Why do RHH, RHW, RHW-2, XHH, XHHW, or XHHW-2 stop at #14?

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Adamjamma

Senior Member
Hmm, my own question in response is what would you need to feed with them that is less than 15 amps? If you are looking at feeding LEDs then you are talking dc which, if I recall correctly, is recommended that you feed with 14 guage stranded, not solid, if distance from source is greater than ten feet. Exception is trailer lighting, or certain boating applications where 16 and 18 guage stranded is used, but, again, dc rules so do not need the ac certifications.

dc wiring can get very confusing as far as sizing, due to loads, distance, voltage drop, all of which are based on source voltage.
 

kwired

Electron manager
Location
NE Nebraska
Hmm, my own question in response is what would you need to feed with them that is less than 15 amps? If you are looking at feeding LEDs then you are talking dc which, if I recall correctly, is recommended that you feed with 14 guage stranded, not solid, if distance from source is greater than ten feet. Exception is trailer lighting, or certain boating applications where 16 and 18 guage stranded is used, but, again, dc rules so do not need the ac certifications.

dc wiring can get very confusing as far as sizing, due to loads, distance, voltage drop, all of which are based on source voltage.
Power and lighting - very few cases can you run less then 14 AWG. Lighting taps is one of the more common places you can do it.

Art 725 control circuits is one place you often see less then 14 AWG, and can be at more then 50 volts for class 1 circuits.
 

hbiss

EC, Westchester, New York NEC: 2014
Location
Hawthorne, New York NEC: 2014
Occupation
EC
The NEC only recognizes them down to #14 (table 310.104(A)). Why don't these cables exist in a smaller size like #16?

A better question is what would you use them for? If there was a use that couldn't be fulfilled by other products they probably would be made in smaller sizes.

-Hal
 

mbrooke

Batteries Included
Location
United States
Occupation
Technician
Sizes below 14 are rarely used in the NEC. One possible reason is conductor breakage- I know IEC 60364 stops at 1.5mm2 for this reason as stated.
 

Jraef

Moderator, OTD
Staff member
Location
San Francisco Bay Area, CA, USA
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Electrical Engineer
That's because the "conditions for use" of wire smaller than 14ga does not coincide with the conditions where you would want to use RHx/XHx insulated conductors.
Below 14ga in AC circuits, you are looking at "fixture wire", which is why THHN (Thermoset High heat, Nylon jacket) becomes TFFN (Thermoset Flexible Fixture, Nylon jacket). RH/XH conductor insulation doesn't lend itself to being flexible, because the XLPE (Cross-Linked Poly Ethylene) material it is made from is essentially "heat shrink tubing" and when it shrinks down to small sizes, it becomes stiffer than you would want for flexible fixture wire. You can get similar performance to RH/XH insulation in smaller conductors by using SIS (Silicone Insulated Switchboard) wire.
 

Skippei

Member
Location
Madison, WI
My question is because VFD cables are commonly available down to #16 AWG. The 2018 release of NFPA 79 states that:

"Electrical conductors and equipment supplied by power conversion equipment as part of adjustable speed drive systems and servo drive systems shall be listed flexible motor supply cable marked type RHH, RHW, RHW-2, XHH, XHHW, or XHHW-2 or selected based on the equipment manufacturer’s instructions."

Problem is that if you were using a #16 VFD cable in the past you know are out of compliance with this standard unless equipment manufacturer instructions explicitly state otherwise.
 

Jraef

Moderator, OTD
Staff member
Location
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Occupation
Electrical Engineer
My question is because VFD cables are commonly available down to #16 AWG. The 2018 release of NFPA 79 states that:

"Electrical conductors and equipment supplied by power conversion equipment as part of adjustable speed drive systems and servo drive systems shall be listed flexible motor supply cable marked type RHH, RHW, RHW-2, XHH, XHHW, or XHHW-2 or selected based on the equipment manufacturer’s instructions."

Problem is that if you were using a #16 VFD cable in the past you know are out of compliance with this standard unless equipment manufacturer instructions explicitly state otherwise.
Well, NFPA 79 is not the NEC, but if you follow it, then it appears as though using 16ga VFD cable will be out.
 
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