• Sign In
  • Create Account
  • Sign Out
  • My Account
  • NEWS
  • PRODUCTS
  • CONTRACTORS
  • ENGINEERS
  • RADIANT & HYDRONICS
  • INSIGHTS
  • MEDIA
  • RESOURCES
  • EMAGAZINE
  • SIGN UP!
cart
facebook instagram twitter linkedin youtube
  • CONTRACTORS
  • BATH & KITCHEN PRO
  • BUSINESS MANAGEMENT
  • HIGH EFFICIENCY HOMES
  • TECHNOLOGY
  • WATER TREATMENT
  • PMC COLUMNS
  • PMC COLUMNS
  • Dave Yates: Contractor’s Corner
  • John Siegenthaler: Hydronics Workshop
  • Kenny Chapman: The Blue Collar Coach
  • Matt Michel: Service Plumbing Pros
  • Scott Secor: Heating Perceptions
  • ENGINEERS
  • CONTINUING EDUCATION
  • DECARBONIZATION | ELECTRIFICATION
  • FIRE PROTECTION
  • GEOTHERMAL | SOLAR THERMAL
  • PIPING | PLUMBING | PVF
  • PME COLUMNS
  • PME COLUMNS
  • Christoph Lohr: Strategic Plumbing Insights
  • David Dexter: Plumbing Talking Points
  • James Dipping: Engineer Viewpoints
  • John Seigenthaler: Renewable Heating Design
  • Lowell Manalo: Plumbing Essentials
  • Misty Guard: Guard on Compliance
  • RADIANT & HYDRONICS
  • RADIANT COMFORT REPORT
  • THE GLITCH & THE FIX
  • INSIGHTS
  • CODES
  • GREEN PLUMBING & MECHANICAL
  • PROJECT PROFILES
  • COLUMNS
  • SPONSOR INSIGHTS
  • COLUMNS
  • Codes Corner
  • Natalie Forster: Editorial Opinion
  • Guest Editorial
  • MEDIA
  • PODCASTS
  • VIDEOS
  • WEBINARS
  • RESOURCES
  • INDUSTRY CALENDAR
  • DIRECTORIES
  • EBOOKS
  • PM BOOKSTORE
  • CE CENTER
  • MARKET RESEARCH
  • CLASSIFIEDS
  • EMAGAZINE
  • EMAGAZINE
  • ARCHIVE ISSUES
  • CONTACT
  • ADVERTISE
  • PME EMAGAZINE ARCHIVES
search
cart
facebook instagram twitter linkedin youtube
  • Sign In
  • Create Account
  • Sign Out
  • My Account
  • NEWS
  • PRODUCTS
  • CONTRACTORS
    • BATH & KITCHEN PRO
    • BUSINESS MANAGEMENT
    • HIGH EFFICIENCY HOMES
    • TECHNOLOGY
    • WATER TREATMENT
    • PMC COLUMNS
      • Dave Yates: Contractor’s Corner
      • John Siegenthaler: Hydronics Workshop
      • Kenny Chapman: The Blue Collar Coach
      • Matt Michel: Service Plumbing Pros
      • Scott Secor: Heating Perceptions
  • ENGINEERS
    • CONTINUING EDUCATION
    • DECARBONIZATION | ELECTRIFICATION
    • FIRE PROTECTION
    • GEOTHERMAL | SOLAR THERMAL
    • PIPING | PLUMBING | PVF
    • PME COLUMNS
      • Christoph Lohr: Strategic Plumbing Insights
      • David Dexter: Plumbing Talking Points
      • James Dipping: Engineer Viewpoints
      • John Seigenthaler: Renewable Heating Design
      • Lowell Manalo: Plumbing Essentials
      • Misty Guard: Guard on Compliance
  • RADIANT & HYDRONICS
    • RADIANT COMFORT REPORT
    • THE GLITCH & THE FIX
  • INSIGHTS
    • CODES
    • GREEN PLUMBING & MECHANICAL
    • PROJECT PROFILES
    • COLUMNS
      • Codes Corner
      • Natalie Forster: Editorial Opinion
      • Guest Editorial
    • SPONSOR INSIGHTS
  • MEDIA
    • PODCASTS
    • VIDEOS
    • WEBINARS
  • RESOURCES
    • INDUSTRY CALENDAR
    • DIRECTORIES
    • EBOOKS
    • PM BOOKSTORE
    • CE CENTER
    • MARKET RESEARCH
    • CLASSIFIEDS
  • EMAGAZINE
    • EMAGAZINE
    • ARCHIVE ISSUES
    • CONTACT
    • ADVERTISE
    • PME EMAGAZINE ARCHIVES
  • SIGN UP!
Columns

Wiring Diagrams For Series And Parallel Circuits
Carol Fey

By Carol Fey
August 1, 2004
More visual stimulation to help wire circuits.

Figure 1
In last month's column you learned about wiring diagrams for a simple circuit. A simple circuit is the building block for more complex circuits.

Series Circuit - Switches: As you know, a series is a group of similar things strung together. For example, the World Series is a string of baseball games. In a circuit, we can put switches in series or we can put loads in series. For a series circuit to work, the electricity has to get through everything in the circuit and back to where it started.

