With another major hurricane bearing down on us, I wanted an alternative solution to running multiple extensions cords to my portable generator because of dealing with gaps when routing them through doors and windows.
Installing a standby generator with an automatic transfer switch was out my budget (my quote was around $12,000).
I also eliminated a dedicated manual transfer switch because it would force me to identify backup circuits in advance.
Instead, I was looking for something that was simple (i.e. minimal failure risk) but with flexible options to support any circuits that would work with my portable generator.
As stated before, I knew adding electronic components exponentially increased failure risk so that ruled out a dedicated manual transfer switch.
That is how I ended up with a Generator InterLock. Generator interlock is nothing more than a sliding metal locking mechanism that allows a user to either turn on the main breaker or the generator backfeed circuit breaker, but not both at the same time.
This simple, but elegant solution prevents a user from accidentally sending electricity from his portable generator back out to utility lines, where it can possibly electrocute and/or kill an utility worker.
In this article, I am going to show you how I installed a Square D Generator InterLock kit, for my Square D QO load center.
In my situation, I needed to move 2 circuit breakers to create space for the backfeed breaker and run a new wiring harness, connecting backfeed circuit breaker to the power inlet box.
Although turning off the main breaker de-energizes circuit breakers, two black conductors (a.k.a. cables or “legs”) from the electric meter will STILL BE “HOT” OR ENERGIZED. That includes anything these conductors touch prior to the main circuit breaker (i.e. lug nuts). Touching them can seriously hurt or kill a person so extreme caution is necessary..
Lastly, I placed my generator in a well ventilated area, which will allow for removal of deadly exhaust gas. I avoided placing my generator near windows, doors and ventilation intakes where exhaust gas could accumulate and enter inside my house.
Carbon monoxide is a silent killer that is odorless and colorless so I deployed extra carbon monoxide detectors inside the house.
- Any portable generator with a 30 Amp interlocking receptacle; must accept NEMA L-14-30 male receptacle;
- Portable Generator Power cord
- Power Inlet Box;
- Wiring harness (a.k.a. service entrance cable);
- Generator InterLock Kit;
- Backfeed circuit breaker;
I currently own a Briggs & Stratton 5500 Storm Responder generator which comes with a 120/240 Volt AC, 30 Amp, locking receptacle that accepts NEMA L14-30 male receptacle.
According to B&S, this receptacle accepts a 4-wire cord set rated for 240 Volt AC loads at 30 Amps (or greater) and powers 60 Hz, single phase loads requiring up to 5,500 watts of power at 22.9 Amps for 240 Volts or two independent 120 Volt loads at 22.9 Amps each. The outlet is protect by a two pole rocker switch circuit breaker.
Portable generators and water do not mix so it is vital to protect it from rain and snow, even if it is a temporary structure (like my “roof” in the corner of my deck; I will be building an enclosure that looks nicer sometime in the future).
Portable Generator Power Cord (GENSET CORD)
I made my own cable (made by Carol Cable, FT-2-P-7K-123033) along with NEMA L14-30 male and female connectors because at the time, I could not find one that was 35 feet long.
But honestly, if I had to do it over, I would just purchase a pre-made cord like this Reliance Controls PC3040 40-Feet 30-Amp L14-30 Generator Power Cord for Up to 7500-Watt Generators. It’s actually bit cheaper and NEMA connectors are water-tight where as build-your-own cable needs duct tape.
Also, I would make sure to get a longer cord than necessary so you have the flexibility to move your generator around without having to buy another cord.
Power Inlet Box
I installed Reliance Controls PR30 power inlet box so that I can connect the NEMA power from my generator. It is an excellent, all-metal box which makes it super durable.
Although this inlet box provides adequate weather protection, if I had to buy a new one, I would spend the extra money and buy Reliance Controls PBN30 Plastic Case Power Inlet Box, 30-Amp.
PBN30 is made of plastic but it has a large inside capacity which makes it easier to bend and route wires inside. More importantly, NEMA connector hookup is located on the bottom so the chance of water dripping inside the box is nil.
Wiring Harness / Cable
I was in a hurry at the time so I ended up purchasing a cable that was larger than I needed: AWG 8 / 3 with AWG 10 which could handle around 45 Amps.
Generator InterLock Kit
- Simpler to install – You just need to add a circuit breaker and a metal slider that will act as a transfer switch in the main panel;
- More Flexible – No need to pre-identify which circuits you want to use during an emergency. You can turn on or off any circuit breakers installed in your main or subpanel, as long as you remain within your portable generator’s capacity;
- More Reliable – because the whole setup has jut two parts, it is less likely to fail. In the event of a InterLock’s circuit breaker, you simply need to replace it. A manual transfer switch have many internal electronic components and when it fails, you may need to replace the entire unit (plus disconnect and reconnect wiring). Not a good scenario when you don’t have power;
Please keep in mind that it is easiest to obtain the generator interlock kit part number for your particular brand of load center. That will also make it easier to get the permit approval.
Backfeed Circuit Breaker
I chose Square D Circuit Breaker, 60 Amp, 2-Pole, QO260 over Square D by Schneider Electric QO230CP QO 30-Amp Two-Pole Circuit Breaker, Model: QO230CP because for extra few dollars, I was getting the double capacity.
It is important to note that over-current protection is provided by the portable generator’s circuit breaker.
With parts out of the way, I will share my installation steps in How I Connected My Portable Generator to My Home – Part 2 post.
If you have any questions, please leave a comment below.
Thanks and good luck with your DIY project!