Continuity Clarified

Continuity is a term often heard when preparing for a fireworks exhibition. Continuity in the purest form is the connection between the igniter and the “cue” on the firing module. A “cue” is the speaker terminal or port in which the igniters connect to the firing module. Confirming a connection between the igniter and the cue will ensure that your igniter receives the power needed to fire the attached product. The COBRA firing system tests for continuity by sending a small pulse of electricity through the igniter to verify resistance is present.

Continuity may be checked locally on the firing modules, as well as remotely using the 18R or 18R2 Controller. It is a smart practice to check local continuity on an individual firing module after it is wired, and then again from the controller to test continuity across all modules. Local continuity checks allow the operator to fix the continuity directly from the module for faster resolution and is a step COBRA encourages.

Parallel or Series

Firework displays that involve two or more igniters firing at the same time from a cue are wired using either a series or parallel wiring technique. Both are effective and simple to carry out, each bearing its own set of advantages and disadvantages, as discussed below.

A series connection is an all-or-nothing circuit, as each igniter is daisy-chained to the next, dependent on one another. If one igniter fails, the whole circuit will fail. Consider a strand of Christmas lights; if one bulb is missing or burns out, the entire strand is defective unless the faulty bulb is replaced. A defective igniter will cause the same issue in a series circuit.

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A parallel connection works differently from a series in that igniters are wired together with each igniter’s lead wires directly connected to the module.

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A parallel circuit, unlike the Christmas light example, has no single igniter dependent on any other igniter. If a manufacturing defect occurs with an igniter, it will not interfere with the performance of a parallel wired circuit.  

When determining which wiring method to use, it is essential to examine the pros and cons of each. Note that traditional e-match and MJG initiators can be fired in parallel or series, but Talon/Clip-on igniter clips can only be fired in parallel. It is also imperative to know that COBRA does not recommend combining series and parallel circuits in a single module. Consider the advantages and disadvantages of series and parallel wiring when deciding which method will work best for you.

Series Wiring

  • The advantages of series wiring include being able to fire more igniters than in parallel, and if an igniter is defective, it is quickly identified as continuity will not be displayed due to a broken circuit.
  • A disadvantage of series wiring is that individual defective igniters could prevent all igniters from firing, depending on the defect.

Parallel Wiring

  • A beneficial component of parallel wiring is all igniters firing in the circuit even if an igniter is faulty
  • Disadvantages of parallel wiring include, fewer igniters can be fired, and not being able to identify a faulty igniter as other igniters will hide the faulty igniter by showing good continuity

Maximum # of Igniters by Power Source

  Energizer 9V* LiPo Battery External 12-24V Input**
Talon/Clip-on Igniter--Max per cue 2-Parallel 4-Parallel 5-Parallel
MJG & E-match--Max per cue 8-Series, 5-Parallel 9-Series, 9-Parallel 16 -Series, 12-Parallel

*COBRA only recommends the Energizer 9V battery brand

** When using external input, the values above assume a 24V source with peak current discharge of 10 amps.

Shooting Wire

Shooting wire, also called scab wire, is used to extend the length of lead wire on the igniter by merely twisting the wires together. Added length decreases the maximum number of igniters that can be wired to each cue. In addition to increasing the length of shooting wire, the gauge of shooting wire can also reduce the maximum number of igniters you can fire. In the pyrotechnics industry, 22 AWG is the most common; however, 24 AWG wire is also used. Please refer to the below chart, which indicates the reduced percent of igniters you can fire. For example, if you have 15m or roughly 50 ft. of 22 AWG wire, you can shoot 80% of the maximums referenced in the Maximum # of Igniters by Power source above table above.

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Conclusion

Testing for local continuity at the module is recommended, and continuity tests should always be performed directly from the handheld controller prior to a show.

When wiring more than one igniter per cue, make sure to choose a wiring method (series or parallel) that best fits your situation and make sure to stay within the maximum limits based on the power source and length of any shooting wire you are using. Please find the general best practice recommendations:

  • Use series if you purchase a good quality e-match or buy MJG initiators only.
  • Use parallel if you only plan to fire Talons/Clip-on Igniters which can only be fired in parallel.
  • Use parallel if you plan to fire e-match, MJG initiators, and Talons/Clip-on Igniters on the same module.
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