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Standby generators

are hardwired to a house electrical system via a transfer switch and permanently connected to an external fuel source (such as liquid propane or natural gas). They can automatically supply continuous power to pre-selected circuits or the whole house in case of emergency for as long as the fuel is available.
The largest US supplier gensets is Generac- its market share is about 65-70%. Generac's generators (such as Guardian®, Guardian Elite™ and QuietSource™) were among the best selling home standby systems on the market. Their 17kW/16kW air-cooled genset models 5873 and 5874 are popular choices for homes with up to 5-ton central air conditioner.
I understand that regardless of place of purchase, you can usually order installation from GUARDIAN® local dealers or use your own licensed contractors.

Main features:

- Average noise level 66 dB(A)
- Comes pre-wired and pre-packaged with composite mounting pad for fast installation
- Automatic Voltage Regulator with quality electrical output for sensitive electronics (THD<5%)
- CARB compliant
- 2 year, 200 hour oil change intervals (first time: after 8 hours of operation)
- 3-year limited warranty
- Works off standard residential fuel pressure: 5 to 7 inches of water column for natural gas, 10 to 12 inches of WC for LP gas at the genset fuel inlet at all load ranges. However you need to make sure your service can provide sufficient fuel flow rate.
Here is nominal fuel consumption: - 183 cu.ft/hr NG; 1.61 gal/hr LPG at half load;
- 261 cu.ft/hr NG; 2.57 gal/hr LPG at full load.

The genset's control panel includes a control logic circuit board. This board constantly monitors utility power source voltage. Should that voltage drop below 60% of nominal (which is 78VAC), a sensor energizes a 10 second timer. After 10 sec., the engine will crank and start if utility is still low.
After the engine starts, the control circuit lets it warm up for about 5 seconds. After that it activates the transfer switch and connects load circuits to the standby power supply.
When line voltage is restored above 80% of nominal (which is 96 VAC), a re-transfer time delay starts timing.
After 15 sec. circuit board de-energizes transfer relay in the transfer switch if utility is still present and transfer loads back to the grid. After re-transfer, the engine cools down for one minute and then shuts down.

Use genset's AUTO/OFF/MANUAL switch and UTILITY/STANDBY handle inside transfer switch according to user's manual.


See Generac generator user reviews.

The model 5873 with steel enclosure is a lower cost version that sells online for about $3500-3600. If you live in a salt air coastal area, and you are concerned of enclosure's corrosion, consider a part with an aluminum enclosure, which typically costs a few hundred dollars more. Unfortunately, Generac has discontinued their aluminum version 5874.

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Rated Power (LP / NG) 17 kW /16 kW (17000W / 16000W)
Rated Amps @ 60 Hz 240 V (LP/NG) 70.8 / 66.6 A
Engine Generac OHVI 992cc / V-Twin 2 cyl.
Alternator RPM 3600
Rated horsepower 32 at 3600 rpm
Displacement 992 cc
Sound Level:
(dBA @ exercise) 60
(dBA @ normal operation) 66
Dimensions (L" x W" x H") 48x25x29
Automatic Transfer Switch (included) 100 Amp / 16 circuit
Full Monitoring System Oil pressure, coolant temperature, engine speed, coolant level, cranking time, starter lockout, utility sensing
Shutdown and LED Indicators Overspeed and overcrank, low oil pressure, high coolant temperature, low coolant level, low fuel pressure, low battery voltage
Included Transfer switch
No. of Poles 2
Current Rating (amps) 100
Voltage Rating (VAC) 250
Utility Voltage Monitor (fixed):
- Pick-up 80%
- Drop out 60%
Return to Utility Approx. 15 sec
Auto exercised 12 minutes weekly
UL Listed Yes
Enclosure Type NEMA 1 (indoor use only)
Dimensions (H" x W" x D") 26.5 x 12.5 x 7
The datasheet does not provide surge capability, but based on data for a similar Generac QT Series (see this motor starting guide), this genset may have 125 LR Amps @ 30% Voltage Dip.
The model may not start all brands or models of central A/C. Make sure the surge capability (amps) of the generator is greater than the LRA listed on the name plate of the air conditioner. Otherwise, you may need to install a "hard start" kit (for more info see our selection guide). For other systems see our detailed rating chart of standby generators.

Notes. All data here are provided As Is. While efforts have been made to provide the most current and accurate data - we are not responsible for any errors. For official specifications and warranty info contact the product manufacturer. The sole responsibility when selecting a product rests with you, the buyer- read important Disclaimer linked below.

Generac® & Guardian® are registered trademarks of Generac Power Systems, Inc.