Reuben's Home Inspection Blog

head_left_image

Is it cheating to use tandem circuit breakers?

Confusion abounds over the use of tandem circuit breakers in panelboards, even among electricians and electrical inspectors.  Today I'll set  the record straight as to when tandem circuit breakers can be used.   This is an adaptation of an article I wrote for the ASHI Reporter, which was published in February of 2011.  

First, a quick definition.  A tandem circuit breaker is a double circuit breaker that takes up the space of a single circuit breaker on a panelboard. You'll also hear them called duplex, slimline, twin, half-height, half-inch, double and wafer breakers, depending on local customs. While a two-pole circuit breaker gets connected to two different poles at a panelboard and has a common trip or a handle tie for simultaneous disconnecting of two poles, a tandem breaker does not.

The photo below shows a 60 amp two-pole circuit breaker at the top, then a 15 amp tandem circuit breaker (highlighted), then a 20 amp tandem circuit breaker (highlighted), then a 20 amp single-pole circuit breaker at the bottom.

Tandem circuit breakers

The next photo shows an older style tandem breaker found in Square D panelboards.

Tandem Square D

Because tandem circuit breakers allow for two circuits to be installed on a panelboard in a one circuit breaker space, they're typically used after a panelboard has been filled to capacity with standard circuit breakers. Because of this, they're often referred to as "cheaters."

Is this really 'cheating'? No, it's not. The use of tandem circuit breakers is a perfectly acceptable practice, as long as the panelboard is designed for tandem circuit breakers and they're installed in locations within the panelboard where they're allowed.

How does a home inspector determine whether tandem circuit breakers are allowed on the panelboard they're inspecting? There are a number of ways to do so.

Class CTL Panelboards

Panelboards must follow UL  Standard 67, which requires all lighting and appliance panelboards to be Class CTL (Circuit Total Limiting). Here's an old formula for determining how many circuits are allowed in the Class CTL panelboard being inspected; this formula is helpful to use when inspecting older electric panels without clear labeling inside the panel. Take the amperage of the panelboard, multiply by the number of poles, and divide by 10. It sounds complicated, but it's not — let's use a 100-amp panelboard as an example:

100 Amp x 2 Poles = 200
200 / 10 = 20

Based on this formula, the maximum number of circuits allowed in a 100-amp 120/240-volt panelboard is 20. For panelboards not manufactured as "lighting & appliance" panelboards, there is no limit to the number of circuit breakers allowed.  This formula is also no longer applicable for today's panels.

The 2008 National Electrical Code (NEC) makes it a little confusing.  Previous editions of the NEC limited the maximum number of circuits in a lighting and appliance panelboard to 42.  The 2008 version of the NEC removed the “lighting & appliance” panelboard designation, however, NEC 408.54 says “A panelboard shall be provided with physical means to prevent the installation of more overcurrent devices than that number for which the panelboard was designed, rated, and listed.”   Manufacturers still list the maximum number of circuit breakers allowed, and must provide a rejection feature to help prevent the use of tandem circuit breakers where not allowed.

Class CTL panelboards have different methods of preventing class CTL tandem circuit breakers from being used in locations where they’re not allowed.  This is referred to as a “rejection feature”.  In the photo below, the highlighted bus stabs are notched to allow the use of tandem circuit breakers; the bus stabs which don’t have this notch won’t allow tandem breakers.

Photo courtesy of Douglas Hansen

Class CTL tandem circuit breakers have a different shape than standard single pole circuit breakers, to help prevent them from being installed where they don’t belong.

Tandem vs standard breaker 2

Tandem vs standard breaker

Tandem circuit breakers are manufactured this way in an effort to prevent people from using them in an improper manner – but this doesn’t stop everyone.  In the photos below, you can see how someone broke the bottoms of the circuit breakers to make them fit where they didn’t belong.  This is probably where the term "cheater" comes from.

broken tandem breaker

Photo courtesy of Douglas Hansen

For panelboards manufactured before adoption of the Class CTL standard,  non-Class CTL tandem circuit breakers are allowed to be installed as replacement circuit breakers only.  Non-Class CTL tandem circuit breakers do not have the ‘rejection’ feature that Class CTL breakers have.  As clearly indicated by the label on the side of the circuit breaker pictured below, these circuit breakers are not allowed in ClassCTLpanelboards.  The difficulty for home inspectors is that the marking is not usually visible after installation, and home inspectors aren't supposed to pull out circuit breakers to try to figure this stuff out.

