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FORWARD
(added December, '03)
Based on a suggestion from an astute reader of this article, the design has been changed somewhat. This design change eliminates any question there may have been regarding the safety or code compliance of the device, without significantly altering the cost, and with no change in performance. My thanks to this reader.
Mark
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The next time you go to check out your local club scene, take a look at how the band is getting AC power to their gear. If they're like just about every band out there, you will see a rat’s nest of orange extension cords strewn behind the power amps, behind the guitar amps; seemingly everywhere. And if the band is fortunate, they've managed to find two separate circuits to get power from, instead of the usual one or two outlets on a single circuit that constitutes what the club owner considers "plenty of power."

As a sound reinforcement supplier having dealt with these frustrations one too many times; I set out in quest of a solution that would be something short of a full-blown professional power distribution setup. I had four primary objectives:

• Provide adequate current to run all audio equipment for a band of up to 12 pieces, and full PA capable of 6000 watts, mains and monitors.
• Reduce the potential for ground loops, reversed neutrals, and other fun wiring anomalies.
• Keep the cost at an affordable level for what was a very low-budget operation.
• Reduce the set-up and tear-down time, along with stage clutter, by reducing or eliminating the need for extension cords.

This article is about just such a device that can be constructed by someone with modest mechanical and electrical capabilities and with materials that are commonly available at a cost of less than $100.

CAUTIONS

This device, as with any device which is connected to AC power, is potentially deadly. Anyone even Considering constructing or using any device similar to what is described is strongly urged to consult with a local electrician and/or electrical inspector to ensure the device's safety and code compliance, prior to construction or use. The writer of this article makes no representation as to the safety, compliance, or usefulness of this device in any given application.

GOING SHOPPING

If you're ready to start building, the first step is a shopping trip. Many people that enjoy building equipment will already have a stockpile of goodies that parts can be gleaned from (if you can remember where you actually saw those parts last). If not, a trip to the local hardware or home supply store is in order. The basic device I'll be describing uses the following parts:

203 feet of 12-3 stranded SO or similar jacketed cable
4 - 3-Pin (grounding) standard Edison style AC plugs (15 ampere or better rating)
4 - Standard Edison (household) duplex receptacles (15 ampere or better rating)
4 - Metal ½" electrical box cable clamps (commonly used to clamp Romex brand cable)
2 - Quad metal electrical boxes (the deep ones are easier to get the wiring stuffed into)
2 - Quad receptacle covers (metal is recommended)
2 - 2 inch length ½" conduit nipples with four nuts each

CONSTRUCTION

Once you've gathered all your supplies, start by lopping about 36" off the 12-3 cable. Set this aside for wiring the grounds in the boxes later. Take the remaining 12-3 cable, and cut it into four equal lengths, which should be about 50' apiece. On one end of these install the four AC plugs. Remember to keep your color-coding consistent in all four cable assemblies. The silver-colored plug terminal is the neutral. Be certain to connect the ground wire to the "U" grounding lug of the plug. Set the four cable assemblies aside.

Gather the electrical boxes, nipples, and clamps. On each box, remove a total of four knock-outs to fit the nipples and clamps, two on one side, two on an adjoining side, so that as you look at the boxes, the openings are on the top and right sides of one box, and top and left sides of the other (See Figure 1). Use the two nipples to join the boxes so they are side-by-side, with the remaining openings being along the top of the assembly. Install the four cable clamps in the four openings.

From the 36" of 12-3 you set aside earlier, strip off and discard the outer jacket and hot and neutral wires so you have only the inner green wire. Cut this wire into 5 equal pieces, about 7" each. Strip each wire end back about 3/4". Use three wires to join the four duplex outlets together at the ground connection only. The wire joining the two middle outlets, if they're set in a row in front of you, runs through one of the nipples joining the electrical boxes; and will have to be pushed through the nipple before the second end of the wire is connected.

Next push the un-terminated end of a 50 foot cable assembly through each cable clamp. Strip back the jacket and wire insulation as needed and connect each cable to one duplex receptacle, again being careful to observe polarity (remember silver is neutral). On each outlet, the ground connection should have three wires; the ground lead from the cable, the wire going to the ground of the next receptacle, or if it's one of the “outer” recepticles, the wire will be connected to the metal box.

The remaining ends of the 7" ground wires from the first and fourth outlets should be mechanically clamped to their respective electrical boxes in a solid fashion (a green screw is often provided for this purpose). Fit the receptacles in place in the quad boxes and screw them down; being careful not to crimp or strain any wiring. Then tighten the cable clamps evenly on the jacketing to securely hold the cables in place, and finally install the receptacle covers.

Other than testing, you're finished. With an Ohmmeter, check to ensure that all receptacles and the quad boxes are connected to the first cable's ground pin on its plug. Ensure there are no short-circuits between any ground, hot or neutral connections. If you are confident the unit is properly assembled, it's time to once again heed the caution earlier in this article and consult an electrical expert before putting the unit to use.

FEATURES

This unit will provide a number of advantages over running individual extension cords. Most orange extension cords are 14 or 16 gauge and only rated for 13 Amps at best. A 12 gauge, 50 foot cable is rated for 20 Amps. This eliminates the bottleneck that's usually placed on power availability by using common extension cords. Most importantly this device, when used to power all audio related equipment, effectively creates a star-grounding scheme, which will help prevent ground loops and other ground related problems. It is important that no audio equipment that is in any way connected to the sound reinforcement system derive its power from any AC source other than this device.

USAGE

This device will usually allow you to access four different circuits (you have a 100' spread to work with), which generally means you'll have the potential for 60 Amps being available, depending on what else is already in use on those circuits. (Note: If 20 Amp rated plugs and outlets are used, as much as 80 Amps may be available). If well distributed, this is enough current to handle the band’s gear and roughly 6000 watts of audio amplifiers.

Other than an extension cord from the device to the Front-of-House (FOH) mixer position, the need for long extension cords is virtually eliminated. On the typical club-sized stage, the device can be centrally located, and very few (if any) extension cords will be needed.

If you will be using this device outdoors, or would like an extra margin of safety, use plastic (PVC) electrical boxes, fittings, and covers, and GFI outlets. Do not install the two grounding wires which are used as a case ground in the basic device. Otherwise all other aspects of use and construction remain the same.

OPTIONAL

An option that will make for a larger finished unit, but provide even less need for extension cord use, is to double the number of box assemblies and duplex receptacles, and wire two duplex receptacles to each cable. If this option is taken, keep in mind that twice as much ground wire will be used for linking the outlets, and only one knock out for cable entry is required in each box.

After having used the device I had made for myself for a while, I modified it in just this way, doubleing the number of outlets.

CONCLUSIONS

In order for this device to work the best, you need to test the available power at the venue. Small plug-in testers that are commonly available can quickly be used to determine if a receptacle is wired correctly and can aid in identifying the locations and how many individual circuits you have to work with. If this is a venue you may work again, it's helpful to make a quick "map" showing which receptacles you're using to make set-up even easier the next time.

By testing your available power before set-up begins, and using this device, your life will get much easier. Set-up and tear-down times will be shortened, the stage will look better, power-related gremlins will go away, and the band will sound better. For a small investment in time and materials, what more could you ask for?

If you want, you can Email me here.

Pro Audio/Electronics and Stuff