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I am having my main circuit breaker panel replaced (by a licensed electrician) and he told me I can run new circuits for him to hook up to the new panel. Is there any benefit to running 240v circuits for computers, network equipment, other devices that support it?

I would probably put a 120v outlet next to any 240v just for convenience (I was thinking on opposite sides of each stud.

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    I'm a bit puzzled by the question. How could 240 volt outlets be any useful for computers and network equipment? – Charles Dec 25 '19 at 23:19
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    @Charles -- most IT equipment uses universal input (85-90 to 264-270VAC) power supplies that automatically adjust for the various mains voltages and frequencies found worldwide, so it will run just fine plugged into a North American NEMA 6 receptacle – ThreePhaseEel Dec 25 '19 at 23:21
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    @charles check on the side of a power supply, it accepts VAC 115-230, so it could use the 240 volt outlet – Tyler M Dec 25 '19 at 23:23
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    Some (mostly older) systems have a switch to flip between 120 and 240. – yakatz Dec 26 '19 at 3:10
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    240V circuits take a lot of spaces. Make wure to get a huge panel (in terns of number of spaces). I'd consider nothing less than a 40 space. – Harper - Reinstate Monica Dec 26 '19 at 5:44
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There's no need to do this for computers/networking gear/...

While the switching power supplies used in IT equipment are slightly more efficient when running on 240V vs when they are running on 120V, this efficiency difference is generally small enough that it can be disregarded as a practical matter. As a result, I would simply provision 120V/20A circuits for equipment closets, office spaces, and the likes.

HOWEVER: there are spaces where this is a good idea

The above, though, is not universal advice in the sense that it is specific to IT equipment. Shop spaces where fixed power tools are used, such as woodshops or metalshops, benefit greatly from having both 120V (NEMA 5) and 240V (NEMA 6) receptacles present; this is also something that's not beyond reason for a well-appointed kitchen, although most of the kitchen appliances that can take advantage of this are commercial types.

In any case, you don't need to pull extra circuits to have both 120V and 240V together...

One benefit of the North American split-phase system over pure single-phase distribution is the ability to use multi-wire branch circuits to provide twice the current/power sourcing capability of a single branch circuit while using 3/4ths the copper and generating half the heat compared to having two independent branch circuits, something that is especially useful when mains wiring is done using individual wires in conduit (vs. prefabricated cables).

While these are normally only used with 120V receptacles and fixtures connected line-to-neutral, the use of a common-trip two-pole breaker (which is the normal way one wires these any more) allows a mixture of 120V and 240V loads/receptacles on the same branch circuit, as per NEC 240.4(C) Exception 2:

(C) Line-to-Neutral Loads. Multiwire branch circuits shall supply only line-to-neutral loads.

Exception No. 1: A multiwire branch circuit that supplies only one utilization equipment.

Exception No. 2: Where all ungrounded conductors of the multiwire branch circuit are opened simultaneously by the branch-circuit overcurrent device.

This also permits the use of NEMA 5/6 combination duplex receptacles, such as the Leviton 5844. These provide access to both 120 and 240V on the same yoke when fed by a properly wired multi-wire branch circuit, without having to resort to a dodgy adapter.

...but this comes with some caveats

However, the requirement for a two-pole common-trip breaker does pose a few caveats when arc and/or ground-fault protection is required. First and foremost, if you have a GE panel, you cannot use this strategy on any circuit where arc-fault protection is required, as the current (Mod 3) GE AFCI breakers are not available in a two-pole common-trip configuration, only single-pole units that can be handle-tied for 120V-only or 240V-only service. (If you can obtain a Mod 2 GE CAFCI used, you can do it that way, but those are likely to be relatively thin on the ground.)

Furthermore, in spaces where both arc and ground fault protection is required (right now, only kitchens, laundry rooms, and bathrooms), you're forced to have a 2-pole arc-fault breaker in series with a 2-pole ground-fault breaker to protect these circuits, as 2-pole dual function (AF/GF) breakers are not available at this point in time, and appear unlikely to become available any time soon. For an individual circuit, this can be accomplished using an arc fault breaker in the panel and a "spa panel" in-line with the homerun to provide the GFCI protection; however, if you are wiring several circuits this way, it's better to use a split-bus (albeit not rule-of-six) panel (such as a Siemens generator panel) to provide this series configuration, with a GFCI breaker replacing the normal utility feed breaker to the "generator" section of the panel and AFCI breakers in the "generator" section feeding the individual branch circuits.

