Generator Setup for House

[GaryBDavis]

Below is a write up of my generator hookup. If there is something I've missed, please let me know. Constructive feedback is welcomed!

Important Notice
An incorrect generator hookup could possibly energize the power company's transmission line creating an illegal and dangerous situation. Any generator hookup should be approved by the local power company and installed in accordance with local and national codes. All work should be performed under the supervision of a licensed electrician. This write up makes available conceptual plans and information that can be helpful in selecting equipment for various applications. These plans do not necessarily represent the most current technology, applicable laws or safety standards. They are not engineered plans and do not replace the need for competent design assistance in developing a safe, legal and well-functioning apparatus. Gary B. Davis does not warranty these plans.

When I built my new house, I planned for a generator hookup that could be connected at the meter loop. I initially wanted to install a transfer switch, but one capable of handling 320 Amps cost several hundred dollars. Instead I settled on mechanical interlock kits and feedback breakers installed on the main feed-through panels.

Electrical Service
My electrical service is 320 Amp single phase. I have two 200 Amp feed-through breaker panels installed at the meter loop. One panel serves the house and the other serves the shop. Each feed-through panel has a 200 Amp main breaker, a few slots for standard type breakers, and secondary lugs that feed the service through to the house and shop. At the house and shop, there are 200 Amp/40 position main lug panels. Main lug panels are panels with no main breaker as they are protected by the main breakers in the feed-through panels mounted at the meter loop.

Mechanical Interlock and Feedback Breakers
The concept behind a mechanical interlock kit and feedback breaker is this: the power from the generator is fed back into the breaker panel from a standard breaker. Instead of connecting the feedback breaker to a load, it is connected to the generator. Current is passed backward through the breaker where it energizes the panel. However, the main breaker must be turned off to prevent power from the power company energizing the panel at the same time as the generator. This is where the mechanical interlock comes into play. A mechanical interlock is a simple sliding plate that prevents the main breaker and the feedback breaker from being turned on at the same time. Only one or the other can be on at any given time. In the particular setup, the feedback breaker must be installed in the top-right position.

A feedback breaker should never be used without a mechanical interlock that prevents both the main breaker and feedback breaker from being turned on at the same time. Interlock kits are not available from all manufacturers for all models. I used SquareD QO series panels. I recommend using an interlock kit that is made by the same manufacturer as the breaker panel and is listed as a compatible item.

Generator Inlet
The two-pole, 50Amp feedback breakers in the main panels feeding the house and shop are connected to a generator inlet installed at the meter loop. This inlet is made by Midwest and contains a 50 AMP 125/250V 3-Pole 4-Wire Grounding Non-NEMA locking connector. This connector is angled and the cover can be closed with the power cable plugged in. It is rated for NEMA 3R while "in use". This means its rain tight and outdoor rated even while the power cable is plugged in.

Generator
The power source is a Miller Trailblazer 302 portable welder with a built in generator rated for 10,000 Watts. Ithas a 50Amp 125/250V NEMA 14-50 outlet. This is the same 50 Amp outlet you see at RV campgrounds.

Grounding
The generator inlet has a dedicated ground wire leading to the ground rod installed at the meter loop. There are also dedicated ground wires from the meter base and each main panel leading to the same ground rod. The house and shop each have their own ground rods as there is no common grounding between the meter loop, house and shop. When the generator is providing power, it has the same grounding scheme as when service is coming from the power company.

Applying The Load
The 10,000 Watt generator won't provide enough power to run everything in the house. So, you have to pick and choose which items you turn on. However, since the generator connects at the main panel, you can pick any combination of items to run just as long as you don't overload the generator.

Pilot Lamp
One drawback of turning off the main breaker is that you don't have a way to tell when power has been restored. Since I live in a rural area, I cannot see any of the neighbor's house lights to indicate power is back on. To solve that issue, there is a pilot lamp installed in one of the main panels. It is fused directly off the meter base feed and operates independently of the main breaker. When the power company is providing power, the lamp is on. It is a very low Wattage bulb and draws very little electricity.

