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Discussion Starter · #1 ·
Hi All,


I have a 200 amp panel and all 40 breaker slots are taken up. My proposed HT room is about 50-60 feet away. It seems that a sub panel in the HT is the way to go, but... Is it possible to add a sub panel in this situation? What would be involved? What size panel if doable?


Thanks for any light you can shed,


-Charlie
 

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Installing a sub-panel is fairly straight forward. You will need to free up a couple of slots in your main panel. Instead of just installing a small (30 or 40 amp) panel just to serve the HT, you might want to go with a 60 amp panel that would allow you some extra slots in the future.


A small 4 slot could serve just the HT equipment. Use 10/3 wiring, and protect with a 30 amp double breaker. Or if needed you could install a 8 slot panel using 8/3 wiring with a 40 amp double breaker.


But a 60 amp panel would be better. A 60 amp panel requires 6/3 wiring. Buy a 24 slot 100 amp main panel, and protect it with the 60 amp double breaker in the main panel. (You can leave the 100 amp double breaker in the sub-panel, and use it as a disconnect) Remember to isolate the grounding bar from the neutral bar in the sub-panel (normally a green screw, just remove it)
 

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Chuck, a 40-circuit (or 42 for 3-phase) panel is designed to reject tandem breakers, because that would exceed the lawful limit. Therefore, you need two sub-panels; one near the main panel, (for the space) and one for the HT; a 125-amp rating is typical. Neither sub-panel needs its own main breaker.


The best bet here is to install a small panel, perhaps 6 or 8 spaces (for future use, too), next to the main panel, and move two 2-pole (move the lowest-rated circuits) or four 1-pole breakers (and circuits) to the new sub-panel. This will give you the space in the main panel for both sub-panels' breakers.


You'll need a 2-pole breaker to feed each sub-panel; the proper rating depends on the wire feeding each one, and that depends on the load expected. For four to six 15- or 20-amp 1-pole breakers, a 30-amp 2-pole is plenty, and a #10 feeder is good. For more, go to 50 amps and a #6 feeder.


In each sub-panel, the grounding (bare) wires and neutral (white) wires must be kept separate. This means that the neutral strip remains insulated from the enclosure, and a second strip gets screwed to the enclosure for the grounds; therefore, the feeders should be 3 conductors (plus ground).


As for who should do this work, the fact that you asked (no insult intended) implies that you should hire a licensed electrician. It's not terribly complicated work, but errors can have dire consequences. If you're extremely handy, and can acquire proper material, you might do it yourself. IN that case, have it inspected!


(Okay, so Impeyr types faster! :) )
 

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Basically here’s what I did. My main 200 amp panel was full. So I installed a new 24 slot sub-panel in my basement workshop. I used 6/3 wiring, and a 60 amp double breaker. To free out a few slots in the main panel, I moved all the basement and outside lights and plugs to the new sub-panel. I liked the idea of moving a related group of circuits and the basement wiring was still (mostly) exposed, thus making the move very straight forward. This freed up 8 slots. Enough to power the new 60 amp workshop sub (4 slots), the new 30 amp sub for the HT (2 slots) and have 2 free for future use. Worked out great. I left the 30 amp 240 volt dryer at the main panel, since I did not want to overload the workshop sub,


Funny enough, all this work was in preparation for my new HT. It is still in the very early stages of construction. In fact, although I have been working for a few months I am still at the stage of moving “things†around. As noted above the electrically work is about finished. I am re-routing the central vac from the proposed HT space, and I still need to move a couple of copper water pipes, and other bits and piece. I do not want to leave any lines running across the ceiling, since once the HT in dry-walled it will be impossible to access the stuff. But I guess this is normal! Once a few more things are completed, I can start on the walls. I am looking forward to the winter construction season.


PS As a bonus, then we installed a new swimming pool this summer, I was able to feed the power to the pool shed from the 60 amp workshop sub. So having the extra slots proved very useful.
 

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Discussion Starter · #5 ·
Thanks Impeyr and Larry Fine,


I owned a commercial greenhouse for 12 yrs and did a bunch of wiring. It was all pvc conduit with thhn and weatherproof boxes. All work was done from the main panels. I never had occasion to add or move panels. Thanks for your clear and concise description of the procedure. It seems straightforward.


Larry,


I understand that the sub next to the main panel is to free up space. Is it better or more cost effective to put the ht sub next to the main and run the circuits or run the #10 to the ht room sub and circuit wiring will already be in the room? The second solution seems best to me.

And I will run everything and have a licensed electrician give it the OK.

A very sensible suggestion.

Thanks again for both of your help-extremely useful


-Charlie
 

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The second; it's easier and more electrically efficient. I've gone into more detail in several threads in the past; do a search.
 
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