Wiring Devices and Firing Systems in a Consumer Fireworks Display
Introduction
In the past I've discussed making electric matches with which to ignite devices electrically, and the construction of Cremora fireballs which can be impressive additions to any show.I've also looked at the issues involved in thoroughly planning a consumer fireworks display.
Now it's time to discuss using those electric matches in conjunction with an electric firing system and shooting wire, and hooking devices up to them out in the field.
In the next article, I'll also show you how to use fireworks fuse like visco fuse, fast-visco fuse, quickmatch, time fuse, and fast-fuse to attach devices to each other for sequential firing.
Using these methods together can result in a nicely timed display, and will also enable you, the display designer, to sit back and enjoy the show with the rest of the crowd.
Shooting Wire
"Scab wire" or shooting wire is the wire that is used to connect the firing panel to the electric match. It essentially extends the length of the leads of the ematch, or connects multiple igniters in one firing circuit. It is important to know the wire's resistance for a known length of it.Scab wire usually comes in rolls that have "duplex" wire on them, which means that the wire is two-conductor wire. Two insulated wires are attached to each other, side-by-side.
Two-conductor, copper, insulated wire is probably the most commonly found scab wire out in the field. There is also copper-clad, aluminum, insulated wire that is being imported and used.
Short Pieces of Two Types of Shooting Wire, and the Tools for Working with It
I cut the wire with the wire-cutters (dykes), split the insulated wires apart with the same tool, or the razor knife, or with my fingernails, and strip the insulation with the dykes or with my fingernails. If I use the dykes to strip the insulation, I'm careful to avoid damaging the wire itself, which is easy to do. I therefore prefer to strip the insulation with my fingernails.
The most important thing to know about the wire that you are using is its resistance. This is listed as "ohms per 1000 feet" in wire data tables. It's easy to determine this for yourself, though.
Digital and Analog Multimeters to use on Electric Circuits
All you need is the wire and a multimeter, which measures voltage and resistance. A digital meter like the one on the left is a good investment because it will be used in this step and also in future testing of firing circuits. The analog meter on the right is good for testing batteries and can be used to check resistance, but it is not as accurate as the digital meter.
Note: In a circuit which contains ematches, I only use the digital meter to check resistance. The analog meter can fire ematches, which is NOT something you want to happen!
To determine the resistance of my shooting wire, I take 50 feet of my duplex (two conductor) wire, bare 1 inch of both wires at one end of it, and twist those ends together securely. I then separate the wires at the other end for 3-4 inches, and bare 1 inch of those ends. Now I set the dial on the multimeter to the setting for measuring resistance (ohms) and wrap one bared end of the shooting wire on one of the meter's probes, and the other end of the wire on the other probe.
I'm actually measuring the resistance in 100 feet of the single-strand wire since the measurement current is going out 50 feet to the twisted ends, and then back 50 feet to the meter.
I should get a reading between 1.6 ohms for the 22 gauge copper wire, and 3 ohms for the copper clad aluminum wire. This exact reading will depend on the actual wire you are using. I then multiply this reading by 10 to get the resistance in ohms per 1000 feet of the wire.
The yellow wire I've described has a resistance of 16 ohms per 1000 feet, and the orange wire's resistance is about 30 ohms per 1000 feet.
Electric Firing Systems
I have a few different firing systems. I have a new Skylighter 12 cue wireless system which puts out 4.5 volts. Then there are my older model 8 and 12 cue wireless panels which put out 12 and 18 volts. I also have a hard-wired 144 cue system which sends out 24 volts, and I've recently seen the 10 cue capacitive discharge, hard-wired system from Skylighter which fires with higher voltages.Skylighter Wireless 12 Cue, and Hard-Wired 10 Cue Firing Systems
To determine the firing voltage of my systems, and to check the batteries in the panels before use, I simply set a multimeter on DC voltage, hook it up to one of the firing cues, and fire that cue. The meter will read the voltage that is being sent to that pair of connectors by the firing panel.
