I am a total newb to home electronics (electronics in general, actually) so I am posting here to get some ideas of what's really possible before I even try to contract an electrician. Allow me to explain my problem.

I live in a home in the United States with a relatively small electrical breaker panel. All of the outlets in my home are the standard 120V three-pronged outlets that have served me well until now. Recently I have found the need to be using larger and larger amounts of power in my home office for computing, and the specialized computing equipment I need uses large amounts of electricity -- so much so that I'm using all of the available power at my home as it is currently set up (I've even tried relocating some of my equipment to other outlets in the house so that I can draw from other breakers breakers in the house). The equipment I'm using uses anywhere from 1100 - 1500 continuous watts of power (I essentially leave most of this equipment on for the better part of the day). The power supply on each of my specialized computers (I have multiple remember) comes from two of these 850W EVGA power supplies (you can see the specifications here: https://www.evga.com/products/specs/psu.aspx?pn=3dae584b-878a-4821-b8ee-ded42fe946a7).

I realize I can probably have a new panel purchased and wired, but I was wondering if there might be a way to do this another way. Would it be possible to re-wire some of the receptacles so that they the I pull 240V from the panel and then convert them in the receptacle (or something similar) to 2 standard 120V outlets? What I'm trying to do is essentially double the number of plugs I can use for this equipment.

The panel is a GE PowerMark Gold TLM1212CCU

Panel Picture 1 Panel Picture 2

  • How many of these specialized computers are you trying to power, what size is your electrical service, and how big is your house (in square feet)? Also, is running dedicated homeruns from the existing panel an option, and what make and model is your electrical panel? Sep 3, 2017 at 3:40
  • Thanks so much. I am a bachelor so I have a small home: 1000 sq. ft. I am stating a new biz and am trying to generate revenue before moving to an official location where I can take care of these things a bit better (on a shoestring budget now). I ideally need about 15 units now (1 per client) and would like to sign up a few more. I have only 4 running now as dedicated homeruns, but with dishwasher, A/C, lights, oven, etc., I need other circuits for basic household stuff and nearly all circuits are in use. I've added an update to the original post of the panel description. Will post pics Sep 3, 2017 at 3:58
  • That's the catalog number of the front cover, not the guts, of a 12-space panel. Most likely it can accommodate twelve 1-pole GE breakers or six 2-pole GE breakers. Or, it might be able to fit up to 24 of the unique Qline half-width breakers. Sep 3, 2017 at 4:17
  • @Harper. Whoops. Sorry about that. I told you I know NOTHING about electricity. I can probably kill the main unscrew the top panel and take another pic if that helps. Sep 3, 2017 at 4:35
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    Red alert! In position 6 (3rd down on right) there's a 30A breaker labeled Liv/BED. That is almost certainly a 15A or 20A circuit that someone has slapped a 30A breaker onto, probably to prevent constant breaker trips. That will burn your house down, and needs immediate attention by an electrician. In the meantime it should be Shut Off Now. Sep 3, 2017 at 7:19

1 Answer 1


Red alert! The breaker in position 6 is wrong!

Looking at your photos, somebody slapped a 30A breaker on your LIV/BED circuit in position 6. I guarantee you that connects to a 14 or 12AWG wire, and the person "upped the breaker" because they are having trip problems. Somehow the house hasn't burned down yet, but it's a disaster in the making. Turn that breaker off NOW and leave it off until an electrician can fix all this.


Start with surveying which outlets are on which breakers, and label each of your outlets for circuit identity and ampacity (15A or 20A - it's on the breaker).

The breaker positions are numbered in the panel, but you may want to avoid using position numbers since you'll surely be moving them around. You could call them A, B, C, Thor, Daisy, Yondu, etc. Whatever.

A circuit can handle:

A 120V/15A circuit can handle 1440 watts continuous, and 1800W total for short time (<3 hours with a long cooldown period between peak runs).

A 120V/20A circuit can handle 1920 watts continuous, and 2400W for short time.

You cannot use circuits larger than 20A.

If you have 10 sockets on a 20A circuit, that's like having 10 checks and $1920 in your account. If you spend your first two checks on $1200 servers, you're overdrawn even though you have 8 more checks. You know this.

240V circuits can carry double the above. We'll come back to that, but for now, 240/15A = 2880 continuous and 3600W max. 240/20A is 3840 continuous and 4800 max.

Your equipment

First, I know that EVGA power supply is in vogue. But we deal with it from a power perspective, and it's super impractical. You don't need 850 frickin' watts unless you're rendering or mining bitcoin with dual 1080's and a stack of server grade drives. Seriously. But the power-side draw of the pig is 10A requiring you provision 1200 watts (inefficient!) Dump that pig unless you have a critical-path business need for it.

Now survey each piece of your equipment, it will have a nameplate rating in either VA, watts or amps - VA is the best number to use, otherwise use the larger of either input watts, or amps x 120. Like the "850 watt" PS is 10A therefore 1200W.

Don't forget your other non-computing loads - survey the whole house, it's common for multiple bedrooms to share a circuit.

You know what to do now. Spreadsheet it all out, and figure how to dispatch the loads you have to the circuits you have. Obviously you will have a shortfall, but now you know how much.

Don't forget air conditioning. Every watt you consume becomes that many watts of heat in the building, which you will need to air-condition to remove, and it costs 1 watt of A/C to remove 2-3 watts of heat.

