2-2-4 AL feeder + ground

[VHF]

A couple questions for the NEC code gurus out there...

If I run 2-2-4 AL URD as a direct-bury feeder to my detached garage 100' from the house, what is the highest capacity circuit breaker I can feed it from? 90A? Or lower because of the #4 neutral?

Is a #8 CU ground wire acceptable, or does it need to be #6? Can I direct-bury bare copper the entire distance, or does it need to have "U" rated insulation?

(I have a piece of rebar from the garage slab stubbed up for a "Ufer" ground, and I plan to also drive 2 ground rods. Hoping to get a decent ground despite the generally sandy soil here. I know to make sure the neutral and ground are NOT bonded in the garage panel. I am probably going to use a 100A Square D Homeline panel in the garage.)

 

[Torque1st]

You may find the answers here:
http://www.selfhelpandmore.com/home...o-dwellings/wiring-a-detached-garage-2002.php

 

[Charles (in GA)]

Probably should consider using 2-2-2-4 direct burial cable instead, then you have the neutral size and the ground taken care of.

Charles

 

[rinny_tin_tin]

A couple questions for the NEC code gurus out there...

If I run 2-2-4 AL URD as a direct-bury feeder to my detached garage 100' from the house, what is the highest capacity circuit breaker I can feed it from? 90A? Or lower because of the #4 neutral?

Is a #8 CU ground wire acceptable, or does it need to be #6? Can I direct-bury bare copper the entire distance, or does it need to have "U" rated insulation?

(I have a piece of rebar from the garage slab stubbed up for a "Ufer" ground, and I plan to also drive 2 ground rods. Hoping to get a decent ground despite the generally sandy soil here. I know to make sure the neutral and ground are NOT bonded in the garage panel. I am probably going to use a 100A Square D Homeline panel in the garage.)

2 2 4 AL AL URD is 165/120 A ampacity direct burial/conduit....Looks like if you run it to max you need a no .6 gnd and you can select breaker iaw OCP for 165/120.

 

[sberry]

The number 8 (copper) ground is fine, breaker this wire at 90A and you are good to go. Dont lose sleep about the neutral size.

 

[VHF]

I originally was looking for 2-2-2-4 or 2-2-4-6 direct burial cable, but my local Mendards only seems to carry 2-2-4. (They did have 2-2-2-4 SEU for above ground service entrance, but not in direct bury.)

The 2-2-4 is only $1.08/ft, so even with a separate #8 copper ground I'll be under $2.00 a foot total. Running it all in copper isn't an option for my 100' run. That would be close to $800! I've heard copper is coming down in price, but that hasn't been reflected in retail wire prices yet!

P.S. I'm not locked into Menards, but as far as I know there are no electrical supply houses in the area... even the pros around here "Save Big Money" at Menards!

 

[Improved700]

I did the same project about 6 weeks ago. I also bought my wire at Menards, because the local Fleet Farm did not have a long enough length of 2-2-2-4 ALU. Had to go to 3 different Menards to find it (Appleton, WI). Purchased 140 feet just to be on the safe side, and told the kid that was cutting it to be generous. I used a 100 AMP Square D box in my shop also. I also ran mine in PVC conduit. Rented a trencher, and dug 3 feet down, layed the conduit, and ran direct burial DISH cable, back filled 1 foot and ran a 1 inch CSST gas tubing, and backfilled the rest. I was going to run a separate #8 copper for my ground, but stumbled upon the wire I wanted at a different Menards. I looked at Home Depot and Lowes, and they all seemed to not carry ALU wire. Where abouts in NW Wisconsin? Not sure if you'll find a 90AMP breaker though, so you have to run either a 100AMP or a 60AMP breaker.

 

[Gary S]

When I did my garage a couple of years ago, I just ran 2-2-2-2 copper. I've never been fond of aluminum as an electrical conductor, so I spent the extra for copper. I put in a 100A breaker, and the wire should easily handle more than that. It is buried in conduit so I could pull it and replace it in the future if necessary.

