Home Standby Generator

Have you wished you could sit warmly in your house when the power goes out? Have you wished you could microwave a hot meal when the ice storms have taken down the power lines? Maybe a home standby generator is for you. I installed one on my new house. It was a significant amount of work. It has already maintained our air conditioning for 3 hours when an underground power line in the neighborhood faulted in May 2006.

I installed a natural gas fueled Briggs and Stratton air-cooled 12KW power generator. This site documents the details of the installation. It is not a how-to site. Your installation should be planned and completed by a qualified electrician that will safely complete the work in accordance with your local codes and standards. You might see something on this site that you haven't thought of and you can make sure your installer addresses it.

Some details are specific to the Briggs and Stratton power generators, but the concepts might be helpful on any brand installation.

System Components

Briggs and Stratton (B&S) uses Cutler Hammer electrical hardware with a B&S engine. Eaton Corporation owns Briggs and Stratton and Cutler Hammer so it makes sense that they combine in this generator system.

I mail ordered my transfer switch and purchased the generator from a local generator supplier. I bought the breakers, panels, cable and other parts from the local home improvement supply stores.

How the generator system works

The system includes the Automatic Transfer Switch (ATS), the generator and the breaker panels. Some generator systems let the ATS close a start switch contact to start the generator. B&S relies on a utility sense circuit. The 220VAC circuit is fused in the ATS and delivers voltage to the generator unit to let the generator know when the utility power has failed. The utility sense circuit is also used to keep the generator starter battery charged.

The generator starts a 6 second timer when the utility sense voltage drops. If the utility voltage is still low at the end of the timer, the generator starts.

The ATS also monitors the utility power and the generator power. The ATS starts an internal timer when the utility power fails and if the generator power is up and stable at the time out, the ATS transfers the load to the generator.

When utility power returns, the ATS transfers the load back to utility and the generator runs a 5 minute cool down cycle before turning off.

It was useful to create an electrical diagram to plan the installation.

Generator vs utility circuits

Proper sizing of the generator and ATS is critical. Make a list of all the circuits in the house. Think about what you would want to run on the generator. The generator may be able to handle 50 or 60 Amps but the panel and ATS have to be sized for the utility source. I ended up with a 100 Amp ATS and generator panel even though my 12KW generator can only deliver 60 Amps. I have two heat pumps in my house, both heat pump compressors are on the generator panel but the upstairs heat pump air handler and resistance heaters are not on the generator panel. The generator panel must be sized to handle both compressors when utility power is present. When utility power is lost, the upstairs heat pump will not run because its air handler and therefor its thermostat control circuits are dead.

We didn't get all the circuits I wanted on the generator panel but the house will be quite comfortable if we lose utility power.

Generator Panel (Amps and Description)
20 1st floor furnace
20 Refrigerator, breakfast, pantry
20 Computer room
20 Home Theater and suite GFCI
20 Microwave, lower
20 Washing Machine
20 Garage Doors
20 Master bath and powder room GFCI
20 Kitchen GFCI, bar and west
15 Guest room and bath L&R
15 All smoke detectors
15 Kitchen lights, back porch L&R
15 Laundry, computer room and powder room lights
15 Master bedroom, bath, closet L&R
15 Suite front room, closet and hallway L&R
15 Suite back room and bathroom L&R
15 Bridge South, lights, closet and attic L&R
15 Den, gallery, stairs L&R
40 1st and 2nd floor heat pump compressors

Main Panel (Amps Description)
100 Transfer Switch
50  Range
30  Upstairs HP
20  Garage GFCI, east
20  Laundry Rm
20  Garage GFCI, west
20  Guest Bath GFCI
20  Garage receptacles
20  Microwave, upper, range fan
30  Garage L30R
30  Dryer
15  Laundry Room Fan
15  Foyer, study front coach lights
20  Dishwasher and disposer
20  Kitchen GFCI, north

Installation Tips

Install on a concrete pad or pea gravel base to lift the generator up off the ground far enough to keep dirt and debris out of the housing and to make changing the oil easier. The generator I installed included a plastic base but without a pad below that, it is difficult to get an oil change pan low enough to drain the oil and dirt blows into the housing.

The generator is heavy, this one is almost 400 lbs. Be careful when installing it. I moved mine on a four wheeled cart purchased at a local farm supply.

Install an electrical disconnect on the 240VAC utility power monitoring line to allow isolating the generator for maintenance.

Conductor sizing. Be sure to use large enough conductors. Also be aware that disconnect devices and breaker panels have lugs sized to match their capacity. You might be tempted to use a 200 Amp panel to have lots of breaker spaces but you might have trouble connecting 100 Amp cable to the 200 Amp lugs. I used a 100 Amp panel near the generator to transition from 100 Amp SER cable to 60 Amp copper wire. The panel also serves as a disconnect.

