April 2006 Issue
Theory and Practice

Power Distro Connections

Of all the mail that I receive, the subject of power distribution seems to bring the most pleas for more info. I have plenty of stories of arcs and sparks, but thankfully, few have emanated from my handiwork. I will tell you a secret: I have been deathly afraid of medium voltage (120, 240 volts) ever since I was a kid; and I think that my healthy perspective has helped me from being overconfident. But my parents do remind me that I, as a toddler, did stick my hands into a few uncovered outlet boxes; received a shock, ran crying back to my parents and repeated my curiosity a few more times that day. And you wonder why I am an electrical engineer today? But this column is about power distro connections, and the do's and don'ts of making them. I am going to let the pictures do the talking, but I will sprinkle in a few anecdotes to explain my thinking.

Cam Locks

Throughout my 30-plus years of being a musician, it has only been the last 10 years that I have discovered what Cam Lock connectors are and how they are used. Most of you have seen them at carnivals and fairs, but never thought they would become part of live sound production. Most high-power feeder wires use these single-conductor, insert-and-twist connectors for 8-gauge wire and larger feeders. Fig. 1 shows a banded and coiled group of 2-gauge feeder wire with 1016 Cam Lock male and female ends for 100-amp, single-phase service.

Cam Lock connectors come in three sizes (1015, 1016 and 1017).

The 1016 size is the most common with a maximum rating of 400 amperes. The 1015-size Cam Locks are typically dubbed mini-cams for 8- to 4-gauge wire and a maximum rating of 150 amperes. I rarely see mini-cams in use, usually with stage lighting dimmer racks and some touring power amp racks. Even rarer are the 1017 maxi-cams with 350 to 750 mcm feeders and a maximum rating of 690 amperes. The usual 1016 Cam Locks can handle #2 to 4-0 feeder wire.

Most Cam Locks are weatherproof, with their colored rubber boots protecting innocent fingers when open and forming a watertight connection when connected. Cam Locks also come in panel-mount as well as cable connectors. When dealing with Cam Lock feeders (carney cable) and Cam Locks, it is best to let a trained person with the right fixtures and jigs do the connector to feeder attachment to ensure a tight seal on the boot to the cable jacket.

Straight-Blade Plugs and Receptacles

Of the lower amperage connectors, the straight-blade dryer and electric range plugs win the popularity contest due to lowest cost and availability. Yeah, many touring racks have 30- and 50-ampere twist-lock power interconnects, but there is almost $100 of brass and nylon involved in each pair of plug and receptacle. For us weekend warriors in the clubs, the presence of a NEMA 14- 50R range receptacle at the back of the stage means that we are plug-and-play, instead of plug-and-pray for the illegal receptacles that force the neutral and safety ground onto a single contact.

Of course, not all receptacles are wired 100% correctly. That is why you should have a working knowledge of the commonly- encountered receptacles and know which slots are supposed to be hot, and which are to be neutrals and grounds. And do not leave it at metering the 120 volts to neutral, but check for no voltage between the safety ground and neutral contacts; then check the resistance between safety ground and neutral for decent continuity. To get to know what NEMA 14-50 range plugs and receptacles look like, take a look at Fig. 2 for the pair.

To get familiar with the families of straight-blade connectors, check out www. leviton.com/sections/techsupp/nema.htm for all the pictures. Everyone should be familiar with the NEMA 5-15 household "Edison" plugs and receptacles. But the most common good distro plugs and receptacles are the four-contact NEMA 14-30 dryer and NEMA 14-50 range devices. The older NEMA 10-30 dryer and 10-50 range connector with the three-prongs (hot-hot-ground), were intended for the older 240 VAC-only appliances and grandfathered out of usage back in the 1980s. But I still see old local soundcos with 10-50 plug adapters on their club distros cheating death and lawsuits to use these older club receptacles. One soundco, which shall remain nameless, even added a green-wire spring clamp to the 10-50 plug in the wishful thinking that the club's feeder conduit might actually be a decent safety ground path. Fig. 3 shows three NEMA plugs, the 5-50P (illegal), the 14-50P (legal) and the 10-50P (illegal).


Distro tails are typical moderately short pieces of feeder cabling that have a receptacle (female connector) at one end, and 6 inches to a foot of loose conductors at the other end. I have 10 to 15 feet tails for both my Cam Lock feeders (2-gauge) and my 14-50 feeders (6-gauge). Most tails shrink with usage as the loose ends are bared a half-inch for screw termination into bull switches, circuit breakers or ground or neutral buss-bars. Be wise and always de- energize your hots before connecting the tail bare ends to the screw orifices. As your bare stranded copper wire ends fray with usage, trim back the frays and strip new ends. And as I have to state, if you are not a licensed electrician, do not play with tails or the legal professionals may lay waste to your financial health for the foreseeable future. While most moderate to bigger clubs do provide distro receptacles, some may only have bull switch/sub-panel breakouts available. Fig. 4 shows my #6 set of tail loose ends with freshly-stripped bare copper wires. Note that I did not pull all the feeder insulation off the ends, but left it in place to prevent fraying before connecting.
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