# 100 amp sub panel hook up?



## ponch37300 (Nov 27, 2007)

I am installing a 100 amp sub panel in my detached garage. the main panel in the basement of the house is a 200 amp. i bought i 100 breaker for the main panel. does the 100 amp sub panel need to be main breaker or can i use a main lug since i have a disconnect in the main panel. If i remember right anything over 6 ft it will need a main disconnect? also can i use aluminum ser cable for the feed in between panels and if so what size? Will 2-2-2-4 sluminum ser cable work for this? Also i bought two ground rods for outside of the garage, do i need these if i run 2-2-2-4 with the 4 ga ground wire? Thanks for any help or advice on this. I used to work for an electrician about 10 years ago so i have good knowledge on electrical, just a little rusty and things have changed and i want to do this right.


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## NateHanson (Apr 15, 2007)

I'm not sure about the main breaker requirement for the sub, but you do need the ground rods for the sub in a detached building.


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## ponch37300 (Nov 27, 2007)

Thanks Nate. I thought so, that's why i bought them but i wasn't sure. I beleive i need a main breaker panel but once that is confirmed and the wire is confirmed i will be good to go! Thanks again


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## HouseHelper (Mar 20, 2007)

If the garage is detached, you must have a main disconnect in the subpanel. Ground rods are required. The 2-2-2-4 cable is only good to 90A, which should be more than sufficient in a residential garage.


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## ponch37300 (Nov 27, 2007)

2-2-2-4 wire only 90 amps? I thought i read it was rated for 100 amps. Is this wire ok to use with a 100 amp breaker in the main panel? The main reason for wanting this wire is i can get it for 1.76 a foot. I was going to use number 2 copper in conduit but that is 1.17 a ft and i would need three lines so i'm looking at 3.51 ft plus conduit compared to 1.76 with the 2-2-2-4 alum. Thanks for your help, it is much apppreciated.


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## HouseHelper (Mar 20, 2007)

Ask your local code official if they allow Table 310-15(b)(6) to be used for the feeder to a detached garage. If they do, then the 100A breaker is OK. If they don't, then Table 310.16 would apply and the limit for #2Al is 90A. 

As I said before, 90A should be more than sufficient for a residential garage.


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## ponch37300 (Nov 27, 2007)

Thanks house helper, i will call them. I already have the 100 amp breaker and i'm not sure if they make a 90 amp? Thanks again for your help


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## Andy in ATL (Aug 28, 2007)

HH, Why would they not allow the table? Local ammendment?

Andy


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## HouseHelper (Mar 20, 2007)

Andy in ATL said:


> HH, Why would they not allow the table? Local ammendment?
> 
> Andy


Some interpret this as: Since a garage is not a dwelling the table doesn't apply.


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## Stubbie (Jan 7, 2007)

Table 310.15 (B)(6) is intended for main power feeders to dwellings and services to dwellings. These are conductors that carry the load to the entire dwelling. A detached garage is not a dwelling and its feeder is not a mains feeder. There is some clarification on table 310.15 b 6 coming in the 2008 code cycle to hopefully put an end to the controversy over using it for non-mains feeders.

Househelper

Can you help me with the main breaker required in that detached garage load center? Is there a code section that makes this clear? 

Here is my understanding based on article 225. You are required to have a disconnect at the nearest point of entrance of the feeder conductors. It can be a disconnect on the outside/inside of the garage then a mlo on the load side of it anywhere you want to locate it once that disconnect is installed at the entrance point of the feeder. Or as you say a main breaker in the sub-panel. Or the inevitable 6 disconnect rule can be utilized.

Having said that I personally like the remote disconnect with a load side mlo sub panel in the garage.

Ponch here is a diagram of the requirements for a 4 wire feeder from the main panel to the detached garage


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## ponch37300 (Nov 27, 2007)

Stubbie...Thanks for the drawing, looks like it took some time. In your reply you say 08 clears up the dwelling issue, you say a detached garage can't go by table 310.15 b 6, so you are saying 2-2-2-4 alum wire is a no go for a 100 amp panel? If that wire is no good, I have about a 60-70 ft run, about 20-25 ft of it outdoors, what size and type of wire would you suggest, or do they make a 90 amp breaker like someone else suggested? I am trying to do this on a budget and already bought the 100 amp breaker for the main panel so i am trying to decide if buying bigger wire or a new breaker and smaller wire would be cheaper. Thanks again to everyone for taking the time to help, your advice is trully appreciated. Also, stubbie, your drawing doesn't show a disconnect for the main lug sub panel, from your reply you say i need one right? And if the sub panel is a main lug within 6 ft of the cable entrance that will do for a disconnect right? Thanks again


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## Stubbie (Jan 7, 2007)

Yes it is not allowed to carry 100 amps in your situation. Yes they make 90 amp breakers.

