QUESTION: Shorting Stick Construction

[David, K3TUE]

I have to make a shorting stick.  I have read in the Navy Manuals and how they say to make one.  But I am unclear about a detail and if it matters.

Should the conductor be better insulated or not?

I am thinking that if it is not then it might be better to more easily notice a broken/open wire (very important in such a device) than if it were insulated.  But I suspect that if a short fried the wire under the insulation it might also be obvious by charring and bubbles in the insulation.

I was thinking of buying some 5kV kink-less test-lead wire to use, but I suspect that 18awg is just too small for this application.  Or should I buy some 1/4" or 3/8" non-insulated braided/tinned copper line?

What wire have you used or would you use?  Or does it just not matter much?

[KB2WIG]

 "I am thinking that if it is not then it might be better to more easily notice a broken/open wire (very important in such a device) than if it were insulated."   I'd say use the insulated conductor; you can test it for conductivity before you use it.

18 AWG might not be too bad. Thers nothing stopping you from paralleling a few pieces- gives you more current  capacity. I think its more important from the standpoint of insulation. How far will you be from the conductor and discharge point? ( your hands). How good is the "stick" in terms of its insulation? Its not a broom handle or something like that, Is it? Probably a no no as the wood holds moisture. Have you considered ignition wire? Its got good insulation values and you can get some at the local NAPA or what have you. You want the copper stuff, not the carbon.  Or try the local neon shop- you maybe able to beg some hv wire from them.   A real FB OM situation would have you discharge the caps with a resistance in the "shorting stick", this cuts down on the trama to the condensers. THEN you tickel them with the shorting stick  and hope you dont get elmos' fire from them............. klc

[David, K3TUE]

I was planning on using a 1-in diameter PVC pipe with at least 1-ft insulating distance between the tip and my hand.

[W2VW]

It's a shorting stick so one end is usually grounded. Bare braided wire works fine. Another thing to use after the H.V. is shorted is a set of handcuffs. That consists of a wire with good sized clips on each end to put right across the H.V. capacitor(s) in case of chemical recovery. Never trust a high voltage supply.

[W3SLK]

Dave, I'm going to attempt to answer these questions individually since I have a 'Navy-version' shorting stick.

Should the conductor be better insulated or not?

The official military style I have IS insulated. It makes sense some what. You wouldn't want it brushing up against a component and taking the brunt of the discharge.

What wire have you used or would you use?  Or does it just not matter much?

Error on the side of safety. Bigger is better. Mine uses 3/4" copper braid. This makes it very flexible. Also getting back to the above question, run the copper braid through a length of tubing. I think mine is clear Tygon tubing. Couple the end with a large alligator clamp, (not the dinky clips that you use for jumpering).
For the business end, I would use about 18" of acrylic rod. On one end, drill and tap a 1/4" hole. Take a piece of solid copper rod (1/4"), tap it and screw it fast to the acylic. Last but not least, Solder the braid to the rod. Make sure that the solder joint is clean and not cold because everything passes through it and if it opens, then you become the path and that may be ugly.
Lastly, keep an eye out for the military shorting sticks at the hamfests. I've seen them as low as $10 and they usually come with a nice mounting bracket complete with derating curve. I hope this helps.

[V73WJ]

Most shorting sticks I have used professionally over the last 50 years or so are most certainly insulated and about 3 feet long, (keeps you well away from the HV) and utilise copper braid housed in a clear plastic tube obtainable from the local hardware store. Drill the end of the stick about 1/4 then tap and then screw in a hook made with brass to hang on the capacitor or whatever, whilst you are working on the circuit. Attach the braid securely under the hook where it screws into the insulated rod. Firstly have a washer then a nut against the top of the rod then a washer, then the braid followed by another washer and nut to clamp the braid securely. Make the rod about 3/4 diameter and solid so it does not wave about and finally attach a stout alligator clip to the end of the braid OR much better have it permanently fastened to a ground point on the equipment stops problems with the clip coming loose! 73 Bill V73WJ

[W1ATR]

All the commercially built Jesus sticks I've seen always use a heavy conductor. Usually it’s a piece of 6ga or 4ga copper or tinned copper. The one I have here is constructed with a wood handle about 2 feet long and painted black. The business end is an aluminum hook made with 3/8" rod and about a 2" radius. The ground conductor is about 6 feet of uninsulated  4ga tinned copper (extremely flexible zillion strand stuff) with an eyelet on the end for bolting down to ground.

Works just fine, but I probably should slip a piece of clear tubing over that ground wire.

Never use cheap roachclips for shorting big caps while you work. They barely make any noise when they slip off, so you may not notice. I use these things that look like small battery clamps. They grip the posts on caps pretty tight and have teeth so they don't slip off without a fight.

[David, K3TUE]

After completing construction of the shorting stick and the shorting cuffs, I want to make sure I am using it everywhere I need/should.

Do I need to be draining ALL of the caps (every single cap in the schematic?), which would seem safest and most sure, or just the ones in the PS?

I understand I would be using it on the filter caps of any PS.

