Electrical Question - Service to Garage

[Adam Carl]

I am running a 100amp service from my house to my detached garage. The garage is 2 stories and my shop will be in the 2nd floor. I live in New York state and I am wondering if I need a service disconnect switch where the feed enters the garage. I am planning on putting the panel on the second floor. Would a main breaker on the panel be sufficient?

[Von Bickley]

Adam,
In my area, you would not need a disconnect at your building. The main breaker in the sub-panel would be sufficient.
You would also have a breaker at the house that supplies the power to the sub-panel.

Hope this helps. This is also in my area of SC. You may want to check with your local inspector.

[Jay Jagerson]

Most people also forget they need 4 wires and need to purchase a second ground bar and remove the bonding strap on the exisitng grounding bar. That is if you bought a new Laodcenter type of panel.

[Tom Godley]

I have not needed to provide a separate disconnect -- but this is with the feed wire running directly to the panel from the outside. I would have had to put one in if I wanted to run the feed wire any distance inside the building -- say if you want the panel on the second floor and the wire enters the structure on the first.

On the one I was not required to have a main breaker in the sub-panel. I like to have one as it makes it easy to turn the whole panel off.

[David G Baker]

I have a breaker in my main house panel that feeds the 220v 100 amp line to my detached shop. I also have a disconnect in my shop so I don't have to run to the house and kill the breaker if I want to do some wiring in the shop. I believe in overkill when it comes to making sure that the power is off when I am working on the lines.
Save your self a lot of confusion and work by running 4 legs to your shop. 2 hots, one neutral and one ground.

[Adam Carl]

Thanks everyone. Looks like I may need a service disconnect. I'll have to do some research. And yes I am running 4 wires.

[Roger Frazee]

Hi Carl

Not sure if you will be back but will add this just in case you or someone else my be interested.


I am running a 100amp service from my house to my detached garage. The garage is 2 stories and my shop will be in the 2nd floor. I live in New York state and I am wondering if I need a service disconnect switch where the feed enters the garage. I am planning on putting the panel on the second floor. Would a main breaker on the panel be sufficient?I think we should see what is required by the NEC since every jurisdiction follows it...:) with very few local exceptions.

When ever you install an outside feeder from the service equipment in the house to a detached garage you'll be spending some time looking at Article 225 of the NEC which covers outside feeders to detached buildings.

225.32 addresses the requirements for a detached building disconnect. And states as follows " the disconnecting means shall be installed either inside or outside of the building or structure served." The disconnecting means shall be at a readily accessible location nearest the point of entrance of the conductors"..ie.. (feeder). So yes you must have a disconnect located at the building/garage very close to where the feeder enters. So where ever the feeder first enters the garage you must locate the disconnect very close to that point. If your feeder is installed in conduit underground then comes out of the ground and runs up the outside of your garage to the second floor then enters the building then you can do as you wish with a main breaker panel. The main breaker will satisfy the requirement of 225.32. If this is not the case then where ever the feeder enters the building either inside or outside install a single main disconnect that is rated as suitable for service equipment (NEC 225.36) then continue from that disconnect to an mlo (main lug only) panel on the second floor. The only problem an inspector may have with the disconnect located on the second floor will be the accessibilty of that disconnect to emergency personnel like the fire department. He may allow it or he may not.

It would be very unlikely that an inspector that is up on the code to allow the breaker at the house panel to satisfy 225.32.

You need a ground rod or possibly 2 ground rods at the garage. If your electrical jurisdiction is following 2008 code then you are required to run a 4 wire feeder and keep the neutral and ground electrically isolated from each other by not bonding them. How you do this will depend on the panel and maker of that panel. Some will require that you purchase an accessory ground bar to install in the panel since there will only be one factory installed neutral bus bar. So in order to isolate neutral and ground you will need another busbar to use for grounding purposes for your branch circuits.

Your configuration for the panels and feeder will follow the attached diagram below. Use this as a guide but remember you should get an inspection to verify what you have done is code compliant and safe.

Some things to remember or consider....:)

There are strict burial depths for underground feeders in conduit usually 18 inches for pvc in residential applications. 24 inches if the feeder is direct buried. This is measured to the top of the conduit if using conduit.

Ground rods probably two 8 footers but maybe 6 footers if allowed by local codes. Drive them vertically if possible to about 6 inches below grade and at least 6 feet apart. Use acorn ground rod clamps and #6 solid copper wire to connect to rods then terminate on the grounding lug of the disconnect panel or the main breaker panel which ever you use. The inspector may have a preference.

For a 100 amp feeder disregarding voltage drop considerations use # 3 awg copper conductors ( hots and neutral) with a #8 awg equipment ground. If they are underground in conduit use thwn or thwn-2 rated insulation for wet locations. If your using aluminum conductors in conduit then #1 awg for conductors and a #6 awg equipment ground. All conductors to be insulated including the ground wire if conduit. Identify the neutral before you pull it.

