Power distribution is a huge subject in concert production, and there’s no way for me to truly do it justice here. Especially when you get into the electrical supply issues for big shows, the topic can get pretty hairy.
Of course, we’re talking about small shows, so that makes things easier. Even so, please be aware of two major points:
1) Handling electricity correctly is absolutely critical to life and safety. Don’t take anything I say and run off towards some sort of homebrew, half-baked solution that can get someone killed. Making something in your garage to fix one problem is very likely to expose you to some other – potentially lethal – problem.
In fact, there’s the first pointer for small-venue power distro: If you made it yourself and you’re not an actual electrician, it doesn’t belong in the mains-power chain. If you ARE an actual electrician, it still might not belong in the chain. If you can’t buy it in an assembled form from a reputable vendor, plugging it into the wall is probably a bad idea.
2) This is not some sort of exhaustive discussion about everything that can possibly go wrong (or right) with power. This is just a few points that I’ve found helpful over the years.
Impedance To Ground Should Be As Low As Possible
A valid connection to ground is imperative for safety. Removing or bypassing the ground connection to “get on with the show” creates a situation where the impedance to ground is effectively infinite. That’s a very, very, VERY bad thing. If you don’t have a reliable, permanently attached, and code-compliant connection to ground, there’s no reason to go any further. Keep your power disconnected until that problem is fixed.
Electricity is very reliable about following the path of least resistance to a 0-volt reference point, that is, “ground” or “earth.” Solid, low-impedance connections to ground are a kind of insurance against accidents. If, say, a piece of equipment suddenly suffers a fault where the case becomes “hot,” a sufficiently low-impedance connection to ground allows a large current to flow across the connected supply circuit. This doesn’t seem helpful, until you realize that large currents are what trip breakers. The (hopefully) enormous surge pops the breaker or blows the fuse, in an effort to prevent people from dying.
An unreliable or absent connection to ground means that YOU may suddenly be the path to ground with the lowest impedance. Such a condition may end poorly for you.
Impedance To Ground Should Be Equal For Everything
Actually getting this exactly right is pretty close to impossible, however, it’s something to consider if you’re having a stubborn hum or buzz problem.
The issue for us audio humans is that our gear all gets connected together in some way. Although this interconnection doesn’t directly involve mains power, the connections to the main power service are definitely a factor. If you’re in the very common situation of the mixing console and other control gear being powered from a different outlet (and, very possibly, a completely different circuit) than the gear “on deck,” different pieces of gear can have multiple paths to ground. If the available pathways have impedances that differ significantly, current can end up flowing back around the various electrical junctions involved.
Since good, low-impedance connections to ground are critical to safety, one solution to this conundrum is to maintain connectivity to ground while using the fewest outlets and circuits practicable. For instance, getting an offending device to use the same circuit as non-problematic devices may help. You have an even better chance if you can use the same outlet box. You must NOT overload an outlet or circuit in the process of trying to achieve quietude, however. Safety has to win all contests of priority. If safety requires that you use multiple outlets and circuits, and you end up with some noise, you just have to live with it.
Resistance To Load Should Be As Low As Possible
Wire has resistance. It may be very low, but it is definitely not zero. Resistance increases in proportion to wire length, and increases in inverse proportion to wire cross-section. In other words, 100 feet of high-gauge (thin) wire resists current more than 1 foot of low-gauge wire.
Resistance causes electrical power to be wasted as heat, and causes noticeable voltage drops across long runs of supply cable. Cable offering too much resistance for the application can overheat under heavy use. This can cause a short, or even a fire.
So, very simply, use the shortest length and lowest gauge of mains power cabling that you can. Keep in mind that everything you connect in series is adding to the length of your run; The 15-foot pigtail on that power-strip counts!
Also, remember that any power cord in direct connection to the wall MUST be rated to carry the entire load that might be present on that connection. “Branches” to individual devices down the line can use lighter-gauge cable, because that single cable doesn’t have to manage the full load on the circuit. The feed to those branches, including any power strip or multitap involved, must be capable of safely operating with the full wattage of the circuit flowing across it. (Speaking generally, “14/3” electrical cable is sufficient for most small-venue power distribution applications. Going down to 16/3 is fine for branching from a multitap, but avoid using that cable for the direct run from the wall.)
As I said, this isn’t everything there is to know about power distro. However, you might find these tips to useful as you go along.