Backup Electrical Generator Capacity or Size Determination
Tables of electrical generator capacity requirements
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Electric generator size tables:
Guide to determining the necessary size or wattage capacity for electrical generators for residential & light commercial use: this article discusses how to determine how much back up generator capacity or power in watts you'll require.
How big should my electrical generator be? How many things do I need to be able to operate if there is a power failure?
This article series discusses the use of emergency generators for electrical power backup at residential properties. We describe generator size requirements, where to buy an electrical generator or voltage converter, and how to hook up or wire a portable or backup electric generator. We also describe methods for obtaining temporary electrical power from a car, RV or other 12-V or 24-V vehicle or system.
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How Much Backup Generator Capacity do We Need?
Our page top photo illustrates an EM portable generator mounted on a utility trailer. This electric generator was to be used to power a sound stage, outdoor lighting, and related equipment during the Guanajuato Film Festival activities in San Miguel de Allende, Mexico.
The commercial-grade backup generator by Katolight Corporation shown above is installed at an adult care facility in New York.
Here we give backup generator size requirements tables for both backup electrical generators for home use and for smaller car or truck AC adapters.
How to Determine the Necessary Home or Office Backup Generator Size or Capacity in Watts
The minimum wattage capacity your standby or backup electrical generator needs to provide depends on your building, its occupants, their special needs, etc. Here we list the more critical electrical circuits and devices you should consider powering. Use this list, with additions or deletions to arrive at the total minimum wattage that your backup or standby generator system will need to provide.
| Critical Home Electrical Circuits That May Need to be Powered | ||
|---|---|---|
| Electrical Circuit or Device | Watts Required | Comments |
| Air conditioning, portable or window unit? | 1,500W - 2,500W | A/C may be critical in some climates and for some building occupants. Central A/C typically consumes at least 5000W, typically about 8,750W for 24,000 BTUH capacity. Do not run flooded equipment before it has been dried, cleaned, inspected for safety; do not run warm air heating or air conditioning systems that use ductwork before assuring ducts are clean and safe to use |
| Emergency medical equipment used in the home | ?? | Check the individual equipment wattage tags. Watch out: for emergency medical equipment or other electrical equipment that must be available full time to avoid personal injury or building damage be sure that your electric generator covers that capacity. Consider automatic transfer switch operation as well as additional battery backup. |
| Emergency lighting | 400 W | Sufficient for safe building occupancy, e.g. stairs, entrances |
| Heat , central boiler, furnace | 500 W | Central heating, if functional. Watch out: Do not run flooded equipment before it has been dried, cleaned, inspected for safety; do not run warm air heating or air conditioning systems that use ductwork before assuring ducts are clean and safe to use |
| Heat, portable heater (s) | 1,300 W | If central heat not functional, weather dependent. Multiply this figure by the number of electric heaters required. |
| Microwave | 1,600 W - 2,800 W | If you require preparing hot foods or certain other applications; |
| Refrigerator or Refrigerator / Freezer | 600 W - 2,900 W | |
| Sump pump | 600 W - 3,200 W | Critical to avoid basement or crawl space flooding during storms, but will be overwhelmed by major disaster flooding in some areas. Multiply this figure by the number of sump pumps installed. |
| Well Pump | 600-900W | Necessary to provide water supply; Watch out: Do not presume that a private water well can provide safe potable water after area flooding; after floodwaters have subsided from ground surface, contaminants may still be in the aquifer as well as silt, mud, and contaminants in the well itself. |
