Jacob's Ladder
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Jacob's Ladder

There is a safer way to for working with a bombarding transformer. Learn how to create your own Jacob's Ladder

By Tom Cage

One thing that never seizes to amaze me in the neon industry is the fact that there is so little exchange of information from one neon shop to the next. When I started learning how to blow glass, the shop setup that I worked in I assumed was the same as all other neon shops. Boy was I ever wrong! To this day I haven't seen two shops that were set up the same, or met two glassblowers who blew glass or bombarded neon the same way!

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  • What is a Jacobís ladder you ask? Well, if you have ever seen any of the old Frankenstein movies or any horror movie with a laboratory in it then you have seen one. It's the funny looking device in the background that has a small electrical arc rising between two steel rods over and over again giving off an eerie electrostatic sound, creating a pretty neat visual effect.

    The Jacobís ladder is mainly used for safety in the neon industry. By incorporating the use of one in a neon shop, it helps protect the transformer, manifold, vacuum pump motor, any electrical gauges, the neon units being bombarded, and most importantly, the operator!

    The high voltage that is used in the bombarding process can create some very unique problems. Probably the first and foremost problem is when the electrical current arcs through two or more areas in a unit, usually between the double backs. What causes this problem is when the pressure inside the unit rises to the point where it is difficult for the current to travel through the glass tubing. It tries to take the shortest route, which is to arc through the glass itself. We all know that by placing mica in these areas, it greatly decreases the chances of this happening, although I have seen the current arc through or around the mica.

    Without a Jacobís ladder, this problem is increased dramatically. I was in a fairly large neon shop near Houston many years ago with one full-time bomber and five glassblowers and they did not use a Jacobís ladder. They had a very large bombing transformer and probably the most severe cases of arc-through that I have ever seen.

    The time that was spent placing mica between every single possible area of arc through, was unbelievable. They would place mica in between areas of 2" or more gap because they said that they had had it jump across that far! And then to make matters worse, to let them know when there was sufficient vacuum to light up the tube to bombard it, they incorporated a short section of green neon that was tubulated and hooked up to the manifold that had a small transformer attached to it.

    When there was a good enough vacuum to light up the unit to be bombed, the current from the small transformer would light up the air inside the green unit and thus give the "green light" to bombard the unit. The electrodes on this unit were burned to a crisp and it was constantly discharging impurities into the manifold and every single unit being bombed. The benefit that is gained by using a Jacobís ladder is to help eliminate arcing through works like this.

    When the current is traveling through a unit during the bombarding process and the main stopcock is closed, the air and impurities in the unit are heating up and increasing the pressure in the glass tubing. This pressure can build up to the point where there is no longer enough vacuum to keep the current traveling through tube and therefore, it starts looking for the shortest route to complete the circuit or go to ground. In other words, you have 10 to 20 thousand volts of electricity looking for somewhere to go.

    Some of the places I have seen this high voltage current travel to without the use of a Jacobís ladder is pretty amazing. It has jumped completely around a 4" piece of mica, straight through a 1/8" thick piece of mica, and believe it or not, over 1 1/2" to a finished piece of neon, through it, and from the electrode wire to a sheet rock screw in the wall that was screwed into a metal stud!

    I have also seen this high voltage current travel back through the manifold to ground and really do a lot of damage to the various pieces of equipment. This is usually referred to as "flashback", and can be a dangerous situation for the operator. It is very important that the operator be insulated from ground to prevent any possibility of electrocution and that is why I recommend a minimum 3" to 4" insulation between the feet and the floor, and never use both hands to hook or unhook the high voltage leads to a neon unit.

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    When flashback occurs through the manifold, the electricity is looking for a ground. This has been accomplished by going through a vacuum gauge and literally frying it. Also, electricity has gone through the main stopcock to the vacuum pump, destroying the motor and any other electrical device that is hooked into the system. Another part of the system that can be damaged by flashback is the manifold itself. I have seen some of the older style lead glass stopcocks "welded" when the arc goes through a closed main stopcock. On the "O" ring style, the arc left etched grooves around the lower "O" ring, rendering them useless and most likely beyond repair.

