feeder entry height above ground

[sky jumper]

how high above ground does a feeder entry to a detached garage need to be? assuming underground feeder and PVC LB. from the NEC it seems 18" but man that document is hard to read.

 

[mike93lx]

Interested in the responses as I've never heard of a height requirement

 

[mm08822]

You might be confusing burial depth. There is no requirement.

I would come out of the ground and go 5' up the wall and LB straight into the upper backside of the panel.

What is the insulation type on the cable/conductors are you running?

 

[Jim greengo]

You might be confusing burial depth. There is no requirement.

I would come out of the ground and go 5' up the wall and LB straight into the upper backside of the panel.

What is the insulation type on the cable/conductors are you running?

 

[sky jumper]

hmm well I know the burial depth is 18". I'm using 2" sch 40 PVC. I could swear I read something about a minimum entry height, or it could've been a minimum height that needed protection from physical damage??

in any case I'd rather not go too high because it would look odd.

for wire I was planning a 2-2-2-4 mobile home feeder or separate XHHW wires, although I'm not quite sure what AWG I need for the separate conductors. 1-1-1-6 if I go with Cu?? I wanted 100A service to the garage.

 

[pattenp]

Cu is #3 and Al is #1 for 100A. So 3-3-3-8 Cu or 1-1-1-6 Al in individual conductors for 100A.

 

[wyliesdiesels]

hmm well I know the burial depth is 18". I'm using 2" sch 40 PVC. I could swear I read something about a minimum entry height, or it could've been a minimum height that needed protection from physical damage??

in any case I'd rather not go too high because it would look odd.

for wire I was planning a 2-2-2-4 mobile home feeder or separate XHHW wires, although I'm not quite sure what AWG I need for the separate conductors. 1-1-1-6 if I go with Cu?? I wanted 100A service to the garage.

There is no minimum. And subject to physical damage is very subjective.

The cable youre using needs to be in conduit. If the conduit could get wacked with a string trimmer, mower etc, then it should be sch80 above ground.

#2 al MHF is max 90a in your application, so if you want 100a, then you would need #1al or #3 cu not factoring in length and possible voltage drop which you havent mentioned.

The next question is, do you really need 100a? What will your loads be?

 

[sky jumper]

thanks. I'll probably go with 3-3-3-8 Cu for ease of pulling. the run is 125ft. I was thinking 100A for arc welder and future EV charger.

 

[wyliesdiesels]

#3 cu will cost a lot more vs #1 al

dont forget 2 ground rods and an isolated neutral bar which usually means you will need to purchase a separate ground bar kit.

 

[sky jumper]

so i've never pulled large cables through underground conduit. is #1 al really that hard to pull? I'm a bit wary of getting half way through it and getting stuck. that's why I bought 2" conduit. I didn't buy wire yet so I have options.

what insulation would you use for this? i know there's USE2, URD, thhn, etc. I've got the conduit so figured direct bury wire would be a waste and hard to pull.

 

[mm08822]

hmm well I know the burial depth is 18". I'm using 2" sch 40 PVC. I could swear I read something about a minimum entry height, or it could've been a minimum height that needed protection from physical damage??

in any case I'd rather not go too high because it would look odd.

for wire I was planning a 2-2-2-4 mobile home feeder or separate XHHW wires, although I'm not quite sure what AWG I need for the separate conductors. 1-1-1-6 if I go with Cu?? I wanted 100A service to the garage.

so i've never pulled large cables through underground conduit. is #1 al really that hard to pull? I'm a bit wary of getting half way through it and getting stuck. that's why I bought 2" conduit. I didn't buy wire yet so I have options.

what insulation would you use for this? i know there's USE2, URD, thhn, etc. I've got the conduit so figured direct bury wire would be a waste and hard to pull.

It won't look odd. paint it.
Anything else you do will a bunch of unnecessary hardware and may look like ****.

I would use xhhw Al, 1-1-1-3.
That fits in 1.5"C so you won't have any problem using 2"c.

 

[pattenp]

I also suggest Al XHHW-2. Since you'll be using individual conductors you don't need a #3 Al EGC as suggested by mm08822, #6 Al is good up to 100A. Assembled jacketed cable such as SER will come in the size 1-1-1-3. Be mindful that SER is not allowed underground even if in conduit. Also URD is not allowed inside of the structure. The pull of #1Al through 2" conduit should be a breeze.

 

[b-boy]

so i've never pulled large cables through underground conduit. is #1 al really that hard to pull? I'm a bit wary of getting half way through it and getting stuck. that's why I bought 2" conduit. I didn't buy wire yet so I have options.

what insulation would you use for this? i know there's USE2, URD, thhn, etc. I've got the conduit so figured direct bury wire would be a waste and hard to pull.

