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Tag: Wiring A Generator Sub-Panel

Completed generator sub-panel with a Square D generator interlock between the utility power main circuit breaker and the generator circuit breaker

How I Wired A Generator Sub-Panel

Dear Mr. Electrician:  How do I wire all of my circuits to a generator sub-panel? Answer:  First get a sub-panel suitable for your application.  Some generator sub-panels are prewired and you just make the correct connections with the existing circuits.  Those types usually have limitations as to the number of circuits connected to the generator. It is possible to make a generator sub-panel out of an ordinary load center circuit breaker panel using an interlock kit.  You just need to get the correct accessories.  In the generator sub-panel circuit wiring installation pictured below I used a standard Square D Type QO, 125 amp, 24 circuit, single phase load center as a sub-panel with a separately purchased Square D Interlock Kit made for this purpose. I also had to purchase separately a grounding terminal bar for all of the ground wire terminations.  Most load centers do not come with a separate ground bar unless it is designated as a sub-panel.  This panel did not have a main circuit breaker installed by the factory.  I installed the QO 100 amp main breaker and a QO 50 amp generator circuit breaker.  NOTE: Text links below go to applicable products on Amazon.com. For this particular generator hook up installation the client wanted many circuits to be powered by a portable generator.  Those circuits included an electric range, electric water heater, oil burner for heat, microwave oven, bathrooms, and kitchen outlets & lighting.  My first thought was to install an interlock kit on the main breaker in the existing circuit panel that would have provided the homeowner access to all of the electric circuits. I chose to install a generator sub-panel rather than install an interlock kit on the entire main electrical panel because at the time of this installation I could not find an interlock kit for the existing panel that would be approved by the electrical inspector.  The panel manufacturer does not make an interlock kit for this particular panel.  There is a company called Interlockkit.com that does make an interlock kit for this main panel.  However the State of New Jersey, where this installation is located, was not accepting the test laboratory certification that the manufacturer was using for their products. The manufacturer has since changed testing laboratories and some of their products have been re-tested by the new lab and are now acceptable to New Jersey.  If you are in New Jersey and need to use an interlock kit from this company, contact the factory by phone to learn if the product that you need is approved.  Click to see some examples of interlock kit installations done by me.   Generator Interlock Kits on Amazon Steps Before Generator Sub-Panel Installation You need to apply for an electrical permit ahead of time for wiring a generator sub-panel.  When I submitted the permit application for this job I included a copy of the installation instructions of the interlock kit, as well as the model number of the load center.  I also included a typed, one page "Scope of Work" briefly detailing...