    By incorporating an electrode into the system that is hooked directly to a ground before any of these other items, you can reduce the likelihood of damage to the equipment. However, this can create a problem of it's own because the current sometimes prefers to go from the closest electrode to ground, instead of through the unit being bombarded.

    The bombarding transformer itself is not immune to damage. In some cases, the electricity can arc through or across the windings inside the transformer casing damaging the transformer and thereby lowering the voltage and/or the amperage output.

    All of the above problems can be virtually eliminated by using a Jacobís ladder, and one can be installed easily and safely and costs next to nothing.

    There are so many different types of transformers and bombarding setups out there that it would be hard to cover the best setup for all of them, but there are a few simple guidelines to follow.

    First, and absolutely the most important, is that it be safe. It should be placed in an area where there is no possibility of the arc that goes across the ladder, ever coming in contact with any person, metal or grounded material, or any combustible material. It should be placed, as close to the bombarding transformer as possible and when the high voltage arcs across the ladder, the operator should easily hear it. This is important for the reason that many systems incorporate safety lights to let the operator know when the high voltage is on. But, in the unlikely event that the foot or push button switch should short out or make contact while a unit is not hooked up and the operator is looking away, they will hear the Jacobís ladder and thereby also have an audible as well as a visual warning.

    Another distinct advantage of using this system is that in the event of the above situation occurring, the high voltage will be traveling across the Jacobís ladder, creating less of a chance of the electricity trying to find somewhere else to go.

    If you are fortunate to have one of the bombarding transformers with the two secondary posts sticking out of the top of the transformer, the installation of a Jacobís ladder is very simple. Make sure that the breaker or cut off switch is in the off position before attempting any of the following procedures. Loosen the nuts on the bombarding transformer that secure the wires to the unit to be bombed and remove these wires. Measure the distance between the two posts and cut 2 pieces of # 12 or larger diameter solid wire to the measured length and strip the covering completely off.

    Then, wrap one end of each of the wires around the metal part of the post. Point each of the wires at the other post and reattach the wires to be connected to the unit to be bombed and retighten the nuts. At the midpoint between two posts, bend the two wires so that they touch at the bottom and gradually spread apart going upward. Cut both of the wires approximately 1" from where they touch going upward creating a "V" shape. Then bend the wires either upwards or side ways to create a 1/4" gap between the wires.

    Now turn the bombarding transformer back on and make sure that the hookup wires are clear of anything and momentarily push or step on the switch. The secondary voltage should have jumped across the two wires creating an arc.

    If it did not, turn off the breaker and adjust the gap closer and try again. Repeat this procedure until you are able to create an arc across the two wires. It is very important that you only create an arc for a minimal amount of time because as the electricity travels across the two wires they heat up very quickly and will melt.

    It will take some adjusting of the gap between the two wires as you bombard units to get the right distance so that you can keep the current traveling through the unit being bombed to satisfactorily heat the glass and process the electrodes without jumping across the ladder. You will still need to place mica between double backs where the electricity will "short out" a large section of glass. Depending on the size of the transformer, the gap may be as far apart as 3/4"-1".

    If you have an overhead trolley system, a good safe place to put a Jacob's ladder is on top of the support structure on the side where the wires hook up from the transformer. In this application, you may use 1/8" rod instead of wire. Bend it in the fashion shown here:

    When you drill the holes in the support structure (be sure it is a nonconductive material), measure them so that the two rods will touch at the bottom of the "V" and that the rods fit snug in the holes. Then, attach a piece of GTO wire to the base of the left rod and the left trolley line. Do the same for the right side. Use the procedure mentioned before to adjust the gap for your particular needs. Depending on the height and the distance of the gap at the top of the "V" and the size of your transformer, you can create quite an arc that is safe and very beneficial to your bombarding process.

    It may take a while to get the proper gap adjusted on the Jacobís ladder and you may need to adjust your bombarding pressures to keep the unit lit while processing, but it will help make your system safer and save some costly repairs on your equipment and the neon that is being bombarded.

    Tom Cage has been in the sign business since 1975. Mr. Cage is a consultant, writer and runs his own neon business, Neon Specialist, in Colorado Springs, Colorado. For more information you may visit his website at http://www.neonspecialist.com

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