Before the show, I use the meter to check the batteries in my firing system, both in the transmitter and receiver. I always have spare batteries for the multimeter and for the firing system in my kit of spare stuff that I bring to a display.
Hooking Devices up to an Electric Firing System
This subject sounds like the simplest thing in the world, doesn't it? But, believe me, there may be no quicker way to insure failure with a fireworks display than to ignore some of the "rules" of electric wiring that I'm about to relate.If you keep these tips in mind electric firing can really be an incredible enhancement to any display.
- Attaching an electric match to the scab wire
The two pairs of wires are then tightly and completely twisted together.
An overhand knot is tied in each pair of wires.
This results in ematch wires that are securely attached to the scab wires. The knots prevent the connections from being yanked apart in case someone trips over a wire. The wires wrapped in opposite directions prevent the two bare-wire connections from coming in contact with each other, which would prevent the ematch from firing when it is supposed to.
- Attaching shooting wire to the firing panel
Once again there are right ways and wrong ways to attach wires to the firing system. First, I separate the insulated wires for about 3-4 inches, and strip the insulation back for 1 inch on each wire.
If I just stick the bare wires into the panel's connectors, there's a good possibility they can be pulled over and into contact with each other. This would short this circuit out and prevent the electric match from firing, as shown in the photo on the left below.
So, instead, I double each bare end against itself, insert those doubled ends halfway into the connectors, and then "pinch" the connectors toward each other to insure that the wires are really crimped into their connections.
Incorrect Way and Correct Way to Connect Wires to Firing System
You'll notice that I've only inserted the doubled-ends into the connectors halfway so that I can visually insure that the connector is not clamping down on insulation instead of the wire. I have also not inserted the wires so far that the clipped ends of the wires are down inside the connector. This could make removal of the wires difficult at the end of the show, and possibly damage the connector.
- Strain-relieving the wiring at the firing panel and at the device
At this point in the show setup, folks need to be reminded to walk carefully and avoid the wiring. And as soon as I do that, I'll sure-as-shootin' trip over a wire myself, yanking it loose from the panel, or worse, pulling way too hard on a fireworks cake fuse or a shell leader.
One simple procedure can prevent a lot of problems in the above scenario: strain relief.
Simply put, anchor your shooting wire and/or ematch leads to something solid near the devices and near the firing system. Often, the ematch leads can be tied off to a mortar-rack. But, if there is not something nearby to tie the wire to, I'll simply drive a wooden or metal stake into the ground and tie the wiring to it with a clove hitch.
I place these wire-knots down the stake, near the ground so that if a wire is tripped over it won't pull the stake over too far.
Strain-Relieving Shooting Wire
- Attaching the electric match to a fireworks device
Wiring Calculations
I now know how to securely connect my wires to each other, to the fireworks devices, to the firing system, and how to safely strain-relieve them.But, how much wire can I actually run between the firing system and the electric match?
Each ematch needs a minimum of 1 amp of electric current to run through it in order for it to fire. Because of the wire resistance which I described above, if too much wire is used between the panel and the ematch, less than 1 amp of current will flow in the circuit. We then run the risk of having the igniter fail to fire.
Ok, here it is: a formula. Don't let it scare you off. I'll actually help save you from having to use it in a moment.
Resistance = Voltage divided by Current
I know the minimum amount of current I want in a firing circuit: 1 amp.
I know the voltage that my firing system puts out: 4.5 volts.
Resistance then equals 4.5 divided by 1 which equals 4.5 ohms. This amount of circuit resistance will allow a current of 1 amp to flow.
If I go above this maximum amount of resistance in my circuit, the current will drop below 1 amp. So, it's fine if I have less than 4.5 ohms of resistance in the circuit since that will simply increase the current above 1 amp.
The homemade electric matches that I detailed in the article cited above all had a resistance of 1.2 ohms. Commercial ematches will have typical resistances of 1.5 - 2 ohms. I'm going to assume we're using the 1.2 ohm matches for the purposes of this discussion. (But you should always test yours.)
