approx. area of USE cable - ECN Electrical Forums

I can't find the area of USE cable in the tables in the code book. I'm thinking of using USE for a feeder to a swimming pool and putting it in conduit, to try and beat the price of copper. Need to know the area to know what size conduit to use. I'm thinking about using 3 4's and 1 # 8 ground, just in case they want to put a heat pump in for this pool later. Don't know yet. This is not covered in the last post I put in. I just need to know the minimum feeder size for it. Thanks Steve...

sparkync- First lets start with the fact that you don't install USE in conduit. USE is a cable Listed for use as an underground direct burial wiring method per the UL white book. Second a feeder for a swiming pool panel will need an insulated equipment grounding conductor per 680.25 the wiring methods are also called out in this article. As for the area of a cable, this can be calulated by measuring the diameter and multiply that times 0.7854

huh??? multiply by .7854?????

Area is pie are square (3.14159 times the square of the radius)

Check out the notes to Table 1 in Chapter 9 for the correct wiring sizing for sleeving as required by 338.10(B)(4)(b). Then use Table 4 for the conduit size.

.....or was it cornbread are square, pie are round!???

Why would USE be any cheaper than THHN/THWN? (metal for metal)

earlydean- You picking on me just because I didn't say diameter squared X 0.7854 [Linked Image]

I just did that to test you.

George, does the code say that you can't put USE in conduit? Just wondering. I'm just trying to make some preliminary decisions now. About the insulated ground, I could get the correct size of ground that's insulated in USE . Like I said I'm just trying different thoughts about it. This is one of them jobs that the contractor is trying to keep cost down, since he's going to have to pay for it, and not the homeowner. It's going to take a 110 ft. ditch to the house, then another 40 ft. to the electrical panel. The reason I'm even giving the thought consideration, is that using USE will be aluminum conductors, verses THHN copper conductors. I haven't even been able to check the differences in prices yet, but I'm just thinking the aluminum will be cheaper. Since the feeder will be so long, I am figuring on pulling a big enough feeder that will allow a "swimming pool heat pump" to be added later if necessary if the homeowner thinks it is a possibility. The last pool I wired, the homeowner decided after the pool was finished that the water was too cold and they wanted a heat pumt [Linked Image]

If I was to do this the feeder size would be around 70 amps. Which according to my calculations, would be a # 4 wire either aluminum or copper, given that the terminals are marked "suitable for 75 degree wire". ( I'm not looking at the code now, but that's what I thought I seen yesterday. I know this is very unusual question, but It's just a thought. If the Code specifies that it can't be done, then I will have the answer to justify the price, that the copper will cost, which as I said there may not be much difference in the price. Thanks a lot anyway. Any advice and suggestions is appreciated. Steve

[This message has been edited by sparkync (edited 08-03-2006).]

[This message has been edited by sparkync (edited 08-03-2006).]

[This message has been edited by sparkync (edited 08-03-2006).]

Southwire has aluminum THWN/THHN in those sizes

I looked in the UL white book and found that USE cable is listed for direct burial and could be run in conduit if it were under a building but not allowed to enter the building. I have never seen anyone use it in conduit except where it emerges from the ground and terminates in a meter can. If you are still interested in using it in conduit I'd check with the local AHJ before I even considered it.

I've pulled a lot of aluminum feeders in THWN or XHWN insulation. Most of the USE I've handled was the three conductor residential service stuff that has an oval or elliptical cross section. Conductors or cables that are not round are sized for conduit by measuring the widest dimension and taking that as the diameter of the circle. I suspect that you meant SER because USE cannot be used for runs inside structures since it lacks a flame-retardant covering. Type USE cable may not extend more than six feet inside a structure for that reason. You can use SER for the portion of the feeder that is inside the dwelling pursuant to section 680.21 (A) (4). The hard part in using aluminum SE is the requirement that the circuit have a copper Equipment Grounding Conductor in accordance with 680.21
(A) (1).

I've excerpted the applicable sections of the NEC below to make it easy for others to follow my thinking.

