Replies

1. Expert Member
   BILL WICHERS | Mar 02, 2023 09:00am | #1

   Don't go by those "upsize x%" tables, calculate by working out voltage drop on the run, which is how the code says you're supposed to do it anyway. Note that the volt drop allowance is a recommendation in the code, not an absolute requirement, so while it's a good idea to do, you aren't required to upside the wire beyond the ampacity table requirements.

   Use aluminum cable here, it will save you a good amount of money over copper. 4/0 over a 200 foot run would be 3.57% volt drop, 250MCM would be 3.13%, and 300MCM would be 2.73%. The recommendation in the code book is to not exceed 3% volt drop on the feeder, so the 300MCM cable would be the best choice here.

   I would check that the lugs on your equipment can handle a 300MCM cable though -- many only go up to 250MCM. Ideally, you'd use compression lugs (crimp style) and not mechanical lugs (the ones with the set screws), since compression lugs are much more reliable over time, especially if you use the ones that are preloaded with no-ox paste for aluminum conductors.

   BTW, regular aluminum electrical cable is not copper clad, and doesn't need to be. Pretty much all larger lugs are dual rated "AL/CU", which means they can be used with copper or aluminum conductors without problems. It is a good idea to use no-ox paste on the aluminum conductors (and be sure to work it in between the strands, don't just coat the exterior of the wire) for a long-term reliable connection.

   One last thing: I would recommend using aluminum conductors of type XHHW, and I'd run them inside PVC conduit and not direct bury them. XHHW is tought stuff, and readily available through commercial supply houses. Running inside conduit will make the system more long term reliable, and help to avoid the need to dig things up if anything ever needs to be replaced.

   Bill

1. 
   fromPok | Mar 02, 2023 05:33pm | #3

   Bill - Thank you.

1. 
   drewintoledo | Mar 02, 2023 09:22pm | #6

   Do you have experience working with thick wire? Similar to your specs, I ran about 180' of 300 aluminum from the road to my transformer. Then again from my transformer to my to my disconnect. I did the work myself and since I don't deal with this on a regular basis I was surprised at how stiff the wire is--it's like trying to bend a baseball bat. You might want to visit a supply house to familiarize yourself with it if you're doing it solo. I saved a ton using Al over Cu as Bill references price delta. But, when it was time to run from my disconnect to my house I opted for copper which was much easier for a guy like me to work with albeit was a much shorter distance. For me, this shorter run was worth the conveince price of Cu. Of course, a licensed electrician would shake his head at me for spending more.

1. Expert Member
   BILL WICHERS | Mar 03, 2023 05:32pm | #8

   I have aluminum from the pole to the meter (all underground), then I used copper from the meter to my ATS (for the generator), and copper from the ATS to the main panel. I used copper since it's physically smaller for the same ampacity, making it a bit easier to work with in the tight bending spaces in the ATS and breaker box enclosures. On the relatively short runs in this part of the system, the cost premium is more manageable. So there you go -- your friendly GBA electrical engineer used copper in the same place you did, and for the same reasons :-)

   Note that for very large wire, you typically pull it into conduit using what is known as a "chugger", which is a sort of power assist device for pulling the rope that pulls the wire. There are also big outdoor cable pullers used by utility crews that look a bit like inverted cement mixers. You can pull by hand, but use a fat rope and a crew of people to make easier work of it. For bending, I have sometimes used conduit benders to help bend the wire, especially large stuff as I've worked with up to 750MCM before (which is not fun). Another trick with large wire is to make the bend around a mandrel (the hub of a wheelbarrow wheel will work), and make the bend BEFORE cutting so that you can use the extra wire like a handle for more leverage. You waste a little wire this way, but it does make the work of making tight bends easier.

   Bill

2. Expert Member
   Akos | Mar 02, 2023 09:24am | #2

   If you look at the overhead feed to your place, it will be well under even 250MCM. Installing a larger feed does reduce the drop in your section but you still have the drop in the overhead wires. If that section to the transformer is long the overall drop to your house is barely effected by the size of your local service feed.

   Since no house will ever run near the 200A rating, going much above code doesn't buy you much here.

1. 
   fromPok | Mar 02, 2023 05:34pm | #4

   Thank you.

2. 
   maine_tyler | Mar 02, 2023 06:31pm | #5

   Wait, what does from street to house mean? I assumed we were talking about the service drop (overhead)?

1. 
   fromPok | Mar 03, 2023 10:07am | #7

   From the transformer on the street to the house. Underground cable

3. Expert Member
   BILL WICHERS | Mar 03, 2023 05:38pm | #9

   Aerial cable can be sized based on the "conductors in free air" ampacity chart. Cables underground have to be sized from the "conductors in conduit or cable" ampacity chart. In free air, due to much better cooling, you are permitted to use smaller gauge wire for the same ampacity, but you do get more volt drop. The aerial cable is usually sized by, and provided by, the utility company though. They will usually install 1/0 or 2/0 aluminum wire for a 200A service when using triplex (the twisty style aerial cable).

   For underground runs, I would recommend sizing for volt drop. The utilities will usually size for around 5%, but for a 200A service, you'd usually see 4/0 cable used.

   Note that if this were my own home, I would just use 4/0 aluminum cable on this run, be OK with the 3.57% volt drop at full 200A load that I'd likely never actually see, and save the money it would have cost for the heavier cable. I'd still run everything in PVC conduit though. If you want to price out the larger sizes, any commerical electrical supply house should have 4/0 and 250MCM in XHHW (which is usually aluminum wire, but ask for aluminum XHHW to be sure). 300MCM is a bit of an oddball size, so if they don't have that, the next size up is 350MCM. That's a good bit heavier than 4/0 though, and you'll want to make sure the lugs at the terminations can handle it before planning to use such large cable here.

   Bill