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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.
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.
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.
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.
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.
For ordinary residential usage, there is generally no need (in the US and other 120/240 areas) for 240V except for:
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.
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.
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!
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.
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
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.
Personally, I would add a few 240v NEMA 6-15R receptacles for:
The 240v UK versions of these appliances top out around 2300 watts, compared to the typical 1300 watts of American 120v appliances, so they heat up much faster. They're easy to get in the US from Amazon UK, and you can replace the plug with a NEMA 6-15P to match the outlet.
