I need to install electricity in my garage by connecting to my main box in the basement of my house. I hope to bore a hole in the basement wall and run conduit to the garage. The circuit must handle a fluorescent shop light, battery charger for boat batteries, and occasional use of small tools. I want safety and economy. Provide insight to any thing I overlooked.

Circuit length 170 feet
Voltage 120 House voltage on 120 reads 123.5.
Amperage ???? Is a 20 amp breaker adequate since I have 2 Sylvania GTE breakers from a 220 well pump no longer used that I think I can separate.

Wire size ???? If an 8 or 6 is required will it connect to the breaker directly. What do I do to connect it to a 120 receptacle and the light switch and light? Could I get by running two large individual wires from the main box and running a ground to a rod at the building or must I run a ground from the main and put in a ground rod also?

Wire type ???? Based on wire size etc.

Number of wires ??

Schedule 40 Conduit size ???? The route taken will require a 120 degree turn about 70 feet from the house. What is the best approach to installing it, all at once and fish or section by section?

Conduit depth ????

 

I infer that the garage is detached. If this is incorrect, stop reading now.

You have several different options. If your needs are as modest as you list, and you don't expect that to change in the future, then I recommend one 20-amp multiwire circuit to the garage. Multiwire circuits are a bit tricky, so read up on them before proceeding.

I would run UF-B cable, buried 12 inches. Connect this to a 20-amp double-pole 240/120 GFCI breaker (a bit pricey, but it saves you the trouble of burying the cable 24 inches deep--or bury it 24 inches if digging is easy). 12/3 (black/red/white/bare) UF-B would be very marginal, but acceptable if the load stays low. 10/3 or 8/3 would be a better (Southwire makes those, but you might not find it at your home center). No conduit would be required (except where going through the wall and where above ground). If you do use conduit, fishing it section by section is not allowed.

A multiwire circuit avoids the need for a subpanel or grounding rods at the garage.

Don't try to reuse an old breaker. Buy a new one.

If your future needs will grow, decide that now. Deciding that later will be a real bummer, essentially rendering everything you do first useless.

There's more, but I'll leave that for others. I'm tired of typing right now.

 

John, the above quote was given by you in http://forum.doityourself.com/showthread.php?t=132185 Your replies were posts #8 and #10

Has there been a Code change about your suggestion to James R (this thread's originator) that "No conduit would be required (except where going through the wall and where above ground)", or is there just another exception to the rule between this case and the one in the thread I quoted?

Reason for my interest is that on the job I'm currently doing, the guy ran UF 18" deep in PVC. I told him that he could have simply buried the UF feeder 12" deep, but now I'm reading different stories. I'm cornfused

There's just a whole helluva lot to this trade, isn't there? I hope to keep learning

-Terry

 

For most situations, there are alternatives. And for similar situations, there are often differences that make the rules different. My advice was for James's question, wihch involved a branch circuit. Your question involved a feeder. Those are two different animals.

Advice given to one person usually doesn't apply to somebody else. "Similar" situations are almost never "identical" situations. In a way, that's the beauty of this forum--individual advice.

 

John the multiwiring you say is tricky and other sites suggest it could get very dangersous generating high voltage if wired improperly. Any light you can shed on this.

How long has UF B been available and how long could one expect it to last in red clay with some sandstone rock?

You indicated there was more but your fingers were tired and you would leave it to others but none have responded. I appreciate you taking time to help.

 

Everything about electricity is dangerous if wired improperly. That's why you should always wire it properly.

UF cable has been around a very long time, and I would expect it to last longer than you or I.

So is the garage detached?

And do you think your needs will ever increase in the future?

Talk to me.

 

John, the garage is detached. It will be a 170 foot run dodging trees and raised beds and go in at the rear near the center of a 24 by 32 garage.

As of right now I can't imagine anything more than a couple of lights, maybe a garage door opener, a small air compressor plugged up when needed, a hand held power saw, hand held power drill, a battery charger for boat batteries, a wet-dry vac. No two things would likely be operated at the same time except the lights and one tool. That might mean though the need for an extension to cord to reach the work station.

