UK vs. NA

Old 08-27-04, 05:56 AM
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Hi guys as alot of you know im a uk Electrician and im trying to learn about Us and Canadian Electrics as i will be moving over there soon hopefully.
What do the terms UF-B, NM-B, THWN, XHHW mean ive been looking for answers but so far cannot find any. Would be greatfull for the help.

Also as far as running in conduit i see no real hazards as long as you take into account that the more cable you run in the conduit the hotter it will get so you should apply some kind of factor to determine cable size, that is how i would go about it over here.

Old 08-27-04, 07:57 AM
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The terms you mention are not even the same in U.S. vs. Canada. And the formal definition of a term like "UF" is really a list of specifications that take up a whole article in the NEC. But informally and generally:
  • UF-B is Underground Feeder. The "-B" means its temperature rated at 90 degrees C. Although called "underground feeder," its use is limited to neither underground nor as a feeder. It can be used anywhere NM-B can be used. But UF-B is rated for both wet locations and direct burial. Some of it is also rated for sunlight exposure, but you'd need to check the specific cable. UF-B is commonly used as an underground feeder to a detached structure, and to supply power to such things as a post light in your front yard. I think Canada calls this NMW (non-metallic wet).
  • NM-B is the dry version of UF-B. It is the most commonly used cable in the U.S. for residential wiring. Some cities like Chicago outlaw it, but it is usable most places. I think Canada calls this NMD (non-metallic dry).
  • THWN and XHHW are just two of dozens of different kinds of individual wires. One letter usually refers to the type of insulation (T=thermoplastic) and the presence of the "W" usually (but not always) indicates suitability for wet locations. Two "H" letters say its rated for 90 degrees. But even though THWN only has one "H", it's also rated for 90 degrees (I guess they didn't want to make the designation too long). The only way to know all the characteristics of wiring designations is to have a table of their characteristics and allowed and disallowed applications.
A google search for any of those terms will yield a lot more information. As for determining cable size, conduit size and other such factors, the only way to "go about it" here is to follow the NEC exactly. You are not allowed to just figure it out on your own.
Old 08-27-04, 10:09 PM
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I thought that THWN is rated for 75C and THWN-2 is rated for 90C
Old 08-28-04, 07:08 AM
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My wiring book has:

THWN dry/wet 75 degrees C
THWN-2 dry/wet 90 degrees C
THWN dry 90 degrees C
wet 75 degrees C

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