If your using a quadplex underground cable then marking will be taken care of by the factory. The neutral usually will have an appropriate colored stripe down its length as will the equipment ground. Be sure the quadplex has insulation (like rhw) that allows it to enter a building if your disconnect is inside.

http://media8.dropshots.com/photos/440526/20090905/212354.jpg

This diagram below illustrates why you do not bond neutral and ground in a sub-panel supplied by a 4 wire feeder. Just so you understand....:)

http://media7.dropshots.com/photos/440526/20091005/144844.jpg

These are my drawings (stubbie) so as with any information you get off the internet be sure to verify with a knowledgable person they are correct for your application.

[Adam Carl]

Roger,

This is what I was looking for, thank you very much. My father in law is a union electrian but does mostly commercial work. He and another union electrian tell me I don't need a service disconnect but based on article 225 of the code I believe I do. My father in law has adviced me correctly on all your other points, but I must say your picture was really easy to understand. I believe many people can benefit from this.

I have already dug the trench (22 '' deep) and laid conduit and my pipe enters the garage on the first floor and the feed will be run to the second floor to a sub panel. Because of this and the fact that the second floor will be behind a locked door I'm sure the inspector will require a disconnect where the service enters the building. I'll plan for this.

Thanks,

Adam








Hi Carl

Not sure if you will be back but will add this just in case you or someone else my be interested.

[George Bregar]

I have already dug the trench (22 '' deep) and laid conduit and my pipe enters the garage on the first floor and the feed will be run to the second floor to a sub panel. Because of this and the fact that the second floor will be behind a locked door I'm sure the inspector will require a disconnect where the service enters the building. I'll plan for this.

Thanks,

Adam I don't think the locked door is the issue, the distance is. My utility requires a separate disconnect if the panel is more then 8' from the service entrance. Not sure what the NEC says about that, or your local code is, but it makes sense.

[Jason Roehl]

Roger, what is the point of running the ground from the main panel to the garage if there are two grounding rods in the ground at the garage, and the neutral and ground are bonded at the main. Why not just run 3 wires to the garage (2 hots, neutral), and bond the neutral to the ground (hooked to the two rods) at the garage?

I spent a couple years in electrical engineering, so I have the basics of electricity down. The code flat out baffles me sometimes.

[Rod Sheridan]

Jason, it's to make sure that the grounds in both buildings are at the same potential.

Obviously the earth has resistance, so when there's a current to ground, the potential of the grounded wire rises above the earths potential.

If the two buildings weren't tied together, this change in potential will cause current to flow along other inter building conductors such as pipes, communication wires, fences etc.

Regards, Rod.

[Rollie Meyers]

If your panel has a main breaker that is your disconnect, as to being required to have a disco outside, unless local rules require it no need, the reason for have service entrance conductors as short as poss. is because they are unfused between the transformer & the cash register (KWH meter) which is not the case for a subfeed. 2 ground rods are required unless you can prove 25 Ohms of resistance or less, a extra rod is cheaper then the testing to prove it meets that requirement.

[Jason Roehl]

Jason, it's to make sure that the grounds in both buildings are at the same potential.

Obviously the earth has resistance, so when there's a current to ground, the potential of the grounded wire rises above the earths potential.

If the two buildings weren't tied together, this change in potential will cause current to flow along other inter building conductors such as pipes, communication wires, fences etc.

Regards, Rod.

Thanks, Rod. I wasn't thinking of a fault condition (or other wires, fences, pipes, etc.) After all, the power company uses the ground as a part of the circuit path. Maybe we could get some $ out of them if we can prove there is current running through our property?

[Rod Sheridan]

Thanks, Rod. I wasn't thinking of a fault condition (or other wires, fences, pipes, etc.) After all, the power company uses the ground as a part of the circuit path. Maybe we could get some $ out of them if we can prove there is current running through our property?


You can try, however my dealings with the utility indicate that their cash flow is uni-directional:D.

regards, Rod.

[Roger Frazee]

Roger, what is the point of running the ground from the main panel to the garage if there are two grounding rods in the ground at the garage, and the neutral and ground are bonded at the main. Why not just run 3 wires to the garage (2 hots, neutral), and bond the neutral to the ground (hooked to the two rods) at the garage?

I spent a couple years in electrical engineering, so I have the basics of electricity down. The code flat out baffles me sometimes.


Jason

After two failed attempts to give a detailed answer with drawings due to being timed out and logged off which resulted in the loss of the posts...:mad: I will just say this...the NEC does allow for 3 wire feeders as you suggest... if a set of conditions are met.

The idea behind a 4 wire feeder versus a 3 wire feeder is that with 4 wires with a separated ground from neutral it is much less likely for a parallel path to be constructed by intention or accident for neutral current to use to return to the transformer.

