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Short Circuits

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  • zscale@retrograde.net
    Thanks for all the responses to the NMRA question. I m still considering it. I ve got so many railroad projects to consume my time and money right now, any
    Message 1 of 12 , Jan 19, 2001
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      Thanks for all the responses to the NMRA question. I'm still considering it. I've got so many railroad projects to consume my time and money right now, any final decision is still some distance off. But thank you for the info and opinions.

      Here's an unrelated question. If a short circuit occurs at the track, is there immediate damage to the loco and/or power pack, damage only if the short is left uncorrected for minutes or hours, or just an embarrassing break in train service until the operator finds the problem?

      For example, if a loco travels around a reversing loop and back across the insulated joint onto the main line, but the main line's polarity was not reversed while the loco was in the loop, what happens?

      Assume that a Z-friendly power pack is being used, with the throttle open most of the way (close to the maximum 8 volts).

      If a loco is running on a simple oval of track (no reverse loop) and a piece of conductive material falls across both rails somewhere on the oval (not in the immediate path of the loco), I assume the loco will stop or at least slow down quite a bit. Would the loco or the power pack be vulnerable to damage in this case?

      Thanks,

      Andy Hunting
    • bjkronen@aol.com
      Jeffrey: Opps. No, you are not incorrect, but there are some issues which do need a bit of discussion. ... In order to have a UL or ECMA rating, you bet they
      Message 2 of 12 , Jan 19, 2001
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        Jeffrey:

        Opps. No, you are not incorrect, but there are some issues which do need a
        bit of discussion.

        > All NA commercial hobby transformers and throttles are required to have
        > short circuit protection usually in the form of a circuit breaker.

        In order to have a UL or ECMA rating, you bet they do. House fires are no
        fun.

        > A direct short such as the ones that you described will immediately stop
        the
        > locomotive and trip the circuit breaker thereby protecting your expensive
        > trains. On most commercial electronic throttles there will also be a
        > warning light.

        Well, let's chat about that. Let's say the wiring this person used was 24 or
        26 awg wire from the power pack to the track. Lots of train stores sell that
        stuff on cute little rolls to hobbyists. Let's give it about 5 ohms of
        resistance including the resistance at the screw head terminals and track
        connectors. Since no short is ever "perfect" let's add another 5 ohms of
        resistance there. If the throttle was set to 5 volts output when the short
        occurred, ohms law say:

        Current = (5 volts) divided by (10 ohms) = 0.5 amps.

        Since that's well under the typical 1.0 amp fuse/breaker rating and actually
        still in the normal current range of a couple of locomotives dragging a load
        around the layout, I doubt the thermal breaker would ever blow. If the pack
        is one of the solid state variety, it would probably still be sitting there
        delivering a full 5 volts to the ends of the wires.

        This example suggests the wire, and the short, will be dissipating 2.5 watts
        of energy doing nothing, for a period of time if undiscovered. Eventually,
        one of several things might happen:

        1. The wire may begin to smoke, since its maximum current rating has been
        exceeded and the insulation starts to melt from the heat of the wire.

        2. If the short is "though" the truck, the wipers inside truck may get hot
        enough to melt down the sideframes, gears and other plastic parts. (I have
        two examples of that in my N scale junkbox from a large club layout when
        derailments weren't noticed fast enough).

        So how do you fix this problem?

        1. Never use undersized wire, period. Large wire will conduct enough
        current to pop the circuit breaker a whole lot faster than undersized wire.
        Wire is the cheapest part of any layout, period. 18 awg should be the
        smallest wire on your layout, even if its 2 foot across, for a really good
        safety factor. For those with roomsized layouts, 12 awg is commonly used by
        a LOT of folks, to control voltage drop at the far side, if nothing else.
        Yes, 22 awg wire works fine when everything is running normally. But its the
        unexpected events that will bite you.

        2. Try to avoid unattended operation of the trains. Turn them off when the
        phone rings.

        3. Some have used an automobile tail light in series with the output of the
        transformer to act as a current limiter. Many unattended "display" layouts
        do that. In normal train operation, the bulb is dark, and the voltage drop
        across it is minimal. When a short occurs, the extra current flow lights the
        filament, which causes the energy to be dissipated as light in the bulb,
        rather than heat in the wiring or the locomotives. That requires a bit of
        experimenting, since some auto lights are pretty high wattage bulbs and would
        not light up soon enough.

