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Quad plex electrical receptacle wiring (C) Daniel FriedmanElectrical Receptacle Wiring in Parallel vs Daisy-Chained
How to wire up a receptacle or "outlet" - two options

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How to wire up an electrical receptacle:

Here we compare wiring an electrical receptacle in series or "daisy chained" (the most-common practice) with wiring receptacles in parallel on an electrical circuit.

Wiring in parallel gives greater reliability to the devices on the electrical circuit, but larger electrical boxes and more wiring connections are required.

In this article series we illustrate basic connections seen in the field for the black, white neutral or grounded conductor), and ground wire when hooking up an electrical receptacle (wall plug or "outlet").

Watch out: mis-wired electrical receptacles are dangerous. Electrical wiring should be performed by a licensed, trained electrician and should comply with the National Electrical Code and local regulations. This article series describes how to choose, locate, and wire an electrical receptacle in a home.

We also provide a MASTER INDEX to this topic, or you can try the page top or bottom SEARCH BOX as a quick way to find information you need.

Wiring in Series or Daisy-Chained vs. Parallel Receptacles

Daisy Chain Wired Receptacles - wiring in series

Back-wire-only electrical receptacle from a 1962 home in Two Harbors MN (C) Daniel Friedman at InspectApedia.comIn our photograph of the back of an older electrical receptacle (synonyms used by normal people include "outlet" or "wall plug"), this back-wired receptacle illustrates wiring electrical receptacles in series or "daisy-chained".

The pair of white wires in the upper portion of this photo are are marked as NEUTRAL IN and NEUTRAL OUT.

White wires are to be connected to the silver terminals or screws or to the terminals marked "WHITE" or "NEUTRAL"

The pair of black wires in the lower photo are marked HOT IN and HOT OUT.

Black wires are connected to the brass or gold colored terminals or screw or to the terminals marked "Black" or "Hot".

Power to all downstream devices flows through the receptacle's internal parts.

Back-wiring is an accepted wiring practice, though on newer receptacles and in my opinion better workmanship jobs you will see the wire connections made at screws or screw clamps more often than in simple push-in backwired connections.

Watch out: we do not recommend back-wiring receptacles that use only a spring-clip type wire connector. Those connections are not in our opinion reliable nor safe.

Details are at BACK-WIRED ELECTRICAL DEVICES

Wire Electrical Receptacles on a Single Circuit In Parallel

Electrical outlet wired in parallel on a circuit to increase circuit reliability (C) InspectApedia.comPhoto: this reader-provided illustration shows how an electrical receptacle might be wired in parallel to the circuit. Using twist-on connectors and pigtail wires the receptacle's neutral and hot terminals are connected to the circuits hot and neutral wires.

In some jurisdictions electricians prefer to not "daisy chain" receptacles in the same box together by using the second pair of screws on each one.

Rather the circuit enters the box and using twist-on connectors, short pig-tail wires are connected to each receptacle at the proper screws. This approach requires a larger electrical box as it will contain more connections, connectors, and so needs more room.

You'll see three wires at teach twist on connector:

Black: (3 wires) hot in, hot out, hot pigtail to the receptacle

White: (3 wires) neutral in, neutral out, neutral pigtail to the receptacle

Ground wires: (4 bare copper wires) ground in, ground out, ground to receptacle, and ground to the metal electrical box

At BACKWIRED RECEPTACLE FAILURE REPORT we illustrate a use of these two wiring practices in which the contributor is replacing a back-wired daisy-chained receptacle with a new receptacle wired in parallel on the circuit.

Check the Size of the Electrical Box When Adding Pigtails

Gang box extender in position but not installed (C) Daniel FriedmanWatch out: when converting from device-wired to a parallel-wired electrical circuit in a string of receptacles, you can not use this pigtailing method unless the electrical box size is of sufficient cubic inches to contain the additional wires and connectors.

In the illustration of parallel wiring of an electrical receptacle shown above we have

all of which have to jam into the electrical box. Using NEC box sizing rules that's a total of 7 #14 wires.

Assuming the circuit we show is a 15A circuit using #14 wire, the U.S. NEC requires 2 cubic inches per conductor. The box must be (2cu.in. x 7 conductor) 14 cubic inches or larger.

Tables in the NEC and given also at ELECTRICAL JUNCTION BOX TYPES tell us that for this wiring we can use a box of these dimensions

The National Electrical Code Article 314 contains complete details and tables of electrical box sizes in dimensions and cubic inches and should be consulted for complete accuracy because the actual size of the box required, in cubic inches, depends on the number of wires that will be within that enclosure.

If you need more space than the present box allows, it may be possible to expand the existing box by adding a "side car" extension described in the article cited just above and illustrated in our photo.

That's a heck of a lot easier than pulling the whole existing box and wall apart to replace it with a deeper or wider box.

Watch for Line and Load Terminal Markings

GFCI wiring details, back view (C) Daniel Friedman

Watch out: some devices such as AFCI and GFCI receptacles will have LINE and LOAD markings on the receptacle side or back.

[Click to enlarge any image]

The photo shows a ground fault circuit-interruptor receptacle that has been back-wired using push-in connectors, and that is wired in the "daisy chain" or "in series" method described above. Devices connected downstream from this one are wired out of the LOAD terminals as I will explain:

In my GFCI photo I have circled in white and black the embossed markings on the receptacle back that indicate "LOAD" and "LINE" terminals.

The incoming or LINE white (neutral) and black (hot) wires are in the bottom of the photo.

The outgoing or downstream or LOAD white (neutral) and black (hot) wires are in the top area of the photo.

Details are at WHICH WIRES GO to LINE or LOAD CONNECTIONS?

Watch out: If you do not make these connections properly power will still be delivered to the GFCI receptacle but it will not provide proper GFCI protection for downstream devices and/or its internal test and reset buttons will not function.

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Continue reading at ELECTRICAL RECEPTACLE CONNECTION DETAILS or select a topic from closely-related articles below, or see our complete INDEX to RELATED ARTICLES below.

Or see ELECTRICAL OUTLET, HOW TO ADD & WIRE - home - for general wiring procedures, connections & advice for connecting electrical receptacles.

Or see this

Article Series Contents

If you are wiring a 2-wire electrical circuit that has no ground wire, also see CONNECTION for 2-WIRE RECEPTACLE CIRCUITS for proper wiring details.

Suggested citation for this web page

ELECTRICAL RECEPTACLE WIRING SERIES vs PARALLEL at InspectApedia.com - online encyclopedia of building & environmental inspection, testing, diagnosis, repair, & problem prevention advice.

INDEX to RELATED ARTICLES: ARTICLE INDEX to ELECTRICAL INSPECTION & TESTING

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