Connecting a Portable Generator to the Home Main Electric Panel – Part 1

With hurricanes coming ashore more often, I wanted a better solution than running multiple extensions cords to my portable generator whenever we experienced a power outage. If you have used this setup, you know those windows and door gaps (where the extension cords are routed) tend to let in water and/or freezing cold air.

Instead, I was looking for a flexible setup that was simple (i.e. minimal failure risk) to operate and maintain.

CHOICES

I quickly eliminated the standby generator (comes with an automatic transfer switch) for three main reasons:

• Cost was out of my budget (average quote was around $12,000);
• I did not like having yet another electronic part (i.e.brain of the standyby gen) to worry about;
• I wanted a flexibility to quickly change out a faulty generator (if needed);

I also eliminated the dedicated manual transfer switch (used with a portable generator) because:

• The cost was high ($800 – $ 1,000);
• I did not want choose a limited number of backup circuits in advance;

I ended up going with a simple Generator Interlock kit ($~250 for parts).

SOLUTION

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. This method only allows either circuit breaker to be ON one at a 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.

SAFETY WARNING – WORKING INSIDE LOAD CENTER

Installing a generator interlock involves working inside the load center (a.k.a. main electric panel).

You need to remember that when you turn off the main breaker, conductors (a.k.a. cables or “legs”) from the outside meter will remain “HOT” OR ENERGIZED.

Touching them directly (conductors) or indirectly (lug nuts) will result in serious injury or death so extreme caution is absolutely necessary.

So please be honest with yourself about your skills when working with electricity. This article shows you how I did it with 20+ years of experience as a DIYer. When in doubt, please consult with an electrician instead.

SAFETY WARNING – WHERE TO PLACE YOUR PORTABLE GENERATOR

The placement of your portable generator is critical to avoid deadly exhaust gas (i.e. carbon monoxide).

I placed my generator in a well ventilated area approximately 45 feet away from the house. You need to make sure that the generator is away from nearby windows, doors and ventilation intakes where exhaust gas could enter the house!

Remember, carbon monoxide is a silent killer because it is odorless and colorless. Being paranoid, I installed a carbon monoxide detector by the mudroom door nearest to the generator. You may want to do the same.

PARTS

This project assumes that your portable generator has a 30 Amp interlocking receptacle (NEMA L-14-30 male receptacle – click here to see). Double check to make sure that your generator has this plug.

• Power Inlet Box;
• Portable Generator Power cord
• Wiring harness (a.k.a. service entrance cable);
• Generator InterLock Kit;
• Backfeed circuit breaker;

PORTABLE GENERATOR

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.

SHELTERING A PORTABLE GENERATOR

Although portable generators are designed to operate in the open, I found that I tend to have less issues when it is well protected from rain and snow, even if it is a temporary structure (like my “roof” in the corner of my deck).

I will be building a more permanent enclosure so look for my post soon.

POWER INLET BOX

I installed a Reliance Controls PR30/PB30 power inlet box (click here) to connect to the generator. It is an excellent, all-metal box which makes it super durable.

However, if I had to buy a replacement, I would spend the few extra $ and buy a Reliance Controls PBN30 Plastic Case Power Inlet Box, 30-Amp.

Although PBN30 is made of plastic, it has a large interior capacity which makes it easier to bend and route the heavy duty wires inside. More importantly, NEMA connector hookup is located on the bottom so you never have to worry about water dripping in.

POWER CORD (GENSET CORD)

This cord is how the generator gets connected to the Power Inlet Box. It’s a heavy duty electric cable designed to be use with portable appliances, tools and equipment.

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 better than my custom made cord (slightly cheaper and NEMA connectors are water-tight).

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.

WIRING HARNESS / CABLE

This cable connects the Power Inlet Box to the backfeed circuit breaker.

The size of the cable roughly depends on the amps, voltage and the distance from the receptacle to the main panel.

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 ground (cable can handle up to 45 Amps)

GENERATOR INTERLOCK KIT

I specifically chose the Square D generator interlock kit over other solutions because it is:

• 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 – The whole setup has just two simple parts so it is less likely to fail than other solutions. In the unlikely event when a backfeed circuit breaker fails, you simply need to yank it out and replace it with a new one. A failure involving a manual transfer switch (which by the way has many internal electronic components) would most likely require you to disconnect all wires and replace the entire unit. Not a good scenario when you don’t have power;

Please keep in mind that in most situations, you will be required install a generator interlock kit that is from the same manufacturer as that of your load center. For example, I have Square D QO Series 200 amp load center so I needed to purchase a Square D QO Series generator interlock kit.

BACKFEED CIRCUIT BREAKER

I chose the Square D Circuit Breaker, 60 Amp, 2-Pole, QO260 instead of the QO230CP QO 30-Amp Two-Pole Circuit Breaker because the price difference was negligible and I always liked the concept of over-sizing specifications.

Although the breaker is rated at 60 amps, please remember that the power inlet box has NEMA-30 connector that can only accept 30 amps.

Should I decide the upgrade to a 50 or 60 amp service, I would need to replace both the power inlet box and the service cable between the inlet box and the main load center.

NEXT STEPS

After purchasing all necessary parts and tools, head over to How I Connected My Portable Generator to My Home – Part 2 to see how I installed my setup.

If you have any questions, please leave a comment below.

Thanks and good luck with your DIY project!