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Incorrect wiring configuration

Incorrect wiring configuration




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.