I'm not an electrician, but my son and I pulled Cu 2-2-2-4 THHN/THWN through 2" conduit.

The pull was 250ft.

It was not really hard until we hit the 90 turns. I had several. I used a heavy nylon rope and a lot of wire lube. At one point we got totally stuck. I attached the rope to my truck bumper and gave a light tug. It pulled right through.

You should be fine.

 

[mm08822]

I also suggest Al XHHW-2. Since you'll be using individual conductors you don't need a #3 Al EGC as suggested by mm08822, #6 Al is good up to 100A. Assembled jacketed cable such as SER will come in the size 1-1-1-3. Be mindful that SER is not allowed underground even if in conduit. Also URD is not allowed inside of the structure. The pull of #1Al through 2" conduit should be a breeze.

Whoops, wrote too many 1's too quickly. #3 was meant for the neutral not the grd.


Yes, agreed 1-1-3-6 AL XHHW works.

 

[mike93lx]

Whoops, wrote too many 1's too quickly. #3 was meant for the neutral not the grd.


Yes, agreed 1-1-3-6 AL XHHW works.

What is the criteria for a reduced neutral? Would that work in a shop that has mostly 120v equipment?

 

[sberry]

I like 2 2 2 4, its got a bigger ground wire.

 

[mm08822]

What is the criteria for a reduced neutral? Would that work in a shop that has mostly 120v equipment?

For a center-tapped single phase system - 120/240vac, the neutral only carries the imbalance between the hots. Reducing a neutral is common practice.

You could try to force an imbalance, but in a panel with buss stabs alternating between hot legs, stacking cb's next to each other minimizes the chance.

There is a limit to the reduction - can't be any smaller than the egc size. I'll look up the article later.

*****************

The article is NEC 215.2(A)(2) for the absolute minimum.

However, if your max neutral load calculates to a higher value, then you have to match that.
A standard reduction of two wire sizes carries mostly all cases.

 

[wyliesdiesels]

I'm not an electrician, but my son and I pulled Cu 2-2-2-4 THHN/THWN through 2" conduit.

The pull was 250ft.

It was not really hard until we hit the 90 turns. I had several. I used a heavy nylon rope and a lot of wire lube. At one point we got totally stuck. I attached the rope to my truck bumper and gave a light tug. It pulled right through.

You should be fine.

gotta be careful with round rope. it can burn through 90's due to the friction, like a hot knife cutting through butter.

flat mule tape is made for this reason...

 

[JohnX14]

gotta be careful with round rope. it can burn through 90's due to the friction, like a hot knife cutting through butter.

flat mule tape is made for this reason...

I've been pulling through pvc for 20 years with round rope and my Maxis puller. Never had a problem. Not arguing the mule tape point. But the puller doesn't grip the mule tape as it does the pulling rope. And I have a very old Greenlee puller that was designed for pulling rope.

 

[wyliesdiesels]

I've been pulling through pvc for 20 years with round rope and my Maxis puller. Never had a problem. Not arguing the mule tape point. But the puller doesn't grip the mule tape as it does the pulling rope. And I have a very old Greenlee puller that was designed for pulling rope.

How could you know whether the 90s got burned through when the conduit is underground?

 

[sky jumper]

question - if I use XHHW-2 isn't #2 good for 100A? unless I'm reading table 310.16 wrong?? (attached)
this is the wire i'm looking at
https://www.wireandcableyourway.com/2-awg-xhhw-2-aluminum-building-wire.html

Also - does the neutral have to be a different color or have a stripe? it would be cheaper to buy a 500ft spool and use the same wire for all conductors but not sure if the code police will allow.

Edit - here's table 310.13 which shows 90C for wet locations for XHHW-2 wire. what am I missing?

 

[exranger06]

You need to use the 75 degree column. The 90 degree column is just used if/when you need to de-rate the wire.

 

[sky jumper]

exranger I get that for XHHW when you look at table 310.13. but for XHHW-2 it says 90C for wet applications which undergound conduit is... so where is the requirement to use 75C? it may well be in there somewhere I just don't see it.

 

[exranger06]

If I remember correctly, the reason you use the 75* column is because you're going to connect the wire to a circuit breaker, neutral bar, etc, and those terminals are only rated at 75*. The wire itself is rated at 90*, which is why it's OK to use that column for de-rating.

 

[sky jumper]

ahh. well that makes sense. not sure I would've ever found that one in the NEC....

do you know if all 4 wires can be plain black? or do I have to get striped or colored wires for neutral and ECG?

