Posts in category electrical

Power Strip, Extreme

I have power tools and those from whom I can borrow power tools which require several different types of power. The mundane things run on your standard 120V 15-amp receptacle. The less mundane tools require 240V 15-amp. And then they get interesting... 240V 30-amp, and two variants of 240V 50-amp receptacles.

Wiring up receptacles on the wall for each of those ties the tools to that one location, and for some things, I want to be able to use them outside, not just in one location. So that means an extension cord, but I didn't want five different flavors of extension cord, either. Maybe one extension cord to rule them all and a half-dozen dongles?

I really wanted a more elegant solution. Ok, maybe a less awful solution?

First, let's talk receptacles. Power receptacles follow a standard set by NEMA with identifiers like NEMA 5-15R, or NEMA L14-30R. The key to understanding these is presented in this document from Essentially, the first number indicates what wires you have available in that connection. An "L" prefix on that number indicates it is a "locking" variant. The second number indicates the amperage. And it ends in "R" for receptacles, and "P"for plugs. (That document is worth perusing; it improved my understanding of practical electrical power in a number of ways, and helped me see the logic in the design.)

The receptacles around your house are NEMA 5-15R; these provide one hot, one neutral, and one ground wire. Higher amperages (NEMA 5-20R, etc) change the configuration of the prongs and the gauge (thickness) of the wires needed, but they all have one hot, one neutral, and one ground wire. But 240V outlets require two hot wires, so for NEMA 6-series, the neutral wire is replaced with a second hot wire. That isn't the only choice for 240V though; the NEMA 10-30R and NEMA 10-50R that you often see for electric dryers have two hot wires and a neutral, with no ground wire. To get to a receptacle with all four wires you move to NEMA 14-series with two hot, one neutral and one ground.

For the selection of equipment I have or can borrow, I needed several types of receptacles:

  • NEMA 6-15R
  • NEMA 6-50R
  • NEMA 10-30R
  • NEMA 10-50R

I didn't want to set up 4 receptacles on the wall with 4 extension cords. I wanted to consolidate this to one extension cord to rule them all. So I needed one that had a superset of the wires of the desired receptacles. The NEMA-6's needed two hot and ground, while the NEMA-10's needed two hot and neutral. So between those, I needed all four wires. That gets us to the NEMA 14-series. And the highest amperage is 50, so the extension cord would have to be a NEMA 14-50P to NEMA 14-50R, with a matching NEMA 14-50R in the wall. As it turns out, those are pretty standard extension cords; they're used for RVs and Teslas. In 50-amp applications, you want 6-gauge wire, not 10-gauge like some on the market are. They aren't cheap; here's a 25' extension cord for $130 for instance, and building your own to cut that cost takes some dedicated comparison shopping for 4-conductor 6-gauge SOOW wire.

So that solves the extension cord; what about all the adapters? I really didn't want a pile of adapters, so I decided to build a power strip with each of the required receptacle types in it. And since I would already have all 4 wires coming into it, I decided to add a boring old NEMA 5-15R to the mix.

Oh, but there is one additional wrinkle. A NEMA 5-15P will plug into either a NEMA 5-15R or NEMA 5-20R. And a NEMA 6-15P will plug into either a NEMA 6-15R or a NEMA 6-20R. Which means that by opting for the 20-amp receptacle, I could gain additional flexibility with no downside.

So that gets us our requirements for the power strip; a NEMA 14-50P on one end, and a box with NEMA 5-20R, NEMA 6-20R, NEMA 6-50R, NEMA 10-30R, and NEMA 10-50R. Given that the wire size depends on the amperage, I chose to order them by amperage, with the highest amperage at the end where the cord comes in, so the most expensive wires are the shortest.




A few disclaimers are likely prudent here: this is showing how I approached the problem, not how to safely solve this. Note the lack of any fuses, and the fact that this is connecting devices that are designed to pull 15 amps to a power source capable of supplying 50 amps. Plug everything in at once, and this will easily throw a breaker. Not to be mixed with water. Use this information at your own risk.

This is working well for me. Combined with a massive extension cord, this gives me the flexibility to power what I need, where I need it.

Improving a Damaged Extension Cord

The humble extension cord is frequently overlooked relative to its value in a garage or shop. Over the course of years of abuse, one of my extension cords wound up with a cut in the insulation, exposing the copper wiring. This resulted in an electrical "POP!" when it was pulled across a piece of metal. I cut out the damaged portion of the extension cord, but didn't throw the cord away. Instead, I gathered up some electrical bits from stuff I had salvaged and bought a few parts from the hardware store.

  • two-gang metal box
  • power outlet
  • dual power switch
  • two-gang faceplate
  • two grommets
  • a bit of copper wire

I wired the switch so that one controls the outlets in the electrical box, and the other (the one closer to where the cord leaves the box) controls the plug on the last foot or so of the extension cord.

Pictures showing the internal wiring:

wired-1.jpg wired-2.jpg wired-3.jpg

Ready for the faceplate:


The end result: