DIY – 15 Amp Portable Generator Transfer Switch

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WARNING

You MUST read these warnings before proceeding.

This is not a task for the electrically uneducated or inexperienced. Electricity can

and does KILL. It is important to keep in mind that electricity can kill, maim and

damage through electrical shock and through such things as fire via arc-induced

burning and high resistance connections. It is also very important to note that if

you incorrectly install transfer equipment, or fail to install transfer equipment,

you can easily harm or kill utility workers and neighbors outside of your

residence through “back feeding.” If you are not comfortable or technically

qualified for this task, spend the few extra dollars to purchase purpose built

equipment and pay a professional to install it.

While proper installation of any electrical components is a major life safety issue,

improper or poor installation can also cause extensive and quite expensive

damage to equipment.

You must be familiar with national codes, i.e. NFPA 70 – National Electric Code

and ICC International Residential/Building Codes, and with any local and/or

utility restrictions, codes or amended adoptions. Yes, that’s right, some utility

companies require notification, inspection and adherence to special utility

requirements for installation of a standby generator (a portable wired into any of

the residence’s circuits is considered a standby generator.)

The information provided here is for INFORMATIONAL PURPOSES ONLY and

should not be considered or inferred as instructional in nature. Basic electrical

knowledge and installation steps were omitted.

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TRANSFER SWITCH BASICS

What is a transfer switch as used with a standby generator and your home? Well, the

simple answer is that it isolates the generator from the home’s electric utility service

and vice versa. Without a transfer switch, the only way to tie a generator into your

home’s electrical system is to perform the very dangerous and likely illegal act of “back

feeding.” Back feeding is done by connecting the output of your generator to your

home’s electrical system, typically by plugging into a receptacle. This is dangerous for

several reasons. The first reason that this is unacceptable is that, with a large enough

generator, can likely overload the circuit that you are back feeding through resulting in

damage, fire or injury. Another reason that one must be mindful of the dangers of

back feeding is the simple fact that you can energize not only your entire house, but

your neighborhood and even primary service lines. It is important to note that when

you back feed, the same transformer that reduces line voltages to your household

voltages can work in reverse. That is, your 120 volts put out by your generator can be

stepped up to line voltage back feeding through a transformer. You could imagine how

dangerous this can be for utility workers repairing downed lines, damaged equipment,

etc.

The basic function of a transfer switch in a standby generator system is to isolate two

separate feed sources for a load(s) from each other, preventing any chance of one

power system feeding the other and vice versa. The following graphic illustrates a

basic schematic of a single transfer switch. The illustrated switch is a single pole,

double throw (SPDT) type. A common example of a SPDT switch is a three-way switch

found in the home. As drawn, the load/appliance is connected to the electric service of

the building and/or residence. The generator supply in this example is isolated from

the load and the electric service. When the transfer switch is actuated/switched, the

connection between the electric service/line power will “break” and then the switch will

“make” the connection between the load and the generator. Note the terms “make”

and “break” for these are important. It is possible to have two different types of SPDT

switches: make before break and break before make. A make before break switch will

actually have a brief period of time during switching where both the line power and the

generator will be connected. The break before make switch, the common type,

theoretically should never allow the connection of the two power sources. Obviously,

this is the type of switch that we need. The three-way switch mentioned earlier is

typically this type of SPDT switch.

There are several companies that manufacture and sell preassembled transfer switches,

basically, off-the-shelf solutions. Two of these companies are GenTran and Reliance.

For what these switches are, sets of SPDT switches and some push button breakers (for

the basic manual options), I have yet to meet anyone that thought these were a

bargain. Based on my needs and what is available on the market, I opted to design

and install a much more economical, custom matched to my needs and just as safe for

property and life transfer switch system.

TRANSFER SWITCH DESIGN & INSTALLATION

The above illustration captures my transfer switch design. Some important safety

oriented characteristics to note regarding this design:

Note that all boxes, grounded receptacles and grounded switches are bonded to

the generator’s ground and in turn bonded to the ground bus at the electric

service panel for my house.

The neutral from the generator is bonded to the neutral bus of the service panel

which, in turn, is bonded to the ground bus of the service panel. Note: My

generator, Honda Eu2000i, does not have a neutral bonded to ground at its feed

points. In this particular example, you do NOT want to bond the neutral and

ground at the generator, Honda Eu2000i, if you are bonding the neutral and

ground buses at the service panel. Some generators come from the factory with

a neutral to ground bond, but that is not so in my case. In my example, if I

were to bond the neutral and ground at my generator and have the neutral

grounded at the panel, I now have two different paths for return current to flow

to my generator. Return current on the ground will create voltage on the ground

and that is NOT good. For now, you theoretically have an “energized” ground

and this is both a life safety and property concern.

All circuits being dual served are 15 amp in size in the main service panel. While

the generator has 20 amp circuit protection, this is too much for my home’s 15

amp branch circuit wiring. So, I would be able to overload a 15 amp branch

circuit with 19.9 amps and never trip the generator circuit protection out. Also,

keep in mind that 15.1 amps will not instantaneously trip a 15 amp breaker. As

a matter of fact, 15 amps on a 15 amp protected circuit could take minutes or

longer before tripping. It is also important to note that a 20 amp breaker will

not trip as fast with higher currents as what a 15 amp breaker would. All of

these concerns/issues could be major fire safety hazards. To prevent any issues,

each transfer switch’s generator side line is protected by a 15 amp breaker (All of

the 15 amp circuits utilize 14/2 W/ Ground wiring).

The feed cable (12/2 W/ Ground) from the L5-20R receptacle (where the

generator is hooked up outside) and the receptacle itself are sized to

accommodate the 20 amp protected circuit provided by the generator as is the

utility receptacle.

