Power to detached shop

[Nick Cook]

I have a 3 car detached garage that I am looking to convert to a shop. It currently only has a single 15 amp 110v line running to it, which just won't cut it for me. So I am looking to purchase the wiring and everything else I need to get a new 100amp panel out there (we have a 200amp service at the house). Of course the house panel is pretty much the furthest point away so I have a long distance to pull wires ahead of me. I have about 60'-70' inside the house, will be running it in basement (drop ceiling, easy access) and then another 70' outside where I will trench and run it in conduit. Should I be using a SER type cable inside and then change to individual conductors for the outside conduit run? What should the sizing be for 100amp? I know there a few electrical guys on here so I hoping someone can point me in the right direction.

Thanks,

Nick

[Todd Burch]

I paid ~$1000 about 12 years ago to have a 100 amp subpanel added to my ATTACHED garage. It was about 70' of attic space. Most expensive aspect was the wire.

All I had to know was how to write the check!

[Chris Tsutsui]

Just as an FYI but Home Depot actually has decent pricing from southwire for the spools of THHN. I'd probably get pricing for that from local suppliers and see if they can beat Home Depot's pricing.

I'm not a professional but the electrical plans I see at work usually have Schedule 40 gray PVC for underground stuff, then switch to Galvanized Rigid steel Conduit for above grade. Metal of course corrodes in the earth unless you have a cathodic protection system. :)

I take no responsibility for this but i'm just estimating #2 wire, $1.15 per foot for say 100 feet run of 4 conductors. You might want to reserve about $500 for wire. Then you still need to buy the conduit, box and breakers. You may want to have a budget of $1K for this project in materials to make sure you're covered.

[Don Jarvie]

A few thoughts... it may be worth while having a subpanel in the middle of the run, Main-sub-garage. 140 ft is a long way and you will have to calculate for the drop in current over that span so you would need thicker wire for the straight run.

Rent a trench digger or some motorized tool to dig the trench. You want to go down 12 - 18 inches and 70 ft is a long way. I only had to dig 10 ft and it wasn't fun by hand.

If you know an electrician run the plans by him and get his thoughts. You can still do the work yourself but knowing any potential snags upfront doesn't hurt.

[Steve Meliza]

I wouldn't bother with the extra sub-panel as I don't see any advantage to having it and something in the back of my mind makes me think I read something about an NEC limit on the number of sub-panels that you can chain together like that.

The size of wire you need depends on the type of insulation and if it is Cu or Al. I think you'll find you need #4 Cu or #2 Al for the feeder, but you could upsize a bit if you plan to run near 100A a lot. It doesn't make sense to drop in a monster copper feeder if your peak loads never exceed say 50A or so. Keep in mind you can buy a 100A or 200A panel with lots of branch circuits and feed it with a 60A breaker and 6/3 wire. You don't have to feed a 100A rated panel with a 100A breaker if you don't need that much power.

[George wilmore]

I installed separate 200amp service. I had to install the meter pan and run wire to the pole. I ran it underground but was lucky the pole was three feet away. It does not cost extra because I always use more than the minimum charge. It is nice to have all the power you will ever use and be able to add more circuits when needed.

[Tom Ewell]

My house was too close to maxed-out so I did what George did, separate service/meter to the shop.
My pole was about 50' away. Local utility ran underground to the panel on the shop.

[Nick Cook]

I thought about adding new service, but the pole is pretty far away and the power company will not add another service for free. Could I run a service entry cable inside the house (thus no conduit) and then a junction and switch to individual conductors for the underground run?

[Joseph Tarantino]

1)you don't need 100A. 60A (6/3 wire) would be plenty unless you are running several WW machines simultaneously. 2) are you pulling a permit on this or is this a " we don;t need no stinking permit!" type of job. i had an electrician friend pull one for my shop subpanel. 3) i have only a 30A subpanel and i've never run out of power (ran 65' of wire from a 30A breaker in the main panel to the subpanel in the shop. 15' of 10/3 romex from main panel into a junction box and switched over to 45' of 10/3 UF for the run to the shop. buried 2' deep.). 4) what you are allowed to do in your area and what will work are 2 diffferent things. specifications allowed in one municipality may not be permitted in another, so i'd suggest getting advice specific to your municipality.