Since my ematch has a resistance of 1.2 ohms, and I want a maximum of 4.5 ohms of resistance in this particular circuit, then 4.5 - 1.2 = 3.3 ohms left over for the scab-wire's resistance.
I can now calculate the maximum lengths of the wires that I can use. For example: the yellow scab wire has a resistance of 16 ohms per 1000 feet.
(Using the 3.3 ohms left for scab wire) 3.3 divided by that 16 equals 0.206.
0.206 times 1000 feet equals 206 feet.
206 feet of this wire would have a resistance of 3.3 ohms. This is the maximum amount of this wire I can have in this circuit. Any more of this wire and my total resistance will be too high.
But, this is a maximum of 206 feet of the single strand wire, and my shooting wire has two strands: one out from the panel to the ematch, and one back from the match to the panel. So, in reality, I can only have a maximum of 103 feet of the double-strand shooting wire between my 4.5 volt firing panel and my igniter.
If I am using the orange (copper-clad aluminum) wire described above, which has a higher resistance of 30 ohms per 1000 feet, then I could only use 110 feet of the single strand wire going out and back, or 55 feet of the double strand shooting wire.
The table below lists these figures for the two types of scab wire, the length of double strand wire between the panel and igniter, and for 4.5 volt, 12 volt, and 24 volt systems.
Max Resistance |
Max ft. of yellow wire |
Max ft. of orange wire |
4.5 Volt Firing System (one igniter in circuit) |
||
4.5 ohms | 103 ft. | 55 ft. |
12 Volt Firing System (one igniter in circuit) |
||
12 ohms | 338 ft. | 180 ft. |
24 Volt Firing System (one igniter in circuit) |
||
24 ohms | 712 ft. | 380 ft. |
Once again, these are the maximum lengths of the double strand wire I can use in the circuit.
Now, it's easy to run a maximum of 103 feet of the yellow, two-strand wire, hook up one end to the ematch, and the other end to my digital meter, and check the resistance in that firing circuit. The resistance should not exceed 4.5 ohms, and should fire successfully with my 4.5 volt firing system.
The test circuit shown below, with 100 feet of the scab wire, read 4.5 ohms and fired as designed.
Ematch and 100 Feet of Shooting Wire, Reading 4.5 Ohms
Firing More than One Electric Match per Cue
This introduces the last bit of complexity into the subject of electric firing. Each firing cue can indeed fire more than one ematch, but as usual we have to be careful when designing the circuit so that our igniters will fire as planned.There are two basic ways to hook up multiple ematches to one set of connectors on our firing panel: in series and in parallel.
- Series Wiring
Three Igniters Wired in Series and Connected to the Firing System
A significant advantage to series wiring is that, since the current has to flow through all the ematches before it returns to the panel, the test lights on the panel will test all of the igniters at the same time. If there is a bad match, the test light will not go on.
Also, with a typical amount of shooting wire in such a circuit, series wiring requires less current to fire the igniters, thereby allowing longer lengths of the scab wire to be used reliably.
In the field, most pyros use series wiring, with few exceptions. Serial wiring is counter-intuitive to some people. They assume that if 2 or more electric matches are serially wired to each other, that when the first match fires, that first ematch will break the circuit and prevent the remaining ematches in the circuit from firing. But in practice, the current flows so quickly that all the ematches in any given serial circuit will fire at the same time.
In this series circuit, the resistances of the ematches are added together to obtain their total resistance: 1.2 ohms plus 1.2 ohms equals 2.4 ohms of resistance for two matches.
We still only need one amp of current in the circuit, though, to fire the matches. So, using the 4.5 volt system, with my maximum resistance in the circuit being 4.5 ohms as determined in the example above, the maximum resistance of my shooting wire can be up to 2.1 ohms.