        Enough rambling.

        Bill Kronenberger
        Houston
      • TrainRunner
        ... From what I know about electronics (granted it s not too much, but it is some) I d be astonished to see 5 ohms of resistance in a wire, even including the
        Message 3 of 12 , Jan 19, 2001
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          > Let's give it about 5 ohms of
          > resistance including the resistance at the screw head terminals and track
          > connectors. Since no short is ever "perfect" let's add another 5 ohms of
          > resistance there.

          From what I know about electronics (granted it's not too much, but it is
          some) I'd be astonished to see 5 ohms of resistance in a wire, even
          including the connections, unless the connections are corroding. I'd expect
          a resistance closer to one ohm or half an ohm. Now, as far as the short is
          concerned, I'd grant that you can see any level of resistance. After all,
          it all depends on how the short is happening. So, if you were to assume
          that the average short is about 5 ohms, and the wires have one ohm, you'd be
          very close to one amp at one volt. (Though, empirically, the ammeter on my
          spikes over one amp when I simply drop a piece of metal across my tracks,
          with the voltage at about five and a half volts or so...)


          -Alex
        • Jeffrey MacHan
          Andy, All NA commercial hobby transformers and throttles are required to have short circuit protection usually in the form of a circuit breaker. A direct short
          Message 4 of 12 , Jan 20, 2001
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            Andy,

            All NA commercial hobby transformers and throttles are required to have
            short circuit protection usually in the form of a circuit breaker.

            A direct short such as the ones that you described will immediately stop the
            locomotive and trip the circuit breaker thereby protecting your expensive
            trains. On most commercial electronic throttles there will also be a
            warning light.

            No harm should come to your trains unless you have built a home made
            throttle that does not have short circuit protection.

            Cheers,
            Jeffrey
            >
            >Andy Hunting
            >

            _________________________________________________________________________
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          • Ole Rosted
            On Fri, 19 Jan 2001 22:05:14 EST, Bill Kronenberger wrote: [snip] I know Bill K. well enough to know that what he says rests on a solid foundation. But I do
            Message 5 of 12 , Jan 20, 2001
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              On Fri, 19 Jan 2001 22:05:14 EST, Bill Kronenberger wrote:

              [snip]

              I know Bill K. well enough to know that what he says rests on a solid
              foundation.

              But I do not understand this short-thing completely.

              >1. The wire may begin to smoke, since its maximum current rating has been
              >exceeded and the insulation starts to melt from the heat of the wire.

              This I do understand!

              >2. If the short is "though" the truck, the wipers inside truck may get hot
              >enough to melt down the sideframes, gears and other plastic parts. (I have
              >two examples of that in my N scale junkbox from a large club layout when
              >derailments weren't noticed fast enough).

              This I do not understand!

              If you have a train running and happen to drop some metallic object on
              the track, they *will* be short circuit'ed - no doubt. The "quality"
              of this short determines how fast your feed-wires, throttle etc. will
              start burning.

              I fail to see however (my fault no doubt) why the short should affect
              the train in any way!

              If the train itself is part of the short , it's quite another story.
              Anything could happen to the parts of the train's chassis involved in
              the short. The lower the effective resistance the faster the
              melt-down. But this is not what Andy Hunting was talking about. (Or is
              it?)

              Nor do I understand why a loc. should be damaged travelling over an
              insulation to a track segment of the opposite polarity. OK - there
              could be something evil happening when the polarity-change starts to
              fight the inertia of the loc. But no matter what polarity - the coils
              on the rotor still has the same resistance. Not using pure dc (=DCC)
              *might* make a difference???

              My limited knowledge regarding electronics hinders me to see thru
              this.

              regards Ole Rosted
            • Jeffrey MacHan
              Great reply, Bill! I knew that my shot from the lip would get the experts squirming in their chairs and fill in the holes in my answer. I certainly used the
              Message 6 of 12 , Jan 20, 2001
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                Great reply, Bill!

