Home Electricity – Electrical Circuit Design

INTRODUCTION

• This article is about one major matter of crucial interest – electrical circuit design.
• Home electricity is a frequent hit on Before The Architect’s website. 
  • Electrical circuit design in a home seems to some the willy-nilly running of high-voltage cables between outlets in walls and ceilings. 
    • Nothing to it.  Right? 
    • A custom builder recently mentioned to this home designer, “House interior lighting?  We move from room to room and slap up some recessed cans."
  • Wrong, in the opinion of this designer at Before The Architect.  Willy-nilly may be the home circuit design majority rule, but willy-nilly is not about safety in many senses, not about convenience, and not about durability.
• Let’s take a look at this designer’s approach to electrical circuit design in a home.

CIRCUITS

• Each circuit from its panelboard
  • Shall include 
    • 1 energized conductor, or hot leg
    • 1 grounding conductor (equipment bonding conductor, etc.) and
    • 1 grounded conductor (neutral, common)
    • Of which the grounded conductor
      • Shall run throughout that circuit exclusively, that is, with respect to any other circuit
      • Shall not be crossed-over to
      • Shall not be interconnected with
      • Shall not be otherwise shared by
      • Shall not be split with
      • Including no interconnection whatsoever between a grounded conductor and a grounding conductor in a panelboard, subpanel, junction box, device, etc.
      • Including no interconnection whatsoever between grounded conductors
      • Without regard to or distinction between types of cable 

Comment:  Sorry for all those shall nots; however, this home designer needs to close loop holes.  Interconnecting grounded conductors is especially a condition seen in commercial and industrial wiring, along with several hot legs each relying on the same grounded conductor.  Tragic consequences can come calling from these so-called “dirty neutrals": AFCIs and GFCIs won’t work as designed with interconnected grounded conductors; loading up a grounded conductor with several energized conductors can overheat the grounded conductor.  

• Each circuit load
  • Shall be judged as to whether it is continuous, i.e., could reasonably operate without interruption for 3 hours or more and
  • If judged continuous, then it shall be derated by 20% (, or the peak load multiplied by 1.25) subsequent to all other deratings  

Comment:  Usually, any given residential load is not regarded as continuous.  Continuous loads come into active play in commercial and industrial applications.  However, this designer knows full well that some loads in a residence can operate frequently well beyond 3 hours continuously, e.g., some exterior lighting and some interior lighting, entertainment centers, computer equipment, attic fans, etc.  It’s these loads and those like ‘em that ought to be singled out for special attention when rating a circuit in a residence.  This home designer knows, for sure, that he’s in the minority on this one.  He’s unphased (a little electrical pun, there). 

• One circuit at a time shall be distinguished
  • As dedicated to lighting loads, which loads shall be connected only to that circuit
  • As dedicated to non-lighting loads, which loads shall be connected only to that circuit and
  • A lighting circuit and a non-lighting circuit shall not be interconnected, including as to grounded neutrals 

• Computer equipment and entertainment centers shall be supplied by dedicated circuitry at not greater than
  • 2 separately boxed hard drives and a printer or
  • 2 printers and boxed hard drive(s) per circuit and
  • A sized Universal Power Supply (a/k/a UPS) with surge protection shall be urged 

Comment:  The home designer and electrical contractor should convey herewith their dedication to applying UPS units of quality between our pricey tools, our precious work and the irregular supply of electricity from our local electric utility.  

     A while back, Before The Architect figured it out it lost 3 motherboards and 2 hard-drives to power dips and spikes, many so fast individually that there was no dimming of lighting or loss of digital readout time.  Now, you can sense these extremely brief power blips listening to UPSes click on and off, sometimes in bursts. 

Comment:  Sooner or later this prescript will lurch into distinctions as between linear and nonlinear loads – distinctions which in commercial and industrial applications can be life- and property-protective.  For matters of load linearity, this home designer thinks that in virtually all applications in a residence, so long as a grounded neutral is pulled from the panelboard (whereat it is securely fastened to its bar) separately for each and every circuit run, all should get along safely. 

• In a kitchen or bar, each of the following appliances shall be connected to a dedicated circuit at 120 volts, 20 amps (or manufacturer’s specification) with a 20 amp (or manufacturer’s specification) singleplex receptacle or hard-wired to a junction box
  • Microwave
  • Dishwasher
  • Refrigerator/freezer, or, if not a combined unit, then separately to a refrigerator and a freezer
  • Wine cooler
  • Trash compactor
  • Chill drawer
  • Heating drawer
  • Etc. 

• A circuit with 15 amp overcurrent protection shall have applied to it only 15 amp rated devices 

• A circuit with 20 amp overcurrent protection shall have applied to it only 20 amp rated devices 

Comment:  The National Electric Code slices and dices this circuit vs. receptacle match-up sure enough to bunch the shorts of the most serious student.  The AG’s in no mood to quibble. 