 

[2LTim]

Guys, something to keep in mind. Direct burial wire is designed to be just that, direct buried. If you run it in a conduit, it can overheat due to the fact that it doesn't have the ground, soil, directly in contact with it to act as a heat sink. The soil is a much better conductor of heat than the air that will surround the wire inside a conduit.

 

[Aceman]

If I run 2-2-4 AL URD as a direct-bury feeder to my detached garage 100' from the house, what is the highest capacity circuit breaker I can feed it from? 90A? Or lower because of the #4 neutral?

90 is fine.

Is a #8 CU ground wire acceptable, or does it need to be #6? Can I direct-bury bare copper the entire distance, or does it need to have "U" rated insulation?

Kind of a gray area here as far as I can tell. #8 Cu can be used bare or insulated, but I don't believe it matters what kind of insulation is on it. With that said I've never direct buried insulated copper wire, this is the gray area to me. In your particular installation, if I was pulling AL wire, I'd be pulling a #6 AL USE "grounding" conductor with 'em.

(I have a piece of rebar from the garage slab stubbed up for a "Ufer" ground, and I plan to also drive 2 ground rods. Hoping to get a decent ground despite the generally sandy soil here.

If you have the ufer, you don't need rods. But if you want the rods too, that's fine.

2 2 4 AL AL URD is 165/120 A ampacity direct burial/conduit....Looks like if you run it to max you need a no .6 gnd and you can select breaker iaw OCP for 165/120.

Please show me the code article that allows #2 AL to be breakered that high. Table 310.16 says direct buried #2 is good for 90 amps.

Direct burial wire is designed to be just that, direct buried. If you run it in a conduit, it can overheat

I think you should back that statement up with some facts. Do you realize they use the same ampacity chart for direct buried wire and wire installed in conduit?

 

[rinny_tin_tin]

90 is fine.

Kind of a gray area here as far as I can tell. #8 Cu can be used bare or insulated, but I don't believe it matters what kind of insulation is on it. With that said I've never direct buried insulated copper wire, this is the gray area to me. In your particular installation, if I was pulling AL wire, I'd be pulling a #6 AL USE "grounding" conductor with 'em.

If you have the ufer, you don't need rods. But if you want the rods too, that's fine.

Please show me the code article that allows #2 AL to be breakered that high. Table 310.16 says direct buried #2 is good for 90 amps.


I think you should back that statement up with some facts. Do you realize they use the same ampacity chart for direct buried wire and wire installed in conduit?

Glad to see you like code cites - maybe you should use them more often yourself. Code name Stephens for No 2 Al URD shows 165/120 A Direct Burial/Duct.

See here
http://customcable.thomasnet.com/vi...urd-cable-600v-triplex-90-c-for-direct-burial

Also - you are wrong in your opinion that ampacity to be the same for any cable re: direct burial v. conduit as shown above - Ever hear of the conduit /fill deration tables in the NEC?

 

[LoneGunman]

"Glad to see you like code cites - maybe you should use them more often yourself. Code name Stephens for No 2 Al URD shows 165/120 A Direct Burial/Duct."

Unless those numbers jive with the tables printed in the NEC they are useless when it comes to anything being inspected. Not saying they do or do not, as I have no idea without looking it up (we don't use AL) but they do sound high for the wire size. Perfect example is the power companies, they regularly run wires WAY undersized according to the tables in the NEC but they are allowed to, they are probably using the manufacturers data you linked to.

 

[rinny_tin_tin]

"Glad to see you like code cites - maybe you should use them more often yourself. Code name Stephens for No 2 Al URD shows 165/120 A Direct Burial/Duct."

Unless those numbers jive with the tables printed in the NEC they are useless when it comes to anything being inspected. Not saying they do or do not, as I have no idea without looking it up (we don't use AL) but they do sound high for the wire size. Perfect example is the power companies, they regularly run wires WAY undersized according to the tables in the NEC but they are allowed to, they are probably using the manufacturers data you linked to.

