Generator Hookup
Zacharie Brodhacker
Wandering through YouTube, I found what may be the best way to hook up a generator to your house. Its brilliantly simple and safe. Manual transfer switches require wiring inside the electric panel, generator interlocks a bit less wiring. This rig, technically called a meter mounted transfer switch, no wiring.
Instead of messing with your electric panel, this unit sits between your utility meter and the electric panel on the outside of your house. An electrician or your utility company has to install it, but it should only take about 30 minutes to do. And, in most cases, no electrical or building permits. How cool is that?
I have a transfer panel in my basement to hook up my generator to the house, and it isn't the perfect solution. My post about it here. You have to run a wiring harness from the transfer panel into the main panel, choose which circuits to control, splice the wires together, its some work to do it all. This meter mounted transfer switch is much closer to ideal. More info on the unit here.
The meter mounted switch supplies power to the whole panel, and you choose which circuits to run based on the wattage of your generator and the appliances you want to use. The beauty is you can turn on and off breakers at will. With a hard wired transfer panel, you can't change which circuits are powered. My transfer panel only has one 220 volt circuit breaker, so it limits what large appliances you can run. With this unit, you can turn off and on different appliances that draw a large amount of power.
The other plus here is many people have a portable generator and plug multiple extension cords into the generator and run them into the house. You can hook up your central AC or well pump with an extension cord. So yes, at this writing, this is the best way to hook up a generator to your house.
I have mixed feelings about these sort of things. It's a great idea but in all reality you don't need an electrician to mount this. It's a plug and play deal. Don't let the little security tag from the utility scare you. Meters are easy to pull and the tags can be purchased from supply houses if your worried about it. I have a whole bag of them with different colors. I've cut those tags on a ton of homes when installing a new air conditioning system. Not a single customer has ever gotten a warning from the utility. The little number on the tag is never recorded so if you can find one of these switches for sale, I say buy it and DIY it. Remember that there is usually live 220 voltage in that meter box, you should exercise caution or call a pro.
A generator is a core component to many people's emergency preparedness plans. (Maybe you have a cool charcoal powered or a multi-fuel generator.) However many fail to think through how exactly they will power the items they want to run when the grid is down.
In June of 2012 my family experienced a 10 day power outage. It was eye opening. It was 100 degrees during the day with periods of heavy rain. I had to run a sump pump to keep my basement dry, a refrigerator, freezer for food preservation, a portable AC unit in the living room to protect my infant, we charged phones, and ran the wifi router. I had power cords everywhere. It was a pain. I decided then and there I would find a better way.
A generator transfer switch is the legal and proper way to power your home with an emergency generator. There are three main types: automatic, manual transfer sub panel and a breaker interlock. Each has varying degrees of complexity, benefits and expense.
Automatic transfer switches will sense a power loss, start your standby generator and automatically move your load to the generator. These are awesome - but very expensive and require a full time dedicated standby generator.
Manual transfer sub panel switches are good option. They are less expensive than the automatic transfer switches (Starting around $300) and can be used with a portable generator. They typically only cover a few breakers which was problematic for me.
Breaker Interlock is the option I chose. It is National Electric Code compliant and is in my opinion the least expensive and most flexible option. My setup cost was just under $150. In this setup you use a breaker to energize your existing breaker box. Switching it on is easy and safe. My wife did an unassisted dry run in under 5 min - which included getting the generator out of the building.
The breaker interlock system has come in very handy for us. We can turn on overhead lights, wash clothes and keep our food cold, charge our phones, run the internet and much more....all while keeping our doors and windows closed and no tripping on extension cords!
Disclaimer:
I am not an electrician. After much consulting and over sight from a licensed 25 year Master Electrician I believe these instructions to be correct and accurate for my jurisdiction. Electrical codes vary from place to place. In my place of residence home owners are allowed to do their own electrical work if it is up to code. You are responsible for any code violations, permits or awesome good stuff that comes from doing a project like this.
First you have to figure out what type of amperage and plug type we are working with. You only want to do this on a generator with a big round plug. This will provide 220V (in the US) and power both sides of your breaker box. You will see the amperage written near the plug. Mine is a 30 Amp L-14-30.
