Basic wiring methods
There are dozens of acceptable ways to conduct electricity from the service point through the building, through the electrical loads in it, and back to the service point. This article aims to provide a quick overview for many of the basic wiring methods most likely to become an issue for end-user customers, along with suggestions on implications of different choices about wiring methods.
Wire and Cable
These range from “Romex” (a brand of type NM non-metalic-clad cable) familiar to most, armored cable (types AC and MC, flexible metalic-clad cable), various raceways (metal and plastic conduit pipes with wires pulled through them), wireways, cable trays, and others. Each method has been approved for use in specific building types, and particular environments within those buildings. For example, in occupied spaces (working and living areas), “Romex” (type NM) cable must route behind a ‘fire-rated assembly’, meaning that it is inaccessible to people, and that the barrier between the space and the wire have an official rating to stop fire for a particular duration (from 1/2 hour up to 2 or more hours).
Type UF (underground feeder) cable serves loads via buried trench or strapped to exterior building surfaces where not exposed to physical damage (up high). Similar in appearance to NM-B (aka “Romex”), it is sunlight and weather resistant and listed for direct burial in earth (at sufficient depth), making it a go-to for line-voltage landscape lighting applications.
Enclosures and Terminations
Missing cover on wiring enclosure. Wire in a building must be protected from damage or accidental contact, and junctions enclosed in Listed (underwriter-insured) enclosures with accessible covers. Wiring ‘outlets’ such as accessible junctions, fixture boxes, and switch- and receptacle-boxes must be covered except during service, to prevent escape of flame in case of short-circuits, and to prevent shock resulting from blind or infant(ile) groping.
Types of Branch Circuits
A branch circuit is a circuit run for end-user equipment, as opposed to a feeder or service circuit (a supply circuit for service and/or distribution equipment such as a service disconnect or a distribution/breaker panel). In the U.S., common building wiring systems other than large buildings or industrial facilities include 120V, 208V and 220V nominal circuits. Unless there is call to use more than 120V, a branch circuit should be 120V. High-power dedicated equipment may be 208V or 220V, typically to reduce the current needed (power = current x voltage or Amps x Volts) for the equipment.
Multi-wire branch circuits are an exception to the 120V rule-of-thumb. Composed of two 120V circuits that share a single grounded (‘neutral’) conductor, the three wires forming the circuit are capable of delivering 220V if connected improperly, or if the ‘neutral’ becomes improperly disconnected or damaged. The two ungrounded (‘hot’) conductors in the circuit have 220V between them. Although they do not normally interact except to cancel each others’ grounded conductor (‘neutral’) current, the removal of the ‘neutral’ current pathway will subject all connected loads (things plugged in, including computers and other sensitive electronics) to twice the normal voltage (2 x 120V = 220V nominal). 220V operation is the most immediately apparent trouble resulting from wiring errors, but there are several other common ways to mis-wire this type of circuit, and these are an oft-overlooked problem for hobbyist (i.e.: other trades) electrical ‘installers’. A building pre-purchase inspection may not catch these errors, either.
Types of Switching Circuits
Basic switching conceptualization: the French word for switch, interupteur, is illustrative. A switch in household wiring typically interrupts the wire in which it is inserted, preventing flow of current through the load and that part of the circuit where the switch is installed.
Switch loop (aka: switch-leg): a switching circuit in which only one pole of the circuit runs between the load and the switch. If a complete circuit runs between the load and the power source, a switch may be added to the circuit by tapping a switch loop that diverts only one pole of the circuit. Pre-WWII installations typically divert the grounded (neutral) conductor for switching, whereas modern methods (and the NEC’s requirements) apply switching only in the ungrounded (‘hot’) pole of a 120V circuit, or, for 220V circuits, both poles.