Type URD Triplex as 2 2 2 4 AL Code name Stephens is 90 degree C cable and is UL listed for 165/120 A DB/Duct. The Nehr-Magrath computations and tests are performed by UL and this is where the NEC gets its numbers from. Where in the NEC are you looking that shows differently for this cable -- oh wait a minute - as you just said - you have no idea as you didn't look it up. Don't you think that you should have looked it up first before pontificating?

Personally, I don't like aluminum either, but it is what it is. However, how do you figure that these numbers are useless when UL/ETL/CSA and the manufacturers say that its 165/120A for the conditions cited?

 

[LoneGunman]

"Don't you think that you should have looked it up first before pontificating?"

Nope

 

[Charles (in GA)]

NEC 310.16 does indeed specify that it is for direct burial or conduit, and #2 AL, 90°C, USE-2 (which is what 2-2-2-4 twisted AL intended for direct burial is rated as) is good for 100 amps at 90C and 90 amps at 75C.

I have 150 ft of this coiled up out in the shop. Down here in the south it somehow gets called "mobile home" feeder cable.

Charles

 

[LoneGunman]

NEC 310.16 does indeed specify that it is for direct burial or conduit, and #2 AL, 90°C, USE-2 (which is what 2-2-2-4 twisted AL intended for direct burial is rated as) is good for 100 amps at 90C and 90 amps at 75C.

I have 150 ft of this coiled up out in the shop. Down here in the south it somehow gets called "mobile home" feeder cable.

Charles

Come on Charles, the ampacitites listed on a website obviously trump those listed in the NEC.

 

[rinny_tin_tin]

NEC 310.16 does indeed specify that it is for direct burial or conduit, and #2 AL, 90°C, USE-2 (which is what 2-2-2-4 twisted AL intended for direct burial is rated as) is good for 100 amps at 90C and 90 amps at 75C.

I have 150 ft of this coiled up out in the shop. Down here in the south it somehow gets called "mobile home" feeder cable.

Charles

USE-2 is not URD

Its URD - Not USE

 

[Aceman]

Glad to see you like code cites - maybe you should use them more often yourself. Code name Stephens for No 2 Al URD shows 165/120 A Direct Burial/Duct.

See here
http://customcable.thomasnet.com/vi...urd-cable-600v-triplex-90-c-for-direct-burial

Try this link, read the note at the bottom.
http://www.southwire.com/ProductCatalog/XTEInterfaceServlet?contentKey=prodcatsheet39

Then try reading 110.14(C)1 too. That's should clear everything else up.

Also - you are wrong in your opinion that ampacity to be the same for any cable re: direct burial v. conduit as shown above - Ever hear of the conduit /fill deration tables in the NEC?

Do you honestly think the last 4 years I spent taking classes, working in the field, and taking tests that I've never heard of the fill/derate tables?

I just want to know why you're even mentioning the fill charts when we're not filling a conduit? And the derate charts when there are not more than 3 current carrying conductors?

I think you need to read the title description of Table 310.16.

 

[Charles (in GA)]

I'm yet to find URD in the table of cable types in the code (0-600 volt) however, the amp specs cited seem to jive with AL triplexed, direct burial, 2001-5000 volt, table 310.86, but that is not applicable here.

Charles

 

[rinny_tin_tin]

I'm yet to find URD in the table of cable types in the code (0-600 volt) however, the amp specs cited seem to jive with AL triplexed, direct burial, 2001-5000 volt, table 310.86, but that is not applicable here.

Charles

Correct - URD is not in the NEC tables yet - however, UL does list URD for the ampacities I previously gave. What makes the cable different is the insulation.

 

[rinny_tin_tin]

"Do you honestly think the last 4 years I spent taking classes, working in the field, and taking tests that I've never heard of the fill/derate tables?"


Did ya pass?