 

[exranger06]

I'm not positive, but I believe you can re-identify the neutral by wrapping white tape around it (it's allowed on wires 4 gauge and bigger), but not the ground wire.

 

[Norcal]

I'm not positive, but I believe you can re-identify the neutral by wrapping white tape around it (it's allowed on wires 4 gauge and bigger), but not the ground wire.

The same rules apply to grounding conductors as grounded, (neutral ) conductors, it is OK to use tape of the appropriate color on 4 AWG and larger.

 

[wyliesdiesels]

The reidentification of conductors applies to neutral and ground. If #4 and larger you can use black jacketed conductors and tape them at their terminations.

 

[sky jumper]

thanks all for the help! here's what I'm going to order. 1-1-1-6 . its the same price as doing a #2 neutral if I buy a 500ft spool of #1 (they don't have #3). I'll get green #6 ECG.

you guys approve?

 

[mm08822]

You're good to go.
I was going to mention the 4 x 125' idea might bite you if the 125' is really 125'++. One or all 4 conductors may have come up short. You're good with 150'.

 

[mm08822]

exranger I get that for XHHW when you look at table 310.13. but for XHHW-2 it says 90C for wet applications which undergound conduit is... so where is the requirement to use 75C? it may well be in there somewhere I just don't see it.

Read NEC 110.14(C)(1) and the NEC 310.15(B) article (not table).

 

[JohnX14]

How could you know whether the 90s got burned through when the conduit is underground?

Same way you know that they didn't when you used mule tape.

The standard practice here for underground residential services is to use type USE "triplex" or "urd" (both local slangs). Which is direct burial rated, and also sunlight rated. So if, in fact, a 90 "got burned", it really doesn't matter. (unless, of course, the cable/ conductors were also damaged. I don't go so far as to megger each pull.

I really don't understand your doom and gloom outlook on pulling rope. But if I shared the fear, I'd use rigid 90's, as allowed by the NEC, to reduce this friction.

 

[wyliesdiesels]

Same way you know that they didn't when you used mule tape.

The standard practice here for underground residential services is to use type USE "triplex" or "urd" (both local slangs). Which is direct burial rated, and also sunlight rated. So if, in fact, a 90 "got burned", it really doesn't matter. (unless, of course, the cable/ conductors were also damaged. I don't go so far as to megger each pull.

I really don't understand your doom and gloom outlook on pulling rope. But if I shared the fear, I'd use rigid 90's, as allowed by the NEC, to reduce this friction.

Maybe because ive seen them burned through

 

[JohnX14]

Maybe because ive seen them burned through

Fair enough. But I think we can agree that there are a lot more factors in the pull than just whether one is using a rope? I wasn't saying that it can't and won't happen, or that mule tape isn't better. The rope just works well for me and what I have available for a puller.

 

[sky jumper]

so rather than pull the 125ft of cable through the buried conduit I was thinking of setting the cable in the trench and then sliding the conduit sections over it one by one and gluing them as I go.

is there any reason this wouldn't work?? seems like it would be much easier than trying to pull 125ft of 1-1-1-6 through a 2" pipe.

I do have one wide 90deg turn I need to make. maybe a 5ft radius or as wide as I need it to be. figured I could just bend the conduit and shove it in the trench.

 

[mike93lx]

so rather than pull the 125ft of cable through the buried conduit I was thinking of setting the cable in the trench and then sliding the conduit sections over it one by one and gluing them as I go.

is there any reason this wouldn't work?? seems like it would be much easier than trying to pull 125ft of 1-1-1-6 through a 2" pipe.

I do have one wide 90deg turn I need to make. maybe a 5ft radius or as wide as I need it to be. figured I could just bend the conduit and shove it in the trench.

Nope. Conduit then wire. Believe code requires it

 

[alfredeneuman]

Yes Code requires it
300.18 Raceway Installations.
(A) Complete Runs. Raceways, other than busways or exposed raceways having hinged or removable covers, shall be installed complete between outlet, junction, or splicing points prior to the installation of conductors.

 

[wyliesdiesels]

so rather than pull the 125ft of cable through the buried conduit I was thinking of setting the cable in the trench and then sliding the conduit sections over it one by one and gluing them as I go.

is there any reason this wouldn't work?? seems like it would be much easier than trying to pull 125ft of 1-1-1-6 through a 2" pipe.

I do have one wide 90deg turn I need to make. maybe a 5ft radius or as wide as I need it to be. figured I could just bend the conduit and shove it in the trench.

in addition to the code violation mentioned above, the glue could stick to the cable and either mess up the insulation or make it hard to pull back out if it ever needed to be replaced