feed to garage - conduit size and depth?

[Innovate1]

Since 2/2/2/4 AL MHF is the cheapest way to run to the shop I am planning for that. Had planned a 60A panel which should be plenty but will go with a 100A main breaker in subpanel and an 90A feed. An electrician I talked to said it was good for 100A but I have seen some mentions of 90A limit. Insulation is rated as USE and 90C temp.

He also suggested 1-1/4" conduit which seems tight. I ran a calculator and came up with about 45% fill which is over the max of 40% unless I did something wrong - entirely possible. It's about a 50' run so the jump to 1-1/2 is only about $5 more in materials - maybe $10 by the time I get the bends and end fittings.

Had planned a parallel run for low voltage stuff (separated at least 12". Not sure what all I will be running. Probably phone, network, alarm, maybe TV. Thinking 1-1/4 should be plenty for that. And a spare run of 1" for who knows what. May run some switches for outside lights through that.


Thinking about PVC expansion/contraction I found some recommendations (requirement?) to go below the frost line. Footing depth minimum here is 30" which is the max frost dept or slightly more. How do I get the conduit that low with the footings in the way? I plan to have the conduit come up within the foundation wall but intended it to exit the wall below ground above the footing which is 8" thick/22" below ground. I could have it come out a few inches above the footing and then just taper down to 30" or come out with a 45 and then a 45 at the bottom. What's the best way to do this?

 

[Toomanytools?]

Thinking about PVC expansion/contraction I found some recommendations (requirement?) to go below the frost line. Footing depth minimum here is 30" which is the max frost dept or slightly more. How do I get the conduit that low with the footings in the way? I plan to have the conduit come up within the foundation wall but intended it to exit the wall below ground above the footing which is 8" thick/22" below ground. I could have it come out a few inches above the footing and then just taper down to 30" or come out with a 45 and then a 45 at the bottom. What's the best way to do this?

I ran about 90 feet 4 wire copper in 2" with two 90 degree sweeps and a couple slights bends along the way. One guy pulling rope, one guy pushing and a third guy me holding wire up making it feed easier. It was a workout, I would at least go 2".
One inch is fine for CAT5/6 line or cable, think I would just make them both 1".
I don't follow the footer stuff you have above. My state electrical in conduit is 24" deep I ran a 90 sweep up into the concrete where the 6" wall was. Code was that it had to go as straight down as possible then to 24", meaning it has to be buried 24" at the point it enters building. If 45's work then ok use them, but the less bends the better. Though at 50' run you won't be too bad. Code also only allows a certain amount of turns.

 

[mike93lx]

I'd run 2". 90a is the limit if it isn't feeding a dwelling. Either way, it won't matter, you'll be fine with 90a unless you have some unique demands or plan to have multiple people working at once.

 

[sberry]

2 will go thru a 1 1/4 straight, with turns its too tight. It's why they make 1 1/2 but 2 is easier if box ko's are not an issue. I don't grease the shot out of it but sometimes take a rag and douse it some and maybe give it a squirt ahead of it.
It goes ok with a push and pull, harder to pull out then in.

 

[Innovate1]

My understanding is that NEC code is 18" minimum depth for PVC conduit. I would be above that slightly where it comes out of the foundation if I did two 45 bends. I need to talk to the code people. I suppose I could put 2" of concrete above it for the short distance before it gets deep enough.

Where is the 90A limit documented? I looked on line and found 100A but it didn't qualify it as to location.

 

[jeepxj]

I'd run 2". 90a is the limit if it isn't feeding a dwelling. Either way, it won't matter, you'll be fine with 90a unless you have some unique demands or plan to have multiple people working at once.

why is there a 90a limit unless its a dwelling feed? whats the logic?

 

[Farmallboy15]

I agree 2" conduit. 18-24" deep. If you already have footers poured you will probably have to come into the rear of the subpanel from the outside of the building vs digging under the footer.

 

[alfredeneuman]

why is there a 90a limit unless its a dwelling feed? whats the logic?

Because of diversity of the loads. It's a tried and true method.
Dwellings are not likely to run everything at once.

 

[pattenp]

The 90A for #2 Al is listed in the tables in 310.15 @75 deg C. The feed to the sub-panel is considered a branch feeder, not a service.

 

[Innovate1]

And if the insulation (and connecting terminals) are rated for 90C the number is 100A. Either is plenty for my use but I am still curious where the distinction between branch feeder and service is noted. I haven't been able to find it.

 

[pbon]

Few complain the conduit is too big so it’s too easy to pull wire.

 

[Bert_]

And if the insulation (and connecting terminals) are rated for 90C the number is 100A. Either is plenty for my use but I am still curious where the distinction between branch feeder and service is noted. I haven't been able to find it.

There are no mechanical lugs rated 90*C, they just don't exist so you can't use that number except for derating.

