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  Facts You Should Know...    
Notice:
NEC is a registered trademark of the National Fire Protection Association, Inc.  All NEC references by Electrical Helper are interpretations of the NEC by the Electrical Helper staff and are not NEC statements. The official position of the NEC requires that the NEC be referred to in its entirety.
 
TEWN wire is the Canadian Equivalent of TFFN    
The nylon jacket on THHN wire serves as a barrier to the effects of gasoline and oil.    
     
Only THHN sizes 1/0AWG and larger are allowed in cable trays per the NEC provided they pass the UL 1581 vertical tray flame test or the CSA FT4 flame test.    
     
    Article 310.8(A) tells us we must use the types specified in the code for dry locations.
XHHW-2 wire is rated as gasoline and oil resistant.   Article 310.8(B) states that in dry and damp locations we must use one of the following types:
XHHW-2 wire sizes 1/0 and larger can be used in cable trays  when marked  "CT Use" or "For use in Cable Trays."    
FEP FE[B MTW PFA RHH
RHW RHW-2 SA THHN THW
THW-2 THHW THHW-2 THWN THWN-2
TW XHH XHHW XHHW-2 XHHW-2
Z ZW      
XHHW-2 type wire 1/0 and largere are marked "Sunlight Resistant."
 
Portable Cord Letters and Connotations
 
 

S = 600 VOLT SERVICE CORD (First recognized by UL)
  J = JUNIOR SERVICE - 300 VOLT
  T = THERMOPLASTIC
  V = VACUUM CORD
  E = ELASTOMER (Looks and feels like rubber, but is actually a thermoplastic)
  O = OIL RESISTANT OUTER JACKET
  OO = OIL RESISTANT OUTER JACKET AND OIL RESISTANT INSULATION
  W = CSA WEATHER AND WATER RESISTANT (Approved for indoor and outdoor use)**
**Do not confuse this with the mining cable Type "W" which refers to "without ground," such as 4/0-3 W.
 
  Article 310.8(C) describes the types to be used in wet locations.
     

(1) Moisture-impervious metal-sheathed
 

(2)

 MEW RHW RHW-2 TW THW
THW-2 THHW THHW-2 THWN THWN-2
XHHW XHHW-2 ZW    
  (3) or of a type listed for wet locations.
 
Table 310.13 in the NEC describes conductor Application and Insulations.
Note: Wires designated with the suffix "2" shall be permitted to be used at continuous 90 degree C (194 degree F) operating temperature, in wet or dry locations.
  Article 334 describes Nonmetallic-Sheathed Cable:
Types, NM, NMC, and NMS.
Consult Article 501.140 of the NEC for more on flexible cords and there usage in Class I, Divisions I and 2 locations.