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The electrical code imposes a variety of requirements for different rooms of the house, in a way that implies that the house is divided up into non-overlapping, specific-purpose rooms at construction/wiring time.

(for example: Kitchens require a large number of GFCI receptacles on high-current circuits, close-together, bedrooms must be AFCI-protected, bathrooms must have a GFCI receptacle by the sink, etc.)

Obviously this gets a bit confusing in the open-plan houses that are popular today, and I have seen no clarity as to how these are to be handled.

Beyond that, I want to know how the code handles an austere one-room house with few or no permanent interior walls at all, where there are no more than two or three rooms and they all have multiple functions, and almost nothing is permanently installed. (This is in a rural jurisdiction with minimal building code requirements, so that won't be a problem). Do I have to combine every requirement for the whole room? Do I just split it up by floor plan, even though there are no actual barriers?

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    Are you restricting yourself to "star bus" systems where all the bussing is in an electrical panel with circuits running out radially from it? Or are alternative topologies for electrical distribution an option for you? – ThreePhaseEel Dec 12 '18 at 0:37
  • Almost certainly star bus, which (unless I'm extremely mistaken) is how residential wiring is always done in America. – ikrase Dec 12 '18 at 10:57
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There are no requirements for GFCI receptacles anywhere in any house. Certain locations need to be GFCI protected, but you can do that with as little as one GFCI breaker if you are committed.

The bathroom must be a separate physical room, Or at the very least, the WC. You might be able to put the shower in open space, but the users of the shower won't appreciate that none too much!

However what is relevant to the electrical codes is the areas which are near water appliances, including the WC and shower, but most particularly, the bathroom sink(s) which might be in open space. Whatever area you designate for the bathroom sink must have receptacles nearby, on a quasi-dedicated circuit according to bathroom rules.

Code will require that your design include areas to prepare food ("kitchen countertops"). Regardless of your design intent, any "counter" areas where a person reasonably might prepare food, must have receptacles such that a machine anywhere along that counterspace only needs a 2' cord to reach a receptacle. That bookends to a law that requires 2' cords on food prep appliances. It's not required for places you wouldn't be able to put an appliance.

The kitchen countertop receptacles must be powered by at least 2 circuits of 20A, that are dedicated to receptacles that you can justify as being in the kitchen area. The bathrom receptacle circuit must also be 20A, and all must be GFCI protected. However, this is not enough in practical terms. The heat applianaces typically plugged in at kitchens (coffeemaker, grill, popcorn popper, toaster) or bathrooms (hair dryer, curler) are almost universally 1500 watts. Two of them will not fit on a 20A (2400W) circuit.

So you are really better off installing considerably more circuits, at least 2 in the bathroom and 3+ in the kitchen. You ought to be able to toast the bread for your George Foreman grill burger while making coffee. Your house has 48,000 watts of service, it ought to be able to support 4,500 watts of appliances. rolls eyes

The extra cost of splitting 1 circuit into 2 is piff, $60 ($50 GFCI/AFCI breaker, $10 cable).

  • So basically, I should put at least minimal kitchen counters in place somewhere, and put kitchen-spec-satisfying outlets on them. It's worth noting that I'm actually envisioning running this on solar, in which case the absolute maximum energy capacity will be around 7 kW at maximum. I do not plan to have many (any) electric heating appliances, but still the code can and should be met. – ikrase Dec 12 '18 at 10:51
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    Or you can omit kitchen counters entirely, but you are legally obliged to recognize that the first thing the homebuyer will do is obtain some (portable) kitchen counters. And you must ask the question "where would buyer want to put them?" And if such a location is obvious, fit receptacles there. – Harper Dec 12 '18 at 15:43
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    Solar is very noteworthy and may change your Code obligations, since obviously you will not do as I described in a PV off-grid home. But watch Out: if you ar merely opting out and it is practicable to get mains power to the building, it may be obligatory to fit the wiring in the walls. Also, no AHJ will permit squalor, and inspectors often see "off-grid" as a dogwhistle for "too cheap to comply with habitability codes", so any "Grid opt-out" system must be absolutely tip-top in terms of health, safety and aesthetics. – Harper Dec 12 '18 at 15:47
  • what do you mean by "fit the wiring in the walls" - like, as opposed to not actually wiring up the house? – ikrase Dec 13 '18 at 14:08
  • @ikrase I'm saying the inspector may require you to install the in-wall wiring that would be required if you were on-grid, as a condition of an occupancy permit. I.e. That he won't let you get away with installing no wiring at all. – Harper Dec 13 '18 at 16:46
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The 2 20 amp kitchen small appliance circuits are for the kitchen counters. If you have a tiny kitchen you still are required to have 2 circuits spaced 4' or no space more than 2' from an outlet. For the larger rooms the walls have to have an outlet within 6' or 12' apart. The bathroom can be fed by 1 circuit but nothing else can be on this circuit. For the walls the measurements I gave are the basics but there are things like doorways, ovens, sinks that are not counted in the wall measurement, most everything requires AFCI's or GFCI'S Now and tamper resistant outlets. So if you have a large room like a studio apartment you still have the wall spacing requirement but the temporary dividers do not require outlets. If within 6' of a sink tub or toilet a gfci is required (or if in a bathroom). Most all the non gfci outlets will be AFCI by the 2017 code so now you just have to have the correct spacing. You can place outlets closer together but not required.

