Long Service Pull for Garage

[bfr57]

Just finished getting my 2700 sq' garage up and need to get power to it. Our property is long and narrow with 400 amps pulled to meter; 200a is already pulled for house and there is another 200 amp box that I want to use for the garage. However, it's about 375' from box to garage. I've looked at numerous calculators on the web and get anything from 350 to 600 mcm wire size requirements (aluminum). While I'll probably never use the entire 200 amps, I do have a few power hogs like my homemade powder coating oven that uses about 13K watts, welder, compressor, and someday an HVAC system. We also plan on putting in a one bedroom guest suite with a small kitchen and appliances. So, like I mentioned, I would like to have the 200a available. So, here are my questions:
1. What calculator out there is accurate to get proper wire size?
2. Is 4" conduit OK? I can pick some 20' lengths up really cheap locally.
3. Anybody used online companies to order that amount of wire? Who?
4. Best way to pull that long of a run through conduit? I was thinking of laying out the wire next to trench and running the conduit over the wire and glueing as I go?
5. I forget, does the neutral wire need to be the same size as the powers?
6. I did have a ufer installed, so I don't need to run a ground.

Thanks for the help!

 

[pattenp]

Need some clarification on your setup. Is the feed to the garage going to be coming from a disconnect at the meterbox or from lugs at the meterbase. In other words is the feed going to be a 3 wire or 4 wire? Wire size I'm thinking #500 Al with neutral the same. 4" conduit is fine.

Edit: I didn't catch your comment about not needing a ground. If you are referring to the equipment ground you will need a 4 wire feed that includes an equipment ground conductor if the feed is coming off a disconnect back at the meter.

 

[bfr57]

If main box is earth grounded with a rod and the garage panel is ufer'd, why would I need to run a ground connecting the two?

 

[pattenp]

The ground wire running from the garage panel back to the main panel is an equipment grounding conductor and does not serve the same purpose as the earth electrode ground conductor. Quite honestly I can't explain technically why it's needed without writing a book. It's a NEC requirement if the feeder disconnect is back at the house. See NEC 250.32

Edit: I assume you are in the US.

 

[2ManyProjects]

Just finished getting my 2700 sq' garage up and need to get power to it. Our property is long and narrow with 400 amps pulled to meter; 200a is already pulled for house and there is another 200 amp box that I want to use for the garage. However, it's about 375' from box to garage. I've looked at numerous calculators on the web and get anything from 350 to 600 mcm wire size requirements (aluminum).

That is very likely because there is no such thing as a single "one size fits all" answer to your question -- which is REALLY at least two questions: What is needed to merely meet code requirements for "ampacity" will be entirely different from what will be needed to hold voltage drop over the run length to acceptable levels; and even what constitutes "acceptable levels" can vary from job to job, depending on several other things (most notably including the person making the judgment call).

1. What calculator out there is accurate to get proper wire size?

Every online calculator I've ever seen has (perhaps necessarily) taken at least some "shortcuts" in the name of "ease of use". How significant these shortcuts will be in any given situation is anybody's guess; but if you want to do it REALLY right, brush off your High School math skills, and figure it out for yourself:

http://www.dolphins-software.com/IEEE_ExactFormulae.htm

4. Best way to pull that long of a run through conduit? I was thinking of laying out the wire next to trench and running the conduit over the wire and glueing as I go?

That technique is generally frowned upon; and I believe that in at least some cases, it is forbidden by code. The most commonly cited potential problem is that the glue you use to assemble the conduit can attack the jacket/insulation of the wire if it comes in contact before curing is complete. Also, this technique will near-certainly lead to the cable being "anchored" to the conduit in various places, thus preventing yo from being able to pull it out and replace it later, if need be.

What you CAN do is, lay out a pull rope instead of the cable itself, and use your "install as you go" technique with that. As long a you are careful to NOT glue the rope to the inside of the conduit, you can then use that rope to pull the cable once the conduit is fully assembled.

 

[pattenp]

I over looked your #4 question. NEC does require the conduit to be completed as a unit prior to pulling in the wire. Being 4" conduit this may or may not work, but if you have a strong enough shop vacuum you can **** a piece of cloth tied to a string through the conduit to use for pulling through a pull rope.

 

[kbs2244]

I have used the rope while laying trick when the inspector didn't like the wire while laying idea.
When I do pull the wire I pull another length of rope with it.
Just in case you need to pull something later.

 

[bfr57]

I have used the rope while laying trick when the inspector didn't like the wire while laying idea.
When I do pull the wire I pull another length of rope with it.
Just in case you need to pull something later.

Great idea!!

Another question on figuring voltage drop values: Is the voltage 220 for the total voltage or is it 110 for what each wire carries?

 

[pattenp]

Calculate the drop based on the total voltage of the feed using the total anticipated load. So if it's 240V then use 240V.

Great idea!!

Another question on figuring voltage drop values: Is the voltage 220 for the total voltage or is it 110 for what each wire carries?

 

[Aceman]

My first step would be to call the power company and see what the price would be for them to set a transformer next to your new shop.

 

[wyliesdiesels]

The ground wire running from the garage panel back to the main panel is an equipment grounding conductor and does not serve the same purpose as the earth electrode ground conductor. Quite honestly I can't explain technically why it's needed without writing a book. It's a NEC requirement if the feeder disconnect is back at the house. See NEC 250.32

Edit: I assume you are in the US.

One reason is, and u already know this, to provide a fault current path so the feed breaker can trip. If theres no main disconnect and the feed comes off of lugs then theres obviously no breaker to trip!

My first step would be to call the power company and see what the price would be for them to set a transformer next to your new shop.

^+1. 375' of 3 ~500mcm wires will be a real fun PITA!