Non-CTL Tandem Circuit Breaker

Does the panelboard allow tandems?

Now that I’ve talked about the general rules for tandem circuit breakers, I’ll discuss the ways that home inspectors or electrical inspectors can determine when tandem circuit breakers are allowed in various panelboards.

The model of the panelboard

The model or part number of the electric panelboard usually will indicate whether or not the electric panelboard is designed to accept tandem breakers and how many can be used. Here are a few examples:

  • G3040BL1200 = 30 spaces, 40 total circuits allowed.
    Up to 10 tandem circuit breakers can be used.
  • G3030BL1150 = 30 spaces, 30 total circuits allowed.
    Tandem circuit breakers are not allowed.
  • BR1220B100 = 12 spaces, 20 total circuits allowed.
    Up to 8 tandem circuit breakers can be used.
  • BR1212B100 = 12 spaces, 12 total circuits allowed.
    Tandem circuit breakers are not allowed.
  • HOMC20U100C = 20 spaces, 20 total circuits allowed.
    Tandem circuit breakers are not allowed.

I think it's easy enough to see the pattern.

A diagram inside the panelboard

The wiring diagram inside the panelboard is a great way to determine if tandem breakers are allowed and, if so, exactly where they're allowed. In the photo below, you can see that the top four spaces allow only full size breakers, while the bottom eight slots allow tandem breakers.

panelboard diagram

Here’s another panelboard diagram – this panelboard allows the use of tandem breakers in four locations.

panelboard diagram 2

And another – this panelboard doesn’t allow any tandem breakers.

panelboard diagram 3

And another – this panelboard allows tandem breakers in the bottom ten spaces only (11-20 and 31-40).

panelboard diagram 4

Another easy thing to look for is a label stating the maximum number of circuits allowed.  In the photo below, you can see that only 20 circuits are allowed at the panelboard.  This panelboard has 20 full-size spaces, so tandem circuit breakers aren’t allowed.

Max Poles

What's the concern with tandem circuit breakers?

When tandem circuit breakers are used in locations where they're not allowed, they could make an improper physical connection to the bus bar in the panelboard, which can create a fire hazard. Tandem circuit breakers also increase the total load on the bus bars in a panelboard; this is where home inspectors need to use common sense.

When a home inspector finds tandem circuit breakers used in improper locations, they'll often recommend repair by an electrician. If the bus bars of the panelboard have been damaged or altered to allow for the installation of tandem circuit breakers, the proper repair is to have the panelboard replaced. There is no way for a home inspector to determine if the bus bars have been damaged without actually removing the circuit breakers, which is something home inspectors shouldn't be doing.

Information for this article was provided, in part, by Alan Manche of Schneider Electric, Stephen Ploszay of Siemens Industry, Inc. and Joseph Fello of Eaton Corporation. Also, a special thanks to Retired ASHI Member Douglas Hansen.

Reuben Saltzman, Structure Tech Home Inspections

        

Comment balloon 21 commentsReuben Saltzman • February 28 2012 02:58AM

Comments

Great discussion Reubs, and suggested by this guy!  I see tandems a lot and when looking inside often there is nothing to indicate whether they are appropriately placed or not within the box.  Just yesterday breakers were labeled with a Sharpie, and no paperwork inside the box at all.  Common.  I had never heard the word cheater before, but can see how it can be done!

Posted by Jay Markanich, Home Inspector - servicing all Northern Virginia (Jay Markanich Real Estate Inspections, LLC) over 6 years ago

Thanks Jay!  I know this discussion gets a little technical, but I tried to make it as easy to understand as possible.  Not everything needs to be dumbed down :)

Posted by Reuben Saltzman, Delivering the Unbiased Truth. (Structure Tech Home Inspections) over 6 years ago

The depth of the discussion isn't as important as the introduction to the topic for those hearing it for the first time.  That is where the education part comes in.

Posted by Jay Markanich, Home Inspector - servicing all Northern Virginia (Jay Markanich Real Estate Inspections, LLC) over 6 years ago

Great job and great blog. Keep up the good work and good luck to ou this year. Thanks. 

