uf cable in conduit ? (2024)

Re: uf cable in conduit ?

340.10 (3). Says (3) For wiring in wet, dry, or corrosive locations under the recognized wiring methods of this Code. RMC articles mentions use of cable inside conduit where permitted by that cables's article. RMC is a recognizd article so I think this is as close as the book comes to telling you it is OK.

Re: uf cable in conduit ?

The important thing is there is no section that prohibits the cable being installed in conduit. There is actually sections that require the cable to be protected by rigid conduit, where subjected to physical damage.

This is a topic that is mis-understood. Thermal conductivity, of material, is the same as electrical conductivity. Metal is a much better conductor of heat than air.

The unit for steel is 46. Air is .024

I noticed the insulation quality of air, while in the Antarctic. Any time the wind increased, the heaters all came on. With no wind, very little heat was lost, even in -60?F.

Re: uf cable in conduit ?

For the 2002 cycle the CMP's wanted to indicate which cable methods could not be used in raceway, but they made a mistake and the NEC now states where allowed by the respective cable article. Hopefull the 2005 NEC will correct this. Right now the only cable method that can be used in raceway is NM cable (that I am aware of).
UF cable has to be protected where exposed to physical damage, this was added in the 1999 cycle.
If you look at article 334 it shows the various methods allowed for physical protection of NM cable,for example short sections of EMT, and the emt does not have to be bonded to an equipment grounding conductor, and a short section could be considered anything less than 10 feet.

Re: uf cable in conduit ?

Tom,

I believe UF is allowed in conduit.

NEC2002 Article 340.10(1) says "For use underground, including direct burial..."

If you can't put it in a raceway underground, then what other methods are there besides direct burial?

Re: uf cable in conduit ?

Jim, sounds logical to me.

Re: uf cable in conduit ?

Free air is the worst case for dissipating heat, or more correctly; the efficient removal of heat from a conductor.

The reason for ampacity to be increased is due to the elevated heat, in free air, is no problem. It has nothing to do with cooling effects of air, allowing more heat.

Glass, and wood, are better heat sinks than air.

Conductors will run cooler inside a metal conduit than direct burial. When direct buried the dirt dries out around the cable and forms an insulator, the thermal conductivity decreases.

When designing heat sinks, the best metal is silver, W/(m ?C) is 410. Copper is 390. These are the same as electrical conductivity (S/m)

Re: uf cable in conduit ?

Table 310.17 says that conductors in free air can have a higher ampacity than conductors in conduit see 310.16. for example 310.17 60 degree # 2 uf cable in free air is good for 110 amps. (more heat) 310.16 # 2 uf cable in raceway, cable or earth on allowed 95 amps. (less heat)

Re: uf cable in conduit ?

Gregory: You are correct. The conductors in free air can be allowed to operate at a higher temperature due to not having a grounded surface for a fault.

The direct buried cable will fault to the earth if insulation is compromised.

Re: uf cable in conduit ?

Many electricians are under the impression that when you put a "parka" on a conductor, you will increase the heat generated. The heat does not increase it just remains longer.

A parka, on a human will not increase his body heat, it just permits it to remain longer.

[ August 02, 2003, 01:15 PM: Message edited by: bennie ]