NEC in the Facility, July 10, 2012

July 10, 2012
Apply the 125% rule to any branch circuit that has one or more continuous loads

In our previous issue, we noted the NEC requires you to apply the 125% rule to any branch circuit that has one or more continuous loads. It's acontinuous load when "the maximum current is expected to continue for three hours or more" [Art. 100]. That rule applies for both conductor sizing [210.19(A)1] and overcurrent protective device (OCPD) sizing [210.20(A)]. We also mentioned that the ampacity tables address only the minimum ampacities required for safeguarding personnel and property [90.1]. This leads to an important consideration for facilities.

Unlike residential structures, commercial and industrial facilities tend to undergo reconfiguration. Over time, loads may change dramatically. Machine moves are common in many manufacturing facilities because of changing production demands. Office buildings rearrange cubicle farms or in some other way reconfigure branch circuit loads.

Consider an office where a large meeting room is repurposed because the business needs to run DVD copier/printers to take advantage of a lucrative new opportunity. If all of the conductors and OCPDs already meet or exceed the 125% rule requirements, the physical plant won't impede the business needs of the organization. But what if you had "saved money" by designating some circuits, and those in particular, as noncontinuous load circuits? You must either derate or rewire.

Planning ahead for operational flexibility prevents confusing user restrictions and expensive rework.

Voice your opinion!

To join the conversation, and become an exclusive member of EC&M, create an account today!

Sponsored Recommendations

Electrical Conduit Comparison Chart

CHAMPION FIBERGLASS electrical conduit is a lightweight, durable option that provides lasting savings when compared to other materials. Compare electrical conduit types including...

Don't Let Burn-Through Threaten Another Data Center or Utility Project

Get the No Burn-Through Elbow eGuide to learn many reasons why Champion Fiberglass elbows will enhance your data center and utility projects today.

Considerations for Direct Burial Conduit

Installation type plays a key role in the type of conduit selected for electrical systems in industrial construction projects. Above ground, below ground, direct buried, encased...

How to Calculate Labor Costs

Most important to accurately estimating labor costs is knowing the approximate hours required for project completion. Learn how to calculate electrical labor cost.