Generator transfer panel wiring

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Transfer panel installation

I didn't bring my camera to get final installation pictures.
This wiring technique switches two poles only. Neutral is not switched.
The transfer panel was prewired allowing quick and easy final installation.
Not switching neutral requires that the generator uses a floating neutral.

Here are pictures of parts, panel as supplied, and panel prewired for installation.
Click thumbnails to enlarge.

This is the starting point. No backup power is available.
The wiring needs to be tidied but plenty of room to the left of the original panel.
The transfer panel is mounted to the left, with bottom of both panels at the same level.
Completed project is similar to this.

Picture of new panel and rubber 10 gauge extension cord.

New breakers, 6/3 and 10/3 wire, panel interconnect harness, and outdoor inlet.

Inside the new panel. This is how the panel is supplied. The jumper wire near the upper left is the switched neutral line. It would remain in place in a panel which switched neutral. The neutral breakers (labelled N) would connect the neutral lines from the main panel and the generator.
The biggest problem I have with this panel is how the circuits are split 8 on one live line and 4 on the other when using all 12 available spaces. You can see the upper and lower breakers feed from one bus, and the middle breakers are on the other one. This makes it difficult to balance generator load. Ideally there would be an equal split, 6 circuits per live line.

Panel prewired and ready for installation. Large white 6/3 attaches main panel 60A breaker to breakers on left, orange 10/3 feeds generator to breakers on right. Harness has 12 conductors of 12 gauge wire which will return power to the main panel circuits which will be supplied backup power. The white wires in the harness have tape over them to signify they are live lines, not neutral. I will be replacing the tape with heat shrink tubing.
The flex conduit mounts underneath the main panel. Each line connects to original wires feeding selected circuits.

Brief instructions

Leave all wires in the original panel as they are installed. Ground and neutral wires remain in their original positions. The only change is for the live lines.

Run a 6/3 from a new 60A breaker in the main panel to the mains input breaker on the transfer panel. This will include both live lines to the breaker, neutral to the neutral bus and ground to the ground bus.

Use a piece of flex conduit between the two panels and install twelve conductors between the two. Connect one wire to each of the new breakers in the transfer panel. You will now have twelve ends inside the main panel. Remove the backup circuit lines from their original breakers one at a time and connect to the desired jumper line. Trim the line length as appropriate and place a wire nut / Marette on the end. Continue for all circuits and you will be done.

From the generator, connect both live lines to its input breaker, and neutral and ground to the appropriate buses. The 6/3 will carry generator ground and neutral back to the main panel as needed.

The harness itself is available for about $80 from Canadian Tire. I've seen them in the electrical aisle. I bought several of them on eBay for considerably less. Of course you could always build your own. Use at least 14 gauge wire for 15A circuits, 12 gauge for 20A circuits.

Quoting from my generator page,
Can you splice wires inside a load center and not violate building codes?
Section 312.8 of the National Electrical Code permits splices and taps in enclosures if the splice or tap does not fill the wiring space to more than 75% of the cross-sectional area of the space. Unless you already have a large number of splices or taps in the load center, adding some more to install the transfer switch is not going to exceed the limits of the Code.

The overall installation using this technique is essentially the same as for the Generac, Coleman, or Gen-Tran two pole switches. Wire the transfer panel to switch two poles only, do not switch neutral. The Generac transfer panel instructions are available here.

If your generator presently uses a bonded neutral and you use this installation technique, you will have to change it to a floating neutral. Details are here.


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