Dear Mr. Electrician: How do I replace a sub-panel?
Answer: To replace a sub-panel requires a certain amount of knowledge, experience, skill, and tools. There aren’t many standard guidelines that apply to replacing a sub-panel other than safety. Each sub-panel replacement will be unique.
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REPLACE A SUB-PANEL
Below are some photos of a sub-panel replacement in a special house. The gray sub-panel depicted was the main electrical panel until another house was moved next to this one and was attached. As a result, a new service was put on the house that was moved, and a new four-conductor cable was installed to feed the old main panel, turning it into a sub-panel.
You work with one wire at a time. After identifying as many circuits as possible and labeling them, you remove each one from the existing sub-panel. If the situation allows it and your new sub-panel can be installed without removing the old sub-panel, move the wires one at a time from the old sub-panel to the new.
The photo at the top shows the blue well pump relay box on the right. The well pump circuit breaker shut-off was located in another basement in a generator sub-panel and inaccessible from where the relay is. In addition, this circuit was spliced inside the sub-panel.
When I went to replace the sub-panel, I removed the well pump circuit from the old sub-panel and brought it into a new switch box installed on top of the blue relay. Now, there is a nearby disconnect switch for servicing the pump relay. I put a hoop over the switch to prevent accidental shut-offs.
The new sub-panel is a Square D single phase 120/240 volt, 200 amp, 40/60 (40 spaces, 60 circuits) main breaker panel. The wire feeding the sub-panel is number one aluminum on a one hundred amp circuit breaker in the main electrical panel in the other basement.
Because the basement foundation is stone, I used vertical struts attached to the ceiling joists and the concrete floor to support the new electrical sub-panel. I used quarter-inch bolts to attach the plywood with spring nuts to the strut.
In the photo above, you can see the water pipe ground/bond connection. The pipe from the well was plastic, so there was no ground from the earth. However, all interior metal piping must be grounded by bonding to a ground rod or the ground terminal when you replace a sub-panel.
The water pipe ground clamp in the photo above is made for grounding electrode conductors with a metal armored jacket. The metal jacket is locked on the small clamp, and the wire connects directly to the ground clamp. When you go to replace a sub-panel, there is a good possibility that a ground clamp will be corroded or loose.
There were a lot of copper pipes in the basement due to the hot water heating system. When you replace a sub-panel, they must be bonded together.
I installed a ground rod through the basement floor for the new sub-panel using an SDS Max rotary hammer with a ground rod driver attachment.
I added an intersystem bonding termination for other utilities to bond to.
Click here to see some generator sub-panel installations.
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