Electrician and Electrical Inspector stumpedp

[jives]

In a nutshell. . .
--Got permit to wire the detached garage $25.
--Dug trench 62' from house to garage. Used a mini-excavator for free ($25 diesel) as my neighbor rented one and let me use it.
--Laid 2" conduit from house to INSIDE the garage. Had previously put in conduit during the concrete pour.
--Paid for 1 hr. of electrician's time for advice and code compliance. Said I needed #2 URD quad (2-2-2-4) from house to garage.
--GJ gurus and NEC say no URD in the building. Unless dual rated.
--GJ says run MHF cable, can run in conduit in the building.
--Other discussion board say that URD quad is the same as MHF cable, so run it.
--Some discussion that 90A is the most for MHF. But my panel is 100A and I want it all.
--Inspector here to measure trench depth. Had to look up the kind of cable to run to the garage (REALLY??). Says URD must be dual rated as RHW or other. He was unsure at best, even saying to run the URD, but then decided to look up the NEC book.

This really cannot be that hard.

4 wire aluminum from INSIDE the house to INSIDE the garage, 75 total feet of wire, 200A house panel, 100A garage subpanel. In conduit, 24" under the gravel driveway.

What's my wire?

 

[larry_g]

I ran into the same dilemma and finally hired an electrician to pull the wire and terminate it. His permit, his inspection. All went smooth for a couple hundred over the cost of materials. RHW sounds about like what he used, but don't take that as advise.

Part of your problem is getting advise from all over the country where common practices are different, and interpretation of the rules differ.

lg
no neat sig line

 

[pattenp]

Bottom line is if using #2 Al it's 90 amps max, and if wire runs inside of structure it has to have flame retardant insulation. URD only has a USE rating and has to be terminated outside the structure because is does not have flame retardant insulation. Wire that has flame retardant insulation is rated as RHW-2 or XHHW-2 or THWN-2. To have 100 amps you need #1 Al.

URD is "Underground Residential Distribution" and MHF is "Mobile Home Feeder" and are totally two different cable assemblies. You need to see what the insulation rating is to determine their suitable use. To say URD Quad is the same as MHF is just wrong.

 

[rlitman]

Bottom line is if using #2 Al it's 90 amps max, and if wire runs inside of structure it has to have flame retardant insulation. URD only has a USE rating and has to be terminated outside the structure because is does not have flame retardant insulation. Wire that has flame retardant insulation is rated as RHW-2 or XHHW-2 or TWHN-2. To have 100 amps you need #1 Al.

But URD may have a dual rating. Lots of wire carries multiple ratings.
If it is "URD RHW-2" for example, then you're GTG.

As for #1 Al, I don't think that will pull in a 2" pipe.

 

[Stuff]

A complicating factor is that you are using direct burial cable in conduit. Most do one or the other, not both.

How about 4 individual wires of THWN? Since this is not carrying the entire service for your residence you use a different table - 3 gauge copper or 1 gauge aluminum for hots with 8 cu/ 6al for grounding conductor.

 

[pattenp]

But URD may have a dual rating. Lots of wire carries multiple ratings.
If it is "URD RHW-2" for example, then you're GTG.

As for #1 Al, I don't think that will pull in a 2" pipe.

If you find URD that has dual rating then more power to you. All the true URD I've dealt with is USE-2 only. You'll see the term URD Quadruplex used on internet sales sites for wire that has RHW-2 rating but in fact it's Mobile Home Feeder. Typically true URD is only USE-2 rated and you need to check the insulation rating to make sure you are getting the correct wire for the intended use. If the #2 Al QUAD URD has a code name of "****" then it's outside only.

#1 will pull in 2" PVC and is within NEC fill limit.

 

[rlitman]

If you find URD that has dual rating then more power to you. All the true URD I've dealt with is USE-2 only. You'll see the term URD Quadruplex used on internet sales sites for wire that has RHW-2 rating but in fact it's Mobile Home Feeder. Typically true URD is only USE-2 rated and you need to check the insulation rating to make sure you are getting the correct wire for the intended use. If the #2 Al QUAD URD has a code name of "****" then it's outside only.

#1 will pull in 2" PVC and is within NEC fill limit.

Completely agreed. Honestly, I'd be VERY wary buying wire over the internet without knowing EXACTLY what is printed on it. A simple description won't do when such a subtle difference in the printing can be a make or break difference at inspection time.

 

[pattenp]

A complicating factor is that you are using direct burial cable in conduit. Most do one or the other, not both.

How about 4 individual wires of THWN? Since this is not carrying the entire service for your residence you use a different table - 3 gauge copper or 1 gauge aluminum for hots with 8 cu/ 6al for grounding conductor.

How is that a complicating factor? Putting direct bury cable in conduit is done quite often. Actually Dominion Power here is now installing residential services using direct bury cable that comes installed in conduit.

 

[Stuff]

How is that a complicating factor?

Everything is a complicating factor when you have an inspector who sees something new for them.

 

[Aceman]

Just to give some background on my answers, I'm an electrician.

Said I needed #2 URD quad (2-2-2-4) from house to garage.

No, true URD, not the dual rated stuff is NOT what you want.