 

[Charles (in GA)]

Ok, so I stop by Home Depot this afternoon on the way home from work, I needed a new red light bulb for my cat house. So, I look at the wire on spools. They had two shelf stickers for 2-2-4 one for a whole spool, and one is a by the foot price of $1.21 ft. The shelf labels say URD. I match the Southwire number on the label with the spool beneath it, the label on the spool says nothing about URD, simply "Underground Service Entrance" and max 600 volt, and the wire on the spool is marked USE-2. At this point, I don't know if HD made a mistake on the label, or what.

Edit: After reading information on the internet from Southwire and Okonite, I found that URD is "Underground Residential Distribution" and is a Power company cable, everything I can find appears to be 15Kv to 25Kv. Nothing tells me that URD is intended for <600v installations. Indeed the temps/amps previously cited for URD are shown in the tables, but not for <600v installations. This is my take on it, given the small amount of research I have done in a few minutes here (isn't the internet a great thing?).

Charles

 

[rinny_tin_tin]

Ok, so I stop by Home Depot this afternoon on the way home from work, I needed a new red light bulb for my cat house. So, I look at the wire on spools. They had two shelf stickers for 2-2-4 one for a whole spool, and one is a by the foot price of $1.21 ft. The shelf labels say URD. I match the Southwire number on the label with the spool beneath it, the label on the spool says nothing about URD, simply "Underground Service Entrance" and max 600 volt, and the wire on the spool is marked USE-2. At this point, I don't know if HD made a mistake on the label, or what.

Edit: After reading information on the internet from Southwire and Okonite, I found that URD is "Underground Residential Distribution" and is a Power company cable, everything I can find appears to be 15Kv to 25Kv. Nothing tells me that URD is intended for <600v installations. Indeed the temps/amps previously cited for URD are shown in the tables, but not for <600v installations. This is my take on it, given the small amount of research I have done in a few minutes here (isn't the internet a great thing?).

Charles

I don't what to tell you either...but Home Depot is not known for keeping their products in order on their shelves - especially in the elek dept. All I know is that UL lists the URD with the same specs proffered by the manufacturers.

 

[Charles (in GA)]

I don't what to tell you either...but Home Depot is not known for keeping their products in order on their shelves - especially in the elek dept.

As noted, I did verify the Southwire p/n on the shelf label with the Southwire label on the spool. Not sure why HD described it as URD.

Charles

 

[rinny_tin_tin]

As noted, I did verify the Southwire p/n on the shelf label with the Southwire label on the spool. Not sure why HD described it as URD.

Charles

Here is 600V URD. However, I also note the 15 kV et al. Most unusual for a XLP with underground UV-resistant properties as generally the "tough" environmental fillers (carbon-black etc) and the cross-link ever ongoing silane process limits cable HiPot to 5kV and below (if that).

http://customcable.thomasnet.com/vi...urd-cable-600v-triplex-90-c-for-direct-burial

 

[thisguy]

I stumbled on this thread while doing some research for an upcoming project of my own and had some questions that I thought could be answered here.

I have a detached one car garage (planning on using this for my workshop) offset about 20' behind my house and a two car garage about 10' behind that. Both are wired incredibly poorly (and I think dangerously) so I'm in the planning process for redoing the whole thing. If I'm planning on a 70A main for the one car (100A panel) can I bury 2-2-4 AL in 1 1/2" PVC conduit for the 20' run? and can I run that feed 30' INSIDE my house (panel is on the other side of the house in the basement)? Plan on buying 75' so I'm doing everything based on a 75' 70A run.

For the two car garage, can I pull two lines of 12/2 from the panel in the one car (through 1" PVC, buried) and disperse to outlets once I'm in the structure?

Any help would be appreciated!

 

[sberry]

For the two car garage, can I pull two lines of 12/2 from the panel in the one car (through 1" PVC, buried) and disperse to outlets once I'm in the structure?

No, one feeder to a building and it must have a disconnect means, can be a simple switch. A 12/3 is ideal for this, breaker at 20A and use a double pole switch as a disconnect. A 12/3 delvers the same current as 2 of the 12/2 and a pinch less V drop when heavily loaded, probably not an issue for a shed.

