I just spent a good chunk of the morning signing papers saying that I cannot disclose certain information about the gig I was about to work on. You know the drill. Before you can work on a show that you'd love to tell everybody about you have to promise not to tell anybody about it. So what better way to spend the evening than to blog about it?
I was part of a crew that was wiring a set with some marquees that have lots and lots and lots (and lots) of lights. The question arose about how to wire them. After showing a couple of us a rather large array of these lamps and explaining how to mount them, I asked if they should be wired in series, in parallel, or in series/parallel. In answer to my question I was led to another part of the set where rows and rows of these lights were already mounted, wired, and ready to go. The chief explainer then found a free extension cord and plugged them in to illustrate what they should look like after the job was done.
Apparently I asked the wrong question. So I thought a little bit and then I asked a different question. What is the rated voltage of the lamps? "Eleven watts," was the answer, albeit not the answer to the question I asked.
I don't mean to demean anyone. It's not their fault that some people were never taught how to wire circuits. Years ago I was lucky enough to sit through a course in circuit analysis, and I learned a lot of concepts with funny sounding names like Ohm, Norton, Thevenin, and Kirchhoff. One of the concepts that has been most useful is probably Kirchhoff's voltage law, which says that the voltage around a circuit adds to 0. The supply elevates the voltage and the circuit elements drop it back down to 0. That's why I know how to wire lamp circuits.
If I had been told that the lamps we were using were rated 12 volts, then I would know I could wire 10 of them in series on a 120V supply because each lamp drops 12 volts. Then we could wire groups of 10 in parallel so 120 volts would be applied to each string of 10 lamps. If we were using 24V lamps, then we could wire 5 of them in series, and then wire those groups of 5 in parallel. But I didn't yet know the rated voltage of the lamps.
So I quietly slipped away and surreptitiously meandered about, looking for a sample of the lamps. I finall found one and it was a rated 130V. Then, back at the array of lamps, I stared down a row of sockets with gleaming copper wire protruding from black and white insulation, and wired them all in parallel so that 120 volts was applied to each one. Since the applied voltage is lower than the rated voltage, they have a nice warm orange glow and they will last much longer than the rated life of the lamps.
One day I'll be able to reveal which television show the set is for. In the meanwhile, if you happen to see a set on television with lots and lots and lots (and lots) of 11-watt lamps, think Kirchhoff.
12V lamps wired in series/parallel.
24V lamps wired in series/parallel.
130V lamps wired in series.