Neon Sign Channel Letter Basics
This page is here to teach you about the basics of neon channel letter construction. Please allow time for the images to load, a picture is worth a thousand words! Each image with a border will click to open a larger picture in a new window. That way you can read and see by changing windows. Pop-up blockers should not be alarmed by my coding, but if you get a block warning, do whatever needs done in your program to allow the pictures to open.
Channel letters are commonly found on commercial buildings for signage. Channel letters themselves are formed from tin or aluminum on a machine or by hand. The metal used makes up the sides and back of the letter. Once formed, the letter "channels" (sides) can be crimped, riveted or welded onto the back piece. Most of the time, a channel letter is covered to protect the tubing from damage and weather. Transparent or opaque acrylic or plexi-glass is used for these covers. Obviously, the light output of the neon or argon tube needs to be able to shine through the cover. A trim edging (called jewelite) goes around the cover and is glued in place to the cover's edges. The trim provides a place to use screws to secure the cover to the letter's channel. Some channel letter signs have no face or cover over the letters and are left exposed. This is done for effect or brilliance or to blend with a certain style. Below is an example of an open-faced neon channel letter sign from my dealership's service garage.
I wanted the brilliance of the neon tubes to be seen because the building sets far back from the road. Works like a champ. Plus, it's made with recycled neon channel letters! Most channel letters are mounted on what is known as a raceway. A raceway is a long length metal box ususally 8 inches square that houses the wiring, transformer(s) and shut off switch of the sign. My service neon sign's letters are mounted directly on the building, so it utilizes what is known as P-K style housings for the electric connections. What is a P-K housing? Well, let's get into it.
In this picture we are looking at the backside of a neon channel letter that is equipped with P-K style housings.
I'm going to start with this style since it is used often.
P-K housings are called such because the original design patent company used that name.
Building code would refer to a P-K housing as "high voltage neon electrode receptacle".
P-K housing is an easier way to refer to a high voltage neon electrode receptacle.
P-K housings have been around for several decades.
These housings are popular with sign industry service professionals.
The letter cover can be removed for easy service of the neon tube should a break or other failure occur.
No electrical wires to disconnect or re-connect!
Plus the tube service is performed without removing the letter from the sign itself.
Aside from channel letters P-K housings are also used on exposed neon tube outdoor signs that do not have channel letters. Glass provides excellent insulation for a high voltage rating of 7,500 volts. That is the most voltage that is ever in any neon sign circuit. What about a 15,000 volt transformer? Sorry, no, that is just two 7,500 volt units wired in series. I'll get into transformers another time on another page.
In the picture below, I show a P-K housing disassembled. These things are quite simple. The main part is the glass insulator. It is almost the full length of the entire housing. The next part is 2 rubber gaskets. These actually serve 2 purposes. One is for sealing the housing to the letter or sign tin. The second is to provide a grip for these hand-tightened snug housings. The next part is the metal outer part of the housing. This part extends from the letter back or sign face into the wiring trough or wall. It simply screws over the glass part with the gaskets to assemble. The final part is the connecting spring. People in the sign industry refer to them as "buttons". Why? Because they come new as a brass disc with a nipple in the bottom center. The other side of the brass has the spring attached to it, but they are made flat to ship in small boxes and not get all tangled together. On a new "button", you simply pull it to size. The spring provides the easy service part. The electrical connection is made permanent by crimping the connecting GTO wire to the nipple. The neon tube electrode then rests in the glass insulator and against the spring to get the electricity it wants and needs.
Here is a photo of a P-K housing disassembled.
It only has 5 pieces comprised from 4 different parts.
- The glass inner insulator which accepts the neon electrode (on right).
- The two rubber gaskets which sandwich onto either side of the channel letter's back (center).
- The metal outer part of the housing which screws onto the glass part (on left).
- The last part is the contact spring which is pictured below.
Here is the contact spring. Not much to look at, but works wonderfully. The left side of the spring as pictured provides contact to the neon tube electrode. On the right, the brass end nipple is crimped in this picture since the spring is used. "GTO" wire is the ONLY wire approved for use in high voltage circuits. High voltage circuits require special wire! NEVER use THN, THHN or ANY type of standard commercial or household wire in neon circuits! eBay© usually has GTO wire by the foot or by a pre-cut length. Buy it and use it! Do not start fires by using standard extension cord wire! Your local neon or sign shop can sell you the proper GTO wire. GTO wire is special because of enhanced insulating abilities for high voltages. GTO wire also has a high degree of flexibilty, which is often needed in tight confined channel letter and sign spaces. I have re-used old springs before on my neon projects. I just lay my new GTO wire right into the indent or groove made by the crimp in the nipple and then solder the GTO wire to the brass nipple.
Neon or argon tubes used in letters or signs with P-K housings have their electrodes mounted at 90 degrees from the tube's face.
In the picture on below, I show such a tube from a channel letter S.
At the end of the electrode you can see there are concave brass washers.
These washers have two holes in them.
The washers are secured by the two electrode wires.
This brass disc contacts the P-K housing spring to power up the tube.
Here is a close-up of the electrodes:
Now that we have reviewed P-K style channel letters,
lets move on to standard channel letters.
By standard channel letters,
I am referring to neon channel letters that do not have P-K housings on them.
These types of channel letters use standard double-back bends commonly found on neon tubing.
What's a double-back? Basically it is just like the electrode on the right in the picture above.
It would differ by not having the 90 degree electrode, the electrode would be parallel with the tube.
Double-back connections are made directly to the GTO wire and are covered by what is called a boot or cap.
It is interesting that Electric code does not allow a "twisted wire connection".
Yet, with a standard double back connection there is no other way to connect it.
So although Electric code doesn't technically allow it, it is commonly done.
Boots or caps come in two basic forms, straight through or parallel.
They also come in various sizes depending on the diameter of the tubing to provide a seal.
However boots or caps do not make for a water-tight seal.
As with any outdoor electrical connection, water that gets in can corrode the connection.
Because of this, many sign installers seal the boots or caps with silicone.
To be continued......
11/15/2008 3:40 PM