I have a sub panel in my attached garage. It has a small heat pump/air conditioner on it for a bonus room (I believe 50 amp) and a 50 amp welder plug that rarely gets used.
I built a detached garage /shop with a 100 amp panel. Can I run my sub panel in my detached garage to the sub panel in my attached garage?
I have the capability to attach it to the main panel but it would be alot of work and would have to move 2 circuits.
You can run a sub off a sub. It is done in commercial all the time.
What is the amperage of the attached garage sub-panel? It should be 100 amps or higher.
If you do end up coming off the attached garage sub-panel, you need to have a 2-pole breaker in there to feed the unattached garage sub-panel. Do not simply tap off of the mains in the first sub-panel.
Both sub panels are 100 amp main breaker panels.
Are feeder taps illegal in your town?
On Oct 12, 12:41=A0pm, "Rich." wrote:
Rich Please advise on what you are basing that last paragraph. In the case of two feeder supplied panels of the same size I would think it better practice to install double barreled lugs on the main breaker of the first panel or insulated taps on the original feeder to supply the second panel without passing the current through the first panels main breaker. The most common misconception in electrical work is that the circuits supplied by a feeder must not have an ampacity greater than the feeder. If I simply fill a 20 slot, one hundred ampere main breaker panel with the smallest breaker normally used in that panel all of which are supplying appropriately sized circuits. I have a theoretical maximum load of three hundred amperes. But the actual load on that panel is likely to be much smaller. The load calculation performed by an electrical engineer or master electrician determines the size of the supply conductors. They are never determined by the total of the ampacity of the breakers they will supply. Circuit breakers are not intended to carry there total ampacity for extended periods. Loads that run for prolonged periods are always supplied by breakers that are listed for one hundred twenty five percent of the load. In other words such loads may not exceed eighty percent of the breakers ampacity. Diversity is the electrical principal that says that in normal operation most loads do not operate at maximum for long periods nor at the same time as all of the other loads.
-- Tom Horne
I didn't mean to imply a code requirement. I based my remark solely on general work habits and safety practices. By having a separate breaker in the first sub-panel to feed the second sub-panel, you gain two advantages. One, you have a more local means of disconnect for the last sub-panel in the event of an emergency, such as a fire, water leaks, etc. Second, you have the means of shutting down the second sub-panel while still leaving the first one powered up.
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