Quote

338.2 Definitions.
Service-Entrance Cable. A single conductor or multiconductor assembly provided with or without an overall covering, primarily used for services, and of the following types:
Type SE. Service-entrance cable having a flame-retardant, moisture-resistant covering.
Type USE. Service-entrance cable, identified for underground use, having a moisture-resistant covering, but not required to have a flame-retardant covering.

338.10 Uses Permitted.
(B) Branch Circuits or Feeders.
(4) Installation Methods for Branch Circuits and Feeders.
(a) Interior Installations. In addition to the provisions of this article, Type SE service-entrance cable used for interior wiring shall comply with the installation requirements of Parts I and II of Article 334, excluding 334.80.
FPN:See 310.10 for temperature limitation of conductors.
(b) Exterior Installations. In addition to the provisions of this article, service-entrance cable used for feeders or branch circuits, where installed as exterior wiring, shall be installed as required by Article 225. The cable shall be supported in accordance with 334.30, unless used as messenger-supported wiring as allowed by Article 396.
Type USE cable shall be installed outside in accordance with the provisions of Article 340. Type USE shall be permitted to be terminated in enclosures at an indoor location where Type USE cable emerges from the ground. The length of the cable extending indoors to the first termination box shall not exceed 1.8 m (6 ft). Where Type USE cable emerges from the ground at terminations, it shall be protected in accordance with 300.5(D). Multiconductor service-entrance cable shall be permitted to be installed as messenger-supported wiring in accordance with Articles 225 and 396.

680.21 Motors.
(A) Wiring Methods.
(1) General. The branch circuits for pool-associated motors shall be installed in rigid metal conduit, intermediate metal conduit, rigid nonmetallic conduit, or Type MC cable listed for the location. Other wiring methods and materials shall be permitted in specific locations or applications as covered in this section. Any wiring method employed shall contain a copper equipment grounding conductor sized in accordance with 250.122 but not smaller than 12 AWG.
(4) One-Family Dwellings. In the interior of one-family dwellings, or in the interior of accessory buildings associated with a one-family dwelling, any of the wiring methods recognized in Chapter 3 of this Code shall be permitted that comply with the provisions of this paragraph. Where run in a raceway, the equipment grounding conductor shall be insulated. Where run in a cable assembly, the equipment grounding conductor shall be permitted to be uninsulated, but it shall be enclosed within the outer sheath of the cable assembly.

--
Tom Horne

"This alternating current stuff is just a fad. It is much too dangerous for general use." Thomas Alva Edison

Tom, He is talking about the feeder to a sub panel. I am not sure 680.21(A)(1) applies since it says "branch circuit". I agree it may be a distinction without a difference but that is the language we have.

Tom, I was talking USE cable. It would not extend over 6 ft. inside the dwelling, as I was going to convert over in a junction box just inside the penetration of the outside wall. As of now I have decided just to go with copper conductors # 8 thhn, just to cover the load of the motors and pool light, and general use receptacle. Homeowner does not forsee a "swimming pool heat pumpt" to be installed. Thanks for the information and input.

gfretwell Member posted 08-04-2006 11:04 AM

Quote

Tom, He is talking about the feeder to a sub panel. I am not sure 680.21(A)(1) applies since it says "branch circuit". I agree it may be a distinction without a difference but that is the language we have.

gfretwell
I buy that. I guess I wasn't reading carefully enough. That raises another question. Could I supply a panel in an out building with three wire cable under the alternate feeder to out buildings rule and then supply pool equipment from that panel? That would seem an invitation to stray neutral current problems. The grounding electrode provided by an in ground pool would likely be a lower resistance electrode than the two driven rods the code would permit for that feeder configuration.
--
Tom Horne

"This alternating current stuff is just a fad. It is much too dangerous for general use." Thomas Alva Edison

Tom- 680.25 covers this. Looks like we need to have an equipment grounding conductor but in some cases it can be uninsulated.

I think Ryan drove a solid copper stake through the heart of 250.32(B)(2) for 2008