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I'm looking to add a hot tub, and after my basement build out a few years ago my panel is full. (By "full" I mean we added a sub panel and now my 400 amps is "technically" spoken for by 400 amps of breakers, though of course our load is never anywhere close to that.)

I'm not unfamiliar with these principles (I wired the basement buildout myself and had my electrician friend and inspector sign off on it.)

What I'm looking for and can't find, likely because I don't know what to look for, is some sort of intelligent switcher or breaker. Something that would allow me to say, share the 50amp 220 from the clothes dryer with the hot tub, so when the dryer was running the hot tub would be shut off.

I don't want to unsafely overload the panel or make modifications that would get frowned on when the house is sold. The power company wants thousands of dollars to "upgrade" my feed to 800 amps. I don't need 800 amps ... I need to safely, legally and automatically share 50 amps between two circuits.

What can I do here?

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This question came from our site for electronics and electrical engineering professionals, students, and enthusiasts.

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    The number marked on the handle of the breaker tells you at about what current the breaker should trip, nothing more. Adding up the values on the handles in a panel is only useful, if you're trying to teach your kid how to do addition. It's completely meaningless. – Tester101 Jun 25 '15 at 22:51
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It is okay to have 800 amps of breakers in a 200 amp service panel. The reason there is a main breaker (200 amp double pole) is to prevent unsafe usage.

When you run out of physical space, there are several solutions:

  • Replace some of the main panel breakers with half-widths (two breakers per slot) to create enough space for a new breaker.

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  • Install a sub-panel which is fed by a double breaker in the main panel. enter image description here

  • Remove unneeded breakers. Maybe some circuits are no longer in use.

  • Replace the breaker panel with a bigger one.

  • Be aware that some panels, especially older ones may not be rated for half-width breakers or they may only be allowed in certain slots. Half-width breakers won't fit into non-compliant slots without modification which is against code. – DoxyLover Jun 26 '15 at 19:48
  • LOL that tiny sub-panel, clearly the person did not learn his lesson with the main panel, he's 60% full and he'll soon have to re-do the job again! – Harper May 6 '17 at 0:48
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You may want to be careful doing this as it my violate code. I suggest you ask your electrician friend to check his IEC book.

Anyways, try looking here: http://www.nktechnologies.com/current-sensing-switches/

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More circuits in a panel, duplex etc.

I wrote a thorough explanation of duplex breakers here, that will show your options for adding to a panel. https://diy.stackexchange.com/a/110152/47125

Amps on the breakers

Yes, the numbers on the breakers add up to more than your main service. That is normal. You don't have to worry about that unless particular things about your operation create a probability of running all that stuff at once. For instance a friend has an all-electric house, and 200A Main Panel 1 has:

  • 60A heat pump compressor (cannot run below -10C)
  • 70A auxiliary heat #1
  • 70A auxiliary heat #2
  • 20A humidifier and air handler
  • 15A furnace controls and electronics

He's oversubscribed, obviously, but he also knows the aux heat will not run if the heat pump is working. So he's fine, but he doesn't have the headroom to add a 30A dryer to this panel. (he has a second panel for everything else.)

Suppose you have a 60A/240V subpanel. Normally it would be no big deal to oversubscribe that panel and put twelve 20A circuits for ordinary household loads, which would cover most of a house's lighting and receptacle circuits.

But in your case you want to run twelve Bitcoin mining rigs, which draw 16 amps continuous at 120V (so you must provision 125% or 20A). You can only get 6 of those (3 per pole) on a 60A subpanel and you must place them smartly so you don't accidentally put 4 on one pole.

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