I won't be welding or buying table saws, drill presses, etc.

If I were to sell which I do not forsee now, what would make a garage like that more attractive.

 

A single 20-amp circuit (not multiwire) will provide you up to 2400 watts of power. But the problem is that 170 feet is a long ways, requiring fairly heavy wire even with a light load. A single circuit will only take up one space in your main panel.

A multiwire 20-amp circuit offers two advantages. It not only provides you twice as much power (4800 watts), it can also reduce the voltage drop, allowing you to use lighter wire. Once you get to the shed, in the first box you enter, you split the two hot conductors and go their separate ways. As long as you connect this multiwire circuit to a double-pole breaker in the main panel, and split the hots in the first box, the chances of screwing up a multiwire circuit are small. A multiwire circuit will take up two spaces in your main panel.

Based on that, what do you think about a multiwire circuit?

Next thing to consider is how deep you are willing to dig the trench, and what exactly it will go under. Will it be under a residential landscape the whole way, or might it go under a road or anything else unusual? And is the digging likely to be easy or hard? You could go as little as 12 inches if you spend $100 on a breaker. Of you can save the cost of the breaker if you go deeper. You could bury it 18" if you are willing to run PVC conduit in the trench. Or you could avoid the trouble of the conduit if you go 24" deep.

Based on that, what do you think about the trench?

 

Could James save the cost of the 20-amp double-pole 240/120 GFCI breaker by protecting each circuit separately with a 15 amp GFCI installed after the first split, once the two hot conductors have gone their separate ways?

Is this possible?

Also may you install additional outlets further down the line from the CFCI protected outlet, (on the load side). I am thinking here of a few lights, maybe a standard 15 amp outlet.

This would provide two 15 circuits, each protected by a CFCI.

Would this met code, and, more importantly, be safe?

If it is possible, it would be a fairly neat and cheap solution.

 

The reason that John identified a 20 amp 240 volt GFCI breaker was to enable the UF cable to be buried at a shllower depth. This provides GFCI protection for the cable between the house and garage.

Placing two GFCI outlets or devices in the garage provides protection in the garage, (which is needed), but does not provide any protection between the house and the garage, meaning that the cable needs to be buried deeper under the ground.

 

The 12" burial depth rule only applies to circuits of 120V or less, so the multi-wire circuit would need the full 18" of cover.

 

John, I am feeling more comfortable with your multiwire setup with UF-B 10/3WG buried 12 inches deep and the 20 amp double pole GFCI breaker for my 170 foot run to my detached garage but it seems I have a dinosaur main box-a GTE Sylvania box. It has a 20 amp GFCI breaker and 10/3 wire with ground circuit like you described that provides power to my outdoor receptacles on the 2 porches of the house-a 35 foot run to each. So that would be a guide to installing the new breaker.

I will start looking for the breaker and wire. Is the breaker out there to be had? If not can you and others offer other suggestions from the main to the garage. Thanks for being here.

 

Bolted raises an issue with this solution. I think the code is ambiguous here, in that it limits the voltage to 120 volts for this solution, but even in a multiwire circuit, there are no voltages to ground above 120 volts. However, as Bolted says, there is 240 volts between the two hot wires. I am unclear as to the proper interpretation of the code. I suggest you consult with your local inspector for his/her interpretation.

 

John, are you saying the depth of burial is the only question? If so how deep should the UF-B be buried to meet the most extensive requirements with and without conduit.

 

24 inches without conduit.
18 inches in PVC conduit
6 inches in rigid metal conduit (not EMT!)

All of that assuming that it's not underneath anything unusual

 

John,

I'd suggest that you step back and consider the amount of time you're investing vs. financial cost vs. long-term potential. You asked some very specific questions and gave some hard criteria about the solution you are looking for - "lowest-cost" is how I'd phrase it. Trying to save money is fine, but you might reconsider a bit and think about the long-term investment of providing a bit more robust electrical service to the garage.