In control work, a series circuit can be either a great thing or a bad thing. It depends on whether we're putting switches in series or loads in series. Switches in series is great. In the controls biz we try to avoid loads in series - they just don't work right.

Let's look at switches in series (see Figure 1).

All of the switches must be closed before the electricity can get to the load.

Often in controls, we have switches in series. That's because switches frequently function as a safety committee. Each switch stays closed unless its safety condition is violated. Examples of safety switches are a pressure switch, a flame roll-out switch, a low water cut-off or a high limit.

Power can't get to the load unless all safety conditions are met. The thermostat can be in series with the safety switches. Just like many other committees, no action can be taken until all parties agree. That means that even though there may be a call for heat (thermostat switch closed) the burner can fire only if all the safety switches are closed.

This brings up the importance of using a wiring diagram. The wiring diagram that comes with a boiler shows all the safety switches. If you're troubleshooting and there's an open safety switch that you don't know about in the series, no amount of replacing the other safety switches or thermostat will fix the problem. The wiring diagram will show you exactly how many switches exist.

Figure 2

Series Circuit - Loads

We can put loads in series, but we don't usually do that in control work. That's because loads in series don't behave right. The reason is that they have to share electricity. For example, two 60W light bulbs in series are only as bright as 30W bulbs. Figure 2 is a drawing of loads in series.

The typical electricity book and electricity class spends a lot of time on loads in series. That's where you do all that math. If you ever suspected the math and loads-in-series part of the class had nothing to do with your heating or air-conditioning work, you were absolutely right.

The classes include loads in series because it's key to electronic circuits. Many schools think the purpose of an electricity class is preparation for electronics. In electronics, much math can be done to figure out the right combination of resistors, transistors and diodes to make a circuit to get the desired magical outcome. In heating and air-conditioning control work, we use electronic devices, but we don't design itty-bitty electronic circuits. That means the only thing we need to know about loads in series is "don't do it."

Figure 3

Parallel Circuits

Instead, we wire loads in parallel. Notice that the components stay the same as in a series circuit. Only the wiring changes. (See Figure 3.)

Notice that a parallel circuit is merely two simple circuits that happen to share a power supply. Just ignore the shaded portion of the circuit to see that each of the two loads can get electricity from the power supply without the electricity going through another load. If these were 60W light bulbs, both would be fully bright.

Figure 4
This is the kind of wiring that's used in house wiring. For example, the row of lights you find above a bathroom vanity is wired in parallel. All the bulbs are fully bright. Also, when one bulb burns out, the others keep working.(See Figure 4.)

Notice there's just one switch shown in this circuit. Also like the bathroom vanity lights, in this case one switch turns on all the lights.

It's easy to add switches so that each light can be switched alone. But the switch must be placed in the circuit so that it controls only that light.

In a "real life" drawing, a parallel circuit with a switch for each load looks like this.

Figure 5
Zone valves are an example of loads wired in parallel, with a separate thermostat (switch) for each load (zone valve). Just image each of the loads in the drawing above as a zone valve. Each switch will be a thermostat. The power supply will be a transformer.(See Figure 5.)

It may simplify your zone valve wiring to think of each zone valve and thermostat combination in this way. You may refer back to my column in the December 2003 issue of PM to figure how many zone valves you can put on a transformer.

Share This Story

Looking for a reprint of this article?
From high-res PDFs to custom plaques, order your copy today!

Carol Fey is a degreed technical trainer, specializing in controls and electricity. She has published four books: Quick & Basic Electricity, Quick & Basic Hydronic Controls, Quick & Basic Troubleshooting, and Quick & Basic House Wiring. You can order books or get on the e-mail list for free technical information at www.carolfey.com. Or e-mail carol@carolfey.com.

Recommended Content

JOIN TODAY
to unlock your recommendations.

Already have an account? Sign In

  • Worker using the Milwaukee Tool SWITCH PACK drain cleaner

    Pipeline profits: Drain cleaning, pipe inspection create opportunities

    Drain cleaning and inspection services offer lucrative...
    Plumbing News
    By: Nicole Krawcke
  • Uponor employee, Arturo Moreno

    The reinvestment in American manufacturing and training

    Plumbing & Mechanical Chief Editor Nicole Krawcke and...
    Plumbing News
    By: Nicole Krawcke and Natalie Forster
  • March 2024 Women in Plumbing hero image of woman engineer overlayed by circle of hexagon shapes with numbers from 1 to 10

    Celebrating 10 Influential Women in the Plumbing Industry

    Celebrating Women's History Month and Women in...
    Plumbing News
    By: Nicole Krawcke
Subscribe For Free!
  • eNewsletters
  • Online Registration
  • Subscription Customer Service
  • eMagazine
  • Manage My Preferences

IPEX celebrates grand opening of new Florida distribution center

IPEX celebrates grand opening of new Florida distribution center

Bell & Gossett Illustrates Path to Net-zero at AHR Expo

Bell & Gossett Illustrates Path to Net-zero at AHR Expo

NIBCO Press Solutions

NIBCO Press Solutions

AI can boost efficiency and profitability for plumbing, HVAC contractors

AI can boost efficiency and profitability for plumbing, HVAC contractors

More Videos

Sponsored Content

Sponsored Content is a special paid section where industry companies provide high quality, objective, non-commercial content around topics of interest to the Plumbing & Mechanical audience. All Sponsored Content is supplied by the advertising company and any opinions expressed in this article are those of the author and not necessarily reflect the views of Plumbing & Mechanical or its parent company, BNP Media. Interested in participating in our Sponsored Content section? Contact your local rep!

close
  • J.J. Keller CMV vehicles on road
    Sponsored byJ. J. Keller & Associates, Inc.

