LAN Power Requirements and Distribution

[Tami]

LAN Power Requirements and Distribution.
Author: Richard 'Dicion' Thomas
Editor: Mary 'dirt' Richert

As the power coordination lead for Ni! Networks and Quakecon, I have been in charge of making sure power distribution is done properly for 3,000+ computers. Doing that job, you get to learn a couple things, mainly, what does and does not work for large LAN events. I've learned a lot the hard way, and I hate to see others make the same mistakes, which are 100% preventable.

Here I'll outline a few basics of power distribution for LAN Parties. Please keep in mind that these are general guidelines, and there are always exceptions to the rules as well as alternative methods. I’m sure others will say "X is a better way of doing it," but this is simply a summary of my experience in doing this job, and the best ways I've found to do some things.

Still, there's always room for improvement, so if you have suggestions on what I discuss here, please feel free to contact me and tell me so. I always like a good debate on new ideas and theories.

Now, down to the reason we're here. Here are a few basic steps that you may find useful in planning your event.

First: Do not underestimate the power requirements of your attendees. Assume that every computer will be on for the duration of your event. No 75% rule, none of that "staged booting" crap, etc. For all intents and purposes, every single computer in that room, will be on 100% of the time, and sucking an average of 2.5 Amps@120v (300W) each.

Second: Do not believe your facility can provide sufficient power unless you see it with your own eyes. I don't care if it can supposedly power New York City; physically inspect the incoming power, and see what it's rated. Having five 100Amp breakout boxes around the facility does no good if the incoming feed is only rated 200Amps.

Third: Plan your consumption WELL ahead of time. Take your number of users, and multiply it by 300 Watts, a good estimation for current equipment -- 280 used to be good enough, but power supplies and systems require more power these days. So, a 500-person LAN will require 150 Kilowatts just for its users. That's not counting servers, switches, etc. For a 500-person LAN, I would recommend no less then 175 Kilowatts, which, in terms of a single 120V main line, is almost 1,500 Amps: far more than what most small venues (hotel conference rooms, friend's garages, etc) will be able to provide.

It's always nice to find a venue that can support your event, power-wise. Sure, it may be a little more expensive, but compared to a few thousand dollars for renting a generator and power distro system, it's nearly always the cheaper route.

If your venue cannot support your event's power needs, you need a generator. Not just any generator will work, either. You need a high-quality, low-ripple generator, a.k.a. a 'clean power' generator. Now, let's say you've got a generator, and a good clean one at that, it's still not over. In fact, it's just begun.

Power distribution is one of the major headaches of every event.

Basically, it goes like this. Each typical eight-foot table with three people requires 7.5 Amps at 120v for the people sitting there. That means every two tables requires 15A, or one standard 120V circuit. If you prefer six-foot tables, then every three six-foot tables will require one circuit. For now, I'll stick with eight-foot.

120V circuits are typically rated at 20A, however the wiring used for them is not. Don't believe me? Look at your nearest extension cord. Read the rating on the wire itself. Chances are it says 15A or less. If you've ever looked at a typical 100A power distro box, it normally has six 20A circuits. Each circuit is only designed to be used at 15A or less however. That makes 90A +10 for safe room on overages. Very Few circuit panels are ever designed to support the full load of all of their breakers 100% of the time. You just don't need that in most installations.

Layout problem #1 is that most commercial power distro systems use 50Amp, 100Amp, or other even number spider/breakout boxes. This means that each 50Amp box with eight-foot tables will get you 6.66 tables, and each 100A will get 13.3. Nice even numbers, huh? You can fix this with proper planning, via layout examples prior to the event.

The other main problem with commercial grade generator power distribution systems, if they're designed for outdoor use, is that they're rubber lined, weather protected, and most detrimental to us, they're all protected by ground fault interrupters (GFIs).

GFIs are such a problem that they deserve to be addressed in-depth in future articles. Until then, in summary, GFIs are not good for LANS and should be avoided when possible. They cause more problems then they are worth.

If you've gotten this far, I thank you for reading. I wish you the best of luck in your LAN event, and welcome another large LAN to our constantly growing nationwide community.

Please, if you have any questions, feel free to contact me at
dicion@ni-online.org.