Thus, I can add a maximum of 66 feet of my double-strand-yellow scab wire, or 35 feet of my orange-double-strand wire to the circuit. This wire can be added anywhere in the circuit: between the panel and the igniters, between the igniters, or both.
Note: I always test my completed circuits to see if the actual resistance in the circuit is close to my calculated resistance. It is also important that all the matches in the circuit are the same type and have the same resistance. If one match ignites before the others do, because of differences in construction, then there is a good chance the rest of the matches in the series will fail to ignite.
- Parallel Wiring
Parallel Circuit Connection
A disadvantage to this circuit is that, since the current has more than one way it can flow, if even one ematch is good, the whole circuit will test "good" with the panel test light. A bad ematch will not cause the test light to remain dark!
Parallel wiring also will allow less scab wiring to be used out in the field.
The circuit above will only show an amount of resistance equal to the resistance of one ematch divided by two: 1.2 ohms divided by 2 = 0.6 ohms.
But, the circuit requires one amp of current for each igniter, or a total minimum of 2 amps of current.
So, with my 4.5 volt system, I can use a maximum of 50 feet of the yellow 2-strand wire, or 28 feet of the orange. The maximum allowable resistance in a circuit with two, parallel matches is 2.25 ohms.
Once again I always draw out a firing circuit, calculate how much resistance it ought to have, and check the actual resistance with my meter to check the circuit in actuality.
The Final Wiring Table
Here is a table which shows the maximum allowable length of each type of double-strand shooting wire, for 4.5 volt, 12 volt, and 24 volt systems, using either series or parallel wiring if multiple igniters are in a circuit.# of Ematches |
Max Resistance |
Max Yellow wire |
Max Orange wire |
4.5 Volt System |
|||
1 match | 4.5 ohms | 100 ft. | 55 ft. |
2 parallel | 2.25 ohms | 50 ft. | 28 ft. |
3 parallel | 1.5 ohms | 34 ft. | 18 ft. |
2 in series | 4.5 ohms | 66 ft. | 35 ft. |
3 in series | 4.5 ohms | 28 ft. | 15 ft. |
12 Volt System |
|||
1 match | 12 ohms | 338 ft. | 180 ft. |
2 parallel | 6 ohms | 169 ft. | 90 ft. |
3 parallel | 4 ohms | 112 ft. | 60 ft. |
4 parallel | 3 ohms | 84 ft. | 45 ft. |
2 in series | 12 ohms | 300 ft. | 160 ft. |
3 in series | 12 ohms | 262 ft. | 140 ft. |
4 in series | 12 ohms | 225 ft. | 120 ft. |
24 Volt System |
|||
1 match | 24 ohms | 712 ft. | 380 ft. |
2 in parallel | 12 ohms | 356 ft. | 190 ft. |
3 in parallel | 8 ohms | 238 ft. | 127 ft. |
4 in parallel | 6 ohms | 178 ft. | 95 ft. |
2 in series | 24 ohms | 675 ft. | 360 ft. |
3 in series | 24 ohms | 638 ft. | 340 ft. |
4 in series | 24 ohms | 600 ft. | 320 ft. |
Redundancy
In the name of successful electric firing, I'd like to mention redundancy, and then repeat it.If I have a critical item in a display such as a set-piece that I simply cannot allow to fail to ignite, I'll actually run two firing circuits (cues) to it. If the first one fails, I have a backup.
If there is any doubt about the capacity of a circuit out in the field, I'll remove the match from the device and test fire that circuit before the display. Then I'll replace that ematch with a new one and reconnect it.
Often on items such as set-pieces, waterfalls, and firecracker walls, I'll have two igniters and ignition points, wired in series. I'll also have a length of quickmatch rigged up as an alternative manual ignition point in case the electric firing fails. I keep a propane torch by my side during the show, and will use it to manually ignite devices if necessary, and if it can be done safely.
Although some of these preparations may end up being unnecessary, they can save the day for you.
With each display I have one shot at having it go off successfully. I want to do all I can to insure that it does.
Stay Green,
Ned