Hello DIYers, this is my first thread here, and this seems like a great forum.

I've been doing my homework before I run power to my detached garage and I was hoping to get some advice about a few specifics.

Here are my plans so far:

- Install 1 new 20amp 120v dedicated circuit to the detached garage.

- The new circuit will run from the panel all the way accross the unfinished basement to the backside of house.

- It will leave the basement and go into a 12” deep trench, in an underground schedule 80 PVC conduit from the house to the detached garage. I will run THWN in the conduit.

Inside the garage I will install:

- 1 disconnect where the circuit enters the garage.
- 1 Interior light, controlled by a single pole switch.
- 1 Exterior light at the side door, controlled by a single pole switch.
- 1 GFCI protected wall receptacle.
- 1 Receptacle for the garage door opener.

Main Panel
Attachment 51161

Detached Garage
Attachment 51164

Crawlspace Exterior
Attachment 51162

Crawlspace from front
Attachment 51163

Crawlspace interior, where I plan to drill for the LB install
Attachment 51165

I have a few questions at the moment and any advice would be much appreciated!

- The distance from the panel to the detached garage is 60 feet. I have been using an online voltage drop calculator, and it seems that I would need to run #10 wire. Is that an adequate gauge, and would there be any concerns about upgrading the grounding with a larger conductor?

- In the last photo above I plan to drill a hole through the joist out to the exterior to mount an LB conduit body. (the exterior is on the right side joist) The joist is 7" wide and rests on the foundation. From what I've read so far, I can drill a hole 2.3 inches maximum, as long as it is more than 2 inches in from the top and bottom of the joist. Would there be any structural concerns with drilling the hole, and should I add any distance from the joist on the left side in the photo?

- Would the joist on the left side in the last photo be an appropriate location for a junction between the THWN and the interior romex?

- I understand that a GFCI receptacle is required by code for this project. Should this be installed in the basement, in the detached garage, or does the location matter?

- I have thought about planning for future expansion (perhaps adding a 50 amp subpanel in the garage down the road) Could I oversize the conduit and THWN and run the 20 amp circuit, or would this be a code violation? For example, running #6 3-phase wire in the conduit only, but wiring it for 120v 20amps at this time?

Thanks in advance for any insight.

 

Can you explain this example with more specific information? What do you specifically mean with: ''in the conduit only, but wiring it for 20amps at this time''? How will you wiring it for 20Amps at this time? Please explain.

 

Schedule 40 is usual and at 18" deep minimum unless protected by a GFCI and does not exceed 20 amps at 120 volts. No #12.No such critter as "3-phase wire" and your house is single phase. Do you mean three single conductors for 120 or four single conductors for 120/240?

There are so many misunderstandings in your post I'd suggest you buy the book Wiring Simplified and read it cover to cover.

 

I think they wanted the option to upgrade to 50 amps later if they installed the larger conduit and conductors now, but initially used a 20 amp breaker.

 

Thanks for the replies!

I was referring to 300.5 column 4 which seems to indicate that 12 inches is aqequate... is that off base? http://www.xwalk.com/images/Table_30...over_Reqts.pdf

Yes, that's correct I was referring to four single conductors, not "3 phase". My apologies it was a long day.

Yes, that is correct.

Anyone have thoughts on the recommended wire gauge, or considerations about drilling into the joist? Thanks again.

 

It says exactly what I wrote.General depth remains 18" minimum (for conduit) if you want potential to upgrade to 50 amps.For 50 amps two #6 black (or black and red), one #6 white, one #10 green (copper). If possible the hole should be centered. ¾" minimum PVC conduit (#6) but 1" would be better.

 

Replied deleted by myself because writing was confusing.

Jos

 

The 240 feed is two 120 volt legs. There is no need to convert voltages. The 240 is between the hots and the 120 is one hot to neutral.

 

For the 20 amp 120 he can use one 20 amp single pole breaker. I'd just use #12 (white, black, green) and just pull new wires if I ever wanted to convert.

However plan "B" would be to pull the future wires now. Use red and black (or tag one black on both ends) for the hots.