[Bob Deroeck]

Hi Nick,

I went through a similar exercise last Fall. My detached workshop/garage required afeeder wire that ran 80' through the basement/crawl space of my house, then 80'underground to the workshop. I wantedabout 100 amp capacity with a separate subpanel in the workshop. But, after doing some research I found thatthe wire ampacity based on NEC table 310.16 was not the onlyconsideration. Since most of the highamperage required in the workshop was for motors, my primary consideration wasvoltage drop (both during motor startup and normal motor operation) based onmotor horsepower. I wanted to be ableto be able to operate two 5 HP single phase motors simultaneously. This would allow operation of a 5 HP cyclonedust collector and a 5 HP "user" machine (table saw, planer,etc). I used table 16-1 from the book"Wiring Simplified, 41 Edition" which I bought at Home Depot. I suspect that this table is derived from anNEC table, but that's just a guess. This table is based on a maximum voltage drop of 7.5% during startup and1.5% during normal operation. Since mytotal one-way wire length was 160', extrapolating Table 16-1, gave me about 11HP total with 2 AWG copper. If usingTHHN type wire, NEC table 310.16 allows 95 amps with 4 AWG copper, 110 ampswith 3 AWG copper, and 130 amps with 2 AWG copper. Based on the motor considerations, I choose 2 AWG wire.

The town electrical inspector was very helpful in helpingme design the system. He stated SERcable cannot be used in conduit underground, so I used four individual THHNwires in the underground conduit (3 are 2 AWG, the ground is 4 AWG). Within the crawl space/basement (note thebasement is not habitable) he said I could continue the four individual THHNwires, but that they would have to be in conduit. Or, I could use SER cable, not in conduit, attached to the bottomof a running board nailed to the bottom of the floor joists. I decided to use the SER cable since wouldbe much easier to install. I used alarge PVC box (probably 10"x10"x4" or so) to make the junctionsbetween these wires just after the conduit entered the crawl space of the house.

Note, I found significant differences in the price ofcable. I ended up driving 50 miles toBoston to a commercial wire dealer since their cost was about 60% that of thebig box stores.

My inspector required the conduit to be buried 24"underground, though my understanding was that the NEC only required 18"for underground wire in conduit. I havea Bobcat with a backhoe, so it wasn't a big deal to meet his 24"requirement. While the NEC would haveallowed me to use 1 1/4" conduit, my inspector recommended using 2"to make the pull easier. I did this andthe pull was quite easy. He alsorecommended installing a separate conduit in the trench for future use. I did this as well, installing a 1"conduit. The cost of the PVC for thisfuture conduit was trivial. I alsoinstalled in the trench a 14-3 (plus ground) UF wire so that I could turnon/off the outside garage lights from both the workshop and the house with3-way switches. The inspector alsorequired that any underground conduit located where a vehicle could go over beschedule 80 PVC, instead of the normal schedule 40. Think about concrete trucks for future foundations or septic tankpumpout trucks. Since I'm located inMassachusetts, frost heaving needs to be considered. PVC expansion joints were required at each end of the undergroundconduit.

I suggest you discuss grounding with your electricalinspector. My inspector required aground wire from the main panel in the house to the subpanel in theworkshop. He also required a separateground for the workshop subpanel connected either to rebar embedded in theconcrete foundation of the workshop or to a separate ground rod located outsidethe workshop.

Hope this helps.

Bob

[Thomas Canfield]

You should make a list of the loads that your will have and then make sure the service is adequate, planning on additional loads also. Not all machines will operate at the same time but you can have the following all working at once: Heating/AC (you got to plan for this at least), 2 or 3 Hp saw, 2 hp dust collector, lights, air filter, and possibly second person using some other equipment. You can also have a shop vac (7 to 10amp) also working. One of the biggest loads is electic heat. I would not consider less than 100 Amp since the incremental cost is mostly wire at this time.

