Server Farm Power Upgrade 2011

To integrate the EGS Sola 4000-series 3kVA UPS systems into my server farm, I needed to replace the four 15A 120V outlets with a pair of 30A 120V twistlock outlets. While I had all of this apart, I decided to upgrade the feeder circuit from 30A to 50A and also install a 50A automatic transfer switch.

Going forward, when I start the generator outside, the transfer switch will wait about 30 seconds then switch the server farm to the generator, automatically. What I used to have to do is start the generator, then run back inside to manually flip switches then run back outside and pull down the choke. Too many steps for a "fast" cutover, and the new wiring will cut some of these steps out.

I selected a "Square-D" 8 space 250V panel from Home Depot mostly because Square-D is one of the better brands and also because it was reasonably priced. I installed two single pole 30A breakers for the EGS Sola UPS systems and four single pole 15A breakers for non-server appliances like sump pumps, the fridge, and possibly the heating system. While my oil-heat furnace was installed on a 20A circuit, the ignition module, fuel pump, and hot water pump draw a mere 5 amps during startup and drop down to 3.5 amps. Going forward this will allow for generator-powered heat and hot water as well.

Here is a picture of the 50A automatic transfer switch mechanically connected to the sub-panel.

I decided to mount the electrics on a piece of outdoor-grade plywood for safety reasons. This is generally not required in home applications if what you're mounting the electrics to does not burn (concrete block for example), however I chose to do it anyway because screwing the electrics to plywood is far easier than screwing them to concrete block. Here I'm measuring out the plywood the easy way - laying the items on it and marking it with a framing square.

Now the "insides" are wired with 55A THHN power cable, which is above the 50A limit of the transfer switch. I generally use a wire of a higher ampacity for high power circuits just to be safe.

Here is the 6-ga 4-conductor wire I will be using. It's Romex, which is allowed in NJ. Since the path this wire will be taking is unobstructed and free of things that might rub on it, I felt going the conduit route would be more work than it's worth, especially considering I upped the ampacity of the wire a bit from what I actually needed.


Since I had wired my sump-pumps through the original panel with a cheesy 3-way switch in order to manually throw the sumps onto the generator, I had to disconnect the feed from the old panel from the sump pump outlets. Had I not done that part of the old sub panel would still be live once I threw the main breaker feeding it. I'm glad I remembered ;-)

Now, I highly do not recommend doing this. Since I wanted my server farm to remain "live" during this upgrade, I chose to carefully remove the screws mounting the old panel on the wall with a magnitized screwdriver. This allows the old panel to remain live and the screws hopefully not to fall onto the buss bars inside the sub-panel. Again, I do not recommend doing this. I did because I'm an over-confident former electrician ;-)

The next step was to cut out the crappy paneling on the concrete block wall and install the plywood backing board. I used "tapco" screws to install it, and cut the paneling as close to the dimensions of the plywood as I could to minimize the uglyness. I'll probably put cheap molding around the perimeter at some point (yeah, sure, right)

The next step is to mount the electrics as I laid them out before, transfer switch on the left and subpanel on the right. Since I already pre-drilled the screwholes this zipped right in.

This is my nasty main panel as I moved in. Whoever installed this in 1981 was nothing short of an ass. However, it's what I have so I removed the old 30A 240V wire and installed the new 55A 240V wire in it's place. For right now, I'm going to recycle the 30A breaker since I'm not attaching my sumps, furnace, or fridge to the subpanel at this time. I just want to get the servers online as fast as possible because just before this picture I had to remove power from the old panel that was dangling and cut it out of the way.

Now that the main feed is run (breaker still off), I'm finishing off the post-sub-panel terminations starting with the first 30A 120V twistlock. The 30A wire for this was the original 30A feed wire that I just removed between the main panel and the old sub-panel. Instead of buying new wire, I simply removed the outside jacket and fed the individual strands in the conduit. I put conduit here because I sometimes store computers just below the panel temporarily and I didn't want them to bash up surface mounted Romex.


Wires for the two twist-locks are run through the conduit and into the sub-panel, each set on its own breaker of course.

Now that the twistlock outlets are done I then wired the 50A feed wire into the transfer switch and used entrance staples to hold it in place against the plywood.

Once I double-checked the feed wiring from the main panel to the transfer switch, and then to the subpanel, I then put the covers on and tighted the screws. Nice and clean.

And, with everything installed and tested, I then wired up the main panel side of the feed in place of the original feed and buttoned everything up. Like I said earlier, I'm re-using the 30A two-pole breaker for now since I'm not wiring up the sumps, heating system, or fridge at this time.