Generator Sub-Panel Installation

Square D Generator Sub-Panel Installation

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Square D generator sub-panel completed and labeled
Square D generator sub-panel completed and labeled.

All circuits must be labeled to pass inspection.  I use a Brother P-Touch label maker.

The completed generator panel The upper arrow points to the 10/3 Romex cable that is coming from the generator inlet.. The lower arrow points to the 10/3 Romex cable that is coming from the main electrical panel
The completed generator panel The upper arrow points to the 10/3 Romex cable that is coming from the generator inlet. The lower arrow points to the 10/3 Romex cable that is coming from the main electrical panel

In the above photo the upper arrow points to the 10/3 Romex cable that is coming from the generator inlet mounted outside which will supply power to the generator sub-panel from the generator when needed.  The lower arrow points to the 10/3 Romex cable that is coming from the main panel to feed the Square D generator sub-panel on utility company power.

Electrical cables must be fastened within 12″ of the box.

Two 30 amp main circuit breakers with the interlock device between them
Two 30 amp main circuit breakers with the interlock device between them.

Note the twin circuit breakers above for the branch circuits.  The generator panel is approved for twin circuit breakers.  Notice that the Square D twin circuit breakers for the furnace and basement lights are connected with a handle tie.  This is required by article 210.4(B) of the National Electrical Code because these circuits are a multi-wire branch circuit.  I forgot to remove my temporary white tape labels before taking this picture.

In this particular installation the furnace and the basement lights were wired originally by the builder using a multi-wire installation method.  This is where a 14/3 cable is used to carry two separate circuits on the red and black conductors and the one white neutral conductor is used for the return current on both.  The original installer probably did this to save labor on installing two separate cables, but it can be problematic for GFCI and AFCI protected circuits.

The electrical code requires that a multi-wire circuit must be disconnected at the same time.  Usually a two pole circuit breaker can do this.  However in the generator sub-panel depicted here there was not a lot of room for a two pole circuit breaker.  So a Square D #QOTHT handle tie was used with tandem (Twin) circuit breakers.

The arrow indicates the two pole, 30 amp circuit breaker to feed the new generator sub-panel
The arrow indicates the two pole, 30 amp circuit breaker to feed the new generator sub-panel

A two pole 30 amp circuit breaker was installed in the existing Cutler Hammer main electrical panel to provide power to the new generator sub-panel.  The generator circuit breaker must be labeled in order to pass inspection.

The L14-30 generator inlet mounted on the exterior of the house with the flap up
The L14-30 generator inlet mounted on the exterior of the house.

A Reliance PB30 generator inlet was installed for the generator to plug into using a four wire L14-30 generator cord with twist lock plug and receptacle.  This inlet was installed outside near the electric meter.  It was very close to the generator sub-panel mounted inside of the basement.  I used 10/3 Romex cable to enter into the rear of the generator inlet.

My post about an interlock kit installation on an existing Cutler Hammer load center shows more details about a PB30 generator inlet installation.

Reliance PB30 generator inlet installed on a house
Reliance PB30 generator inlet installed on a house

The generator inlet has a concentric knockout in the rear for a 1/2″ and 3/4″ cable or conduit connector.  More details about a generator inlet installation can be seen on my blog post here.

Generator inlet is a 30 amp 4 prong twist lock plug
This Generator inlet is a 30 amp 4 prong twist lock plug

You can see photos of an interlock kit installation on a GE load center here.

All of my generator related posts can be seen here.