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  • I did not know those Leviton receptacles existed. I like the idea, but I will probably need to clear that one with my electrician first. – yakatz Dec 26 '19 at 3:31
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    "One benefit of the North American split-phase system over pure single-phase distribution" - is the ability to use 3/2ths of the copper of a pure 240V system :P – user253751 Dec 26 '19 at 12:13
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    @yakatz the electrician will insist on a 2-pole breaker rather than 2 singles with handle ties. Because it is an exception to normal MWBC rules. – Harper - Reinstate Monica Dec 26 '19 at 15:22
  • @user but we get half of the protection of the British construction site 110V center-ground scheme... 240V is a nasty customer, and it's almost impossible for an American (or Filipino) to handshake with it. The Philippines grasp the issue... – Harper - Reinstate Monica Dec 26 '19 at 15:27
  • @user253751 IECville has its own way of doing MWBCs which is just as nice (230Y/415, 3p4w) -- 2/3rds of the copper compared to 3 individual branch circuits, to supply 1.5x the current those four wires could supply otherwise – ThreePhaseEel Dec 26 '19 at 16:03
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For ordinary residential usage, there is generally no need (in the US and other 120/240 areas) for 240V except for:

  • HVAC
  • Electric Dryers
  • Electric Water Heaters
  • Electric Car Chargers
  • Electric Ovens and Cooktops (aka stoves aka ranges).
  • Welders and some other shop tools

For most computer users, 240V may give a very slight increase in efficiency, but not enough to be worth the hassle. However, if you are installing racks of servers - i.e., your own mini data center - then it is another story. You get twice as much power from a 20A 240V circuit as from a 20A 120V circuit for the same installation cost. However, you do need to be careful what equipment you buy - e.g., laser printers are often specific to 120V vs. 240V and can't be swapped just by replacing the removable power cord and flipping a switch.

But for ordinary users - one or two computers per room - don't bother with 240V.

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    For example: Dell Precision T7500 (up to 1100 watts), 2x HP LP2475w monitors (120w each), plus two more monitors (probably another 200w), 2 laser printers (Dell 1355cn, HP CP2505x, 320w+465w), network switches (Cisco SG300-10PP and HP 2530-8G - 240w+90w?), firewall (255w) = 24.25 Amps when running on 120 volts. Probably doesn't represent the ordinary user. The Dell printer doesn't appear to support switching voltage, but the rest appear to. – yakatz Dec 26 '19 at 3:28
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    A power user in every way. – manassehkatz-Moving 2 Codidact Dec 26 '19 at 3:41
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    I wish I could get answers this quickly to my computer questions too: serverfault.com/questions/995960/… – yakatz Dec 26 '19 at 4:30
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    Far more generally useful to have multiple 120V circuits for the same room (I like to use different colored outlets to make it more obvious which outlets are which) than to fuss with 240V outlets - IMHO – Ecnerwal Dec 26 '19 at 15:45
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    @Ecnerwal I've wired a few homes, I always run two circuits to each room, but I alternate top/bottom. I.e. two adjacent outlets will share a circuit on the top of one, and the bottom of the other. People tend to gravitate towards plugging permanent (higher-draw) devices into the bottom outlet. This means that two adjacent high-draw devices on the bottom outlet are on different circuits. – Der Kommissar Dec 26 '19 at 19:36
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It's funny, how perfectly handy people, who make things all the time, assume nobody makes anything or has Maker pastimes. Atoms are the new bits, as they say. Everything from Burning Man floats to artisan manufacturing are ever more popular. More people than ever are using hooty tooty Euro or quality machine tools like Saw Stop that commonly take 240V. So 240V outlets are definitely a value-add.

Yes, definitely do it!!

Sure... the other answers aren't wrong... that most people don't need this. You aren't "most people". The very fact that you're asking this question proves that.