The transfer switches are 20 Amp models with Heavy Duty Contacts to prevent

welded or sticking contacts in order to meet the break before make requirement

as mentioned above.

The basic “flow” of the system is as follows:

Generator > Service Cable > Twist-Lock Receptacle > Split to Utility Outlet & Generator

2 Breaker, 4 Circuit Load Center > Transfer Switch > Load (E.g. Appliance)

The materials list is as follows:

Outdoor Receptacle (See Part 2 below.)

L5-20I Flanged Insert Receptacle

Outdoor, Deep Receptacle Box

Hubbell Flanged Insert Outdoor Receptacle Box Cover

Vinyl Siding J-Block

Generator Load Center

Cutler-Hammer 2 Breaker, 4 Circuit Load Center (Cutler-Hammer to match

existing service panel)

Cutler-Hammer Twin 15/15 Amp BR Breakers

Utility Outlet

Single Metal Box

20 Amp 120V Duplex Receptacle

Duplex Receptacle Cover

Transfer Switches

20 Amp Heavy Duty Three-Way SPDT Switches

Double Metal Boxes

Double Switch Covers

Miscellaneous: Wiring, Conduit, Etc.

12/2 W/ Ground

14/2 W/ Ground

3/4” EMT Conduit

3/4” Conduit Clamps

3/4” Conduit Setscrew Connectors

Wire Nuts & Electrical Tape

At a minimum, your design, layout and installation must comply with the current

revision of the National Electric Code. In my case, the current revision that must be

complied with is NFPA 70 – National Electric Code 2008. Remember, your local

jurisdiction may require drawings, permitting, inspections and requirements in excess of

code requirements.

Some of the items of importance from the National Electric Code that apply to this

installation are as follows:

Grounding Requirements - Article 250.20 (Previously discussed.)

Article 100 Definitions

Separately Derived System. A premises wiring system whose power is derived from a

source of electric energy or equipment other than a service. Such systems have no

direct electrical connection, including a solidly connected grounded circuit conductor, to

supply conductors originating in another system. (My system is a non-separately

derived system. This definition later determines various requirements for installation.)

Article 312.8 Enclosures for Switches or Overcurrent Devices

Enclosures for switches or overcurrent devices shall not be used as junction boxes,

auxiliary gutters, or raceways for conductors feeding through or tapping off to other

switches or overcurrent devices, unless adequate space for this purpose is provided.

The conductors shall not fill the wiring space at any cross section to more than 40

percent of the cross-sectional area of the space, and the conductors, splices, and taps

shall not fill the wiring space at any cross section to more than 75 percent of the cross-

sectional area of that space. (This Article covers the use of wire nuts inside of a service

panel. It is OK given compliance with this Article is maintained.)

Article 702 Optional Standby Systems

Scope: The provisions of this article apply to the installation and operation of optional

standby systems.

The systems covered by this article consist of those that are permanently installed in

their entirety, including prime movers, and those that are arranged for a connection to

a premises wiring system from a portable alternate power supply. (This Article and its

various sections dictate the actual design, installation and integration of a standby

power system, i.e. generator, into your existing electrical distribution system.)

Following the design schematic above, installation and integration was actually very

rudimentary and easy. One important safety note here is that you should NEVER work

inside of a “hot”/energized panel. It is best if you can not only de-energize a service

panel that you are working in but lock out the main disconnect as well! All it takes is a

mistake or inattention lasting only a few milliseconds to permanently change your life!

My main service panel for the house…

Installation of the transfer switches. Note that I have number markers on the wires to

assist in keeping the installation straight as well as troubleshooting if ever required…

It is important to keep your routing clean and out of the way…

The finished product. Note I have a copy of the basic schematic in an envelope at the

transfer switch…

Outside hookup to the standby generator transfer system…

The parts that you see here are as follows:

Hubbell 2315 Flanged Insert – This is the receptacle that is basically a recessed

male plug.

Hubbell 2313 Equivalent L5-20C Connector – This is the receptacle end of the

patch cord.

Hubbell WP-2 Flanged Cover Plate – This is the spring-loaded flip cover for the

flanged insert.

Note: The above listed parts, if purchased through a catalog supply house can easily

total more than $140. However, in this instance, Ebay is your friend! I picked up all

three pieces above for approximately $40 shipped.

The Honda Eu2000i and patch cord that will power it all…

IMPORTANT NOTE:

It is very important that you utilize the proper flanged inlet and female connector for

the hookup on the exterior of dwelling and the patch cord respectively. The inlet and

connector are not readily found at Lowe’s, Home Depot or similar “Big Box” store. It is

easy to want to cut corners and use a standard receptacle and plug. However, this is

very, very dangerous. If you use a standard receptacle and plug, you will end up with

what is labeled as a “suicide plug” or “suicide cord”. That is, you will wind up with a

patch cord that has two male plugs rather than one female connector and one male

plug. In turn, there is potential for one set of the exposed prongs of the plugs to be

energized while operating the generator if installed as detailed in this post. The

National Electric Code has the following to say regarding connection of attachment

plugs…

Article 406.6 (B) Connection of Attachment Plugs

Attachment plugs shall be installed so that their prongs, blades, or pins are not

energized unless inserted into an energized receptacle or cord connectors. No

receptacle shall be installed so as to require the insertion of an energized attachment

plug as its source of supply.

So, this type of connection is illegal and has the potential to kill you…

(Thanks Millerized for helping to keep me safe!)

In addition to everything mentioned above, I authored a set of startup instructions for

the system in the event that I am not home for any other adult to utilize. These are

stored in an easy to access location on our main floor.

Stay safe and remember, when in doubt, call a professional!