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    No space more that 2" from an outlet?? Please tell me that's a typo!! – FreeMan Dec 11 '18 at 15:18
  • In kitchen not a typo NEC 210.52.C.1. Any space wider than 12" , no point measured horizontally 24" from an outlet or 4' apart. Outlet within 2' of sink each side. It's all there. As I said behind the sink, range etc is not included in the measurement but this has been code for decades. Ok re read it was supposed to be 2' but 4' between did clarify. – Ed Beal Dec 11 '18 at 15:32
  • Whew! I thought 2 inches was overkill... :) – FreeMan Dec 11 '18 at 15:40
  • Since the "bedroom" isn't separated from any other room, does that mean that every single outlet needs AFCI protection? – ikrase Dec 12 '18 at 10:59
  • In the 2017 NEC code 210.12 arc fault circuit interrupter protection. all 15 & 20 amp circuits in dwelling unit kitchens, family rooms dining rooms, living rooms, parlors, libraries, dens, bedrooms, sunrooms, recreation rooms, closets, hallways, laundry areas,or similar rooms or areas shall be protected. By any of the means described in 210.12.A.1 through 6. So if your state is on the 17 code yes you need arc fault protection. – Ed Beal Dec 12 '18 at 14:15
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Real-world open plan spaces are often not wired the same way a house is

If you were to condition your expectations of commercial and industrial wiring practice on what you see in the residential world (just beefier), you would probably expect wiring methods that look like a heftier version of residential wiring: lots of metal-clad cables, lots of conduit-and-wire jobs, but with no fundamental change to the "star bus" topology used in typical buildings, where the busbars are all located within loadcenters/panelboards, and "home runs" from said loadcenters feed circuits in a star fashion. And if you limited yourself to things such as offices and small retail spaces, you would be right.

However, manufacturing plant/shop floors, laboratories, and such are also run on an "open plan" basis, and also need to be reconfigured frequently. As a result, having to re-configure conduit runs in those spaces whenever things need to be rearranged becomes untenable from a cost standpoint, driving these spaces to use alternatives to standard "star bus" topology wiring. Most notably, one thing you will see in such spaces is a product called track busway -- this is a beefier version of the lighting track sometimes seen in residential and light commercial applications, capable of carrying several times the current as well as more than one leg or phase of electrical service.

While not cheap (it's roughly on par with wiring your house in EMT, as would be required in Cook County, IL), it can be flush-mounted into ceilings and walls, and can provide most of the flexibility needed in an open-plan, reconfigurable space when it comes to the location of power outlets. In particular, the busway in this scenario is treated as a feeder, with the receptacles and lighting fixtures protected by individual 20A Dual Function breakers located in the busway plug boxes. As a result, each of these circuits meets or exceeds the requirements for a residential branch circuit, and the busway itself can provide ample power to run the entire house, or at least all the lighting and receptacle circuits within it. It follows that the main panel would be far simpler as well, with a feeder breaker for the busway, a breaker or three for central HVAC circuits (since those are unlikely to move), a breaker for outdoor receptacles, and perhaps a couple of miscellaneous breakers tossed in for other fixed loads.

The primary challenge raised here is switching of lights, but that can be handled using power-line-communicating "smart switch" technology such as X10 or its successor Insteon -- each light fixture assembly would have a control receiver/relay built into it, and the remotes would simply hang off fused busway taps as they draw minimal current and aren't expected to to be a source of overloads.

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