM
equipment is generally operated in COMMERCIAL circuits and must comply
with local electrical codes.

In article ,
Amos Keag wrote:

Ground Loop. Took time to find it though.

The Astron RS-35 power supply connects utility power neutral to the
case. It also connects the 13.8 volt return to the case. [This is
commercial common practice but is prohibited in Military Systems
design.]

*yoicks*!

The latter, I can believe is common practice.

The former - tying the powerline neutral directly to the case -
strikes me as being *extremely* contrary to electrical code and common
sense. It'd turn the supply into a deathtrap-waiting-to-happen if it
were plugged into an outlet having the hot and neutral reversed... and
these are (alas) not at all uncommon.

Now, having the utility power safety ground wired directly to the
case, I can very well believe... this is quite common.

--
Dave Platt AE6EO
Hosting the Jade Warrior home page: http://www.radagast.org/jade-warrior
I do _not_ wish to receive unsolicited commercial email, and I will
boycott any company which has the gall to send me such ads!

Dave Platt wrote:

SNIPPED

*yoicks*!

The latter, I can believe is common practice.

The former - tying the powerline neutral directly to the case -
strikes me as being *extremely* contrary to electrical code and common
sense.

It happens at the service panel! White [COMMON] is connected to the non
current carrying bare wire at a many input terminal block. The block is
then connected to an 8 foot ground rod installed by the utility or your
electrician.

It'd turn the supply into a deathtrap-waiting-to-happen if it
were plugged into an outlet having the hot and neutral reversed... and
these are (alas) not at all uncommon.

Agree, I found three miswired circuits in this house. I was present at
the house inspection and ran the tests myself. The mis-wiring was
corrected the day we moved in. [Radio Shack sells a simple tester for
this. It is worth checking every circuit in your house or apartment].


Now, having the utility power safety ground wired directly to the
case, I can very well believe... this is quite common.

Maybe my terms are not up to date.

My electrical service connection is 3 wire 240 volts AC at 60 Hz. Within
the distribution panel RED is connected to one feed; BLACK is connected
to the other feed and white is connected to the common connection
[return]. The common connection is then distributed throughout the house
as the bare wire in standard wiring. The common, white and return,
connection is connected to an external earth connection [ground] by an 8
foot ground rod.. So, the WHITE wire serves as return for both RED and
BLACK circuits and has a single earth connection. So, your 3 prong
socket contains connections to power as follows: HOT [either RED or
BLACK] circuit, RETURN [WHITE] and GREEN [GROUND] [supposedly zero
current carrying. A GFI works on this part of the connection].

In the ASTRON RS 35 the primary wiring has the GREEN connected to the
chassis. The BLACK/WHITE go to the transformer primary. This is fine.

The secondary, transformer isolated, has the 13.8 volt return connected
to the chassis. It is now possible for the chassis to become part of the
current carrying circuit, 13.8 volt return to utility WHITE wire to
groud wire. The 13.8 volt return now runs to the ICOM 756 Pro II, ICOM
746 and Kenwood TM-G707. The cases of the three radios and the ASTRON
are connected to a common return on the operating table [1/2 inch copper
pipe that connects directly to the service panel common return/ground
point]. The cases of the three radios are connected together by the
braid on the various lengths of coax and the 13.8 volt return. ERGO, a
ground loop among the 13.8 volt return, the coax braid, equipment cases
and the utility ground.

With a nearby lightning strike that blew the utility 3 phase transformer
and affected approximately 50 consumers there are several possible
causes of trouble. Among these are imbalance in utility service [i.e.
the 240 into the house becomes seriously imbalanced] a lightning induced
magnetic transient that couples to all ground loops, or my system was
still connected to antennas and power.

I had ALL connections to antennas and power plugs removed except the 1/2
inch copper pipe earth connection at the service panel. My neighbors
lost garage door openers, multiple tv sets, numerous telephone circuits,
numerous internet circuits, COMCAST had to rewire approximately 1/4 mile
of cable tv in front of the house, several homes lost expensive stereo
and sound lab setups. In my house all ground fault interuptors
activated. And two circuits in my PRO II exploded to charcoal with dust
and stench. The LAN blew up, and one computer was lost.

My station was the equivalent of being mounted on a copper sheet, each
chassis connected to the copper sheet with bond wires, the 13.8 VDC
return connected to the copper sheet [making a loop into the circuits]
and the copper sheet was/is directly connected to earth/ground at the
power utility panel.