--GJ gurus and NEC say no URD in the building. Unless dual rated.

Correct.

--GJ says run MHF cable, can run in conduit in the building.

Correct.

--Other discussion board say that URD quad is the same as MHF cable, so run it.

It is not the same, do a simple search on Southwires website for URD and MHF. Now ask yourself, why would a wire manufacturer go to the trouble of making the same product by two different names? They wouldn't, because they are ACTUALLY different.

--Some discussion that 90A is the most for MHF. But my panel is 100A and I want it all.

Then buy bigger wire, #2 is 90 amp. #1 would get you 100 amp.

--Inspector here to measure trench depth. Had to look up the kind of cable to run to the garage (REALLY??). Says URD must be dual rated as RHW or other. He was unsure at best, even saying to run the URD, but then decided to look up the NEC book.

This really cannot be that hard.

4 wire aluminum from INSIDE the house to INSIDE the garage, 75 total feet of wire, 200A house panel, 100A garage subpanel. In conduit, 24" under the gravel driveway.

What's my wire?

Your electrician, inspector, and other message board are out of their depth. I do this for a living and myself and a bunch of others on here have fielded this EXACT question for YEARS on here. This is not a new development and there is NO question about what is required.

 

[Speedy Petey]

Some areas will allow #2AL on a 100A breaker. Around here it's SOP, but I usually use a 90A just in case.
This is one of the stupidest parts of the code IMO. #2AL is good for an entire dwelling main panel, but it's not enough for a 100A sub-panel off an existing dwelling main service? Hogwash!

I realize your panel is rated for 100A and "you want it all", but do you honestly think that 10A will EVER make a difference? I can all but guaranty you it will not. Not in a residential shop with one or even two people working.

 

[jives]

Your electrician, inspector, and other message board are out of their depth. I do this for a living and myself and a bunch of others on here have fielded this EXACT question for YEARS on here. This is not a new development and there is NO question about what is required.

THAT is what I want to hear, and confirms my own reading of the NEC (albeit I'm a hack). . .I find it troubling that my guys, to whom I paid money, had different responses. Troubling.

And 90A it will be. Wow the cost difference to upgrade to 100A.

 

[DTE]

I ran 1/0 aluminum , I would have to look and see what the ground was. But that is what the inspector said to run for the full 100 amp service. I pulled 4 indidvidual wires through 2 inch conduit.

 

[pattenp]

I ran 1/0 aluminum , I would have to look and see what the ground was. But that is what the inspector said to run for the full 100 amp service. I pulled 4 indidvidual wires through 2 inch conduit.

Are you sure he didn't say #1 Al? 1/0 Al is good up to 120 amps. #1 Al is 100 amps.

 

[Falcon67]

And 90A it will be. Wow the cost difference to upgrade to 100A.

This. I used MHF on my run, fused at 70A at the panel off the meter because that's the biggest breaker HD had on the shelf and I didn't want to special order anything. No trips, plenty good. My 100A 20 slot shop box, the breaker for the box off the meter and the wire all came in under $250 retail.

 

[laser3kw]

Some discussion that 90A is the most for MHF. But my panel is 100A and I want it all

use the 100 amp panel in the garage and supply it with a 90 amp breaker at the house.
I doubt that you will ever approach 90 amp continual draw, the extra 10 amp will not get you much more.
I have 60 amp breaker feeding my garage from 75 feet away. I power (40) 4foot t8 tubes, (10)120v 20 amp receptacles, 50 amp welder receptacle, 2 lines of 240, 30 amp for a lathe and a mill. Never come close to even dimming the lights - even when the shop is full lit and the air compressor kicks on while running a piece of equipment.. The thing is, I never use the welder and the mill or lathe at the same time.

 

[theoldwizard1]

--Some discussion that 90A is the most for MHF. But my panel is 100A and I want it all.

You are wasting a lot of time an effort for that last 10A !


IANALE, and IIRC, the issue is aluminum wire used in a "branch" circuit. Yes, because you are connecting off of another load center, it is considered a branch circuit.

 

[theoldwizard1]

use the 100 amp panel in the garage and supply it with a 90 amp breaker at the house.

Yep. Simple. Done.

 

[DTE]

Are you sure he didn't say #1 Al? 1/0 Al is good up to 120 amps. #1 Al is 100 amps.

I when back and looked at my posts and I was all set to use the #1 al. Then I stopped by the inspection dept. and they said I needed 1/0 so for me the easiest thing to do was get what they wanted to see. Because it is out of my skill set.

 

[wyliesdiesels]

I when back and looked at my posts and I was all set to use the #1 al. Then I stopped by the inspection dept. and they said I needed 1/0 so for me the easiest thing to do was get what they wanted to see. Because it is out of my skill set.

How long of a run was it?

Distance plays a factor in wire size...

 

[mburrus]

you have a 2" pipe in the ground... just pull individual #2 coppers... i dont see what the big deal is? we never use cable assemblies like that down here anyway. i am planning to pull #1 copper to my garage, around 60' per leg, for 125A. i know aluminum is OK in larger sizes, but i have worked in the utility industry long enough to see exactly what happens to aluminum cable when there are dissimilar metal or moisture intrusion issues... its not for me.

my take on direct burial cable in pipe: direct burial cable MAY rely on the soil being in contact with the cable, conducting heat away from the cable assembly. you dont get that effect in pipe.

