Adding sub panel in basement beside main panel

[TheBarn]

Hi all, I have a 24 space, 24 circuit Square D Homeline 100 amp load center in my basement that is completely full. I would like to add a sub panel beside the main panel in order to add more circuits for a mini-split and a wood lathe. I am thinking of installing the subfeed lug kit HOML2125 (listed for my panel) in my main panel (pulling the 2 pole breaker for my heat pump water heater which I will then move to the new sub panel) and using #3 copper THWN in emt to feed a new 20 space 100 amp main lug load center. I believe I will also need to add an LK100AN neutral lug kit to allow the main panel's neutral buss to accept the larger #3 copper wire.

Is my understanding correct that as long as the new sub panel is rated for 100 amps and 3 awg copper is used to feed the sub, additional overcurrent protection is not required as the main panel's 100 amp breaker would protect everything?

Alternatively, I think I could use a 2-pole 100 amp circuit breaker instead of the subfeed kit. With two panels in close proximity in the same room, is there an advantage to using one method over the other?

Is my understanding correct that I can use #3 copper for the two hots and the neutral, and then use #8 copper for the ground to feed the sub panel from the main panel?

Is there a better /easier solution to my problem of a filled 100 amp panel?

Thanks for looking it over.

 

[theoldwizard1]

What are the major loads on the main panel ?

Is there a better /easier solution to my problem of a filled 100 amp panel?

Personally, I would install some tandems if you really only need circuits for those items.

 

[Jim greengo]

What is the model # of existing panel?

 

[sparky 1971]

You can do it as described, but there is absolutely no reason for the sub panel to be 100 amps. 60 would be more than sufficient. Move a couple of circuits to the sub to free up the space for a two pole 60 and use #6 wire. A 50 would also work using #8. Put an offset ****** between the panels.

 

[sparky 1971]

What are the major loads on the main panel ?

Personally, I would install some tandems if you really only need circuits for those items.

Homeline tandems won't physically fit in a 24/24 panel.

 

[theoldwizard1]

Homeline tandems won't physically fit in a 24/24 panel.

Bummer !

Somewhere in the 80s/90s Square D changed the design of their panels and tandems. New tandems do not fit old panels. I lucked out and found 4 NOS or I would had to install a new panel.

 

[wyliesdiesels]

Bummer !

Somewhere in the 80s/90s Square D changed the design of their panels and tandems. New tandems do not fit old panels. I lucked out and found 4 NOS or I would had to install a new panel.

24/24 is the space and circuit count. if it was say a 24/28 then you could add 4 tandems- 20 spaces for single pole breakers, 4 spaces for tandems totaling 8 addl circuits

 

[TheBarn]

Hi all, thanks for the replies. The Homeline bxh26-24a panel is from 2004ish, installed by the previous owner, and unfortunately does not allow for tandem breakers. My thinking with using a 100 amp feed to the subpanel was to not have to think about what circuits are placed in which panel, and as the run is rather short the cost of wire did not seem to make a huge difference, however it would be easier with #6 wire.