100 amps is huge for a garage most are done with 60 amp feeders to a 100 amp panel. Are you going to have a large shop out there or just the typical
power tool stuff? Welder? Big air compressor?

I was in the process of adding the disconnect rule to the drawing... it shows up there now....sorry I was in a hurry. You may use the ruling that if you do not install more than 6 swipes of the hand to disconnect all power in that sub-panel this will be acceptable as a disconnect. This for example means 6 single pole breakers, or 5 singles and 1 double ....get the idea? A main breaker works for compliance or a remote disconnect works. Once you add that 7th swipe of the hand you must install a main breaker...is this making sense to you?

That wire is an excellent price so use it just step down on the breaker size. You might be fine with a 70 or 80.


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## Stubbie (Jan 7, 2007)

One other thing are you using the ser underground in conduit? It is not listed for direct burial. I read the thread but didn't notice where you said one way or the other.


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## ponch37300 (Nov 27, 2007)

Thanks stubbie you really share great advice. I do have a big welder and compressor, not sure the exact amprage. I understand the 6 rule now thanks to you. I will get that wire and a new breaker and a main breaker sub panel. Yes the wire will be in conduit for the underground part, what size should i use for this, 1.5 inch? One last thing what size does the stranded ground wire have to be from the sub panel to the ground rods, 6 ga? Thanks again


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## Stubbie (Jan 7, 2007)

PONCH

I'll have to calculate the conduit size for you it is a little different than individual wires I'll let you know in bit if 1 1/2 is good.....FYI cables are rarely ran underground in conduit however SER is rated for wet location so you can run it in conduit if you like just be freakin sure to be careful pulling it thru the bends and use sweeps whenever possible, you may have to upsize the Lbs that transition your conduit into & out of the structures.

If I may.... see what you can get mobile home feeder for this will really work great if you want that much amperage out there in that garage, you can direct bury it or run it in conduit your choice. If this works for you just direct bury at 24" and use sch.80 pvc where it comes out of the ground for protection with a sweep at the bottom of the trench. Here is what I'm talking about......

http://appprod.southwire.com/ProductCatalog/XTEInterfaceServlet?contentKey=prodcatsheet15


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## Stubbie (Jan 7, 2007)

Ponch

You are good to go with 1 1/2 pvc if you choose to run the ser. You are allowed a 53% fill of 1.052 inch squared for a cable in 1 1/2 pvc. Ser 2-2-2-4 is 955 mils.... converted it is .7159 inch squared so it is well below the max. 53% fill.

Yes.... 6 guage copper gec to the ground rods.


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## ponch37300 (Nov 27, 2007)

Thanks for all the info and advice stubbie. I will see what i can come up with for the wire but whatever i get i will know it is done right thanks to you. Why not run cable in conduit? What would be my other options? mobile home wire? THHN in conduit?


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## Stubbie (Jan 7, 2007)

Yes... those are good options I posted a link to mobile home feeder in a post just before this. IMO the biggest draw back to cable in conduit is it is really hard to pull through and it is not quite as good at getting rid of heat in conduits as it would be with individual conductors like thwn.....thhn is not wet rated but most thhn is now dual rated for wet location and will show thhn/thwn on the outer insulation.. (w) = wet rated. Underground runs of conduit are considered wet locations as the conduit over time will get water in it.

If we had the input amperage of the welder and the amperage of the air compressor and voltage requirements we might be able to get a little more accurate with the amperage you need out at the garage. If you can give me that or the names of the manufacturers and model numbers I might be able to figure that up and get a better handle on the power requirements for the garage. At any rate 90 amps will certainly take care of now and future needs. So look at it in terms of cost benefit. If you can get by on 60 or 70 amp feed we can get the wire size down and conduit size down etc...Direct bury saves a little in labor and conduit costs. 

Also if you use conduit you can always install larger conductors someday if needed. You just have to try to be realistic about the demands of your equipment in the future and not overkill for no good reason it's too costly with no benefit. 

Hope this is helping and not confusing you.