• For the 20 amp 120 circuit install a 20a single pole breaker.
• At the breaker use a #12 pigtail to reduce the #6 black to fit the breaker (if needed)
• White and green will not need reduction. Connect as usual.
• Cap off the red (or tagged second black). It is not connected.
• At the shed install a 4x4 box and a single pole 20 amp switch to act as a disconnect.
• Cap the red (or tagged second black).
• Run #12 to receptacles and fixtures.
• Use a GFCI receptacle for the first receptacle and daisy chain the other receptacles off the load side.
• Lights do not need GFCI protection.

Plan "C" Install a 20 amp multiwire 120 volt circuit using all four wires. You would use a double pole 20a 240 breaker or two handle tied single pole 20 amp breakers.This gives you two 20 amp 120 volt circuits without needing a subpanel. You would use an unfused two pole air conditioner disconnect at the shed instead of a single pole switch and a 4x4 box.

 

This is very helpful, thank you.

Ray, you mentioned using #12. Would it be worth upping the guage to compensate for voltage drop? (60 foot run between the panel and garage)

Looks like when I plug the values in to this calculator, I can reach ~52 feet with a voltage drop of 3% or less: Voltage Drop Calculator

 

Chris-B,

I has been the entire day debating, getting myself in trouble trying to compose complex questions and statements according to what you previously stated in the last paragraph of your first post in this thread:

And now you are re-considering to just run the #12 maybe upping to #10 conductors??? No way, run the #6... Hahahaha, I'm just kidding my friend. I am not mad at all.


Jos

 

You are planning a 20 ampere circuit, what will the maximum load be and will it exist for more than three hours? Voltage drop is dependent upon the actual load and the length of the circuit. If your load is only 3 amperes then the voltage drop in the proposed circuit using #12 copper conductors will be only 0.7 volts or about 0.6%. If the load is 10 amperes the drop is about 2.3 volts or 1.9%. At 15 amperes you would have a voltage drop of 3.4 volts or about 2.8 percent.

If the load is for more than three hours it is by definition a "continuous load" and that will reduce the 20 ampere circuit to one that supplies only 80% of 20 amperes or a maximum of 16 amperes. At that point the voltage drop is 3.7 volts or 3.1% and is still within the guidelines for voltage drop.

 

Chris-B,

Furd's calculations are absolutely correct.


Chris, I visited the Link you provided with the Voltage Drop Calculator, and maybe your mistake was that you input 20Amps on current. You have indeed by general rule to limit that current to 16Amps that is the 80% of the maximum ampacity allowed for a 20Amp circuit.

Therefore, I filled the correct parameters in the calculator and screenshot them for you:




As you can now notice you can go to up to 64feet with #12 (according to the calculator) wire for a maximum load of 16Amps (its 80%) and you will be just under the maximum volt drop allowed for that circuit running that length with that wire. According to the calculator at 65feet you will then need to upsize the wire to #10 to keep the voltage drop under 3%.


Hope this helps.


NOTE: In case previous image was blurred:








Jos

 

While limiting the circuit to 80% is a good idea, there is no need. The 80% rule applies to continuous loads of 3 hours or more.

 

Thanks again for all of the assistance with planning this project. In the end, I have decided to run 50 amps out to a subpanel in the detached garage.

So far I have:

• Buried two 8' ground rods 6 feet apart
• Ran 1" conduit from the house to the garage (18" deep to the top of the conduit)
• Pulled the THWN (6 guage, with a 10 guage ground) wire through the conduit

I plan to run 6/3 NM-B cable from the main panel, and junction to the THWN in a box where the conduit enters the house.

I have a couple of questions:

- Could anyone advise, or direct me towards documentation on the best practice for junctioning wire of this gauge? Seems that it's a bit too large for twist on wire connectors. Would split bolts be preferred in this instance?

- I suspect that I may have underestimated how much 6/3 NM-B to purchase. Could I make a junction in between the main panel and the underground conduit to extend the feeder? Or should I plan to replace the whole run if necessary?

 

Large grey or blue wire nuts can be used and are cheap. Polaris pre-insulated connectors are nicer and easier than split bolts, although costly.

You can splice the cable ina junction box if needed.

 

If you bought the #6 NM at a big box store they will probably take the return and cut you a longer piece, even though the official policy is not to. I'd try that before adding another junction box.

 

Thanks for the advice, I'll see if they will work with me on exchanging the feeder cable.