What are the RHW Conductor Types?

Wire is coded for both safety and usage description.
Wire is coded for both safety and usage description. (Image: Jupiterimages/Photos.com/Getty Images)

All electrical wire in the United States must be coded according to National Electrical Code (NEC) specifications. RHW wire is a specific type of wire that has been coded so that anyone who knows the code will know the capabilities of the wire as well as the materials used to make it.

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RHW Wire

Wire coding is a relatively simple system where, in most cases, each letter in the name of the code stands for one of the properties of the wire. Although there are exceptions to this rule, the coding can be taken literally in most cases. For example, in the case of “RHW,” the “R” stands for rubber or neoprene outer insulation, the “H” stands for a heat resistance of 75 degrees Celsius (it would be “HH” for 90 degrees Celsius) and the “W” stands for the ability of the wire to withstand water damage.


The outer layer (insulation) of the wire is important because it allows the user to purchase and use the material most suited to his needs. Rubber and neoprene are best suited for use underground or in buildings. They are also suitable for use in damp or wet locations such as basements. The user would also know that rubber is not very suitable for outdoor use in sunlight or anywhere it might receive UV exposure, due to the fact that this type of material breaks down under UV lighting.

Heat Resistance

The heat resistance of the wire is determined not only by the length of the conductor but also by its width. The ampacity of a wire is defined by the length and breadth of the conductor inside. The longer the length of a conductor, the less ability it has to retain electrical power and heat. The thinner a conductor is, the more resistance it holds toward conducting electricity over a distance. This means that the thinner and longer a wire is, the hotter the wire will get. In some cases, this means that the “R” coating on the wire might melt and cause damage to the area around the wire. The “H” on the RHW wire section indicates that this type of wire can only handle heat up to 75 degrees Celsius.

Water Resistance

Because of the “W” rating on the RHW wire, a user will know that the wire is water resistant and can even be submerged if necessary. The wire has been sealed with an appropriate material such as rubber or neoprene so that it can be used under these circumstances. However, it should be noted that if a wire contains an “R” rating but not a “W” rating, it should not be exposed to dampness or water because doing so may cause shorts and or corrosion, regardless of type of material it is made from.


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