RHW and RHH – We see these letter designations on all kinds of cable products, whether it’s when we’re choosing a cable and placing an order, or when we’re reading the stamp on a cable in front of us. But what do those letters mean?

These letters are code to identify the cable, its ratings, and how it can be used. You just need to decode the letters to understand the cable. For RHW and RHH cables, this is what we need to know:

• R = Rubber Insulated
• H = 75°C
• HH = 90°C
• W = Moisture Resistant

Now, if we put those meanings together, we can figure out what kind of cable we have. RHW* = rubber insulated cable, good up to 75°C, and moisture resistant. RHH = rubber insulated cable, good up to 90°C.

You may see RHW and RHH cables marked with a USE-2 rating as well. The USE-2 label indicates that the cable meets the National Electrical Code (NEC) specifications for underground service entrance cable. USE-2 cable is designed for direct burial in environments with maximum temperatures of 90°C, wet or dry. It is often used in solar cable applications to connect grounded photovoltaic modules.

Although cables that carry multiple ratings may be used in different applications, be sure to check that the way you are using the cable (as USE-2, as RHW, or as RHH cable) matches up with the specifications you are following. For example, if you are using the cable as USE-2 or RHW-2, the conductor temperature may not exceed 90°C in wet or dry locations. If it is being used as an RHH cable, the conductor temperature may not exceed 90°C in dry locations.

If you learn the meanings of the letters on your cable jacket and follow these simple rules, you should have no problem finding an appropriate cable solution for your application.

*Note: If a cable is rated as RHW-2 wire, conductor temperatures must not exceed 90°C in wet or dry locations.