But what about cap stacks, like this below, where each is not connected directly to ground?  What if you short the stack and one is bad, so they all don't end up drained?

[W3SLK]

If a cap and a resistor open up. Yep. So, is it worthwhile to take the time and plant that probe across each cap terminal? The one time you don't, chances are you will be scraping your bohunkous off of the wall.

[W1GFH]

If you look in the real old handbooks say 1940's and 1950's they talk about keeping a shorting stick with your transmitter. Many commercial broadcast xmtrs used to have one mounted inside the cabinet.

Jesus sticks

I have heard it called the Jesus stick, too. Also the nut that holds the rotor blade on a helicopter (and a wheel drum on a car axle) is called the Jesus nut. I've also heard of Jesus bolts and Jesus springs. I've often wondered what the origin of the term is. According to Wikipedia, if the Jesus (whatever it is) fails, the only thing left to do is to pray to Jesus because you ain't long for this world.

[W2NBC]

From TM 11-826 (BC-610 manual) page 36:

http://www.dealamerica.com/shorting%20stick.jpg

Heavy copper braid bolted to the chassis would be best..

Jeff W2NBC

[V73WJ]

The guys are 100 % right , simply do not take any chances! Despite terminal cancer which I've somehow survived and numerous battles as a soldier the other reason I'm still around after 50 + years as a broadcast engineer is because I shorted just everything to deck before working on the equipment and still do, although I limit my TX powers to a max of 25 KW these days! Just take care and you'll still be around for a lot of years to come.

73

Bill V73WJ.

[David, K3TUE]

can anyone think of a good reason to use either Aluminum instead Copper, or vice-versa for the shorting hook?  The only reason I can think to use Copper over Aluminum is because I think aluminum would become more brittle from pounding the mounting end flat than copper.  Or am I wrong?

[KB2WIG]

The only thing I can think of is a dissimilar metal problem connecting Al to Cu. Thats if you use a copper conductor; a Al conductor to an Al hook sounds like it'll work. I dont think the difference of conductivity of Al v Cu is a major factor for this application.... unless u r using somthing like #30 ga. conductor.  KlC

[John K5PRO]

We use them at work on all of our large capacitor banks, at the particle factory. We used to make them, but now buy them from companies like White, Ross Engineering. We use 2 to 6 AWG single conductor, similar to Monster cable for speakers, in clear jacket. The connection to the stick and lug bolted to ground must be mechanically crimped, and conductor entirely visible through the jacket - clear so that they can be inspected before use. Some of the newer style have a built in low value resistor at the tip, a bulk carbon type about 1 kohm, followed by a second hook that is solid ground. The first contact is made with the tip, to discharge caps, before the solid ground is applied. This prevents the cable from whipping around if applied across a charged capacitor of large stored energy (kJ).

For series strings of charged caps, it takes at least two ground sticks, and preferably more. One is applied to each end of a capacitor, to discharge it, then a shorting clip is bridged across it, as the pair of sticks moves to the next cap. Each time, keeping the stick on the cap while applying the clip leads. Otherwise, if this proceedure is not used, you may chase the charge around the circuit, and recharge capacitors which you have already shorted, and unshorted due to the lack of enough sticks.

One more thing. The low side of the power supply, is not necessarily ground if the plate current shunt resistor opens. It is best to connect all ground sticks to earth/chassis, and hang one on the low side of power supply first, before using the second stick to touch the hot sides of capacitors.

There are standards for grounding sticks for power linemen, and also for stored energy capacitor banks. IEEE is a source.

[Rick K5IAR]

That's great info, John, and answers some questions I had.
Thanks,
Rick/K5IAR

[David, K3TUE]

I understand the value of the idea of clipping and shorting the cap leads after it is discharged.  But do I understand correctly that you don't take the grounded stick and just short the 2 leads of the capacitors with the hook of the shorting stick?  Do I need a bleeder resistor stick?  Is the current through the cap too great if I do not use a bleeder resistor stick?

[John K5PRO]

If the spacing of the terminals on the capacitor are close enough, then by all means, short them together with a single, grounded hook. There may be a spark there if the bleeder resistance is failed open, but otherwise shouldn't be any. With most filter capacitors, the current shouldn't be excessive, or need a resistor stick. This helps with really big capacitors, in limiting the short circuit current, and helping to prevent ringing (damped oscillation) of the discharge waveform, which causes excessive voltage reversal on the capacitor. Again, this is mainly in LARGE capacitors. Here is a good test, if the shorting action causes such a large spark and noise as to blow a chunk of metal off the hook or cause a big melted spot, its probably not a good idea to ground it this way.

But in a series string of capacitors, you should hold a short on the end of the string, and then try and short out each capacitor, if you are planning to reach into the network. They should bleed off due to the parallel resistor, unless its burnt open. Series capacitors are the hardest to safe, as if you short and then move the short to the next capacitor, you can actually redistribute the charge around to the other series capacitors that were already shorted. Hence the advice to put clip leads on all the caps as you do it. Once the string is shorted, then you can leave them or remove them at your discretion.