For your convenience these are the most common sizes:
Nema L14-20 - 20 amp
Nema L14-30 - 30 amp
Nema CS6365 - 50 amp
Breaker interlock kit. Buy a UL rated device that fits your specific breaker box. These have been tested and validated to work. Many insurance companies and jurisdictions require the UL rating.
30 Amp 2 pole (double) breaker. Again you will need to buy one that fits your breaker box. All breakers are not the same.
Measure 5 times drill once.
My house had an conduit old hole in the foundation. Most people will need to drill one. A hammer drill is extremely helpful for making one. Try to get the conduit hole as close to the panel as you can.
Remove the cover on the conduit body. Pull the wires through one at a time attaching them to the plug as you go along. Remove about 3/4 of an inch of the insulation. Use a large flat screwdriver or a nut driver to tighten the terminals.
The breaker interlock method requires the to most upper and right breaker space to be free.
Generally you will need to move a breaker or two down. Most boxes will have enough spare wire to move things around a bit. If you do not have enough room and your breaker is 30 amps or less you can use a short piece of insulated wire and a wire nut.
DO NOT wire nut copper and aluminum wire together. They will corrode over time. You will need to pick up a wire splice at your local home store.
Note: In a 2 wire home like mine - meaning no 3rd ground wire in the outlet box or the outlets in the home. It is acceptable in my jurisdiction to put the green ground wire to an open common terminal. It is not appropriate to use the ground wire for the common at the outlet.
Turn the panel back over and install the sliding interlock bolts.
Reinstall the panel with all the breakers in the off position. With the main in the off position turn the generator breaker to the on position. Ensure the interlock allows for the on position. You may have to shift the position of the panel cover.
Turn the generator breaker to the off position and drop the slide so it can not be turned on. Ensure the Main can be turned to the on position. Adjust panel cover if it will not.
If it does turn the breakers on one a at a time - with a 5 second delay between breakers. This will distribute the start up load.
Attach decals included in your kit to your breaker box and the outside service box.
Avoid turning on HVAC, standard hot water heater and the stove unless your generator can handle it. As long as you can get past the initial start up load you can run a lot off of 30 amps.
Power off sequence:
I need to add both a 120v (probably 20a) circuit as well as generator hookup (120v 30a) to my backyard. The 120v circuit will be used for landscape lighting, that sort of thing. The generator hookup will be wired to a weatherproof outlet at the back of house, and a manual transfer switch (adjacent to the main 200a load center) in the garage to run stuff like a fridge, lights, select outlets, etc..
House is block construction on stem wall, so I will be surface mounting sch80 conduit on the exterior, run is approx 60-70 feet. With conduit derating I'm looking at probably 6AWG for the generator hookup. While I only have a 120v genset now, I was going to future proof and run 3 conductors for when I go 240v. Of course any ampacity for 120v will be plenty for 240v. The other circuit is probably going to be 10 or 12AWG copper.
My question is can I share the ground between these or will that be unsafe from a line/generator isolation standpoint? Im assuming sharing neutrals is big no-no. Is running in the same conduit problematic? I assume if sharing ground is fine, then same conduit is okay.
No matter how many circuits you run in a single raceway, you only need one equipment grounding conductor for the whole lot (unless you require redundant or isolated grounding conductors, of course). This is implied by 250.122(C):
(C) Multiple Circuits. Where a single equipment grounding conductor is run with multiple circuits in the same raceway, cable, or cable tray, it shall be sized for the largest overcurrent device protecting conductors in the raceway, cable, or cable tray. Equipment grounding conductors installed in cable trays shall meet the minimum requirements of 392.10(B)(1)(c).
For your use case, a single 8AWG EGC (adequate for all circuits up to 100A) is sufficient here. Note that this conductor must be a wire in the setup described below as it serves as the separately derived system's grounding electrode conductor as per 250.30(A)(4) and the Exception to 250.121 in addition to being the equipment grounding conductor for both circuits, and the ground wire from the transfer switch to the main panel must likewise be an 8AWG wire.
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