• Certain motor-driven or heater-driven loads shall be on a circuit dedicated to that single load and either hard-wired or singleplexed, e.g.
  • Dishwasher
  • Clothes washer
  • Built-in space heater
  • Clothes dryer
  • Each kitchen appliance that’s built-in
  • Any other appliance or heater that’s built-in or required by residents
  • A bathroom lavatory individually and
  • Similar 

Comment:  This means, among others, no splits or branches to or from a microwave circuit. 

• A two-pole circuit
  • Shall be dedicated
  • Shall be applied only to a unique, two-pole load
  • Shall not be interconnected with any other circuit 

Comment:  This prescript must be followed absolutely.  Of note in a two-pole circuit to supply a motor, the grounded conductor regularly carries bits of electrical energy back to its seat on the panelboard.  Interconnecting the grounded conductor in a two-pole cable or harness with other grounded conductors can be a lethal mistake. 

• The grounding neutral (often bare or with green insulation) shall be connected in parallel and not in series to each device, i.e., one grounding conductor to each device wherein each grounding conductor is securely tied to the line’s grounding conductor
  • In an outlet of ganged switches and
  • In an outlet of ganged receptacles, that is,
  • A device shall be pigtailed to its line 

• Not less than 2-2 linear inch diameter solid, smooth, straight conduits
  • Shall extend from lowest level of a residence, including but not limited to a crawlspace or basement or on L1 on a slab-on-grade up to and into the attic of the residence
  • Shall be located
  • As closely as possible to the panelboard
  • Physically accessible to conduit interior from the panelboard on finish
  • Shall be clearly identified at each terminus with bright coloring or other visually distinctive means
  • Shall serve as post-finish raceways for cable between levels 
  • High-voltage in not less than one
  • Low-voltage in not less than one.
  • Shall be temporarily sealed to air flow at each opening to abate flame spread between levels 

• In any circuit with more than one device or appliance or similar, cable connections shall be by pigtail in parallel, i.e., sequential circuitry shall be prohibited

• In a bathroom, each lavatory shall have its own dedicated 120V/20A circuit for a GFCI-protected duplex receptacle 

• There shall be no less than 2 utility receptacle circuits in a kitchen and bar (whether or not the bar is adult) 

• Hallway receptacle circuits shall be dedicated 

• A smoke alarm circuit
  • Shall land separately to circuit breaker of an actively used lighting circuit, which breaker shall be designated for a double tap or
  • Shall be the first branch on that actively used lighting circuit, before any switch device connection 

• Two circuits shall not serve the same receptacle device. i.e., a receptacle shall not be split-wired

• Circuits serving kitchen loads shall serve only kitchen loads 

ELECTRICAL CIRCUITRY DIAGRAM

• Let’s look at a small chunk of a recent Electrical and Lighting Plan by Before The Architect
• It’s in plan view of a Masters Bath suite with circuitry drawn right on the plan set’s floor plan 

Electrical Circuitry, Plan View

Key: CLO = closet; D = dimmer; G = ground fault interrupter; H = height; HR = home run; L = lighted switch; lm = lumens; MIR = mirror; PS = pressure switch; S = single pole switch; S3 = three-way switch; S4 = four-way switch 

• See how several points of electrical circuitry design guidance play out (along with points elsewhere herein under on receptacle design and switch design)
  • You can reckon illumination levels in each space as between ambient and task site, remembering that all this is much further identified in a Lighting Schedule and Lighting Notes, again, elsewhere on this website
  • There’s one area of further limit to lighting pros works and that’s the height and spread of sconces in both HIS and HERS
  • Note the squared circuit lines as opposed to the looping, curvy style.  Imagine the mess all those curves would have made in this tight, complexly circuited space.  Straight lines mean a lot herewith to convey meaning.
  • See how Before The Architect handles almost all aspects of luminaires after establishing circuitry siting, e.g.,  “TO SHOWER LIGHTING AND FAN" and “TO HALL LIGHTING."  Lighting pros are only proscribed by Before The Architect generally in two aspects of lighting: illumination level and type.  The rest – luminaire choices, numbers, and sites are up to them; that their day job.
  • Mention should be made of the dedicated receptacles to each of the lavatories which are symbolized by the HR designation, along with outlet height over finish floor level.  HERS, you’ll recognize, gets 2 dedicated receptacles along her counter.  Missing in this version of the floor plan is design of a seating area open below-counter in HERS.
  • Look at all the dimmers
  • Look at all the lighted switches
  • The pressure switches are applied in each smaller closet.  So convenient – as long as you close the closet doors
  • Please note the many switches throughout these spaces, in order to ensure convenient control of lighting and appliances

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