Portable Power Pedestal
Sometimes I take the generator to off-site locations to provide temporary power. In these situations, I use a portable power pedestal. This allows me to place the generator a bit further away from the application to keep the noise down, etc. The pedestal consists of a 50 AMP 125/250V 3-Pole 4-Wire Grounding Non-NEMA locking inlet, two-pole 40 Amp 24 hour timer, breaker panel with four 20 Amp GFI breakers and standard NEMA 5-15 outlets. All items are rated for NEMA 3R while "in use". This makes the pedestal operational during rain, snow, sleet, etc. The 50 Amp inlet is a different style from the meter loop, but when used in conjunction with a matching connector mated with a rubber cover, it is NEMA 3R while "in use". There are two types of standard 5-15 outlets one quad box with a wet location cover and four corded outlets with rain tight rubber covers.

The reason for having a main timer is so that the pedestal can be used for temporary seasonal light displays. For example you could run a Christmas light display where the timer turns the power on at 5:00PM and off at midnight. The pedestal can be plugged into any 50 Amp RV outlet as well as a generator.

 

[rtdiggr]

wow that is quiet the setup, that would have been nice for our 3hour power outage last night.
Shane

 

[tommu56]

Gary

There is doing it and doing it right and it looks like you did it right

tom

 

[billbill1]

Gary, I have the same breaker setup at the meter pole that you have. Can you explain to me how the lock device that shuts off the main and allows the breaker on (or vica versa) works? Do you physically have to remove the screws and move it? I am interested in doing the same. Where did you purchase the lock plate? I have a QO 200 amp panel that feeds the house main and the shed main at the meter pole. Is there no danger of back feeding through the neutral? Since it is a current carrying conductor, that is why I ask this question. At least in my panel, it isn't shut off by the main. Very nice setup you have, thank you so much for sharing!!

 

[Red55]

Billbill1-
I was wondering the same on how the lockout worked. If you look at the lockout it sides and will move into the other positon only when you move the top (in the on postion) to the left and off Then you will be able to move the lockout up so that the bottom breaker can be turned to the right and to the on positon.

GaryBDavis-
Really nice setup for back-up power and your techinical skills far exceed mine. Only suggestion I would make is some kind of roof to protect your electrical meters from the elements. Nice job -Ed

 

[billbill1]

I was looking at it wrong, I see how it works now. Thanks for the advice. I still need to locate one of them.

 

[chh]

I like the setup. My power company requires a transfer switch, I had never heard of a setup like yours with the lockout and the feedback breaker. Looks very neat. I missed installing the indicator light. That is a good idea and would be very helpful.
Is your Miller welder voltage stablized for electronics? My Lincoln Ranger 10 is not and they do not recomend hooking computers or sensitive electronics to it when it is used as a backup power source. I have a pto drive generator that is so the Lincoln is a backup to the backup kind of thing but, the electronics warning bothered me.
The portable power plug setup you built is very slick. I really like that. Got a spare on around you don't need?
Very professional looking neat work all in all. IMHO

 

[gordon21]

What is the part # for the Square D mechanical transfer plate? I would like my electrican to add one when he installs the circuit breaker box next week. that seems to be a fool proof method at hundreds of dollars less than adding a second panel. It insures a break before make connection. The guy at Home Depot this morning has never seen one. I know it will have to come from a "real' electric supply place that sells Square D.

 

[Highbeam]

I had my old primary 200 amp Zinsco panel replaced with a new 200 amp panel last year. I purchased a new panel that was already equipped with the mechanical interlock much like Gary's. By having an OEM interlock, the whole panel has stickers on it that state it is a UL approved generator transfer panel. We got it all up and running and one of my future projects is to run the backfeed circuit to the generator outlet. The additional cost for the panel being a "generator transfer panel" was very minimal. To the extent that I would always put one in.

The NEC allows this UL listed device so I don't think your utility company can really prohibit it.

 

[GaryBDavis]

I've seen some home made mechanical interlocks that looked pretty scary. Having one that is made by the manufacturer and that is UL listed is the way to go. The SquareD part number for mine is QORBGK2, but note that they sell several different ones so note your panel model number and check with your local SquareD dealer. Google "Generator Interlock Kit SquareD" and you will find more information.

I'm not sure how clean the output from my welder/generator is, but I have a centralized 3KW UPS that powers all of my sensitive electronic equipment (computers, networking gear, etc). It's a pretty high dollar version and is supposed to clean things up.

As far as the neutral goes, the interlock kit does not disconnect the neutral from the power company. The generator's neutral is tied to the power company's neutral when the generator is hooked up. However, there is no voltage present on the power company's neutral or on the generator's neutral.