Additional, non-critical electrical components desired for longer building occupancy in a disaster zone |
||
| Computer | 25-250W | |
| Clothes dryer, Electric | 5,000 W | |
| Clothes dryer, Gas | 2,500 W | [11] |
| Dehumidifier | 1,450 W | [11] |
| Electric cook stove | 5,000 W | |
| Fan, window 1/8 HP Fan, window 1/4 HP Fan, window 1/2 HP |
1,000 W 1,850 W 3,500 W |
|
| Freezer | 2,900 W | [11] |
| Garage door operator | 1,400 W | Useful if the garage door is too heavy for safe manual operation when disconnected from the automatic operator track. |
| Saw, circular 81/4" | 1,400 W | |
| Television | 200 W | |
| Vacuum cleaner, wet-dry shop vac | 900 W -1,300 W | For shop vacs up to 2.5 hp. |
| Washing machine | 1,200 W - 3,450 W | |
| Water heater, electric | 5,000 W | |
Notes to the Table Above
- Watt requirements numbers: For some of these items we list the watts required based on the total inductive starting watts necessary to get the equipment going. Its running load watts are generally less and will be the lower number where we show pairs of figures. Some of these wattage data were taken from wind generator wattage requirements tables.[11]
- Watch out: Do not run flooded or storm-soaked electrical equipment of any kind before it has been dried, cleaned, inspected for safety; do not run warm air heating or air conditioning systems that use ductwork before assuring ducts are clean and safe to use
- See also this SOLAR POWER GENERATOR SIZING GUIDE
Car or Truck DC to AC Power Adapter Capacity Requirements
DC to AC Power Adapter Volts, Amps, Watts Data for Common Small Electrical Devices
| Table of Electrical Power Requirements for Small Electrical Devices | |||||
|---|---|---|---|---|---|
| Device | 120 V Circuit Input | 12-V Circuit Input |
Device Adapter Output | Typical Nominal Device Watts1 | Comments |
| Cellphone charger | 0.15A @ 120V AC | 1A @ 12VDC | 1 A @ 5V DC | 5 Watts | Most chargers at 100V - 240V, 50 or 60 cycle electrical input |
| Tablet Computer Charger | 0.15A @ 120V AC | 1A @ 12VDC | 1 A @ 5V DC | 5 Watts | |
| Laptop Computer | 1.5 A @ 120V AC | 15A @ VDC | 1.56A @ 32V DC | 25 - 100 Watts | Varies by laptop model |
Notes to the table above
1. Generally, without considering more accurate & technical power factors, we can use three trivial formulas to convert between amps, volts & watts
- Amps = Watts/Volts
- Watts = Amps x Volts
- Volts = Watts/Amps
also
- Volts = Amps * Resistance (Ohms Law)
2. Details are at
DEFINITIONS of ELECTRICAL TERMS
DMM DIGITAL MULTIMETER HOW TO USE
Backup Generator Capacity to Handle Demand Surges
It may bear repeating that the compiled list is the minimum total wattage, i.e., when everything on the list is happily running.
You also need to consider a potentially massive surge rating, if you're using an automatic transfer switch and have a bunch of motorized loads. Everything restarts simultaneously.\ Motor starters sometimes need several seconds at triple their rated operating power.
The generator may run fine with all of them randomly cycling on and off over time (AC, fridge, sump pump, well, hydronic heat circulators0, but might be overloaded if they all restart at once. Some generators are designed to handle 110% of the load for up to a minute; others (less expensive, poorly designed) may simply burn out instantly.
Better transfer panels have load-shedding features to avoid overloads by sequencing cut-over, according to priority, when necessary. For instance, would you rather have the lighting on, air conditioning, or the elevators running ten seconds after a power outage? 05/05/2015, NHFireBear
...
Continue reading at HOW TO WIRE UP an ELECTRIC GENERATOR or select a topic from the closely-related articles below, or see the complete ARTICLE INDEX.
Or see these
Recommended Articles
- BACKUP ELECTRICAL GENERATORS
- ELECTRIC GENERATOR CAPACITY REQUIREMENTS
- HOW TO WIRE UP an ELECTRIC GENERATOR
- ISOLATION SWITCH REQUIREMENTS
- DOUBLE THROW TRANSFER SWITCH
- AUTOMATIC TRANSFER SWITCHES
- ELECTRICAL GROUNDING for GENERATORS
- CAR or TRUCK 120V GENERATORS
- WHERE TO BUY of 12-volt to 120-volt DC to AC power converters & inverters
- WHERE TO BUY ELECTRICAL GENERATORS
- DISASTERS: BUILDING INSPECTION & REPAIR
- ELECTRIC POWER LOSS / FLICKERING LIGHTS
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Citations & Reviewer
In addition to any citations in the article above, a full list is available on request.