The only time #2 AL is good for 100A load is for a residential service. It's in article 310, just before the conductor ampacity table. I'll look it up when I am by my code book.

 

[mm08822]

And if the insulation (and connecting terminals) are rated for 90C the number is 100A. Either is plenty for my use but I am still curious where the distinction between branch feeder and service is noted. I haven't been able to find it.

NEC 310.15(B)(7)(1) thru (4) is where you will find the details for a single, two or multi-family dwelling service conductors to have an ampacity rated at least 83% of the rating of the service.

Examples
The ampacity of #2 AL @75C is 90A. For a 100 Amp service rating - 83% of that rating is 83A. 90A is greater than 83A.

The ampacity of 4/0 AL @75C is 180A. For a 200 Amp service rating - 83% of that rating is 166A. 180A is greater than 166A.

Your garage is not a dwelling and therefor this article does not apply to that feeder. (This is what your electrician was incorrectly thinking of.)

 

[jeepxj]

Because of diversity of the loads. It's a tried and true method.
Dwellings are not likely to run everything at once.

does the 10a really matter that much here on 2/2/2/4?

 

[Innovate1]

Few complain the conduit is too big so it’s too easy to pull wire.

Couldn't agree more! Or a garage that is too big.

Thanks for the explanations.

As for if it matters... Yes, it needs to be to code. No, I think for most people the use of a 90A breaker instead of 100A isn't going to be an issue.

My general rule for hiring contractors is they should know more than me about their trade. I know a fair amount about most construction stuff but don't claim to know it all (not even close), don't do it on a regular basis and it's not my line of work. Unfortunately I have met some in various trades that completely fail that rule. That isn't always realized until after they are on the job.

 

[Innovate1]

Still wondering about depth of the run between buildings and PVC thermal expansion/contraction. Seems good to put it below frost line which is the bottom of footings. Bottom of footings is 30" minimum here.

I could just direct bury but conduit isn't that much for a 50' run. Besides I want a run for low voltage that allows me to pull in other things later. While the depth isn't as much an issue for that from a code standpoint I don't want it cracking.

I want to bring the conduit up in the wall to avoid an exterior conduit. I suppose I could bring in up inside but I would still have to get around the footing.

I could use a 90 at the bottom and come out just below the 18" required depth and then just taper to lower over the next 10' or so. Or I could 45 out of the foundation higher and then 45 at 30" deep. Would need to cover a very short part of the 45 with concrete where it is above 18".

Am I overthinking this?

 

[alfredeneuman]

There are no mechanical lugs rated 90*C, they just don't exist

https://www.ideadigitalcontent.com/files/10975/ID-SPE-v1-TA.pdf

 

[Bert_]

https://www.ideadigitalcontent.com/files/10975/ID-SPE-v1-TA.pdf

Ok I worded that poorly. The equipment must also carry the 90* rating (Panel in this case).

 

[Innovate1]

This is getting into more detail than I need or care about but a 90C lug does not automatically mean you can use the 90C rating of the wire. I suppose for a long run you could run a larger wire from the equipment to a junction box and then splice on 90C wire with 90C lugs but I doubt that is worthwhile for most cases. It doesn't appear to be as simple as replacing the lugs in equipment with 90C rated ones.

Here is some detail from an equipment mfg:
https://www.schneider-electric.com/resources/sites/SCHNEIDER_ELECTRIC/content/live/FAQS/286000/FA286185/en_US/Wire%20Terminations%200110DB9901R2-02.pdf

 

[mm08822]

This is getting into more detail than I need or care about but a 90C lug does not automatically mean you can use the 90C rating of the wire. I suppose for a long run you could run a larger wire from the equipment to a junction box and then splice on 90C wire with 90C lugs but I doubt that is worthwhile for most cases. It doesn't appear to be as simple as replacing the lugs in equipment with 90C rated ones.

Here is some detail from an equipment mfg:
https://www.schneider-electric.com/resources/sites/SCHNEIDER_ELECTRIC/content/live/FAQS/286000/FA286185/en_US/Wire%20Terminations%200110DB9901R2-02.pdf

Agreed, no need for you to be concerned with this for your application. Stay on course with #2 AL w/90a cb.

I doubt there is any lower-end equipment available where changing out lugs is possible. Even if possible, then you need be concerned about violating the overall equipment listing.

An excerpt from the Schneider Pdf linked above:
"When terminations are inside equipment such as panelboards, motor control
centers, switchboards, enclosed circuit breakers, safety switches, etc., follow
the temperature rating identified on the equipment labeling instead of the rating
of the lug itself. Manufacturers commonly use 90 °C-rated lugs (i.e., marked
AL9CU) on equipment rated only 60 °C or 75 °C. The use of the 90 °C-rated lug
in this type of equipment does not allow the installer to use 90 °C wire at the
90 °C ampacity"