[Rollie Meyers]

4 AWG copper, & 2 AWG aluminum is NOT suitable for a 100A subfeed, as it does not meet the criteria in the NEC allowing one to UNDERSIZE the conductors for 1Ø, 3- wire service entrance conductors... See table 310.16 for correct sizes & the 90 degree column cannot be used to size conductors also.

Another note, if on the 2008 or newer code cycle, SER type cable must be sized from the 60 degree column of table 310.16, just like NM cable.

[Kevin W Johnson]

I thought about adding new service, but the pole is pretty far away and the power company will not add another service for free. Could I run a service entry cable inside the house (thus no conduit) and then a junction and switch to individual conductors for the underground run?

Have you priced having seperate service installed? I'd find out what the cost is both ways before I settled in on one or the other.

[Carl Beckett]

Hi Nick,

You can see its not all that simple of a project, and some good questions here. I am right in the middle of a very similar project. I put some 'temporary' power to the shop via routing up through the house and then an underground line as somewhat of an extension cord (I used fully rated underground power). This allowed me to swap out extension cords and run one machine at a time, and have a light.

But now I am doing the proper install. This means PERMITS, with inspections - and an electrician to provide oversight. The inspectors in my town have the position that they wont provide ANY design input, only veto stuff after the fact. They want everyone to hire contractors. In my area a full blown underground service runs $50 - $55 per foot. I have about 100ft between the shop and the street. It has to be buried with 2ft of sand under the wire, another 2ft over the wire, and a tracer ribbon on top of this. So the trench is >4ft deep and this is a problem with all the rock.

I will be putting a new higher rated service to the shop with the meter there, and then drop the house off this. A pain and more $ - but otherwise its several hundred feet to the house and then all the way back across the lot to the shop.

One other note: You likely dont need 100amps. Voltage drops are as important as max amperage. Grounding, and conduit/wire sizing are also important. I choose to consult with a couple electricians that had done it in my area, and that knew what my particular inspector would look for. I will say the project was so $$ and complicated that it motivated me to put it off for a year and just 'get by' with my extension cords.

[George Bregar]

I went with new service. My shop, a converted three car garage was 220' from the house. Far enough away for the utility to allow a second service. It was close enough to the pole to be free. They also buried the service entrance cable. Only charge is $8/month meter charge.

[Matt Meiser]

It sounds like you've already looked into it and you could do it, but in a recent discussion on our club's forum about our local utility, they won't do separate service to an outbuilding on the same property anymore. The outbuilding would have to have a separate address.

I disagree on the 100A service. If you are running a 3hp cyclone, a 3hp Unisaw, lighting etc and/or add the startup load of a central AC unit or a large air compressor you are getting up there on load. Have a friend over working with you and you could go even higher. I'd consider 100 to be the minimum for anything bigger than an average 2 car garage. You might not need it now but if you decide you do later you have to spend the money all over again.

[Tom Ewell]

I thought about adding new service, but the pole is pretty far away and the power company will not add another service for free. Could I run a service entry cable inside the house (thus no conduit) and then a junction and switch to individual conductors for the underground run?
Nick, my shop garage combo was new construction. Permits, inspections etc. were all in play. My electrician (who did my house) already knew that additional load from my existing service was insufficient to feed the shop so the point was mute.

My house service was actually further away from the shop than the utility pole so any trenching and other costs associated with it worked out to be actually cheaper.

Loads calculated should be all potentials, the "well I'm not going to use machine A at the same time as machine B so I don't need X amount of current" argument can be of some merit but if both machines are wired or plugged in then the service should really be capable of handling both.

In my case I know already that I'm in good shape, when I get around to replacing my smallish compressor with a big boy, all I need to do is run a new heavy circuit from the panel and I'm covered,don't need to worry about what happens if the compressor kicks in while I'm in the middle of ripping some good stuff on the table saw.

A smaller sub service may/should be just fine for your purposes just do it with safety first in mind.

We're all adaptable, we can figure out how far we can load the wire before tripping the breaker, that's part of the fun, just hope we don't overheat stuff enough to cause a potential breakdown that costs a lot more than the intitial investment. :)

[Stan Krupowies]

Bob, just a friendly note that the space bar is your friend. It really helps to make things more readable. :)

[Kevin W Johnson]

Bob, just a friendly note that the space bar is your friend. It really helps to make things more readable. :)

I'm guessing that he uses it already, but maybe it doesn't always register the hit. At best he may just need a new keyboard.