Where possible, it is usually better design to run the power source through the switch so that every outlet installed has a complete circuit in it. NEC 2011 edition requires that all switch outlets have a complete circuit in them to provide for smart switching (such as timers and occupancy sensors and network-controlled lighting systems), so the switch-loop will likely become disused in new construction. Older timers featuring mechanical clocks powered by the circuit where they are installed, were designed and installed when filament-type lamps (incandescents) were the only ones widely in use in homes or even many offices. They rely on a low-current connection to grounded conductors via the filament of the connected lamp(s), too low-power to heat up and light the lamp. Having no filament, high-efficiency lamps such as CFL’s and LED’s may not provide this current path to grounded conductors, and will therefore disable any timer not operating on a complete circuit that includes a grounded conductor at the timer outlet location.
Multi-location coordinated switches (3-wire and 4-wire switches): although hard-wired coordination for multi-location switch installations may be increasingly superseded by solid-state network-controlled lighting systems, old-fashioned electro-mechanical switches continue to dominate. Even the most straightforward installations can prove challenging for beginner installers, while cases of switched neutrals, alternative wiring, Carter System wiring and other oddities can make restoring or maintaining an existing multi-way switching system very difficult.
- What is a Service Disconnect?
- What is Arc Fault Circuit Interrupting (AFCI)?
- What is Grounding & Bonding?
- What is knob-and-tube wiring?
Off-site Links ->
- Annapolis Home Inspection, LLC Aluminum branch circuits, homes 1965-1972
- ComplianceAndSafety.com OSHA Electrical Safety Training
- Electric Monk TV (YouTube) Video channel for PhillyLicensedElectrician.com Robert Monk
- EnergyConservation HowTo A tinkerer genius discusses energy conservation and his ladder system for accessing the attic (where a lot of energy-saving work happens).
- PennFuture Energy Center Energy and energy efficiency news for the Commonwealth of Pennsylvania
- Phila area rife with building efficiency upgrade opportunities Philadelphia Inquirer article discusses recent study showing Philadelphia’s inner-ring suburbs stand to save from energy conservation retrofits.
- Philadelphia Row-house Manual A design, maintenance, and modifications manual for our most widely-used form of housing.
- Robert Monk Robert Monk’s personal blog
- SolarCities (DOE) Solar PV Levelized Cost Interactive Comparator Simple graph compares ‘levelized cost’ of energy from solar PV to conventional grid rates, with a time-slider interactive feature.
- The Circuit Detective – Solve Home Electrical Problems Yourself! Electrical troubleshooting procedures pitched to homeowners.
- The Energy Co-op Blog from a leading alternative energy provider in PECO territory, includes fun conservation tips.
- Weatherization: the anti-Solyndra Salon.com article praising the continued success of the federal Weatherization Assistance Program (WAP), low-income energy-savings and job-creation.
- West Philly Tool Library Official site of WPTL, Philly’s own community tool lending library: like a book library, but tools!
- WestPhillyLocal .com Site name say sit all.
- Bartram's Gardens Founded in Philadelphia’s colonial era, today the gardens continue pioneering in horticulture and agriculture with a variety of herbs, trees and other vegetation in an arboretum/gardens on the Schulkill River banks, and a new farm abutting sadly neglected
- HiddenCity Philadelphia Surprising places it takes an adventurer to discover; events, too.
- Philly Household Hazardous Waste Drop-off Schedule City of Philadelphia dates and places for disposing of spent batteries, CFL lamps, unused paint and cleaning products, etc. LovePhilly: don’t pour these in the drain or send them out with the trash.
- Reading Terminal Market Purveyors of fine foods and foodie stuff, all under one roof downtown under the PA Convention Center
- Secret Garden on the Rails Jacques-Jean Tiziou shows some dramatic natural and urban and naturalized-urban scenes along abandoned rails of Philadelphia
- Sketch Burger, Fishtown A vegan-friendly burger joint with a #1 in Philly contender beef burger, best fries that somehow stay fresh for 1/2 hour while you tackle burger, and a vegan cafe vibe of friendly folks.
- WXPN: Philly sings in key of love Love songs by Philly artists