    The dash cam game-changer for small business safety

Popular Stories

Underfloor heating installation with drain sewer hole in bathroom close up on water floor heating.

Using hydronics to leverage time-of-use electrical rates

Watts Nexa mobile image

Behind the Wall: Where smart plumbing gets smarter

Six tankless water heaters that feed the nutraceutical manufacturer’s operations.

How to deliver large volumes of hot water quickly and intermittently

PMCE Home-X April 29 Free Webinar: From Legacy to Leadership: Preparing Your Home Services Business for the Next Generation

Events

November 13, 2024

Future Proofing MEP: Navigating the 2026 High Efficiency Water Heating Standards

Join our deep dive into DOE’s new standards so you can future-proof your MEP practice.

EARN: 0.1 ASPE CEU; 1 AIA LU/HSW; 0.1 IACET CEU*; 1 PDH

View All Submit An Event

Poll

Will business be up or down in 2025?

Do you anticipate business in 2025 to be up or down in comparison to 2024?
View Results Poll Archive

Products

The Water Came To A Stop

The Water Came To A Stop

See More Products

Download the FREE Water Conservation, Quality & Safety eBook: Plumbing Trends Increasing Safe Water Availability

×

Keep your content unclogged with our newsletters!

Stay in the know on the latest plumbing & piping industry trends.

JOIN TODAY!
  • RESOURCES
    • Advertise
    • Contact Us
    • Directories
    • Store
    • Want More
    • Supply House Times
  • SIGN UP TODAY
    • Create Account
    • eMagazine
    • eNewsletter
    • Customer Service
    • Manage Preferences
  • SERVICES
    • Marketing Services
    • Reprints
    • Market Research
    • List Rental
    • Survey/Respondent Access
  • STAY CONNECTED
    • LinkedIn
    • Facebook
    • Instagram
    • YouTube
    • X (Twitter)
  • PRIVACY
    • PRIVACY POLICY
    • TERMS & CONDITIONS
    • DO NOT SELL MY PERSONAL INFORMATION
    • PRIVACY REQUEST
    • ACCESSIBILITY

Copyright ©2025. All Rights Reserved BNP Media.

Design, CMS, Hosting & Web Development :: ePublishing

search
cart
facebook instagram twitter linkedin youtube
  • Sign In
  • Create Account
  • Sign Out
  • My Account
  • NEWS
  • PRODUCTS
  • CONTRACTORS
    • BATH & KITCHEN PRO
    • BUSINESS MANAGEMENT
    • HIGH EFFICIENCY HOMES
    • TECHNOLOGY
    • WATER TREATMENT
    • PMC COLUMNS
      • Dave Yates: Contractor’s Corner
      • John Siegenthaler: Hydronics Workshop
      • Kenny Chapman: The Blue Collar Coach
      • Matt Michel: Service Plumbing Pros
      • Scott Secor: Heating Perceptions
  • ENGINEERS
    • CONTINUING EDUCATION
    • DECARBONIZATION | ELECTRIFICATION
    • FIRE PROTECTION
    • GEOTHERMAL | SOLAR THERMAL
    • PIPING | PLUMBING | PVF
    • PME COLUMNS
      • Christoph Lohr: Strategic Plumbing Insights
      • David Dexter: Plumbing Talking Points
      • James Dipping: Engineer Viewpoints
      • John Seigenthaler: Renewable Heating Design
      • Lowell Manalo: Plumbing Essentials
      • Misty Guard: Guard on Compliance
  • RADIANT & HYDRONICS
    • RADIANT COMFORT REPORT
    • THE GLITCH & THE FIX
  • INSIGHTS
    • CODES
    • GREEN PLUMBING & MECHANICAL
    • PROJECT PROFILES
    • COLUMNS
      • Codes Corner
      • Natalie Forster: Editorial Opinion
      • Guest Editorial
    • SPONSOR INSIGHTS
  • MEDIA
    • PODCASTS
    • VIDEOS
    • WEBINARS
  • RESOURCES
    • INDUSTRY CALENDAR
    • DIRECTORIES
    • EBOOKS
    • PM BOOKSTORE
    • CE CENTER
    • MARKET RESEARCH
    • CLASSIFIEDS
  • EMAGAZINE
    • EMAGAZINE
    • ARCHIVE ISSUES
    • CONTACT
    • ADVERTISE
    • PME EMAGAZINE ARCHIVES
  • SIGN UP!