PCARES - Generators

What Should I Know About Clearance Requirements When Installing a Generator?

Always check with AHJ for local codes as those will supersede these recommendations.
Do NOT install a home generator under a wooden deck or platform.
Units that do not feature the SwRI logo must be installed 5 ft. from combustible materials and 3 ft. from non-combustible materials.

Permits are required when installing a permanently mounted whole-house or standby home generator in Placer County.

Types of Permits Needed for Standby Generators

A permanent home backup generator installation typically requires multiple reviews and permits through Placer County Building Services

Generator Checklist for Placer County 2019 CALIFORNIA BUILDING STANDARDS CODE OF REGULATIONS TITLE 24

Home Standby Generator Clearance Requirements

Clearance requirements ensure the generator is operated at a safe distance where heat and fumes will not cause fires or health hazards. The exhaust gets extremely hot and remains hot after shutdown. Flammable material may ignite and burn from the heat of the exhaust system.

NFPA 37 Overview

The National Fire Protection Association’s standard for the installation and use of stationary generators.
Its requirements limit the spacing of the generator from a structure or wall.
The unit must be located where it’s readily accessible for maintenance, repair, and first responders.
Minimum clearance requirements are for adequate airflow, maintenance, and safety.

NFPA 37 Requirements

5ft. from openings in walls (operable windows, doors, vents, window wells, or openings in the wall).
18 in. of clearance from the back of the generator to a stationary wall or building (based on testing done by the Southwest Research Institute or SwRI).
5 ft. of clearance above the generator.
3 ft. of clearance at the front and both ends. This includes trees, shrubs, and bushes. Vegetation not in compliance could obstruct airflow and exhaust fumes could inhibit plant growth.
In addition to these requirements, verify all potential for water intrusion is directed away from the generator enclosure: sprinklers, roof run-off, down spouts, and sump pump discharge.

Protect the structure

Verify the structure itself as correctly caulked and sealed to prevent air from leaking in or out. Voids, cracks, or openings around windows, doors, soffits, pipes, and vents can allow exhaust gas to be drawn into the structure. Some examples of entry points are described and included in, but not limited to, the accompanying table.

Transfer Switches

Transfer switches whether manual or automatic, allow you to choose between utility power or backup generator power
Transfer switches are the only way to safely power your home’s electrical system
Using a transfer switch prevents backfeeding. This occurs when your generator becomes a power source for the surrounding area and can damage your home, your neighbor’s home, and injure workers trying to restore power

Portable Generators

Location

- Always keep generators at least 20 feet away from your home
- Never operate a generator in an enclosed space
- Make sure the generator has 3-4 feet of clear space above and on all sides for proper ventilation
- Keep generators away from door, windows, and vents
- Always direct exhaust away from your home

Use

- Always use grounded cords and inspect cords for damage prior to use
- Use the proper cord for the wattage being used
- Always use GFCI protection
- Make sure to start/stop the generator when no electrical loads are connected
- Keep generators dry, do not operate when wet, and refuel when cool
- Do not overload generators
- Do not plug a generator directly into your home, connect items being powered directly to the generator

Site selection and preparation

Potential CO entry points

Generator exhaust can enter a structure through large openings, such as windows and doors. However, exhaust and CO can also seep into the structure through smaller, less obvious openings.

Improper use and installation of generators could cause CO poisoning
Make sure your home has carbon monoxide alarms outside each sleeping area and on every level of the home
CO can kill in as little as 5 minutes
Symptoms of CO poisoning
- Dizziness
- Headaches
- Nausea
- Tiredness
If you experience CO poisoning systems, get fresh air, do not reenter areas, and call 911.

CO Levels

What are the exposure levels numbers. This is expressed in Parts Per Million (ppm). (1% of a gas equals 10,000 ppm)

Safe Levels:

0-9 ppm: Considered normal CO levels in air and poses no significant health risk for healthy individuals.
9 ppm: The World Health Organization (WHO) recommends an average of 9 ppm for indoor air exposure for 8 hours.

Dangerous Levels:

- 10-29 ppm: Prolonged exposure to these levels may cause chronic health problems like headaches and nausea.
- 30-35 ppm: Flu-like symptoms may begin to develop, especially in vulnerable populations.
- 50 ppm: OSHA (Occupational Safety and Health Administration) has a permissible exposure limit (PEL) of 50 ppm as an 8-hour time-weighted average (TWA).
- 100 ppm: Maritime workers must be removed from exposure if CO concentration exceeds 100 ppm.
- 200 ppm: Slight headache, fatigue, dizziness, and nausea may occur after 2-3 hours of exposure.
- 400 ppm: Frontal headaches may occur within 1-2 hours of exposure, and the condition can become life-threatening with prolonged exposure.
- 800 ppm: Dizziness, nausea, and convulsions may occur within 45 minutes, followed by unconsciousness within 2 hours and death within 2-3 hours.
- 12,800 ppm: Death may occur within 1-3 minutes.

So how does CO behave, to understand that you need to have a basic understanding of its chemical property, One of which is Specific Gravity (Sp).

The specific gravity of carbon monoxide (CO) is 0.9657 when compared to air, which is considered to have a specific gravity of 1. This means CO is slightly lighter than air. Due to its slightly lighter nature, CO may rise towards the ceiling if it's mixed with warm air from sources like combustion

Here's a more detailed look at each type:

Portable Generators:
These are generally smaller, more lightweight, and can be moved easily from one location to another. They are often powered by gasoline or diesel and are suitable for powering tools, appliances, and even some electronics when a power source is needed.
Inverter Generators:
Inverter generators are known for producing cleaner, more stable power than traditional portable generators. They use an inverter to convert DC electricity to AC electricity, which is essential for powering sensitive electronic devices. They are often quieter and more fuel-efficient than portable generators.
Standby Generators:
Also known as whole-house generators or emergency generators, these generators are designed to provide power to an entire home during a power outage. They are typically larger and more powerful than portable or inverter generators. Standby generators often have an automatic transfer switch that connects the home's electrical system to the generator when power is lost.

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