- [1] "What to look for when looking at back-up electrical generators", Bud O'Connor, The ASHI Reporter, April 1998 p. 11
- [2] National Electrical Code (U.S.A.), Article 702
- [3] "Double-throw switches used as transfer switches", Electrical Code issues and answers, Vol. 1. No. 1, January 1998, Janet Lewis, Chief Electrical Inspector, Washington State, web search 07/13/2011, original source: http://www.lni.wa.gov/tradeslicensing/electrical/files/currents/elc9801.pdf
- [4] "Basic Housing Inspection," US DHEW, S 352.75 U48, p.144, out of print, but is available in most state libraries.
- [5] Eaton Corp., Cutler Hammer Products Adjustable Retrofit Kits, E-CH Load Centers and load center parts can be purchased through any E-CH distributor. Cutler Hammer Contact Points: Telephone: 800-330-6479 EMAIL: FlexCenterLincoln@eaton.com.
- [5] Reliance Controls Corporation ,
2001 Young Court, Racine, WI., USA 53404 Tel:
(262) 634-6155 (800) 634-6155
Email: support@reliancecontrols.com The Reliance Controls corporation has been in business for more than 100 years and supplies backup electrical generators and generator controls such as switching panels and transfer switches. - [6] Sima DC to AC power converter/inverters, distributed widely including online via TheEpicenter.com. Epicenter Supplies, LLC 384 Wallis Street #2, Eugene, OR 97402, Tel: 541-684-0717, Email: info@theepicenter.com Website: http://theepicenter.com/dc_to_ac_power_converters_and_inverters.html
- [7] Stanley power converters, (distributed at WalMart stores) include the little Stanley 100W inverter that plugs directly into a vehicle cigarette lighter socket and provides a 120V AC electrical receptacle, the larger Stanley XO Vision DC to AC 300W Power Inverter and other higher wattage models.
- [8] Wagan DC to AC power converter/inverters, including the tiny Wagan - Smart AC 80 USB Power Inverter that includes both a USB adapter (for your cellphone or tablet computer) and a 120V electrical outlet, as well as higher capacity power inverters ranging from 100W to 5000W - distributed widely including online via BestBuy.com. WAGAN Corporation, 31088 San Clemente Street, Hayward, CA 94544, USA, Tel: U.S. & Canada Toll Free: +1.800.231.5806, Email: sales@wagan.com, Website: http://www.wagan.com/
- [9] Nicholas D. Kristof, "A Failed Experiment", The New York Times, Opinion Pages, 11/22/2012
- [10] Electric Generators Direct, distributes nearly all brands of backup generators. Electric Generators Direct 1325 Rodeo Drive Bolingbrook, IL 60490, Tel: 1 (866) 437-7998, Website http://www.electricgeneratorsdirect.com/
- [11] Winpower, Inc., "Miscellaneous Wattage Requirements", HOV Series, 1999
- In addition to citations & references found in this article, see the research citations given at the end of the related articles found at our suggested
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- Carson, Dunlop & Associates Ltd., 120 Carlton Street Suite 407, Toronto ON M5A 4K2. Tel: (416) 964-9415 1-800-268-7070 Email: info@carsondunlop.com. Alan Carson is a past president of ASHI, the American Society of Home Inspectors.
Thanks to Alan Carson and Bob Dunlop, for permission for InspectAPedia to use text excerpts from The HOME REFERENCE BOOK - the Encyclopedia of Homes and to use illustrations from The ILLUSTRATED HOME .
Carson Dunlop Associates provides extensive home inspection education and report writing material. In gratitude we provide links to tsome Carson Dunlop Associates products and services.
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