Whether you are conducting a fireworks display or launching a high power rocket with a cluster of engines, there is obviously a limit on the number of electric matches you could fire on one cue of an electrical firing system. There are many factors that play into this number, a couple of the most important ones are the electric match resistance, internal firing system resistance, and the order in which you wire them. The ematches can be wired in many different series parallel combinations, which will each allow different amounts of current to flow through them. The following graphs will allow you to see how much current is passing through each ematch for these different series parallel combinations. By comparing this current to the "All Fire Current" given by the manufacturer's data sheets, you can determine if your electric matches will have enough current to fire when wired in that particular order. This will allow you to find the maximum number of electric matches you can fire per cue. In order to clarify a "series-parallel" combination, see the figure below. There are three graphs, each assumes an internal firing system resistance of 4 ohms, and a different electric match resistance. Each of these values is at the top of each graph. For my complete published paper on this subject, which comes with the mathematics, experimental test results, and other technical info, go to Journal of Pyrotechnics and order issue 20.
The data below was used to simultaneously set off 47 rocket engines (twice!) for the Discovery Channel Show Mythbusters in the episode titled "Ming Dynasty Astronaut". For more information and pictures on this event, visit our television and movie pyro page. That event was sponsored by the Friends of Amateur Rocketry. Visit their web site for additional info on the event.