Posted by JOSH EVANS *JoshEvansHomes 516-655-5000 (Village Properties of Mineola, LLC) over 6 years ago

Good point, Jay.

Josh - thanks for stopping by.

Posted by Reuben Saltzman, Delivering the Unbiased Truth. (Structure Tech Home Inspections) over 6 years ago

Most people will miss it (but not the free market boy) but you mentioned how the NEC made things harder to understand!  That's why they issue thousands of "changes" every year to last year's changes or the last NEC update.  Explanation, explanation...

Posted by Jay Markanich, Home Inspector - servicing all Northern Virginia (Jay Markanich Real Estate Inspections, LLC) over 6 years ago

That's a lot of information, Reuben! You did a great job of explaining it--so thanks for taking the time to write this!

Posted by Peggy Chirico, REALTOR® 860-748-8900, Hartford & Tolland County Real Estate (Prudential CT Realty) over 6 years ago

Reuben - Great post.  Thank you for taking the time.  Make it a great day.

Posted by Steve Hall, Make the Call to Hankins and Hall (RE/MAX United) over 6 years ago

Reuben, This is an awesome post. I had thought about doing one very similar. This was very thorough on them and should be a read for all HI's. 

(I hit suggest also ; )

Posted by Donald Hester, NCW Home Inspections, LLC (NCW Home Inspections, LLC) over 6 years ago

Great info but all Greek to me.  That is why I hire a qualified installer when I need work done.

Posted by William Feela, Realtor, Whispering Pines Realty 651-674-5999 No. (WHISPERING PINES REALTY) over 6 years ago

Tandems are great for getting multi-wire circuits all mixed up :)

Posted by Charles Buell, Seattle Home Inspector (Charles Buell Inspections Inc.) over 6 years ago

Jay - you sound like a conspiracy theorist ;)

Peggy - If I didn't put you to sleep by the end, thanks for reading!

Steve - you too, thanks.

Donald - thanks buddy.  This one took a couple months and a lot of phone calls and emails to write, but it's nice to have the information in one place. 

William - and even then, half of the qualified installers won't know this stuff.  I've seen state electrical inspectors sign off on tandem breakers used on panels that aren't designed for them.

Charles - it's easy to understand why.

Posted by Reuben Saltzman, Delivering the Unbiased Truth. (Structure Tech Home Inspections) over 6 years ago

Not really.  I think it's funny how organizations get more and more bureaucratic and less efficient.  And the NEC spends as much times explaining itself as it does any thing else!  They made over 1000 changes last year, many being "clarifications!"

Posted by Jay Markanich, Home Inspector - servicing all Northern Virginia (Jay Markanich Real Estate Inspections, LLC) over 6 years ago

Gotta sell more books.

Posted by Reuben Saltzman, Delivering the Unbiased Truth. (Structure Tech Home Inspections) over 6 years ago

Good explanation of "cheaters". Sometimes it can be hard to sort out if they belong and where they belong. 

Posted by James Quarello, Connecticut Home Inspector (JRV Home Inspection Services, LLC) over 6 years ago

Thanks.  I used to have a hard time with it, but after doing the research for this article, it all kinda falls in to place now.

Posted by Reuben Saltzman, Delivering the Unbiased Truth. (Structure Tech Home Inspections) over 6 years ago

Good article, solid points and easy for even a entry level home inspector to understand ( not one). I am willing to wager you could get this published in a trade magazine....................Wishing you a very busy spring season.. Best DL

Posted by Don Lovering over 6 years ago

Hi Don, 

That's a great idea.  I'm going to follow up on that.  Thanks.

Posted by Reuben Saltzman, Delivering the Unbiased Truth. (Structure Tech Home Inspections) over 6 years ago

Excellent review!  Thanks for the lesson.  Been to many a class on electrical but don't recall this coming up.

Posted by Howard Maxfield over 6 years ago

I'm a beginng home inspector.  Thank you for the information, it was very helpful in all aspects.  Great job! 

Posted by William B over 6 years ago

Howard - I've never seen this stuff covered in any electrical seminars either.

William - thanks, glad to help.

Posted by Reuben Saltzman, Delivering the Unbiased Truth. (Structure Tech Home Inspections) over 6 years ago

Participate