 

[Charles (in GA)]

What you need is 2-2-2-4. I assume you are looking at the twisted triplex or quadplex that is not in a jacket, commonly known as "mobile home feeder" and it can either be direct buried or run in conduit.

Charles

 

[BigJohn20]

Vampire thread.

 

[Falcon67]

What you need is 2-2-2-4. I assume you are looking at the twisted triplex or quadplex that is not in a jacket, commonly known as "mobile home feeder" and it can either be direct buried or run in conduit.

Charles

This is what I just bought for my shop. I got it from HD and made sure it was USE-2 for wet locations. I'll run it in 2" conduit where it exists the house to protect it - too may sprinker pipes and such in the ground around here that might require digging. I asked a local master electrician about the install and he told me that in the attic, no conduit was required for that cable.

Be sure to keep the neutral and ground separate in the remote panel. The why of 4 wires are required.

 

[Aceman]

This is what I just bought for my shop.

Is the cable you bought have an overall outer sheath or is it just 4 individual wires twisted together?

 

[thisguy]

I was looking at triplex, but why would I need 2-2-2-4? Per code, I will be grounding the sub-panel separately. And if that is the case, would 2-2-4-6 be sized properly, or would I need that #2 neutral?

 

[Charles (in GA)]

You need quadplex such as 2-2-2-4 because you need two hots, a neutral, and a ground, carried from the main panel to the sub panel in the detached structure. Code requires you carry the ground back separate from the grounded conductor/neutral back to the main panel/disconnect (NEC 250.32), where it joins the neutral from the Power Company.

You also will be providing ground rods or a UFER ground at the detached structure, but you need to carry the ground back to the panel to be code compliant.

There are cases where you are allowed to undersize the neutral, ref NEC 220.61(A) thru (C), but unless you have calculations to prove that it is OK to reduce the neutral size (to building inspectors, assuming your work is being inspected) you are not allowed to reduce the neutral.

You also must have a disconnect at the detached structure. NEC 225.39

While this is a resurrected thread from early 2009, I got the chance to read it over and see that while we are now in a new code cycle (2011) and the book has changed (they even renumbered the sections with the wire ampacities, and did make some changes to the tables, the URD cable that rinny_tin_tin made such a deal out of is still not in the code book. You might find wire that has the URD rating on it, but it also needs to have some other rating, most likely USE or USE-2. You cannot take URD (only) inside a building, you would have to splice it to something else outside in a junction box, then go inside. It is of course, OK to take USE or USE-2 inside a building (or dual rated USE/URD wire).

Charles

 

[Charles (in GA)]

I asked a local master electrician about the install and he told me that in the attic, no conduit was required for that cable.

Be sure to keep the neutral and ground separate in the remote panel. The why of 4 wires are required.

You might re-think the attic routing of the cable. In Texas attics can get pretty hot, way hot in fact. Above 86F you get into temperature derating. Table 310.15(B)(2)(a) gives the derating factors. For a 90C rated cable (you use the highest temp rating of the cable for this calc.) in an attic from 123F to 131F your derating factor is .76

While we have to use the 75C column for determining the amperage of the circuit (there are no residential devices such as circuit breakers and terminals in panelboards rated at 90C) for the derating for temperature, we use the 90C column. Thus #2 USE-2, rated at 100 amps at 90C will be only good for 76 amps at the 123F to 131F temp range we mentioned above. Decrease the temp of the attic to 114F to 122F and the correction factor is .82, thus you still are below the desired 90 amp circuit you were hoping for. Raise the attic temp to 132F to 140F and the correction factor becomes .71 and thus a 71 amp circuit. You might eve have trouble connecting the #2 wire to a 70 amp breaker, not sure if the terminals will accept it.

Charles

 

[Falcon67]

>You might eve have trouble connecting the #2 wire to a 70 amp breaker, not sure if the terminals will accept it.