You might study some of these drawings in my albums to help with your understanding.......double click a drawing to enlarge it. The last 3 drawings are very relevant to this thread. The other albums may be of interest also. Feel free to copy or 'save as' if you like. Like I have said these drawings are mine and accurate but be sure they apply to your situation. The username you see on the drawings may be different,.. It depended on the forum I was posting the drawing on.

http://www.dropshots.com/stubbie4#albums/Grounding%20and%20bonding

[Chris Padilla]

Roger...OT about your sig line.

I understand its intention but technically, if you are scared half to death and are scared half to death again...assuming you were already scared half to death, then you are only 1/4 dead...then 1/8...then 1/16.... ;) haha sorry :D

[Roger Frazee]

Roger...OT about your sig line.

I understand its intention but technically, if you are scared half to death and are scared half to death again...assuming you were already scared half to death, then you are only 1/4 dead...then 1/8...then 1/16.... ;) haha sorry :D

:D You are certainly right..... I'll let the author of the qoute 'the cable guy' know that he is not technically correct....LMAO

[Jason Roehl]

Roger...OT about your sig line.

I understand its intention but technically, if you are scared half to death and are scared half to death again...assuming you were already scared half to death, then you are only 1/4 dead...then 1/8...then 1/16.... ;) haha sorry :D

Actually, Chris, you're going the wrong way. After the second time, you'd only be 1/4 alive. :D :cool:

Thanks, Roger!

[Chris Padilla]

Actually, Chris, you're going the wrong way. After the second time, you'd only be 1/4 alive. :D :cool:

Thanks, Roger!

Doh! Good catch, Jason!! Goshdarnitalltoheck! :p

[Roger Frazee]

I was really busy tonight but had time to squeeze some thought in after my nap. I realize we are off subject ( I didn't start this ..:rolleyes:) but looking at it in terms of a linear graph ... the cable guy may actually be correct. If fully alive is our maximum parameter then 1/2 scared to death is a magnitude of 1/2 of a fully alive life. If I get a scare again that is equal to 1/2 scared to death of fully alive....then I'm fully scared to death. Seems simple to me......:confused: It's all in the details.....;) 1/2 scared to death + 1/2 scared to death = 1 Scared to Death

The issue is what qualifies for fully alive. Some of us would probably not need a 1/2 scared to death ......twice.... to expire.

http://media7.dropshots.com/photos/440526/20091105/190540.jpg

http://media6.dropshots.com/photos/440526/20091105/182406.jpg

[Jason Roehl]

See, I disagree, Roger. Consider that if one has 100 life units and is half scared to death. This leaves the unfortunate fraidy cat with but 50 life units. Since there is no indication that one can recover life units, this is now the sum total of what separates him from death. Along comes the second episode of being half scared to death, which now removes not 50 life units, resulting in death, but a mere 25 life units, half of the 50 life units said fraidy cat previously enjoyed, and leaving him with the meager total of 25 life units, 1/4 of his original supply.

[Roger Frazee]

:D You know I think the problem is we are 'considering this'......:)

[Roger Frazee]

Roger,

This is what I was looking for, thank you very much. My father in law is a union electrian but does mostly commercial work. He and another union electrician tell me I don't need a service disconnect but based on article 225 of the code I believe I do. My father in law has advised me correctly on all your other points, but I must say your picture was really easy to understand. I believe many people can benefit from this.

I have already dug the trench (22 '' deep) and laid conduit and my pipe enters the garage on the first floor and the feed will be run to the second floor to a sub panel. Because of this and the fact that the second floor will be behind a locked door I'm sure the inspector will require a disconnect where the service enters the building. I'll plan for this.

Thanks,

Adam

Adam

I just wanted to say that Rollie is correct you can use a main breaker panel to satisfy the building disconnect even though you will have redundant breakers of equal rating...one at the house panel and one in the detached buildings panel..... but it will have to be located pretty close to the feeder entrance to the building.

But also understand that we are talking about a disconnect that will open the two ungrounded conductors so it does not have to provide over current protection. The breaker in the house panel protects the feeder...it can simply be a manual disconnect (100 amp disconnect) at the detached building inside or out located very close to where the feeder enters...then continue the feeder on to an mlo panel. This is my preference a bit more money but awfully convenient and gives you more options as to where you want to locate the mlo sub-panel.

[Roger Frazee]

Roger,

This is what I was looking for, thank you very much. My father in law is a union electrian but does mostly commercial work. He and another union electrian tell me I don't need a service disconnect but based on article 225 of the code I believe I do. My father in law has adviced me correctly on all your other points, but I must say your picture was really easy to understand. I believe many people can benefit from this.

I have already dug the trench (22 '' deep) and laid conduit and my pipe enters the garage on the first floor and the feed will be run to the second floor to a sub panel. Because of this and the fact that the second floor will be behind a locked door I'm sure the inspector will require a disconnect where the service enters the building. I'll plan for this.

Thanks,

Adam

Sorry I didn't acknowledge your reply...sometimes I get distracted....:)

I was glad to help and hope your project goes well. I too was union (Ford skilled trades) for many years.