Insulation Types

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jsinclair

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Just a quick question. Can anyone point me to a reference that could explain what the different letters in the insulation designations mean? I.E. - What does the "R" in RHH stand for...etc.

Thanks,

John
 
Re: Insulation Types

Table 310.13 Conductor Application and Insulations refers to the insulation types. I am more curious as to what each letter stands for, if it stands for anything. Another for instance, I have always understood the letter "T" to stand for thermoplastic and the letter "W" to stand for wet location. I am looking for some sort of refernce for this.
 
Re: Insulation Types

</font>
  • <font size="2" face="Verdana, Helvetica, sans-serif">?R? means ?Rubber,? and comes with a 60C rating.

    ?T? means ?Thermoplastic,? and comes with a 60C rating.

    ?H? means ?add one unit of heat ? 15C ? to the previous rating.

    ?W? means ?wet locations.?

    ?N? means ?nylon outer jacket.?

    ?X? means ?cross-linked polymer."

    "-2" after a name means "90C rating in wet or dry locations."</font>
<font size="2" face="Verdana, Helvetica, sans-serif">The reference is my notes from an NEC class I took once. I?ll see if I can find a better reference.
 
Re: Insulation Types

The following link will take you to the UL ?Wiring and Cable Marking Guide,? dated October 2003.

Underwriters Laboratories

Appendix A (page 21) has the code letters and their meanings. It defined code ?R? as ?thermoset insulation.? I do not know if that means ?rubber.?
 
Re: Insulation Types

Most manufacturers use the R to mean rubber, however it always seems UL does not like the simple generic terms when something scientific is available.

T -> thermoplastic -> Insulation that will soften and distort from its shape by heating above a critical temperature peculiar to the material.

R -> thermosetting -> Term describing insulation that will not re-soften or distort from its formed shape by heating until a destructive temperature is reached.
 
Re: Insulation Types

Jim:

Do you have those backwards? I would think rubber is the one that can be bent and shaped without melting it.

Steve
 
Re: Insulation Types

Jim is correct, a thermoset will remain on the insulation when external heat is applied such as fire and will not spread the fire. It will stay in place until it turns to ash.

Where as a thermoplastic will melt and drip and spread a fire of the LOI is high enough.

You can prove this to yourself with a bread wrapper.
 
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