ICEinLAVA's Domain

Q: “How do you hook up your system to a generator, and not worry about safety issues like equipment damage and ruining the show? Most professionals have unique methods and all look extremely dangerous.”

The answer to this FOH reader’s question is subject of this month’s “Theory and Practice” column. First off, I recommend refreshing yourself with the two power distribution articles I wrote in 2003 about the basics and load sharing. Tying in to a portable generator is similar to tying in to house power, but there are extra tasks for both the sound and lighting production providers (load side), and the generating equipment operator (source side).

I equate making power distribution connections to doing medical surgery; if done right by experienced professionals, everything goes well with no issues. But the wrong way has very serious consequences, including extensive damage to gear, serious injuries and possible loss of life due to electrocution. That is why I endorse only licensed electricians to do this work, and especially electricians who routinely do portable generator tie-ins. These specialists are typically concert venue electricians, tour electricians and senior regional soundco personnel holding electrician’s licenses.

Now that I have done my obligatory scare paragraph, if you plan on making electrical connections, please commit to memory most of the contents of the National Electric Code (NEC). The NEC books are updated every few years and available through the National Fire Protection Association (www.nfpa.org). These code rules and regulations guide how generator connections are to be made along with the essential information on grounding, wiring, interconnects and specifics for indoor (theatrical) and outdoor (carnival) live music performances.

Cam-Loks

Most generator tie-ins will be made to your power distribution rack, and done via individual wires, called feeders, that are not jacketed together but kept bundled by “banding” every few feet with tape or other means. Most feeder wires are black rubberized and weatherproof insulated, and vary in size from 2-gauge to 4/0 (four-ought) gauge. Most of these feeders are terminated with high current capable weatherproof twist-lock connectors called Cam-Loks, and retain a color on the connector rubber jacket (boot) that corresponds to the wire’s function. For example, green boots indicate safety grounds, white boots neutral wires, and black, red and blue boots hot wires. For sound and light production, all the hot wires are set to 120 volts AC with respect to the neutrals and safety grounds. Although Cam-Loks come in three sizes, the middle size (type 1016), is the standard type used most often.

Of the generators provided for performance use, almost all will have a single or three phase switch for load selection. Smaller production companies will lean towards single-phase use at 240 volts AC (120-0-120) as most of their power distribution is geared for 100 amperes or less, and do house power gigs also in single-phase. Three-phase systems tend to be run by larger regional or national soundcos, as they need the extra power transfer that this system offers. In single-phase systems, a four-wire loom of feeders is usually employed (green, white, black and red). With three-phase systems, the third hot wire is added (blue) and 208 volts AC can be measured between the hots (120VAC to neutral). Larger ampacity power distribution systems will double up on neutral and safety ground feeders (7-wire), as the NEC requires neutral and ground ampacity to be double any one hot feeder in three-phase systems.

Some generators may not use Cam-Lok connectors for feeder termination, and you may wish to have a spare 10-foot to 25-foot set of feeder “tails” that have bared conductor ends for bus strip connections on the generator’s output panel. In this case, have your electrician make these connections and ensure no live voltage exists on the busses while making the connections. Even with Cam-Loks, meter the voltages coming out of the operational generator before connecting your distro rack to the feeders. Also make sure to have spare ground and neutral Cam-Lok “turn-arounds” (female to female adaptors) as some generator (genny) carts may have male Cam-Lok receptacles on the output panel. Do not rely on the genny rental house to have these handy adaptors. See Figure 1 for a typical single genny cart to distro rack setup.

Checklist

When employing a portable generator for a gig, the soundco and genny rental house should coordinate via the phone before the event to make sure everything will be the right configuration before generator is set up on site. Ideally, the soundco personnel should get a brief training on generator operation before the rental company personnel depart for the next task.

Sometimes, all you can hope for is that the generator is sitting at idle, nicely earth-grounded, fully fueled and ready to tie in. The following is a typical checklist that the soundco and genny operator should run through:

Check fuel, oil and coolant levels for proper levels. This is usually an operator task.
Select single or three-phase operation, 60Hz operation and make any pre-start voltage level selections (i.e. 120VAC phase to neutral).
Set ground rod, and run rod feeder tail back to genny safety ground Cam-Lok or bus bar connection (green).
Start engine and allow several minutes for warm-up prior to loading with the distro.
Adjust and meter hot phases to neutral for 120VAC. Verify that neutral and ground have zero volts across them, with very low resistance across them and across the genny chassis.
Connect your feeders to the genny output panel during warm-up in the sequence of ground, neutral and then the hot feeders. Trip-off the breakers first if doing bare tails connections.
Make the final connections to your distro rack, and verify on the distro panel meters or hand metering that the correct voltages are present.
Place any mats, feeder anti-trip devices and yellow-jackets on feeder path to prevent accidental wire strain or damage.
Incrementally bring on your loading at the distro for the show.

After the show, the process is somewhat reversed, with the priority that all the distro loads must be off before taking the generator off-line. Many thousands of dollars of equipment damage may result if a hasty genny operator keys off the engine with all the audio still live. Things like blown speakers, amplifiers and signal processing may become real if you hear the dreaded “bang” as the supply voltage crashes. Been there, witnessed that...

Genny Selection and Operation

When I speak of portable generators, I am not talking about these little hardware store, gas-powered units for camping, RVs or household power back-up systems. We are talking about trailered or truck-mounted diesel-powered generators of 40 kilowatts capacity or much larger. The rule of thumb is about a two-to-one ratio or more of genny capacity to distro maximum load capacity. For example, a single-phase, 100A per hot feeder leg could draw 24kW (240 volts times 100 amperes). The reason for the genny derating is that music performances tend to be very dynamic in loading, and the generator must be able to handle low-load to full distro-load almost instantly. Generators use a slow reacting throttle mechanism to add more fuel to the engine in the attempt to keep the generator spinning at 1800rpm for 60Hz. Thankfully, the genny has a flywheel to store rotational energy for sudden demand changes, and a properly lightly-loaded genny will handle most show dynamics.

Some constant loading will help in many generator usage scenarios. With stage lighting, the lighting console operator can be an ally by keeping the stage lighting more continuous or creating a “load bank” of backstage always-on light fixtures to reduce the min/max loading range of the generator. In live sound, audio loading will be mostly at the mercy of performers.

When working with the show promoter, insist on helping with generator provider selection and generator type, or be specific on your contract riders. Finding a reputable genny provider with a good selection of “show-power” or “whisper-quiet” generators is to be strived for. Getting a low-bid, construction-grade generator should not be acceptable. Prevent these kinds of disasters before day-of-show.