                I knew that my shot from the lip would get the experts squirming in their
                chairs and fill in the holes in my answer.

                I certainly used the auto tail light trick with my large N scale layout once
                upon a time.

                I have had hundreds of shorts on the VEC over the years most notably from
                derailments after a hard knock from an enthusiastic bystander. In some
                cases the short went undetected for a minute or so because I was being
                distracted at the far side of the layout. From what I gather from reading
                your detailed analysis of the possible outcomes, I was lucky to have never
                had any damage occur to train motors, wipers, and wiring or was I?

                My intuition tells me that the short circuit protection circuitry of my
                MRC1400s must have had something to do with it. The output voltage is cut
                off immediately when a short occurs. In the MRC1400 design, the voltage
                indicator lamp goes out instead of lighting up.

                I can only say that if one uses a good quality commercial transistor
                throttle, there should be no danger to locomotives or wiring, at least in my
                experience.

                Cheers,
                Jeffrey MacHan




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              • Dieter_Mac_Nolte@t-online.de
                Dear Bill, please explain to a humble English reader what do you mean with X awg wire ? greetings Dieter ... Dieter W. Nolte E-Mail
                Message 7 of 12 , Jan 20, 2001
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                  Dear Bill,

                  please explain to a humble English reader what do you mean with 'X awg wire'?

                  greetings

                  Dieter




                  bjkronen@... schrieb:
                  > Jeffrey:
                  >
                  > Opps. No, you are not incorrect, but there are some issues which do need a
                  > bit of discussion.
                  >
                  > > All NA commercial hobby transformers and throttles are required to have
                  > > short circuit protection usually in the form of a circuit breaker.
                  >
                  > In order to have a UL or ECMA rating, you bet they do. House fires are no
                  > fun.
                  >
                  > > A direct short such as the ones that you described will immediately stop
                  > the
                  > > locomotive and trip the circuit breaker thereby protecting your expensive
                  > > trains. On most commercial electronic throttles there will also be a
                  > > warning light.
                  >
                  > Well, let's chat about that. Let's say the wiring this person used was 24 or
                  > 26 awg wire from the power pack to the track. Lots of train stores sell that
                  > stuff on cute little rolls to hobbyists. Let's give it about 5 ohms of
                  > resistance including the resistance at the screw head terminals and track
                  > connectors. Since no short is ever "perfect" let's add another 5 ohms of
                  > resistance there. If the throttle was set to 5 volts output when the short
                  > occurred, ohms law say:
                  >
                  > Current = (5 volts) divided by (10 ohms) = 0.5 amps.
                  >
                  > Since that's well under the typical 1.0 amp fuse/breaker rating and actually
                  > still in the normal current range of a couple of locomotives dragging a load
                  > around the layout, I doubt the thermal breaker would ever blow. If the pack
                  > is one of the solid state variety, it would probably still be sitting there
                  > delivering a full 5 volts to the ends of the wires.
                  >
                  > This example suggests the wire, and the short, will be dissipating 2.5 watts
                  > of energy doing nothing, for a period of time if undiscovered. Eventually,
                  > one of several things might happen:
                  >
                  > 1. The wire may begin to smoke, since its maximum current rating has been
                  > exceeded and the insulation starts to melt from the heat of the wire.
                  >
                  > 2. If the short is "though" the truck, the wipers inside truck may get hot
                  > enough to melt down the sideframes, gears and other plastic parts. (I have
                  > two examples of that in my N scale junkbox from a large club layout when
                  > derailments weren't noticed fast enough).
                  >
                  > So how do you fix this problem?
                  >
                  > 1. Never use undersized wire, period. Large wire will conduct enough
                  > current to pop the circuit breaker a whole lot faster than undersized wire.
                  > Wire is the cheapest part of any layout, period. 18 awg should be the
                  > smallest wire on your layout, even if its 2 foot across, for a really good
                  > safety factor. For those with roomsized layouts, 12 awg is commonly used by
                  > a LOT of folks, to control voltage drop at the far side, if nothing else.
                  > Yes, 22 awg wire works fine when everything is running normally. But its the
                  > unexpected events that will bite you.
                  >
                  > 2. Try to avoid unattended operation of the trains. Turn them off when the
                  > phone rings.
                  >
                  > 3. Some have used an automobile tail light in series with the output of the
                  > transformer to act as a current limiter. Many unattended "display" layouts
                  > do that. In normal train operation, the bulb is dark, and the voltage drop
                  > across it is minimal. When a short occurs, the extra current flow lights the
                  > filament, which causes the energy to be dissipated as light in the bulb,
                  > rather than heat in the wiring or the locomotives. That requires a bit of
                  > experimenting, since some auto lights are pretty high wattage bulbs and would
                  > not light up soon enough.
                  >
                  > Enough rambling.
                  >
                  > Bill Kronenberger
                  > Houston
                  >
                  > "Z" WARNING! HANDLE WITH CARE! Highly addictive in Small DoseZ!
                  >
                  >

