Aluminum vs Copper

[dgkrzy]

Falcon 67, I can't disagree with you, the NEC has a lot of rules I have a hard time justifying. I interpret that to mean if the cable is encased or surrounded by insulation, the ampacity will be reduced, because the heat can not dissipate as readily. So only if the cable is buried in the insulation would the ampacity rating be restricted to the 60 degree column.

 

[pattenp]

You are missing in 338.10(B)(4)(b) that USE has to meet all the requirements of part II of article 340. 340.80 says you use 60 degree rating.

I assumed the OP was talking about an outdoor installation as his distance listed was 100' +/-.
I understand your point, so I don't see why you would disagree with my original statement, the USE is not allowed to be installed indoors, so it would not be in thermal insulation, therefore the ampacity is only limited by the 'weakest link' of the chain, not the specific statement in NEC 338.10 (B)(4).

 

[dgkrzy]

Falcon67, they are probably using NEC 310.15 (B)(7) - which is supposed to be restricted to main service conductors only. But if the inspector was OK with it, he has the final say as the Authority Having Jurisdiction.

It was not my intention to drag this out - I would recommend the 1/0 AL and 100 amp panel

 

[Falcon67]

Falcon 67, I can't disagree with you, the NEC has a lot of rules I have a hard time justifying. I interpret that to mean if the cable is encased or surrounded by insulation, the ampacity will be reduced, because the heat can not dissipate as readily. So only if the cable is buried in the insulation would the ampacity rating be restricted to the 60 degree column.

Agree - heat is the derater. I made sure to keep it out of the insulation so as not to pack it down and cause cold spots, and to let air move around the cable. Lots of venting in our attic.

In any case, like I said - I figured 70A ought to do it unless I start running a factory out there If it's good to 90A, that's just a safety factor!

I used 2-2-2-4 because ot was handy at HD, I could get it for 1.47/ft and it fit the 70A breaker at the meter, easy fit in 2" conduit, fit the panel and had the USE-2 rating. I got out the door at HD with 130' of cable, a 20 slot 100A panel and a 70A breaker for under $300.

 

[dgkrzy]

pattenp, You are correct - I did miss that I will edit my original post

 

[dgkrzy]

Falcon67, sounds like you did alright. I am jealous I haven't even built my garage yet, and when I do I will probably be limited in terms of building space & electrical capacity.

 

[Provincial]

I'm not an expert, but I always understood that "free air" meant the wires were separated by an air space. I took this from the "single conductors in free air" language in the ampacity tables and the fact that multiple conductors in conduit don't have as much ampacity. In my thinking, the insulation would have to be exposed to air that is capable of carrying away the heat around the full diameter of the insulation.

Anybody have a reference to cite for this?

 

[pattenp]

I'm probably using the term free-air in the wrong context when talking about the 60 degree rule when sizing wire when running the wire/cable inside of an insulated wall vs. not being run within insulation. I was using free-air to mean not being run within insulation.

 

[Aceman]

Where in the NEC does it allow an exception to the 60 degree requirement because of being RHH/RHW. The code in article 338 and 340 are blanket in coverage of SE and USE to me regardless of the make up of the conductors in the cable.

Also SE and USE as to article 338 are cable types not conductor types. RHH/RHW/USE-2 are conductor types, can be used to make up USE.
Plus USE is being used with two meanings, one as a multiwire cable and also as a conductor type which adds to the confusion.
We also may be talking pass each other. The 60 degree requirement is for when buried or run inside of insulation. If in free air then 75 degree is used.

You were making me think too hard Pattenp, but it's good code excersize! I searched all over Mike Holts site trying to come up with a code article that backed my statement up but couldn't find anything. So I made a post:

http://forums.mikeholt.com/showthread.php?t=142612

So if Southwire's MHF is straight rated USE and direct buried, you're absolutely right. 60 degree column all the way. If installed in conduit, and it is indeed slash rated as USE/RHH/RHW-2, we can use the 75 degree column. I don't have any MHF to look at so I can't verify what the rating is exactly.