A 32' x 24' freestanding garage is, to many guys (and gals), a dream workshop. That workshop could be for woodworking or other hobbies like auto restoration. In short, you really might consider running a subpanel to the garage. It would give you a lot more flexibility in meeting your current and unknown future wiring needs. It's going to be a lot of work to dig a 170' trench. Given that work, I wouldn't just run a 20 amp circuit. The incremental work now to give yourself a subpanel just isn't that great and would allow you to honestly call it a workshop as well as garage when you sell it. You would need to check with your local AHJ (Authority having Jurisdiction, aka the building inspector) to see if they have any specific local rules you need to know about. An example of that is that my town did not want me to drive ground rods, create a Grounding Electrode System and bond the subpanel as part of installing power in my shed - they wanted it all bonded back through the main service panel.

John mentioned it early in the trhead, but based on the length of your run, you need to upsize your conductors. Here's a voltage drop calculator.
Voltage Drop Calculator

• For a 20 amp circuit, you'd run #8.
• For a 30 amp circuit, you'd run #6.
• For a 40 amp circuit, you'd run #4.
• For a 60 amp circuit, you'd run #2.

Were this my garage, my house, my yard - I'd run 1 1/2" Schedule 40 PVC conduit, pull #6 THWN, install a 20 slot subpanel and 30 amp breaker. That gives you capacity for what you might be doing now and room for growth. If someone wants to upgrade the panel in the future, they can pull larger conductors and swap the breaker. That's one reason to run larger conduit. It's also easier to pull over that distance (will be a "treat" anyway).

Whatever you decide to do, I wouldn't put the GFI in your feeding panel. If it trips, you have to travel from the garage all the way back to the house to reset the breaker. Trying to troubleshoot a trip could wear you out. You could use a standard 20 amp, 2-pole breaker and run a multiwire circuit out to the garage as already described. Use the MW-circuit to feed a pair of GFI receptacles. You'd pigtail the GFI receptacles' line side neutrals to the MW-circuit neutral and just make sure that you keep the hot/neutral pair straight as you feed your garage circuits. That gives you GFI protection if you're trying to stay at the 20-amp GFI limit, but makes your life easier when dealing with trips.

Your AHJ may require a disconnect at the garage regardless of what you install. It's a good idea anyway.

Rob

 

John Nelson and Rob,

I ran 6/3 UF B WG from my Main Panel through a 40 Amp double pole breaker(a local electrical supplier had a Zinsco in stock) to my detached garage some 170 feet. I ran it 24 inches deep without conduit. I put a 6 breaker sub panel in the garage(3 for the red and 3 for the black) and used 12/2 UF B WG. I have one 15 amp light and receptacle circuit connected to the black wire and one 20 amp receptacle connnected to the red wire using the neutral wire for both in a multiwire circuit. I put a GFCI at the end of the 20 amp circuit since I was told by Cooper wiring that it would work only at the end and without attaching the ground to it. Their testing system indicates it works that way. As of yet I have no GFCI in the 15 amp circuit.

Am I limited to 40 amps total usage at any one time in the garage? As I presently understand it I would be.

Any and all information you can provide on proper wiring for GFCI receptacles on multiwire would be of help.

I appreciate all the help and advice provided on this project. I could never have done this without help like yours. I was out 600 dollars assuming all holds up but would have been out 2000 dollars over years putting in a meter.
I ruled it conduit thinking I could not make the pull myself and I could not find THWN wire packaged 6/3. There was a lot of confusion regarding using THHN locally. Conduit is a wet environment and it should not be used yet many said it was happening daily and inspectors okayed it even though one inspector told an electrical supplier I talked to that it should not be done.

Thanks again.

James R

 

With a 40-amp double-pole breaker protecting the feeder, you are limited to 9.6KW of power at any one time. This is a more useful way of thinking about it than in amps.