Ya, that's a key thing I have to look at. IIRC, the last SD breaker I looked at was good for #2 AL but I need to check. There is no other decent route from service panel to shop except through the attic. Our attic temps run 110ish~120 in the high summer because I vented the **** out of the place. The roof deck temps don't get over 120F and it's less on top of the insulation. I don't mind a 70A feed if the breaker can handle the wire. If I have to, I could put a weather tight plastic box right next to the service panel and change there from AL to 12" of #4 CU into the panel. I may do that anyway to keep from wrestling that #2 though an elbow into a hot panel.

>Is the cable you bought have an overall outer sheath or is it just 4 individual wires twisted together?
Twist. I know where you're headed. BUT - local codes allow it. I asked more than one master AND the inspector. Where my consultant said I might have trouble is grounding. Apparently, the big town locals want TWO methods and he said in the big city (not my city) the inspectors just walk if they don't see a piece of re-bar sticking up for a UFER ground. He told me that if I was building in Abilene, my 20' of #4 copper UFER would not be enough, that inspection would require that plus two copper rods minimum and they would really try to make me jack hammer into the slab to find a piece of re-bar. Never mind the copper is tied next to it for 20 and fully encased (per NEC reqm'ts). They are supposed to be on 2008, with local amendments. Being that I'm not in that town, I cleared my UFER plan (before the pour) and the feed with the inspector our city hires.

Ref Post #22 - this is LOL. I was quoted 1.69/ft for the quad. When they got the roll down, it was stickered 1.49. I got it at 1.49.

 

[Charles (in GA)]

Step the attic temp down to 105F to 113F and you get a correction factor of .87.

If you could be assured you will never see temps above 113F in the attic, I'd just go with the 90 amp breaker, especially since the circuit is probably not going to be that heavily loaded in the heat of the day anyhow (unless you have A/C systems cooling the shop) plus air compressor, welder, plasma cutter, flood lights, etc.

Charles

 

[Aceman]

There's no way in hell I'd run individual conductors in an attic with no outer sheath, codes or no codes.
I don't get it, they go above and beyond on grounding, but then don't give a **** your running unsheathed wire through an attic...?

I'm just glad I don't live in your area, dealing with your inspector would be more than frustrating....

 

[hub]

USE-2 is not URD

Its URD - Not USE

So is USE-2 acceptable for direct burial or not.
This was never answered.

I have just picked up 12' of (2,2,4)
the cable marking says;
[AL use-2 600v sun-res (UL) E-207803 (919063-001) Kingwire Chase-2]
from Elliot Supply in Texas. They say it is ok for direct burial. But nothing on the cables says URD or UF.
They infact call it "Stephens URD" on the invoice.
it is catalog # URD21000.
$1.04 per foot.

After reading this thread I am afraid to use it.
It is to be spliced with hydraulic crimp **** splices and those placed in 3-m 82a-1 splice kits (in resin).

The residence is a 125 amp svc.
There is no inspection necessary.
The existing underground supply is the same size 2,2, 4neutral.

Please help.
thanks

 

[Speedy Petey]

So is USE-2 acceptable for direct burial or not.
This was never answered.

I have just picked up 12' of (2,2,4)
the cable marking says;
[AL use-2 600v sun-res (UL) E-207803 (919063-001) Kingwire Chase-2]
from Elliot Supply in Texas. They say it is ok for direct burial. But nothing on the cables says URD or UF.
They infact call it "Stephens URD" on the invoice.
it is catalog # URD21000.
$1.04 per foot.

After reading this thread I am afraid to use it.
It is to be spliced with hydraulic crimp **** splices and those placed in 3-m 82a-1 splice kits (in resin).

The residence is a 125 amp svc.
There is no inspection necessary.
The existing underground supply is the same size 2,2, 4neutral.

Please help.
thanks

URD is the cable assembly, USE is the conductor identification. Just like NM-B cable has THHN conductors.

#2AL is good for a 100A service, not 125A.

 

[pattenp]

USE-2 is suitable for direct bury. But as Speedy has said, #2Al is only good for 100A as a service. Also if the wire is straight USE rated then it can not enter the structure because of not being fire resistant rated.