As reguested copper USE cable.

http://www.southwire.com/ProductCatalog/XTEInterfaceServlet?contentKey=prodcatsheet7

The point I'm trying to make is how many diyer's do you figure are going to pay for and install the more expensive copper USE direct buried versus using THHN/THWN in conduit?

I don't see the reasoning behind stating 60 degree copper ampacities when you get past the common UF cable sizes. Nobody uses copper USE around here, I've only come across it a handful of times in old installs, and I've never seen it installed new. Doesn't make sense to buy copper and then direct bury it.

 

[pattenp]

Well Aceman I read all of the Mike Holt post and I didn't get a definitive answer from what was being discussed. One point to make is your comment about the MHF being direct buried vs. in conduit as having a bearing on using the 60 degree rule or not. The code section 338.10(B)(4)(b) says installed in ground, it does not specify as to how it's installed in the ground. You call it 75, I call it 60, the world still turns.

 

[Aceman]

. You call it 75, I call it 60, the world still turns.

Sure.

I was a little bummed when I was searching because I swear I've seen the topic come up a time or two in the past but I sure couldn't find it to save my life. Without actually seeing if the cable is dual rated I can't be sure.

Carry on.....

 

[PRH44]

The point I'm trying to make is how many diyer's do you figure are going to pay for and install the more expensive copper USE direct buried versus using THHN/THWN in conduit?

I don't see the reasoning behind stating 60 degree copper ampacities when you get past the common UF cable sizes. Nobody uses copper USE around here, I've only come across it a handful of times in old installs, and I've never seen it installed new. Doesn't make sense to buy copper and then direct bury it.

Thanks for the input Aceman. The reason I stated 60 degree copper is the direct burial method seems to be very popular with DIYers on GJ, and it was a copper VS aluminum question. You do raise a good point in respect to the cost of copper USE. VS Aluminum USE.

If the OP wanted to install a complete conduit system he could take advantage of the 75 degree column. He could then use THHN/THWN copper single conductor or an Aluminum single conductors such as XHHW.

 

[snturner]

Holly Cow! I have read through all the posts and come to a conclusion.

I bought 400 ft of 12 ga speaker wire, tied it to a 10 amp breaker in the house, ran the wire through a hole I drilled in the side of the house. Stretched the wire as tight as I could pull it across the yard to the neighbors house. Stripped of 1/2 inch of plastic on the end and plugged it into a receptacle. Spliced another piece into that and ran it back to my detached garage, via the trees. I don't want anyone to hit it with the mower and I think this also covers the "free air" issue. I ran the wire through the garage window and plan to just tie the wire to what ever piece of equipment I am using at the time.

This should work right?

I hope everyone gets my humor.

You all have great information and it has helped me out a lot. Falcon67 I like the way you think. I plan to do what you did, except with bigger wire and 100 amp.

Thanks for sharing your knowledge guys/gals.

 

[Falcon67]

Two things - you'll need a tube of 2 hour fire rated RTV to plug that hole in the house and every where that wire touches plant material the plant requires a 6' ground rod. I would have put in a couple of grounded metal clothes line poles for the shop run to get some double duty out of that service feed. And put a twist lock socket on the shop end - It'll be potentially dangerous and for sure irritating when the wind yanks that wire out the window.

We got a LOT of rain yesterday, so I haven't got out to the shop yet to look at the 2-2-2-4 and get the numbers off the wire. I know it's OK per the locals, but I 'd still like to know more about the details.

Note I used 30' of 2" conduit between the house and the shop panel - I did not want to direct bury as there are sprinkler lines all over this place (previous owner) at various depths and I for sure didn't want to chance hitting the wire when looking for a leak. I already chopped through two water lines just digging the conduit trench.

 

[rburke65]

I ran direct burial feed for a neighbor and we had to re-do it after 8 years or so because of the stoney, rocky soil which had nicked the wire and caused the one leg to open. Second time around we ran 2" PVC conduit like we should have in the first place. Highly recommend the 2" conduit.