Locate the generator breaker panel adjacent to the main panel. Connect the two panels with a 2" nipple so the circuits can be easily moved from the main panel to the generator panel. In most recent residential electrical systems the whole electrical system is on the same grounding/neutral system so only the hot conductor has to be moved to the generator panel for lighting and utility circuits. I moved the neutral and ground on the 220VAC heat pump circuit. It was easiest for me to move the whole cable. About half of the circuits I moved did not require splicing because the conductor was long enough.

Leave spare space in the generator panel and install empty conduits in the panel for future additions. It will save you from having to rip open drywall and repair walls when a circuit needs to be added.

Don't forget to include the NFPA 702.8 signage identifying the location and fuel type of the generator for emergency personnel.

If your house has two electrical panels and you want circuits from both panels on the generator, you will have to be very careful with the grounding and bonding. Make sure your installer addresses this issue.

Grounding

There is often confusion over the correct grounding for a home standby generator. My system is not considered a separately derived system by the National Electrical Code. This is because the Briggs and Stratton ATS does not switch the neutral conductor. Since the generator is not a separately derived system, it uses the ground system of the main breaker panel. Our municipality only requires three conductors, two hots and a neutral, from the utility meter to the main breaker panel service disconnect. The neutral and ground are bonded at the main breaker panel and only at the main panel. The only ground rod is at the utility meter where the service entrance neutral is grounded. This means I did not drive a new ground rod at the generator and I did not bond the neutral and ground at the generator housing.

This is an important issue and I know one generator provider that does not understand the principals. Be sure your installer does understand and installs the system per the NEC and local codes.

There are several Internet electrical and electrician web sites that are good references for understanding the NFPA National Electrical Code (registered trademark). These sites are handy for calculating load estimates, conductor sizing and grounding methods.

Natural Gas Piping

The Briggs and Stratton 12KW generator consumes 195 cubic feet/hour of natural gas at full load. That is probably more than your gas furnace and about 3 times as much as a gas water heater. My contractor used a 1" natural gas header from the meter to the generator location. Be sure that the installer takes into account the water heater, furnace and gas fireplaces when sizing the piping. Also check the capacity of the gas meter. It should be labeled with its maximum capacity. You many need the gas company to install a larger capacity meter.

We live in a close neighborhood and have had a complaint about the weekly-automated test. I agreed to change the test day to run when the neighbor is not home. I think that resolved our conflict.

Status Monitoring

The system includes an LED that can be located remotely from the generator. It indicates generator status and the status of the weekly automated tests. There are also relay contacts available in the generator and in the ATS to provide additional status indicators. The LED should be installed someplace so you can notice it daily. If your generator has faulted, you want to know immediately so you can get it fixed. A broken generator will not be any good when the utility fails.

A meter to monitor the load on the generator is recommended. This installation is on its second metering system now.

The standard monitoring indicators were not enough for me so I added some relays and interfaced the ATS and generator to my home computer. An ADAM 6050 distributed I/O module from Advantech was used to provide status on the home computer. I added three relays to the ATS to monitor the utility, generator and panel status. Those inputs, the generator trouble alarm inputs and the transfer switch position status were wired to the ADAM.

A simple PERL script on the home computer polls the ADAM with the MODbus/TCP protocol to build a status web page and send email when the status changes. I receive my email on a cell phone so I always know when the generator is running.

Another generator status monitor was built with a USB data acquisition device. The installation of that is described on another page of this site.

This is a sample of the status and log pages.

Utility:	Off
Generator:	Running
ATS:	Generator Position
Panel:	On
Alarm 1:	Normal
Alarm 2:	Normal
LED Status:	On

• 11:09:07 Jun 21 2007 Generator Stopped
• 10:49:17 Jun 21 2007 Generator Running
• 11:10:10 Jun 14 2007 Generator Stopped
• 10:50:17 Jun 14 2007 Generator Running
• 10:54:07 Jun 7 2007 LED Status On
• 10:53:01 Jun 7 2007 LED Status Off

Maintenance

My generator doesn't require much maintenance. Suppliers offer maintenance programs but I opted to do it myself. 50 hour oil changes and 100 hour filter changes are about all that's required. That doesn't happen very often when the generator is only running 20 minutes during its weekly self test. However if you have an extended utility outage, you will need to perform maintenance during the outage. In just a matter of days you should change the oil and replace filters. These items may not be easy to obtain during an outage and your supplier may not be available either. I keep a maintenance kit available, with oil and filters so I can tend to the system in the event of an extended outage.

An important maintenance activity is to frequently look at your generator system. Look it over ever couple weeks. Look for dirt or water infiltration into the generator housing. If you located your status light in a convenient place you should notice it every day to assure the generator is ready to perform when you need it.

References:

The National Electrical Code is available on-line. Some state building codes are available on-line. Mike Holt has a very informative site about electrical code issues. Here is an informative page about home generator installations.