Electrical Help needed. Add power to detached garage.

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daito

daito

10 Year
Joined
May 28, 2013
Threads
12
Messages
131
I'm not a pro and I need some help on recommendations to rewire my power from my house to garage. The previous owner used a lot of creativity in how they wired my garage so my breakers easily trip. I am going to run wire from my house to my detached garage.

New plan questions/assumptions:
  • Not sure of house box amperage
    • I'd assume below normal since my house is old
  • Install second breaker box on house to go to garage
    • Should breaker to garage be 50A?
  • Run 6/3 cable from second breaker on house to box on garage
    • Whats the third wire for?
    • Its 70' of cable from the house box to the garage box.
  • 100A distribution on garage
    • Is this bad since its more than the 50A breaker at house?
Other info:
  • Not sure of max load so make assumptions for amperage load of a welder, compressor, then 110v lights and what not.
 
You don't need to put a box in your house if you have space in your panel to add 2 breakers.
You do need to find out what you panel is. It should have a label.
At least see what your main breaker is rated at.
We don't know how much power you will need. It is like how big a trailer do I need to tow my stuff.
Always err on the side of over capacity. Won't be much more work or money to do 100A.
Even so you can use a 100A main panel with 50a breaker in house panel if that is all your wiring is rated at.
Wire amperage capacity depends on guage, temp rating and length.
I have a shed and I plan on running 100A to it so I can power my welder and other tools. 50A would be more than enough for now but maybe not in the future. Trenching will be the biggest expense.
The third wire is for 220v, 2 power. 1 neutral and one ground. The ground and neutral don't get tied together.
 
If you have circuit breakers in the house, it can't be THAT old. I would guess 200A? If so, you could do as SE2000 says and add 2 50A breakers on each 110v leg to go to the garage.
 
I have used the black and Decker guide to home rewiring. I have used it to put a new subpanel in my basement and run a myriad of 120 and 240 volt wiring. Saved me lots of headaches and book is easy to follow with all kinds of circuit examples.
 
what state?
100 amps for a house isn't absurd. 50 for the garage will go a long way. read the amps of your main breaker; post a pic of the panel front, too. if your service is 100, then do you have space for a 2 pole 50? what kind of breakers are they? if you have a 200 amp service, then find space for 2 pole 50 and run a conduit to your garage and set a sub panel inside the garage. from there, take off and take over any circuits in the garage. if you aren't savvy inside electrical boxes, CALL A PRO. you can do things like dig the trench and whatnot, but there are alot of variables here to be jumping into it head first without floaties. don't get me wrong, anyone can do it, but there are alot of questions needing answers to help you go the right way...
 
Ok here is some info and pics of my main breaker and the breaker in the house.

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If your not running A/C and you don't heat with electric on a older small home 100 amp could be all you have. I believe you need four wires not three unless everything you plan on running is only 115 volt. For 220 you need four wire. Two hot wires to make
220, one nuetral and one ground. Total of four wires. You could use only three if everything we 220 including lighting and all hand tools. Could get a transformer to make 115 from 220 but cheaper and less hassle to just run four wires. Even if you only install fifty amp breakers I would run wiring to handle a 100 amp later if you want.
 
quick and dirty...run conduit under ground from main to garage sub panel. make conduit 1 1/4" or bigger to pull 3 # 3 minimum and 1 # 6. 2 of the #3s are for the hot L1 and L2, the other #3 is the neutral, the #6 is the ground( which can be omitted if there is a driven ground rod at the garage and the sub panels neutral is bonded to the driven ground rod...) have and electrician double tap your main breaker- this would be done by pulling the L1 and L2 legs off the main breaker and splicing the garage feeders and a pair of jumpers to the bundles. the jumpers will land back on the main breaker. this will feed both the house sub and garage sub from the 100 amp main breaker. as long as the wiring is sized for that level of over-current protection, you'll be fine. you still only have a 100 amp service. in the garage, run circuits as needed(don't overload too much) with individual circuit over-current protection. HAVE AN ELECTRICIAN tap the mains, and maybe have them go over your work in the garage sub panel too. a good guy should be able to do the terminations and splices inside of a couple three hours or so...as long as the rest of it is in place. trench should be 18" minimum in depth, conduit needs to be metallic or extra heavy wall for portions that will see daylight(above ground) in ground, conduit can be schedule 40 PVC. on the garage, rise up with extra heavy or metallic conduit and penetrate building behind where sub panel will go, use an LB condulet and threaded nipples to make entry to the building/panel. a main breaker needs to be installed in the sub, make it 50 or 60 amps. the wires from the main will land on this breaker and this breaker will be installed to the bus of the sub, thus feeding the sub and limiting the amp draw to the garage.
 
glue underground pipes together making certain all fittings are bottomed onto the pipes they attach to. use a shop vac to pull a string tied to a plastic baggie thru the pipe. tie a 1/4"-3/8" rope to the string and pull the rope in(using too small a pull will cut thru the sweeps of PVC schedule 40 or 80) use the rope to pull in the wires. as much as I enjoy comic relief, watching people fish wiring thru 10 foot sections of pipe and gluing together(gluing the wire to the pipe...)is just depressing. HTH
 
Wire

Lambcrusher,
I read your response about the wire gauges and so on. Thank you for the info on my previous response I hadn't worked that info in fully such as the ground wire.

