NEC in the Facility, April 20, 2010

April 20, 2010
THHN is a good, general-purpose insulation. However, suppose you need to rewire a machine tool. Would THHN be the most appropriate kind of wire?

The typical maintenance department has several spools of THHN wire on a rack or pallet, ready for projects or repairs. THHN is a good, general-purpose insulation. However, suppose you need to rewire a machine tool. Would THHN be the most appropriate kind of wire? Would it be appropriate at all?

To ensure you use the correct insulation type for the application, turn to Chapter 3 of the NEC. Article 310 contains Table 310.13(A), Conductor Applications and Insulations.

Most application descriptions are very general. For example, you can use moisture-retardant thermoset (RHW) in "dry and wet locations." A few application descriptions are specific. For example, you can use moisture, heat, and oil-resistant thermoplastic (MTW) in machine tool wiring. Before using wire from those maintenance spools, check the table for applicability. If that insulation isn't allowed for your application, then look for that application in the table to find the allowed insulation types.

For most applications, this table will give you several insulation types from which to choose. Your ultimate selection will depend first on the temperature range and ampacity (Tables 310.17 through 310.20) and then on other factors (e.g., cost and availability).

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...

Fiberglass Electrical Conduit Chemical Resistance Chart

This information is provided solely as a guide since it is impossible to anticipate all individual site conditions. For specific applications which are not covered in this guide...

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.