When GFCI is required, it is not advisable to use a multiwire circuit. In fact, I don't recommend multiwire circuits at any other time either. The slim advantages seldom outweight the disadvantages.

To put GFCI protection on a multiwire circuit, you must do one of the following:

1. Use an expensive and hard to find double-pole 120/240 15-amp or 20-amp GFCI breaker.
2. Install a GFCI receptacle at every outlet where you want GFCI protection, using only the line side connections of each GFCI.
3. Split the multiwire circuit into separate runs (essentially making it no longer a multiwire circuit), and put a GFCI on each leg.

If it was me, I'd just rip out all the 12/3 and use two runs of 12/2 instead.

You mentioned 12/2 UF-B, but I'm not clear where that cable is. It does cause me a bit of worry.

 

John,
You said, "When GFCI is required, it is not advisable to use a multiwire circuit. In fact, I don't recommend multiwire circuits at any other time either. The slim advantages seldom outweight the disadvantages." But you did recommend multiwire due to voltage drop in thread #8 above.


You said as a way to install GFCI, "Split the multiwire circuit into separate runs (essentially making it no longer a multiwire circuit), and put a GFCI on each leg." How do I do that since the red and black wires both share the white as neutral between the house Main Panel and garage subpanel?

You said, "If it was me, I'd just rip out all the 12/3 and use two runs of 12/2 instead." Where was there mention of 12/3 in my writings? I used 12/2 UF B WG to run the circuits from my subpanel in my garage out into the garage. The 6/3 UF B WG wire from the Main panel in the house to the subpanel in the garage is the only 3 wire cable used. It has a black, red, white, and bare ground wire

You said, "You mentioned 12/2 UF-B, but I'm not clear where that cable is. It does cause me a bit of worry." I used 12/2 UF B WG to run the circuits from my subpanel in my garage out into the garage. It is not a completely dry environment and I read on the box of one brand of the cable where they suggested use of it in such an environment.

Thanks,

James R

 

I have no problem with sharing the neutral in a feeder. I recommend providing GFCI protection downstream from the feeder, in the first outlet on each circuit from the subpanel. Applying GFCI protection downstream from the last point at which the neutral is shared is no problem.

I was confused by your statement that you "have one 15 amp light and receptacle circuit connected to the black wire and one 20 amp receptacle connnected to the red wire using the neutral wire for both in a multiwire circuit". After your clarifying post, I now understand that this is not a multiwire circuit. I was also confused because you said that one circuit was "connected to the black wire" and the other was "connected to the red wire." Although each circuit is connected to a breaker which is connected to a bus bar which is connected to a lug which is connected to the red or black wires in the feeder, I got the impression that the circuits were directly connected to red and black wires.

Now that I am no longer confused (I think), you can ignore my previous post.

 

John,

By using 6/3 UF B WG connecting at the House Main Panel the black to one pole of a double pole breaker and the red to the other pole of the same double pole breaker and the white neutral to the ground bar as well as the bare ground I have created a multiwire set up to be sent to the garage. Is this correct?

At the garage I connect this to a subpanel where the black is connected to connection that has 3 circuit breaker slots. The red is attached to a separate connection that has 3 circuit breaker slots. The white is connected to the ground bar as well as the bare wire. This makes for a multiwire set up. Is that correct.

I put a circuit breaker on the black wire side in the sub panel and attach the black of a 12/2 WG to the circuit breaker. The white of the 12/2 WG and its bare ground are attached to the same subpanel ground bar as the neutral and bare of the 6/3 from the house main panel. The circuit from the sub panel out into the garage is no longer a multiwire. Is this correct?

Again I appreciate your help.

James R

 

Words have definitions, and without agreeing on a precise meanings of terms, we cannot communicate. In the electrical world in the U.S., the agreed-upon authority is the National Electrical Code. What you describe undoubtedly has multiple wires, but none of it fit the NEC definition of "multiwire".

It might be like describing interstate 80 as a "driveway" because you can drive that way.