Electrical Engineer needed

[Greg]

I have a question for an Electrical Engineer

I want to run 100 amp 220V to a detached Garage, it is approx 80 feet between service entrance and fuse box in the Garage…

what size wire do I need;

I prefer Copper

of course aluminum would be cheaper, but I’ll buy Copper wire. and install in gray plastic

last question; it needs to have a ground rod at the garage also ?

I called the Power Company Engineering Dept, they no longer (provide/advise) the needed wire size !

thanks in advance

[daniel lawecki]

Use 1awg wire for the service two hot one neutral use ground rod at garage with # 4 bare for ground. Mark neutral with white phasing tape.

[JonB_in_Glencoe]

I am not an engineer or a lic. electrician...but I've built and wired industrial controls panels for a few decades.

It should be safe for me to tell you, 1 gauge.

But, depending on the type of wire/cable and it's type of insulation it has, you may be able to get by with 2 gauge.

[farmerjim]

copper as above or 1/0 aluminum

[Greg]

thank you for the help

P.S. wood shop tools, and of course casting, so no reason to scrimp on the wire, # 1 it is

again thanks for the help

[Wolfer]

I am a licensed electrician and #3 copper is all you need to run 100 amp 80' away. Two hot wires colored black or black and red with a third wire phase taped white.
You should have a ground rod drove at the garage with #6 AWG bare solid copper going to it.

At the new panel you need to bond the neutral and ground wires. This is usually done with a green screw that comes with your panel. This should be the only place your white wire and your ground wire are connected.

I generally run 1-1/4 conduit in these applications.

[bangerjim]

You do NOT need an electrical engineer!

Listen to the above electrician. That is his job!

[Lloyd Smale]

lineman here and we used to run 1/0 underground with a #2 neutral (aluminum) for a 100 amp service. When the customer did his own we allowed 1/0 aluminum or #2 copper. We required two ground rods with #6 solid copper for grounding. Keep in mind that this is for underground installs. You can get away with smaller wire if its open to the air (overhead) I agree with wolfer. Install it in electrical rated pvc pipe (gray pipe) if it ever goes bad its much easier to replace and is also a lot less likely to ever go bad if its in conduit. Don't scrimp now. Do it right the first time.

[doc1876]

I F you use aluminum, remember to tighten the lugs every year. Heat causes aluminum go get loose.

[Wayne Smith]

You almost certainly have some local codes that specify the minimum required. Check them first.

[popper]

Direct burial cable is EXPENSIVE. Put it in sched 80 pvc, stub above ground level about a foot, seal both ends with good RTV. Copper coated Al is OK, plain alum is poor because of bends - I'd use solid copper. Put a good strong rope in the PVC when you put it together - before burial as a puller. Or put the wire in first before gluing. I used 1/0 on my son's garage. You will need to get a licensed electrician to CONNECT it (think INSPECTION). Go with the larger gauge due to start currents in your machines. Low voltage start is hard on motors.

[Duckiller]

Install the PVC then blow a rag attached to a pull rope, small cheap poly. Blow it through with a compressor , borrow/rent a larger portable construction compressor. For a single install it may be simpler to put the rope in as you install the PVC ,

[Flexy]

Just how much I want to reply, I'll just keep it short. Google some wiki page, you will get the answer, provided the answer is around the same neighbourhood... Allways opt to bigger dia. Savings on that are minimal, compared on the leighbour... atleast around my corner of the world.

[HATCH]

use copper only.
Use direct burial and put in conduit.
No matter how good you are, water will get into the conduit if its underground.
Pull a string in so you can pull something else in later.
I have coax run in with my power and have no issues.
#1 copper is what you want.

[popper]

Don't try pulling 300 or 500 MCM with a rope.

[garym1a2]

Being an EE, for my own need I always double what I need in capability so I can upgrade later to use more current.

You may want to add A/C, Heat, a welder or other items down the road.

[Lloyd Smale]

Aluminum wire is just fine. You just need to use some allox on the conections and tighten it good. Go back in about a year and retighten and it will be fine from then on. If aluminum is such a bad deal do you really think the power companys would use it? One trouble call caused by aluminum use would more then offset the cost of going with copper. Bottom line is its cheaper and works fine. I did my own service in aluminum and its been fine for 25 years now. I did this for a living and think ive got a bit more experience then most.

Easy way to pull rope through is to cut a pices of 2inch foam rubber to a round cylinder that matches the size of the pipe (just a bit smaller) put a hole through it and push a piece of twine through the hole and tie it off on the other side. (you may need to make a plastic washer to keep it from pulling through. Take your shop vac and it doesn't take a big one and tape the suction to the far end and it will easily pull the foam and twine through the pipe. Then use the twine to pull in your rope. One poster did hit this right though. You have to look at your electrical codes for your area. they vary and some are very specific about what kind of enterence panel you must use, how many amp panel it must be and exactly what wire you are required to use. One bit of advice another poster touched on is your needs. I allways tell people to figure out your expected load and then double it. It doesn't cost all that much in the big picture and its a lot cheaper then upgrading everything later.

[TheCelt]

Thought I'd chime in here on the "ground" as you have the wire size pretty much covered. DO NOT SINK A GROUND ROD!!! You will be grounded through the rod at your main panel and if you ground at a separate rod at your detached garage you have created a ground loop. It's laborious to explain why a ground loop is a bad idea but you'd find out during the next electrical storm.

[tomme boy]

Pulled lots of 300 and 500 with rope. And a skid loader to pull!

[popper]

And a skid loader to pull! with a bucket of soap, steel cable with basket, pulling machine that bogged down. Most states will let you do the labor work but it must be connected and inspected by licensed person, keep the inspection report for any insurance claims. Problem with Al is stress cracks and cold flow. Copper clad doesn't show the same problems, nor does copper. KCI terminal buildings were done with Al, the redone with Cu clad which did work (cost + 10%, a good profit). Residential allowed Al in the 70's but builders are using Cu now even with push-in terminals. They do tend to undersize long runs to AC.