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## ponch37300 (Nov 27, 2007)

It is making sense and really helpful. According to the manual for the welder the input is 53 amps at 230 volts. I'm not sure about the compressor but it is 230 volts, probably 30 amps or so, i will have to check later. Then i will have the misc. lighting and receps, nothing major here, just a 2.5 car garage. So does that 53 input amps meen that if i 60 amps feeding the sub panel and use the welder that is about all i can use? If this is so i think the 2-2-2-4 ser cable is my best bet for the price and a 90 amp breaker? I don't think i am going to find any cable cheaper than 1.76/ft. The mobile home wire would have to be in conduit from the main panel to the outside of the house, about 30 ft or so in the basement? Thanks

P.S. I like your avator(sp?), I have a 00 f150 and a 03 f250 powerstroke with alot done to both trucks. I love the diesel!


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## Stubbie (Jan 7, 2007)

Well 53 amps is the maximum required input amperage to produce the rated output amperage for the arc of the welder. You would probably not use the welder at that setting often. If you don't consider duty cycle that is pretty hefty. Most of the time your probably going to be welding at around 30 to 40 amps or less input. It is likely that the compressor will cycle while you are welding and that will usually work out as long as you are not welding at maximum output setting. But you have to design for the correct operation of the equipment.... so 60 amps is cutting it too close.
I would say that you might as well use the Ser which will not have to be in conduit till you get outside with it. Put it on a 90 amp breaker or an 80....can you return the 100 amp? Hope so.
Yes the mobile home feeder would have to be in conduit till you leave the house and go underground and back into conduit at the garage. So from what you posted as distance from your main panel to the outside it doesn't look like your going to save anything.
Normally you should assemble the conduit with a pull string and pull the cable thru. If you elect to not do that be very careful of the glue and don't let a bunch of it get on the cable. It will eat up the cable jacket. At the sub I like bottom entry with the panel lugs to the top. Just use the side gutter to go up and over to your main lugs and neutral lug. Some panels are designed to be rotated 180 degrees....top down so to speak....to facilitate bottom entry...I hate this but it is acceptable so just a heads up. You likely will need a ground bar kit for the sub. It will install in prepunched swaged hole sets in the panel back. Like this...do not install the bonding means in the neutral bar. Remove it if it has been factory installed. Every panel is a little different and some have two neutral bars that can be arranged so that one can be configured into a ground only..... isolated electrically from the neutral. Just remember the neutral bar is the one on the insulated stand offs with no bond to the metal of the panel or the ground bar unless you want it that way. 









The image below is a bonding jumper it can be used in some cases to convert a neutral bar to a grounding bar. But mostly this is to bond the neutral to ground in a main panel situation. You see these a lot in panels with two neutral bars that have a metal strap between them. The jumper bonds the neutral to the metal of the panel for a service equipment application. You don't want this in your sub-panel. You will not install this jumper and add the ground bar like the image before this. Remove this jumper if it has been installed by the factory, Then install your ground bar kit. Just want you to see that not all panels are the same. Some use a green bonding screw.


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## LawnGuyLandSparky (Nov 18, 2007)

Let me point out, It's one thing to understand how, another thing to understand why. 2-2-2-4 is OK for a 100a residential service, even though #2 isn't quite rated for 100 amps, because the instances when a residence with a 100a service actually approach a 100a load on either of the 2 120v service legs is rare, and any such load would surely be intermittant.


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## Andy in ATL (Aug 28, 2007)

Hey Stubbie, 225.31 is the applicable code.

Andy


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## Stubbie (Jan 7, 2007)

Thanks Andy

I read househelper to mean a main breaker is required in the sub-panel as the only form of disconnect allowed. I have actually heard this before but have not been able to find that to be clear in the NEC. Maybe I just read too much into hh's post.


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## rjbham (Dec 1, 2007)

*Wire for underground conduit*

Maybe this is a good place for a related question. I have a detached garage. I messed up and only got 3 wire 222 Type SEU to run from the house panel. But I believe I can use it if I ground the garage panel to the rebar in the foundation and a 8' ground rod. Then the neutral bar and grounding bar will be connected. I will run the SEU through the attic and wall to a junction box on the outside wall of the house. Then I will splice to XHHW and pull through buried PVC conduit to the garage. The neutral is bare stranded wire. Should the neutral be spliced to a jacketed XHHW to pull through the conduit? In other words, 2 jacketed hots and a bare neutral spliced to 3 jacketed wires for the conduit.


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## Stubbie (Jan 7, 2007)

You need to start a new thread


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