Thinking about 240V circuits

Your idea of splitting 240V into two 120V half-circuits is called an MWBC and it's too difficult to do given current codes. But it's just as easy to wire two full circuits. (you couldn't have used existing /2 cable for an MWBC, so you'd have to pull a /3; well then pull a /2/2 (4+ground) or dual /2's and done.

You can also bring real 240V into a bedroom, and that can run on /2 cable. However there must still be 120V outlets in all the usual places (within 6' of any point along a wall), so you can't re-task a 120V line unless it's an extra that isn't needed to meet the minimum service.

A 240V-only line can be run with /2 cable, but if you're in the walls you might as well pull /2/2. Most of your equipment will already work directly on 240V. Read the spec, most has multi-voltage power supplies.

All of this involves pulling new wire through the walls.

You never, ever connect a 240V circuit to a common standard NEMA 5 receptacle. They make NEMA 6 receptacles specifically for 240V (without neutral). They also make NEMA 14 for hot-hot-neutral 4-wire connections, but those do not exist in 15 or 20A, so they are irrelevant to you.

Upping the panel

Changing a main panel is a huge and very expensive project for an electrician. Avoid if feasible, especially since GE Qline is a fine panel. You do have far too few spaces, however, and the way to fix that is a subpanel. And please, get lots and lots and lots of spaces - 40 is not excessive.

Then you put a decent size breaker in the main panel (e.g. 70A) to power the subpanel. The subpanel doesn't need its own "main" breaker, but if it has one, it just needs to be same or bigger. (e.g. 40-space panels tend to have 225A mains, fine.)

If you have no empty space in the existing main panel for a fat 2-pole breaker, pick some small circuits whose wire length is favorable to moving them to the new subpanel; do so; and use the freed space for the new main breaker.

I would assume to put the new main panel right next to the existing main panel. Depending on what's possible with moving otehr circuits over, right in the server room may be a good place.

Load planning for the entire house

Anytime you make changes like this, you should also survey all the loads for the entire house and make sure that adding circuits is reasonable and legal. There are plenty of Q&A here and articles elsewhere on that.

The presence of a subpanel has nothing to do with it. The main and subpanel loads are counted together to determine if the main panel has the capacity for what you need. It's much more involved than adding up all the numbers on the breakers.

Separate to that, you also do a load survey on just the subpanel to make sure it isn't being overloaded.

Wait. You are rendering or mining bitcoin!??

Hoo boy. Start by seeking PC power supplies that are more than 70% efficient. 1200W for 850W is terrible.

Do your load planning based on your actual loads, and then when you wire it, install 2 circuits where you would've installed one - running 2 cables instead of 1 costs next to nothing, and it's in the walls for future use. But that's just more of what I talk about above.

Fair chance you'll need more service, and have that conversation with the power company. Again you don't want to replace that main panel. So fit your LARGE subpanel where new service can easily reach it - and at that point, flip it so the new panel is the main and the old panel is the 'sub. That'll work just fine.

Air conditioning is HUGE. Every watt turns into heat, in the room and you must remove it or the room will overheat and the CPUs can't cool. A/C is not optional here. Your whole-house A/C is not designed to remove that much heat from a single room. I have told bitcoiners who had an empty house to scatter servers all over the house, for that reason (also power). However there's a better way.

Use water cooling, and ship the hot water outside. These guys here did exactly that, because they had the same problem: five max'd out rigs in one room and the house A/C couldn't deal. It was very effective. But they made blunders:

  • They did not insulation-wrap their supply and return pipes.
  • Being a "review site", they are obliged to use the free stuff manufacturers send them, that's why they spooged together their radiator. They should've gone to an auto junkyard and bought an SUV radiator, with electric cooling fans, thermostat and relay. Which is way more than they'll ever need, and is made to go outside.
  • They mounted the radiator in direct sun.

(and by "water" I mean 50/50 propylene glycol, a more rarely-made automotive antifreeze. You will have leaks, and propylene glycol, being basically a foodstuff, is nontoxic and no worse than a Mountain Dew spill. Common automotive ethylene glycol antifreeze is the wrong stuff, it's used because its cheeaper, but it is both toxic and sweet-tasting, so it will kill your pets.

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    this is amazingly helpful! I can't tell you enough how much I really appreciated your detailed answer. One point to make, however, is that, in fact, I do need wattage on the level of bitcoin mining. The units I'm using are actually performing statistical computation using 10 high end GPU's each (just like bitcoin does), but instead of mining, I perform gigantic machine learning, and liberal algebra problems (think inverting enormous matrices.). So in fact, I do need 2 850W power supply units. I could probably drop to 2 750W PSU, but did this just in case. Sep 3, 2017 at 10:10
  • Nonetheless this is a fantastic answer. I'm going to wait to see if there are any other answers, but this looks like it will likely be the accepted answer. Thanks again. Sep 3, 2017 at 10:11
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    @StatsStudent I updated at the top to cover an urgent defect and at the bottom to address serverfarm-unique problems. Sep 3, 2017 at 17:31
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    Get a Kill-a-Watt and measure the actual usage of your computer under load. The specs indicate 92% efficient, but also indicate 10A input (=1200W, which would be 70% efficient as Harper mentioned in the answer). The specs also don't list a separate input current for 240V, so there's something janky going on there. Best to measure it and be sure.
    – mmathis
    Sep 11, 2017 at 17:32
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    @mmathis it really matters, because of the 16A continuous cap on 20A circuits (avoidable by jumping through many silly hoops). This means it's rather helpful if he can get an 8A supply, he can two of those on a 20A circuit without jumping through all the hoops. Sep 11, 2017 at 23:42

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