Power is such an important detail to get right at events… it’s also one of the most complicated pieces of the puzzle. Hundreds of thousands of dollars of lighting equipment depend on the right amount of power; no more no less. If this detail is overlooked, this could create an expensive bill!
Luckily, this is a detail one of our production experts has mastered. Tyler Herron, our technical director, will walk you through exactly what to look for when planning and executing power for your show.
What’s the Formula
AMPS = WATTS / VOLTS
When plugging fixtures into a wall, a SOCA breakout, or an L21-30 lunchbox, that fixture will be receiving 120V of single-phase power. So when calculating this, you will always use 120V. For the purposes of this article, we will not consider 240V power.
There’s another thing we need to consider with lighting fixtures though. Power Linking.
Many of our fixtures have powercon In/Thru allowing us to use DMX looms to keep things tidy. But there’s a catch if you look at the specs of the fixture. For example. Let’s go through a power plan using just the R1 spots.
- Take a look at the manufacturer’s specs.
- Two things to take note of here:
- Power and Current: 303W, 2.34A @120V.
- Power Linking: 5 units @120V.
- Do the math.
- 303W/120V = 2.525A
- 2.525A x 5 units = 12.625A
Do you see any issues here? What gives? 2 things are at play here. First is the amperage rating. Why is it wrong? Well, in this case, I actually think this is a typo on the product page. If you look at the R2X page, their math checks out. This is why we: DO THE MATH OURSELVES.
So what’s the other issue? Look at the amperage of 5 units linked together. It’s 12.6A. But we have 20A circuits, right? (sort of, more on that later) Is that just an abundance of caution with headroom? Why would they give 7.4A of headroom on this? Answer; They’re not.
If you open one of these fixtures, you’ll find the powercon In/Thru outlets are wired directly together. Power flows directly from blue to grey. But, it’s wired with 14AWG wire. Why is that significant?
Take a look at this link. 14 AWG is rated for 15A max. The National Electrical Code (NEC) has a lot of standards for how electrical systems should be set up. There is a standard you’ll see out there that states: “Unless otherwise marked, circuit breakers should not be loaded to exceed 80 percent of their current rating, where in normal operation the load will continue for 3 hours or more.” This standard gets thrown around a lot, and it’s a good rule of thumb to live by. However, for what we do we can push the limits a little bit. We can push this to 90% when calculating our power plans. This is because, in our experience, no equipment runs at full power 100% of the time. Most of our equipment barely gets over 50% on most shows.
So, what are the major takeaways when designing a power plan:
- All circuits should get 10% headroom.
- 30A should be loaded with no more than 27A
- 20A should be loaded with no more than 18A
- 15A should be loaded with no more than 13.5A
Power is fickle, and we like headroom. That 15A rating for 14AWG already has the 80% NEC rule built in. You can safely run 15A on this wire. So how does the 5-unit link max make sense? You don’t want to overload the WIRE because the wire is the weak link. Regardless of what size breaker these are plugged into. Now, are we just resigned to only having 5 R1 spots on a circuit? Well, no. Doing that math how many can we have on one 20A circuit?
Take the total number of amps available and divide that by the amps per unit.
16A / 2.525A = 6.33 units.
So we can safely run (6) R1 spots on one 20A circuit. But, you have to consider what wire it’s being carried on. If we plug 6 units into a power strip are we okay? Well, take a look at the wire gauge on most power strips and answer that for yourself. (hint: they’re mostly 14AWG) On top of this, you have to consider what the actual outlet your plugging into is rated for. You’ll see 2 different kinds of outlets:
 Socapex Cables
Socapex, SOCA, for short. Pronounced two ways: Soh-ca-pecks and Sock-ah-pecks and for short soh-ca and sock-ah.