                  Dieter W. Nolte
                  E-Mail Dieter_Mac_Nolte@...
                • Reynard Wellman
                  Hello Dieter, The AWG stands for American Wire Gauge. Regards, Reynard
                  Message 8 of 12 , Jan 20, 2001
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                    Hello Dieter,
                    The "AWG" stands for American Wire Gauge.

                    Regards,
                    Reynard

                    Dieter_Mac_Nolte@... wrote:

                    > Dear Bill,
                    >
                    > please explain to a humble English reader what do you mean with 'X
                    > awg wire'?
                    >
                    > greetings
                    >
                    > Dieter
                    >
                    >
                    >
                    >
                    > bjkronen@... schrieb:
                    > > Jeffrey:
                    > >
                    > > Opps. No, you are not incorrect, but there are some issues which do
                    > need a
                    > > bit of discussion.
                    > >
                    > > > All NA commercial hobby transformers and throttles are required
                    > to have
                    > > > short circuit protection usually in the form of a circuit
                    > breaker.
                    > >
                    > > In order to have a UL or ECMA rating, you bet they do. House fires
                    > are no
                    > > fun.
                    > >
                    > > > A direct short such as the ones that you described will
                    > immediately stop
                    > > the
                    > > > locomotive and trip the circuit breaker thereby protecting your
                    > expensive
                    > > > trains. On most commercial electronic throttles there will also
                    > be a
                    > > > warning light.
                    > >
                    > > Well, let's chat about that. Let's say the wiring this person used
                    > was 24 or
                    > > 26 awg wire from the power pack to the track. Lots of train stores
                    > sell that
                    > > stuff on cute little rolls to hobbyists. Let's give it about 5 ohms
                    > of
                    > > resistance including the resistance at the screw head terminals and
                    > track
                    > > connectors. Since no short is ever "perfect" let's add another 5
                    > ohms of
                    > > resistance there. If the throttle was set to 5 volts output when
                    > the short
                    > > occurred, ohms law say:
                    > >
                    > > Current = (5 volts) divided by (10 ohms) = 0.5 amps.
                    > >
                    > > Since that's well under the typical 1.0 amp fuse/breaker rating and
                    > actually
                    > > still in the normal current range of a couple of locomotives
                    > dragging a load
                    > > around the layout, I doubt the thermal breaker would ever blow. If
                    > the pack
                    > > is one of the solid state variety, it would probably still be
                    > sitting there
                    > > delivering a full 5 volts to the ends of the wires.
                    > >
                    > > This example suggests the wire, and the short, will be dissipating
                    > 2.5 watts
                    > > of energy doing nothing, for a period of time if undiscovered.
                    > Eventually,
                    > > one of several things might happen:
                    > >
                    > > 1. The wire may begin to smoke, since its maximum current rating
                    > has been
                    > > exceeded and the insulation starts to melt from the heat of the
                    > wire.
                    > >
                    > > 2. If the short is "though" the truck, the wipers inside truck may
                    > get hot
                    > > enough to melt down the sideframes, gears and other plastic parts.
                    > (I have
                    > > two examples of that in my N scale junkbox from a large club layout
                    > when
                    > > derailments weren't noticed fast enough).
                    > >
                    > > So how do you fix this problem?
                    > >
                    > > 1. Never use undersized wire, period. Large wire will conduct
                    > enough
                    > > current to pop the circuit breaker a whole lot faster than
                    > undersized wire.
                    > > Wire is the cheapest part of any layout, period. 18 awg should be
                    > the
                    > > smallest wire on your layout, even if its 2 foot across, for a
                    > really good
                    > > safety factor. For those with roomsized layouts, 12 awg is commonly
                    > used by
                    > > a LOT of folks, to control voltage drop at the far side, if nothing
                    > else.
                    > > Yes, 22 awg wire works fine when everything is running normally.
                    > But its the
                    > > unexpected events that will bite you.
                    > >
                    > > 2. Try to avoid unattended operation of the trains. Turn them off
                    > when the
                    > > phone rings.
                    > >
                    > > 3. Some have used an automobile tail light in series with the
                    > output of the
                    > > transformer to act as a current limiter. Many unattended "display"
                    > layouts
                    > > do that. In normal train operation, the bulb is dark, and the
                    > voltage drop
                    > > across it is minimal. When a short occurs, the extra current flow
                    > lights the
                    > > filament, which causes the energy to be dissipated as light in the
                    > bulb,
                    > > rather than heat in the wiring or the locomotives. That requires a
                    > bit of
                    > > experimenting, since some auto lights are pretty high wattage bulbs
                    > and would
                    > > not light up soon enough.
                    > >
                    > > Enough rambling.
                    > >
                    > > Bill Kronenberger
                    > > Houston
                    > >
                    > > "Z" WARNING! HANDLE WITH CARE! Highly addictive in Small DoseZ!
                    > >
                    > >
                    >
                    > Dieter W. Nolte
                    > E-Mail Dieter_Mac_Nolte@...
                    >
                  • Daniel Baechtold
                    Hi gang! ... The train isn t involved in the short, if its not the train making the short! ... A loco doesn t get damaged. It will only stop exactly above the
                    Message 9 of 12 , Jan 31, 2001
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                      Hi gang!

