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5214 W. Village Parkway, Suite 120
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Figure 1.1

Figure 1.1

Figure 1.2

Figure 1.2

Incorrect wiring configuration

Incorrect wiring configuration




ArticLe: Receptacle Outlet Requirements for Dwelling Units

 By Reeba George

The requirements for laying out receptacle outlets for residential units are extensive.  The intent of this article is to give an insight to Article 210.52 in the National Electrical Code (NEC) which includes specific requirements for dwelling units in terms of spacing, type, and locations of receptacle outlets.  

Receptacle outlets specified in this section are the convenience outlets for circuits rated 125-volt, 15 and 20 amperes.  This implies that any other receptacle outlet rated for higher voltage/ amperage (for example, a 30-ampere, 240-volt receptacle outlet dedicated for a kitchen appliance) will not be counted as a required outlet for spacing requirement.  The spacing criteria is based on a general reasoning that one would never have to extend an electrical cord for appliance/ personal device more than its available cord length in either direction. 

General Wall Space (Living Rooms, Bedrooms, Family Rooms etc.)

Receptacles must be installed such that no point measured horizontally along the floor line of any general wall space is more than 6 feet (ft.) from a receptacle outlet.  In other words, the spacing between the receptacles could be a maximum of 12 ft.  Doorways, door-side windows that extend to the floor, and similar openings are not considered wall space. A wall less than 24 inches (in.) does not require a receptacle outlet.  (Figure 1.1)

Countertops and Work Surfaces (Kitchen)

A receptacle outlet must be installed at each wall countertop and work surface that is 12 in. or wider.  They must be installed so that no point along the wall line is more than 24 in. measured horizontally from a receptacle outlet.  In other words, the spacing between the outlets could be a maximum of 4 ft.  However, a receptacle is not required on a wall directly behind a range, counter-mounted cooking unit, or sink.  It must be located on or above, but not more than 20 in. above, the countertop or work surface. At least one receptacle must be installed at each island or peninsular countertop space with a long dimension of 24 in. or greater and a short dimension of 12 in. or greater.  Countertop spaces separated by ranges, refrigerators, or sinks are considered as separate countertop spaces and all the above conditions apply.  (Figure 1.2)

Other Areas

At least one receptacle outlet must be installed in bathrooms within 3 ft. of the outside edge of each basin.  The receptacle outlet must be located on a wall or partition adjacent to the sink, located on the countertop, or installed on the side or face of the basin cabinet.  In no case can the receptacle be located more than 12 in. below the top of the basin or basin countertop.  

Hallways of 10 ft. or more in length must have at least one receptacle outlet. The hallway length is measured along the centerline of the hallway without passing through a doorway.  

Foyers that are not part of a hallway and having an area greater than 60 sq. ft. must have a receptacle located in each wall space 3 ft. or more in width.  

The code dictates many more dwelling unit requirements for different areas like laundry rooms, exterior receptacles, garages etc.  It also explains the type of receptacles required in each space.  It is typical that most of the design criteria is based on the minimum NEC requirements.  But with the growing emergence of electronic gadgets/appliances, it is a good design practice to provide recommendations for increased convenience and functionality for the occupants by providing more-than-minimum receptacle outlets at convenient locations.

Reeba George is an Electrical Designer at HP Engineering’s Tulsa, Oklahoma office.

Real-world Tip — Correct Wiring for Lighting Control

By Dustin Anderson

This photo is a real-world example of incorrect low-voltage wiring for lighting control. The yellow 0-10V control wires are routed from the light switch through the conduit and then routed outside the junction box to splice the cables. This is a National Electrical Code (NEC) violation.  

According to the NEC, there are two acceptable methods for a correct installation.  

First Method: The control cabling can be routed inside the conduit with the 120V conductors. Once the cable reaches the junction box, the cabling is allowed to be spliced inside the box—as long as there is a barrier in place. From there, the cables may then be routed to the light fixtures.  

Second Method: The control conductors can be routed from the light switch on the outside of the conduit up to the light fixtures. Note that the control cables must be strapped to the conduit through which the 120V conductors are routed.  

Either method is acceptable, however, National Electrical Code does not allow for the two methods to be mixed, as shown above.  

To correct this particular violation, the low voltage wiring should be routed outside the conduit, down inside the wall to the switch box with a bushing for entry and then connected to the light switch. 

For additional reading, refer to NEC Sections 300.11B, 725.136(B), and 725.136(D)b for further information.

Dustin Anderson, PE, is a Sr. Vice President at HP Engineering, Inc. in Oklahoma City. In addition to leading the OKC office operations, his design focus is Electrical Engineering.

Building Envelope graphic.jpg

Article: With energy Conservation in mind…

By Bill Hodge

The building envelope has the largest impact on energy use—more impact than HVAC efficiency, more than site orientation, and even more than the building’s geometry.  Here, I’ll focus on the windows, walls, and roof.   

ASHRAE 90.1 is the most widely used design resource for architects who want to comply with the Energy Codes in your respective regions.  The 90.1 manual is exhaustive, but once you get a feel for it how it works, it becomes pretty straightforward. 

I highly recommend you use ComCheck, a web-based program with extensive information on local and state building energy codes.   ComCheck is a free program (yes, absolutely free) that allows you to vary  the building envelope components to compare your proposed building envelope against the code reference you choose. Find ComCheck at

As an example, you may choose to compare your building against the 2007 version of 90.1, or the 2009 version, or the 2013 version, or the latest 2016 version.  You may also choose different versions of the International Energy Conservation Code (IECC.)  ComCheck even has some other state codes such as Florida, Oregon, Vermont, etc.  An appealing feature of this program is the instant feedback you get as you input your building envelope components. 

Once you’ve entered which code you want to compare your building against, start modeling your building using the Envelope tab,  then add walls, roofs, windows, doors, etc.  No need  to worry about the other tabs,  such as Interior Lighting, Exterior Lighting, and Mechanical requirements, because your favorite MEPF consultant (for example, HP Engineering) will complete those sections for you when you send your file.  As you add walls, doors, windows, and roofing, you’ll get feedback on how you’re doing against the code you’ve chosen;  it will tell indicate not only if you “pass” or “fail” but also by what percentage you passed or failed. 

The beauty is that you can mix and match the U-values of the different components to get an “overall” score for the building envelope.  For example, you can use better roof insulation if you want to use a more economical  glass.  You can upgrade the wall insulation and use more cost-effective roof insulation.  You can use premium glass windows in conjunction with basic doors.  If at first you don’t succeed, keep playing with different wall insulation values, roof insulation, and window factors until you pass or exceed the code minimums for the overall building envelope.  You could find that you can beef up the roof insulation or use wood stud walls so that you may not need continuous rigid insulation on the walls in addition to the typical wall cavity insulation.  What?!?  You’re welcome! 

For more complicated buildings, where you want to trade off the HVAC efficiency or lighting for building envelope components, you’ll have to perform a full-blown computer energy simulation.  (By the way, I can recommend a good engineering firm to do that for you.) 

If you would like to schedule an AIA approved lunch-and-learn on how to use 90.1 properly, please contact me.  HP Engineering has a presentation that is accredited for one Health, Safety and Welfare (HSW) credit.  Or feel free to call your local HP Engineering office or the central office at 479-899-6370.