work shed wiring
- Thread starter olegert
- Start date
nwav8tor
Well-known member
How far is it from the house's main panel to the shed?
What do you mean by plastic encased wire? Are you using PVC conduit or direct bury wire?
AL or CU wire?
Paul
What do you mean by plastic encased wire? Are you using PVC conduit or direct bury wire?
AL or CU wire?
Paul
lakee911
Well-known member
The NEC has a table that shows the requirements for cover. I don't have my book handy for the reference, but plastic (e.g, nonmetalic, PVC) conduit has a cover requirement of 18" from the top of the conduit to the top of grade (that is the dirt, not the grass). If it's under concrete, it could be more shallow. Also metalic conduit can be as shallow as 6".
As a feeder #2 is allowed at 125A for copper or 100A for aluminum. That is before you upsize for voltage drop (if necessary). I'm assuming you're putting in a subpanel here. Your TIG welder should have information supplied with it on the required size of the feeding breaker.
As a feeder #2 is allowed at 125A for copper or 100A for aluminum. That is before you upsize for voltage drop (if necessary). I'm assuming you're putting in a subpanel here. Your TIG welder should have information supplied with it on the required size of the feeding breaker.
pattenp
Well-known member
Those amps ratings are for when the feeder is providing the main power feed to a dwelling. As a feeder to a sub-panel in an outbuilding the #2 Cu is 115A and #2 Al is 90A.
nwav8tor
Well-known member
I'm not doubting you pattenp, but I just don't understand why the #2 CU is OK for 125A to the main panel, but only 115A to a sub-panel. Can you (or anybody else) explain why?
Thanks,
Paul
wyliesdiesels
Well-known member
LoL. We've debated this one before on here @ least once. No one could come up with a technical reason other than that's what the NEC requires....
wyliesdiesels
Well-known member
Yeah. That references the NEC articles but still doesn't explain in a technical way, why the same piece of wire has 2 different ampacities depending on how its used!
nwav8tor
Well-known member
Being ex-USAF I can live with the "that's just the way it is" explaination. I don't understand it, but like the military, the NEC sometimes just doesn't make sense. Anyway, I know it's not worth beating my head against the wall trying to figure it all out.
Paul
Paul
Aceman
Well-known member
#2 Cu is rated 115 amps. Period.
The NEC has a table allowing #2 to be used for 125 amp dwelling panels. That's not saying #2 is rated 125 amps, just that it can feed a 125 amp panel. They know a home has a lot of load diversity, not everything will be on at once, etc etc. That wire will never be pushed past 115 amps anyhow.
Now what I just said only applies to a home.
Now you want to do a shed panel with #2 Cu. That copper as you know is still rated 115 amps. Since the code doesn't want to speculate on the load diversity of every other type of electrical installation(other than homes) they require you to use either a breaker less than 115 amps OR if you want the full capacity of that 115 amp wire you can go the next breaker size up, 125 amp. As long as the load doesn't exceed 115 amps, you can do that.
Maybe this will make it a little more clear?
pattenp
Well-known member
I'm going to play semantics on this, but the NEC table 310.15(B)(7) is saying the feeder is rated at certain amperes for the particular use as a main power feed.
lakee911
Well-known member
What it comes down to is what the AHJ will accept. Around here, I can use that table to feed a sub panel in the garage and I have gotten written confirmation, did just that, and it has passed inspection. So, that being said I would certainly check with your AHJ.
When I do my own work or design for residential or commercial stuff I generally do design to the NEC because cost is generally of concern. If there is any doubt and clarification is unavailable it's best to upsize. I wouldn't even think of using that table for my industrial work (not sure I can anways).