 

[Falcon67]

FWIW - the wire I used is marked USE-2 or RHH or RHW-2 or SIS 60 MILS XCP.

 

[PRH44]

After reviewing the Southwire specification on Mobile Home Feeder cable and the 2011 UL white book category code TYLZ I have made the following observations.
1. The Type is stated as RHW or RHW-2 or USE-2 all recognized by the NEC and UL listed.
2. The term” Mobile home feeder cable” is a trade or brand name not a recognized wiring method in the NEC or UL. It is a quadruplexed assembly containing NEC recognized and UL listed RHW or RHW-2 or USE-2 Type conductors.
3. UL white book Appendix A page 8 states Some wire and cable may be marked with multiple Type designations. These products have been evaluated for uses of all Type designations marked.
My interpretation would be one designation or rating would not limit another. For example the THHN portion of a dual rated THHN/THWN wire does not limit the THWN portion to a dry location. Refer to the example from http://www.iaei.org/magazine/2009/03...ked-nplf-150v/
I Conclude the Southwire “Mobile Home Feeder Cable” used as RHW or RHW-2 would qualify for 75 degree column ampacities.

4. NEC 338.12(B).1 and 2 will not permit USE cable to be used for interior wiring. When used above ground it must be terminated in an outdoor enclosure. This in my opinion would make feeding a mobile home panel with a single rated USE cable through the interior provided sleeve a code violation. However if one would use the above mentioned “Mobile Home Feeder cable” according to the UL listing and pertaining articles of the NEC for RHW or RHW-2 this would be an acceptable installation.

The UL category Service Entrance Cable TYLZ states USE is not suitable for use in premises. USE is not suitable for above ground except to terminate at service equipment or metering equipment. One might interpreted this to be acceptable to feed an interior service panel. I believe the statement above “not suitable in premises” rules this assumption out.
Please be advised these are my observations/interpretations and opinions based on some diligent research.

 

[Falcon67]

As an ex-10CFR50 Nuc QA guy that spent years reading tons of QA, PO, NRC and what not specs, I appreciate your research and your detailed posting. Digging through the regs is always a task.

 

[Aceman]

After reviewing the Southwire specification on Mobile Home Feeder cable and the 2011 UL white book category code TYLZ I have made the following observations.
1. The Type is stated as RHW or RHW-2 or USE-2 all recognized by the NEC and UL listed.
2. The term” Mobile home feeder cable” is a trade or brand name not a recognized wiring method in the NEC or UL. It is a quadruplexed assembly containing NEC recognized and UL listed RHW or RHW-2 or USE-2 Type conductors.
3. UL white book Appendix A page 8 states Some wire and cable may be marked with multiple Type designations. These products have been evaluated for uses of all Type designations marked.
My interpretation would be one designation or rating would not limit another. For example the THHN portion of a dual rated THHN/THWN wire does not limit the THWN portion to a dry location. Refer to the example from http://www.iaei.org/magazine/2009/03...ked-nplf-150v/
I Conclude the Southwire “Mobile Home Feeder Cable” used as RHW or RHW-2 would qualify for 75 degree column ampacities.

4. NEC 338.12(B).1 and 2 will not permit USE cable to be used for interior wiring. When used above ground it must be terminated in an outdoor enclosure. This in my opinion would make feeding a mobile home panel with a single rated USE cable through the interior provided sleeve a code violation. However if one would use the above mentioned “Mobile Home Feeder cable” according to the UL listing and pertaining articles of the NEC for RHW or RHW-2 this would be an acceptable installation.

The UL category Service Entrance Cable TYLZ states USE is not suitable for use in premises. USE is not suitable for above ground except to terminate at service equipment or metering equipment. One might interpreted this to be acceptable to feed an interior service panel. I believe the statement above “not suitable in premises” rules this assumption out.
Please be advised these are my observations/interpretations and opinions based on some diligent research.

Thank you for posting this, I also agree with your interpretation.