                      I either do not understand this:

                      > >2. If the short is "though" the truck, the wipers inside truck may get
                      > hot
                      > >enough to melt down the sideframes, gears and other plastic parts. (I
                      > have
                      > >two examples of that in my N scale junkbox from a large club layout when
                      > >derailments weren't noticed fast enough).
                      >
                      > This I do not understand!
                      >
                      > If you have a train running and happen to drop some metallic object on
                      > the track, they *will* be short circuit'ed - no doubt. The "quality"
                      > of this short determines how fast your feed-wires, throttle etc. will
                      > start burning.
                      >
                      > I fail to see however (my fault no doubt) why the short should affect
                      > the train in any way!

                      The train isn't involved in the short, if its not the train making the
                      short!


                      > Nor do I understand why a loc. should be damaged travelling over an
                      > insulation to a track segment of the opposite polarity. OK - there
                      > could be something evil happening when the polarity-change starts to
                      > fight the inertia of the loc. But no matter what polarity - the coils
                      > on the rotor still has the same resistance. Not using pure dc (=DCC)
                      > *might* make a difference???

                      A loco doesn't get damaged. It will only stop exactly above the polarity
                      change, and wait there till you get the polarity in order. It might be that the
                      Motor will get a bit warm, ut this shouldn't really damage the loco.

                      Rgds. Daniel

                      --
                      Daniel Baechtold
                      Jurastrasse 37
                      CH-4242 Laufen

                      Dani@... or d.baechtold@...

                      Sent through GMX FreeMail - http://www.gmx.net
                    • Garth A. Hamilton - VE3HO
                      ... Not so depending on the wiring of your loco. When you locomotive staddles the insulated block and the power is applied on both sides but of opposite
                      Message 10 of 12 , Jan 31, 2001
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                        At 02:22 AM 02/01/2001 +0100, you wrote:

                        >A loco doesn't get damaged. It will only stop exactly above the polarity
                        >change, and wait there till you get the polarity in order. It might be that the
                        >Motor will get a bit warm, ut this shouldn't really damage the loco.