For instance, gaming PC power supplies keep getting bigger, and already at the hard limit for a 120V/15A circuit. Euro kitchen appliances are popular, not least because they ignore the crippling UL-imposed 1500W limit for 120V appliances.

It's so very easy to set it up exactly the way you want it, just do it!

Most likely, this will happen in the short tern

If you wired it up NEMA 6-20, you'll end up needing more 120V so you'll just move the white wire to neutral and fit a NEMA 5-20. Because dedicated circuit, yay!

Or if you wired it up with a NEMA 14-20, you'll end up fitting a NEMA 5-20, possibly splitting it into a MWBC as ThreePhaseEel discussed.

All of which is fine. More usefulness is always better than less, and we're talking under $25 here in materials.

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    I think the one caveat to It's so very easy to set it up exactly the way you want it, just do it! is don't do anything that would confuse or frustrate potential future owners of your house. A 240v circuit in a kitchen or shop is pretty expected. Who knows what sort of reaction you might get to one in a home office. – dwizum Dec 27 '19 at 16:30
  • @dwizum NEMA 6 is often seen in older homes to power window A/C. But the seller should make it a selling point, in any case! So won't be a surprise. – Harper - Reinstate Monica Dec 27 '19 at 16:42
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There is not reason to do it. The 120 or 240 AC is always transformed down to a very low DC voltage (1.5 to 12 Volt) to be used by the computer or other electronic appliances. If u have many appliances you can just use mutiple dedicated 120 outlets which can be used directly.

I tried in the past to anticipate the future and I was very often wrong. Install what you need right now or in the very near future. Adding a 240 outlet in a garage might be a good idea but the breaker-box is near by anyway and you can add it later as well. Keep it simple is a good advise...

Washer and Dryer Stove etc. need 240 otherwise no need

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  • The reason is because you can bring 6600 watts to the bedroom instead of 1800. (Mandatory 15A circuit plus 4800W more). A PC doesn't care, but two PCs and two laser cutters might. (I know someone with all that in a bedroom.) – Harper - Reinstate Monica Dec 26 '19 at 15:18
  • ``` 110 Volt X 15 Amp = 1650 Watt => two phases = 3300 Watt 110 Volt X 20 Amp = 2200 Watt => two phases = 4400 Watt ``` He did not ask that in the question that he has a need of mayor appliances. In general I would I would consider that a waste of material. Probably smarter to run multiple dedicated 110 Volt lines. – Ride Sun Jan 28 at 18:49
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    If it's confusing, it's because I calculated all those numbers based on 120V not 110V coz my country is. . But yes, I'll meet you at least halfway, and say use /3 so you can use it either in 220/240V mode or 110/120 MWBC mode. I do have to say, sometimes you really do need that much power in a room, and when you do, far better to have overkill in the walls than extension cords all over the place. – Harper - Reinstate Monica Jan 28 at 22:14
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One specific consideration is provision for an electric car charging circuit per parking space.

A downside is that it is really hard to know exactly what you (or a future home owner) will need for their vehicle. Could be 120V will be fine but will charge slower, whereas 240V will permit the possibility of a quicker charge, and a higher voltage like 440V may allow more options.

Even if you have no intention of owning an electric car, a small amount spent on pre-work at this time might make a future change easier and cheaper. Conversely there's no gain spending a lot of money now for something that could be irrelevant in decades. Consider homes with 10base-2 cabling, satellite aerial cabling, or SCART plugs in the wall.

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    In the history if homes, no one has ever complained that 240V was brought to their garage unnecessarily. Whereas loads of people with welders, compressors, table saws, EVs, you name it, have gone "heck yeah!" Why does everyone assume nobody makes anything or has Maker pastimes? Atoms are the new bits. Artisan manufacturing is a thing. – Harper - Reinstate Monica Dec 26 '19 at 15:34
  • @Harper-ReinstateMonica concur - the point of this answer was to focus down on the possibility of future-transport needs. Its cheap to run an extra wire when you can do so conveniently. Adding it later is expendy, but the challenge is not overdoing it. Also, cars might park elsewhere than the garage, like carports or just "outside" – Criggie Dec 26 '19 at 22:52

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