Basics of 3-Phase Power in Large Stage and Event Lighting Systems

Three-phase power is a supply with three live conductors whose voltages peak at different moments, 120 degrees apart. Stage and event fixtures still run on ordinary single-phase power. A three-phase distro takes the large feed and splits it into normal circuits, and your job is to spread the fixtures across the three phases so that no single phase carries most of the load.

When a lighting rig needs three-phase

Most mobile DJ, church and school rigs run fine on a few single-phase circuits. Three-phase comes in when the total load grows past what wall outlets can supply. For scale: at 230 V, one 16 A socket circuit gives you about 2.9 kW of continuous load at the usual 80% planning limit. A 32 A three-phase supply gives you about 17.6 kW, spread over three phases.

You will usually meet three-phase in one of these places:

• A venue stage power point. Theaters, arenas, larger halls and some hotel ballrooms have a dedicated outlet or disconnect for touring rigs. In the US this is often called a company switch.
• A generator. Festival, tent and outdoor stage generators above a few kilowatts are often three-phase.
• A rental distro. Production rental companies supply distribution boxes that connect to either of the above.

Voltages and connectors by region

Each phase measured to neutral gives you the normal single-phase voltage. Measured between two phases you get a higher voltage, 1.732 times the phase-to-neutral voltage.

Japan's three-phase supplies are usually 200 V and arranged differently, so leave the connection to the venue's electrician. Anywhere, the lower voltage is what your fixtures expect. Many LED fixtures accept 100–240 V, but a fixture wired between two phases on a 400 V system will be destroyed. That is why you only plug into the outlets a distro provides and never improvise an adapter.

What a distro actually does

A power distribution box takes the three-phase input and splits it into outgoing single-phase circuits. Each circuit connects to one phase plus neutral and earth, has its own breaker, and on a well-built box has RCD or GFCI protection. Outputs are labeled by phase: L1, L2 and L3 in Europe and Australia, often A, B and C or X, Y and Z in North America. Many distros also have meters that show the current on each phase.

Each outgoing circuit still follows normal single-phase rules. A 16 A circuit at 230 V can carry about 2,940 W continuously, which is ten fixtures rated 285 W. A 20 A circuit at 120 V can carry about 1,920 W, which is six of them.

Phase balancing with real numbers

Take a mid-size event rig: twelve ZQ02253 285W moving heads (3,420 W), twenty-four 145 W PAR lights (3,480 W) and eight 250 W wall washers (2,000 W). That is 8,900 W in total. Use the power figures from each fixture's manual for your own plan; these numbers are for the example.

On a single phase, 8,900 W would draw about 38.7 A at 230 V or 74.2 A at 120 V. Spread over three phases, it looks very different.

In the balanced plan, the currents on the three phases mostly cancel in the neutral. In the unbalanced plan, L1 does most of the work, the neutral carries real current, and the voltage on the heavy phase can sag. On a 32 A supply at 230 V, the 80% planning limit is 25.6 A per phase, so the unbalanced L1 is already close while L2 and L3 sit mostly idle. Neutral figures here assume simple resistive loads. Large numbers of LED drivers and switch-mode power supplies can add neutral current even when the phases look balanced, which is one more reason to keep the neutral full-size and leave distro wiring to people qualified to do it.

How to build a phase map

1. List every fixture with its power from the manual or label. Include fog machines, hazers you rent, media servers and the control position.
2. Group fixtures into circuits. Keep each circuit at or below 80% of its breaker rating.
3. Spread each fixture type across all three phases. When a cue brings all the moving heads to full, the load should rise on L1, L2 and L3 together. This also means one tripped phase takes out a third of each fixture type rather than every wash light in the room.
4. Total each phase. Aim for the three totals to be as close as you reasonably can. A difference of a few hundred watts is normal; a phase carrying twice the load of another is not.
5. Label everything. Mark phase and circuit on each cable end and on the plot, and write the per-phase totals where the crew can see them.
6. Check it live. With the rig at full white, have the distro technician or electrician read the per-phase meters. Recheck after any fixture is added or moved.

Running from a three-phase generator

Generator nameplates usually give kVA and kW. The kW figure is what you plan with, and many nameplates assume a power factor of 0.8, so a 20 kVA unit is typically rated around 16 kW. Plan your continuous load at or below 80% of that, about 12.8 kW in this case, which is roughly 18.6 A per phase at 230 V if the load is balanced.

• Balance matters more on a generator. Uneven phases make the generator's voltage regulation work harder. Ask the rental company what imbalance their unit tolerates.
• Tell the supplier your loads are mostly LED. Electronic power supplies can affect how a generator should be sized and regulated.
• Earthing and placement follow the supplier and local rules. Keep the generator away from audiences and air intakes, and plan fuel for the full run time plus setup and focus.

Safety lines you don't cross

• Connections to a venue's three-phase supply are made by a qualified electrician. In many places that is a legal requirement, not just good practice.
• Don't open a distro or rewire connectors yourself. Report damaged plugs, warm connectors or tripping RCDs to the person responsible for the power.
• Never use an adapter that drops or shares the neutral. If the neutral breaks on a three-phase system, the voltage on lightly loaded phases can rise toward phase-to-phase voltage and destroy fixtures plugged into them.
• Use RCD or GFCI protection on outgoing circuits, especially outdoors, and keep connectors off wet ground.
• Follow local rules. Temporary power requirements differ between countries, venues and insurers. When in doubt, ask the venue's electrician before the load-in, not during it.

FAQ

Are there three-phase stage lights?

Almost all stage fixtures, including PARs, moving heads and wall washers, are single-phase loads. What is three-phase is the supply and the distro feeding them. Some large dimmer racks and chain hoists take a three-phase input directly.

Does phase rotation matter for lighting?

Not for single-phase fixtures. It matters for three-phase motors such as some chain hoists, where wrong rotation makes the hoist run the wrong way. The rigger or electrician checks it when the hoists are connected.

How do I know if my rig needs three-phase?

Add up the continuous load and compare it with what the venue's single-phase circuits can supply at 80% of their rating. If the rig needs more circuits than the room has, or more than a single supply point can deliver, ask for a three-phase stage supply or a generator.

Can the phases be perfectly balanced?

Rarely, and they don't need to be. Fixtures come in fixed wattages and cues change the load all night. Keep the totals close at full output and make sure no phase goes past its planning limit.