                        Not so depending on the wiring of your loco. When you locomotive staddles the insulated block and the power is applied on both sides but of opposite polarities a dead short is created by the locomotive wiring which collect power from both side of both trucks. The junction between the wiper and what ever it is touching is the highest resistance in the circuit and it will heat like a resistor very rapidly unless you have a crowbar protection circuit in your poser pack or packs. It will indeed very quickly start to melt plastic. The motor is not damaged in this senario because it is not a cause or part of the circuit causing the short but is connected beyond the short.

                        For those who do not have a crowbar protection circuit in your power supplies there is simple solution. Purchase a lamp which requires half an amp supply at 10 volts to light it and place it not across the power pack output but in series in one lead of your track power from the power pack. When the lamp lights you have short. The lamp will go out when the short is cleared. If you are running multiple engines you will have to increase the half amp rating to an amp. The idea is that in normal running the light is not lit because the motor load is of lower resistance it takes the power but as soon as you short the two tracks together then the lamp has less resistance than the short and it lights saving heat damage to your loco.

                        Garth
                      • Ole Rosted
                        On Thu, 1 Feb 2001 02:22:44 +0100 (MET), Daniel Baechtold wrote: Hi, ... I m the unfortunate soul who wrote this as a reply to Bill K s very good letter on
                        Message 11 of 12 , Feb 1, 2001
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                          On Thu, 1 Feb 2001 02:22:44 +0100 (MET), Daniel Baechtold wrote:


                          Hi,

                          >> >2. If the short is "though" the truck, the wipers inside truck may get
                          >> hot enough to melt down the sideframes, gears and other plastic parts.
                          >>
                          >> This I do not understand!
                          >>
                          >> If you have a train running and happen to drop some metallic object on
                          >> the track, they *will* be short circuit'ed - no doubt. The "quality"
                          >> of this short determines how fast your feed-wires, throttle etc. will
                          >> start burning.

                          I'm the unfortunate soul who wrote this as a reply to Bill K's very
                          good letter on shorts. I had hoped, that no one would notice my
                          blunder - but alas!

                          Bill clearly stated: "through the truck" which I didn't realize at the
                          time of writing. Sorry.

                          >A loco doesn't get damaged. It will only stop exactly above the polarity
                          >change, and wait there till you get the polarity in order. It might be that the
                          >Motor will get a bit warm, ut this shouldn't really damage the loco.

                          [Garth wrote:]

                          >>Not so depending on the wiring of your loco. When you locomotive staddles
                          >>the insulated block and the power is applied on both sides but of opposite
                          >>polarities a dead short is created by the locomotive wiring which collect
                          >>power from both side of both trucks.

                          Ah, yes of cource: "both trucks" makes the difference!
                          All I had in mind was my 8800.

                          The sign they put up in my booth where I used to work: "Make sure
                          brain is on before using keyboard" was put there for a reason - I
                          guess :-((

                          regards Ole Rosted







                          >
                          >Rgds. Daniel
                        • Daniel Baechtold
                          Hi gang! ... This comes near to my opinion! ... Do there really exist power supplies without crowbar protection? My power supplies have all a crowbar
                          Message 12 of 12 , Feb 1, 2001
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                            Hi gang!

                            > >A loco doesn't get damaged. It will only stop exactly above the polarity
                            > >change, and wait there till you get the polarity in order. It might be
                            > that the
                            > >Motor will get a bit warm, ut this shouldn't really damage the loco.
                            >
                            >
                            > Not so depending on the wiring of your loco. When you locomotive staddles
                            > the insulated block and the power is applied on both sides but of opposite
                            > polarities a dead short is created by the locomotive wiring which collect
                            > power from both side of both tru

                            This comes near to my opinion!

                            > For those who do not have a crowbar protection circuit in your power
                            > supplies

                            Do there really exist power supplies without crowbar protection? My power
                            supplies have all a crowbar protection, thank god.

                            >there is simple solution. Purchase a lamp which requires half an amp
                            > supply at 10 volts to light it and place it not across the power pack
                            output
                            > but in series in one lead of yo
                            >

                            That's a great iedea and simple to install! Bravo Garth!!!

                            Regards Daniel

                            --
                            Daniel Baechtold
                            Jurastrasse 37
                            CH-4242 Laufen

                            Dani@... or d.baechtold@...

                            Sent through GMX FreeMail - http://www.gmx.net
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