Since I was not connected to POWER or antennas, and the connection to
utility common and earth ground are installed to code [circa 1978], I
concluded a ground loop that I subsequently found and measured [after
the fact of course] was the susceptibility.

Conclusion: Nearby or direct strike lightning causes havoc. Solution:
have good insurance. I recovered replacement costs for all except the
depreciated computer. I have a specific INSURANCE SCHEDULE on my radio
and camera equipment.

Sorry your email address dosn't work but thanks for clarifing the
hookup i must have missread the original statement you made whereby i
thought you said the pro was completely disco i totally understand if
it had anything connected that explains it!!

however you confused me more so, now that you said the pro getting fried
somehow 'saved' your other gear from being damaged... i can't see how
that happened unless you feel the rig it self actually absorbed ALL the
energy i presume the odds of that are slim

so can you help unconfuse me??

and it was great to read about how the mil does stuff pretty cool

again sorry about your damage hope you had arrl rig insurrance


m



In article ,
Amos Keag wrote:

ml wrote:

Hi

FYI, seems your email addr here dosn't work, if it's a real one

Dear Amos

i saw your post and hope you wouldn't mind if i asked you a quick
quesiton


Your Icom that was damaged, was unplugged from everything so how did
lightning 'get to it'??

I was kinda distrubed trying to figure it out
\

Ground Loop. Took time to find it though.

The Astron RS-35 power supply connects utility power neutral to the
case. It also connects the 13.8 volt return to the case. [This is
commercial common practice but is prohibited in Military Systems
design.] Although everything on the operating table was isolated from
the utility power and external antennas, everything was connected
together by coax braid, connections to the operating position common
'ground', and the 13.8 volt return.

Remember, this strike caused large area damage. Close to 50 homes
suffered some damage. Several homes took up to 6 weeks to have their
internet functioning again.

The lightning strike tripped all [ALL] ground fault interruptors in the
house. The ground loop in my system connected chassis and power returns
and coax cable together. The weak link were circuit boards in my 756 Pro
II filter and tuner. The boards VAPORIZED. Smoke all over the place.
Pungent smell, etc. That failure protected my IC-746, Kenwood TM-G707,
etc from damage. [Expensive fuse!!]

I wonder if it also protected my swimming pool pump and heater from
damage grin?

Robert 11 wrote:
"For either unit is the arrester placed between the Balun and the
antenna, or between the Balun and the radio? Why?

It likely is superflous.

Coax connectors make lightning arrestors of sorts. They clamp voltage to
the arc sustaining voltage (less than 100 volts), once they fire. If you
are transmitting, r-f may keep the arc alive. Broadcast transmitters
sense the arc and shut the transmitter down for an instant to quench the
arc. Communications radios usually don`t bother as their transmissions
are sporadic and usuallly short.

Remember, coax shield is impenetrable to r-f. D-C conducts right
through. R-F does not due to skin effect.

In countless VHF antenna installations atop tall towers around rhe world
we never used a Polyphaser or similar arrestor on the coax, yet never
had damage to radio antenna circuits, even to transistorized radios.

We always used folded driven antenna elements. We grounded the coax at
the top and bottom of the antenna tower. The tower due to its size has
lower surge impedance and carries the bulk of the lightning current to
ground. The tower is well grounded.

We found it necessary to use brute-force pi-filters on every power wire
feeding the radio including the neutral wire. We used tower lighting
chokes in the pi-filters to cary the current required to power the
radios. We shunted the filter inputs and outputs to ground with MOV`s
(across the a-c capacitors).This limited surge voltage on the radio and
on the powerline. It eliminated all damage to the power supplies in the
radios. These filters were found necessary only when transistor radios
were introduced. Before that, the grounded antenna system sufficed for
tube-type radios.

Best regards, Richard Harrison, KB5WZI

Peak current of 100,000 A for 1 microsecond in wire with resistance of
(say) one ohm gives energy of 10,000 Joule.

If the wire is No. 12, that would warm it up pretty well, but vaporize?

Where have I gone astray?

TIA

Chuck

chuck wrote:

Peak current of 100,000 A for 1 microsecond in wire with resistance of
(say) one ohm gives energy of 10,000 Joule.

If the wire is No. 12, that would warm it up pretty well, but vaporize?

Where have I gone astray?

TIA

Chuck

So far, correct. But, that 10,000 J equates to 1E16
[100,000,000,000,000,000] watts peak power.

There is a thermal shock wave that occurs in the wire. There is a
transient magnetic wave in the wire.

The failure mechanism has been empirically correlated to peak power
times [pulse width^1/2].

The wire, or portions of it goes away!!