 

[DTE]

How long of a run was it?

Distance plays a factor in wire size...

130 feet

 

[jives]

You are wasting a lot of time an effort for that last 10A !


IANALE, and IIRC, the issue is aluminum wire used in a "branch" circuit. Yes, because you are connecting off of another load center, it is considered a branch circuit.

To finish up the story, I picked up 80' of 2-2-2-4 MHF wire from the local electric supply house. The counter guy was positive that the wire could run a 100A circuit. But, as mentioned above, it can under some circumstances, and not under others. I'm not smart enough to know the difference.

At any rate, the wire is in the conduit, trench backfilled using my trusty Wheel Horse with a plow, and now time to move to the indoor wiring.

 

[pattenp]

I know too that #2 MHF can handle 100A, but being used as a branch feeder the NEC says not to use over current protection greater than 90 amps. If following the NEC requirements are of no concern then by all means put a 100A feeding breaker on it.

 

[-Brent-]

You are wasting a lot of time an effort for that last 10A !

I now realize how effing true this is - absolutely. I purchased 1/0 and a #2 ground just to have the 100A and there's so much confliction, confusion and debate that I should have just run the MHF.

 

[wyliesdiesels]

130 feet

Well sadly, your inspector cost u a bit more money than u needed to spend.

#1 AL wouldve easily handled 100a at that distance.

 

[wyliesdiesels]

I now realize how effing true this is - absolutely. I purchased 1/0 and a #2 ground just to have the 100A and there's so much confliction, confusion and debate that I should have just run the MHF.

How long of a run was it?

 

[-Brent-]

How long of a run was it?

55 feet from panel to panel.

 

[theoldwizard1]

In a nutshell. . .
.
.
.
--GJ says run MHF cable, can run in conduit in the building.
.
.
.
--Inspector here to measure trench depth. Had to look up the kind of cable to run to the garage (REALLY??). Says URD must be dual rated as RHW or other.

From Southwire

Southwire mobile home feeder (MHF) consists of four quadruplexed type RHH or RHW-2 or USE-2 AlumaFlex AA-8000 series aluminum alloy compacted conductors. The cable contains 2 triple extruded phase conductors, a white striped neutral conductor and a green grounding conductor to eliminate the need for field marking per the National Electrical Code.

 

[Speedy Petey]

I know too that #2 MHF can handle 100A, but being used as a branch feeder the NEC says not to use over current protection greater than 90 amps. If following the NEC requirements are of no concern then by all means put a 100A feeding breaker on it.

This is quite an over-dramatic statement.

If using #2AL for a 100A service to a complete home is safe, what is unsafe about using it to a small residential out-building?

I am for blindly following the code, but when it is blatantly contradictory, with no good explanation as to why, even I question it.

 

[pattenp]

This is quite an over-dramatic statement.

If using #2AL for a 100A service to a complete home is safe, what is unsafe about using it to a small residential out-building?

I am for blindly following the code, but when it is blatantly contradictory, with no good explanation as to why, even I question it.

Gee Speedy..you are putting words in my statement that I did not say. I said I know #2 Al can handle 100A and in no way said it was not safe to use it for a 100A. I'm just saying if he doesn't want to follow NEC to the letter then so be it. I was not waving my hands around and yelling when making my comment, so there was no dramatizing going on.

Oh, and I agree with you that the amperage use difference makes no sense.

 

[DTE]

Well sadly, your inspector cost u a bit more money than u needed to spend.

#1 AL wouldve easily handled 100a at that distance.

I can believe that, but when you are the homeowner acting as the GC they tend to treat you different . At least that has been my experience.

 

[wyliesdiesels]

55 feet from panel to panel.

Well u got poor advice as well that wasted your money.

#1 al would have EASILY handled 100a @ 55'...

Geez lot of crappy building inspectors out there dont even know theyre wire gauges and voltage drop distances...

 

[-Brent-]

Well u got poor advice as well that wasted your money.

#1 al would have EASILY handled 100a @ 55'...

Geez lot of crappy building inspectors out there dont even know theyre wire gauges and voltage drop distances...

Actually, I priced the two out. The 1/0-1/0-1/0 and #2 ended up being $8 less at the electrical supply house than buying the MHF from HD.

Anyway, that was info I got here (from reputable members) and from my electrician. It's going to work, no doubt. Other than that, what can I say? I have learned a lot in the last couple months about electrical but all that info has come after a bunch of dumb questions and reading and asking some more. Ha ha ha.

 

[sberry]

I like the idea of 2 being good for 90. It never seemed right for 100 but the people build it are above my pay grade.

 

[sberry]

This is quite an over-dramatic statement.

If using #2AL for a 100A service to a complete home is safe, what is unsafe about using it to a small residential out-building?

I am for blindly following the code, but when it is blatantly contradictory, with no good explanation as to why, even I question it.

Someone splained it to me but I forget the reasoning behind it. They don't do much just for giggles.