[Todd Burch]

I'm guessing that he uses it already, but maybe it doesn't always register the hit. At best he may just need a new keyboard.

I'm guessing it was due to a copy/paste operation from some other previous use of the explanation.

[Mike Heidrick]

I just got a bid from Ameran for dedicated 200a service to my shop. $1915.75 just for their bill. The engineer said it was considered commercial since it was second service on the property.

I am 186' from my existing service meter on my house. I am now considering 320amp service to that meter and a seperate new trenched line to the shop - a 200amp panel there.

Right now my shop is the third panel - it connects to the attached garage panel and that to the main panel.

I want to run a 20-30hp phase converter eventually so that is my driver for 200amp to the shop.

I found 200' of service entrance 4/0-4/0-4/0 aluminum on ebay for about $550 - momouth triplex URD. It says used to feed a panel - that could be used from a breaker at the meter to the shop (buried outside in conduit and ran to a new shop panel) correct for 200A service?

I am in the county and do not have to have permits/code for electrical work on my existing property here but I would like to have it sized correctly.

[Nick Cook]

Thanks for all the advice guys. As I'm adding up all the costs to run from my main panel, I think I'm going to try to get a firm quote for new service. I'm not close to a pole and but at the end of the day it may be cheaper or at least the same price, with the added advantage of me not having to do all the work. ;)

Ill keep everyone posted on what I come up with.

-Nick

[Richard Jones]

".......He stated SER cable cannot be used in conduit underground, so I used four individual THHNwires in the underground conduit....."

Pretty sure you can't use THHN in underground conduit. You sure it wasn't THHW?

[Gary Max]

I contacted the city engineer who came out and did a inspection-----showed him what I wanted to run (amps I needed). They upgraded my can and I hung a second meter. I worked with the building inspector making sure his wants where meet. He wanted a GFI next to the door--- I didn't ask why. The trick is pleasing the folks that run the show and get what you want at the same time. Don't look for short cuts they will haunt you later in the game.

[Bob Deroeck]

Richard queried "".......He stated SER cable cannot be used in conduit underground, so I used four individual THHNwires in the underground conduit....."

Pretty sure you can't use THHN in underground conduit. You sure it wasn't THHW?

Richard is correct. The wire I used was dual rated for both THHN and THHW.


Bob

[Carl Beckett]

A smaller sub service may/should be just fine for your purposes just do it with safety first in mind.

We're all adaptable, we can figure out how far we can load the wire before tripping the breaker, that's part of the fun, just hope we don't overheat stuff enough to cause a potential breakdown that costs a lot more than the intitial investment. :)

This is a good question and that is: Should we apply a safety margin on top of the margin that is built into the electrical codes?

Im an engineer and by nature like to overbuild stuff. A neighbor does electrical liability claims as a consultant - his view is that the codes are designed to allow for a safety already. If its overloaded then thats what a circuit breaker is for. So as long as wires, outlets, connector boxes, etc are all sized properly then the system is working and is safe. He asked me how many times I have ever tripped my breakers and I admitted - never (thus, I dont know if I have 10% overcapacity or 50% overcapacity)

Philosophical, but I know I do overdesign and sometimes the cost is significant to me.

[Tom Ewell]

Carl, I worked out of my basement for a while using a few dedicated circuits and knew the limits for each circuit before the breakers would trip and adjusted my work flow accordingly. So using an a smaller service can be done but it is a pain and does not allow much in the way for expansion.

As you say, a safety factor is built in for the circuits per code, no problems there. How much to consider over and above code is hard to figure, I can see using 12awg for all standard circuits be they 15 or 20amp, maybe bumping things up for dedicated circuits if the upper limit is close but much beyond that might be superfluous for a shop assuming of course that the service itself is adequately spec'd for load.


My point about safety first is the potential consideration by some to do an easy fix like strapping in a 20amp breaker to feed a 15amp circuit, I've seen it done.