I had a question on terminology. Is #3 wire the same as saying 3 gauge? I know someone who is selling some wire that is 6 gauge so I was wondering if that would work.

Also when looking for different wires to run from the house to the garaqge, is there specific type to get? Like THHN, Romex (I think this is a no), underground, etc?
 
#6 or 6 gauge is good for 55 amps, #3 is not a common size, but is good for 85 amps. If you are running in conduit get some THWN or any conductor that has insulation that can tolerate moisture. I've run romex in conduit because that's what I had, but separate conductors will pull easier.
 
Dang, that is going to be a bit of work- all those sidewalks... Lambcrusher is spot on.
Just for fun call an Electrical Contractor and get a free estimate if they do that down there or pay someone for a one hour consult.
I definitely like the idea of conduit with wire pulled in vs. direct bury cable or wires. With all of the brick and concrete I see in the pictures that looks like a lot of cutting/chipping out to get the power there or tunneling.
I would also check into code and permit regulations in your area.
If you end up with nearly 100 feet of wire and plan on running a welder I would stick with sizing it for 100 amps (#3 copper) just for voltage drop. Sometimes the lights are going to flicker just due to the size of your house service/ utility transformer size etc., when the welder or compressor are running.
According to the NEC table 310.15 90 degree C chart THHN is good for 115 amps but if I remember right you have to derate for the temp of the breaker @ 75 degrees C which puts it back to 100 degrees. #2 is more common but copper isn't cheap..
Man- this sounds like work- I'm out of here!! ;)
 
#3 is rated at 105 amps(copper) it is a sub standard size- I use it frequently, it is the same as saying 3 gauge. not to be confused with 3 ought (3/0) 3/0 is about 6 times larger and twenty times more expensive.


use thhn


do NOT direct bury the conductors(wires) use PVC schedule 40 conduit for in ground and schedule 80 PVC for daylighted sections- or EMT or RIGID for the daylighted sections.


use a piece of 1/2" pipe fit over the end of a spray nozzle of a hose and jet the dirt out from under the walkways- keep the tranch about 20" deep.



if you are never going to sell, maybe don't do a permit, as that can add costs to the job(build as tho it were to be inspected however) if you might sell or get the house appraised soon, get the proper paperwork done- this will require permit costs and a county/city inspection. A homeowner is still allowed to do this work here in Cali, not sure about your neck- they may require a licensed contractor. if you get inspection, you will need to make certain the garage wiring is up to snuff, or they will tell you to do so before giving you a pass.



100 feet is not enough to consider upsizing for voltage drop. I don't bother with those calcs till I'm over 150 feet or so- usually 200+. the welder is a 180 that is wired for 120/240??? I'd bet 30 amps draw at 120, maybe 15 or so at 240. your compressor is likely to use more current than your welder- again, depending on if it's 120 or 240...lights; you estimate 30 amps in lights? holy cannolly, what are you going to be growing?


size the circuit for 100 amps, parallel tap the house feeds in the main- after the breaker!!! (using NSI Polaris tap splices or Kearnies[split-bolts with a wrapping of each of rubber tape, friction tape, then vinyl tape]), and use a 60 amp sub main breaker in the sub. unless you've got employees working with you, you're gunna hafto work to utilize that much current. HTH. feel free to ask. don't tell anyone I hinted at NOT getting a permit;)
 
TLC76 said:
#6 or 6 gauge is good for 55 amps, #3 is not a common size, but is good for 85 amps. If you are running in conduit get some THWN or any conductor that has insulation that can tolerate moisture. I've run romex in conduit because that's what I had, but separate conductors will pull easier.
Click to expand...

FYI, romex is not thermally rated to be installed into conduit(not that I've never done so...)
 
It's frequently run surrounded by insulation in walls, conduit can't be any worse in terms of thermal. I couldn't find any actual code restriction against it, although I remember finding somewhere in the NM section your HAD to have it in conduit or otherwise protected where it was subject to damage, but it's been a while since I looked at it.

I wouldn't worry about voltage drop with a 100A service at that distance, your compressor will be the worst culprit due to starting current and unless you really have a beast I think you'll be fine.
 
TLC76 said:
It's frequently run surrounded by insulation in walls, conduit can't be any worse in terms of thermal. I couldn't find any actual code restriction against it, although I remember finding somewhere in the NM section your HAD to have it in conduit or otherwise protected where it was subject to damage, but it's been a while since I looked at it.

I wouldn't worry about voltage drop with a 100A service at that distance, your compressor will be the worst culprit due to starting current and unless you really have a beast I think you'll be fine.
Click to expand...

in Methods, under Romex...it's a nuanced thing pointed out to me by an inspector. as I said, not like I've never done it;) you're supposed to strip the jacket when sleeving it. really, the biggest thing to me is it's a bitch to pull in and it takes up all the real estate...
 
I did a little searching, other than exterior installations where you run into the "wet location" issue I couldn't find anything prohibiting it as long as you don't exceed fills. Lots of questions on it out there though. I've only done this on my personal projects, for example running through an attic then transitioning to EMT outside for an A/C unit, or dropping into the garage for an outlet with the conduit stubbed up into the attic.

Anything over 500MCM I pull THWN :D
 
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