How do I add a subpanel from my current 200amp panel

[maxspeed96ct]

So to start, im a plumber / pipefitter by trade.

I know enough about electricity to be dangerous. But my experience is limited to adding outlets and lights, wiring boilers and water heaters , swapping or adding breakers.

I'll be building a attached 2 car , and I have plently of room in my current 200amp panel. What would be the easiest/best way for me to run a sub-panel off this into my garage.

If someone could just point me in the right direction on where to start.

For example what type of wire to run from the main panel and how to tie it in.

So far this link is helpfull, but id like more then 50 amps.
http://www.hammerzone.com/archives/elect/panel/sub_panel/01/overview.htm

 

[JakeKohl]

So to start, im a plumber / pipefitter by trade.

I know enough about electricity to be dangerous. But my experience is limited to adding outlets and lights, wiring boilers and water heaters , swapping or adding breakers.

I'll be building a attached 2 car , and I have plently of room in my current 200amp panel. What would be the easiest/best way for me to run a sub-panel off this into my garage.

If someone could just point me in the right direction on where to start.

For example what type of wire to run from the main panel and how to tie it in.

So far this link is helpfull, but id like more then 50 amps.
http://www.hammerzone.com/archives/elect/panel/sub_panel/01/overview.htm

Obviously, wire size is dictated by the amperage of the service. All you need is a breaker to pull from in the main panel, four wire conductor to bring in separate hot, hot, neutral, and ground, a subpanel (designed to be a subpanel), tie in the four conductors to the appropriate terminals and make sure the neutral and the ground bus bars are NOT joined in the subpanel (you usually need to remove a jumper between the busses). As I recently learned, having the structure joined to the house means you can use the existing grounding rod system in the main panel. If the structure is separate from the structure with the main panel, it would need it's own grounding system and the neutral and ground busses would need to be connected in the subpanel (which, I don't think, is really a subpanel at that point).

I would recommend running a 90amp service since you have room. The cost difference only comes down mostly to the wire and you can use a fairly cost effective and very available aluminum 2-2-4-6 (commonly called "trailer feed" or similar). Make sure the breakers are rated for use with aluminum wire.

 

[VHF]

If the structure is separate from the structure with the main panel, it would need it's own grounding system and the neutral and ground busses would need to be connected in the subpanel

Correction needed here: A detached structure would need its own grounding system (Ufer and/or ground rods), but under recent codes 4 wires must be run from the main pannel and the neutral and ground busses kept isolated.

For an attached garage 4 wires are required and the neutral and ground busses are kept separate in the subpannel, but no additional ground rods are required.

There are lots of options for wiring to the subpannel, but any wire must be rated for use inside a structure. Some cables are intended for outdoor service entrance use only.

For a 100A feed to the subpannel, you could run #3 CU wires in conduit. For 60A service to the subpannel, #6/3 NM (Romex) would be an option as long as the cable is protected from physical damage.

 

[JakeKohl]

Good info - thanks for setting me straight...which makes me ever-more glad that I hired a genuine electrician to upgrade my primary house panel and pull the feed to the subpanel I installed in the garage.

 

[aka Larry]

I would recommend running a 90amp service since you have room. The cost difference only comes down mostly to the wire and you can use a fairly cost effective and very available aluminum 2-2-4-6 (commonly called "trailer feed" or similar). Make sure the breakers are rated for use with aluminum wire.

I'll be in this same situation soon and also have a question. I was planning on having a 100A service but the inspector told me 2-2-4-6 was only good up to 90A as you say.

My question is where do you get a 90A breaker? I haven't seen one at Lowes, which doesn't mean there isn't one, just that I haven't seen it.

 

[cderalow]

try your local electrical supply house, who should be able to source an appropriate breaker for your panel.

 

[pattenp]

Since your garage is attached you can use SER cable and not Mobile Home Feeder. SER cable can be run within walls and attic or crawl spaces without the need of conduit. SER cable is kinda like a big NM cable. Mobile Home Feeder will need to be run in conduit from panel to panel because it's four individual wires without an outer sheathing. For 90A you can use AL 2-2-4-6 but you may fine that AL 2-2-2-4 is more common.

.......
I would recommend running a 90amp service since you have room. The cost difference only comes down mostly to the wire and you can use a fairly cost effective and very available aluminum 2-2-4-6 (commonly called "trailer feed" or similar). Make sure the breakers are rated for use with aluminum wire.

 

[pattenp]

Depending on the type of panel you have most likely you have to special order a 90A breaker. I think you'll find that 90A to a typical DIY'er garage is not needed. If you can find a 70A or 80A breaker I think you'll be good to go. I have the capability to go to 90A in my garage/shop but I elected to just use a 60A breaker and have had no problems. The 60A breaker was $13 compared to $50-$60 for a 90A.

I'll be in this same situation soon and also have a question. I was planning on having a 100A service but the inspector told me 2-2-4-6 was only good up to 90A as you say.

My question is where do you get a 90A breaker? I haven't seen one at Lowes, which doesn't mean there isn't one, just that I haven't seen it.

 

[matt151617]

If you know how to run wiring, you can easily do this. Run SER cable... 6 gauge should work just fine unless you plan on super heavy current useage. Make sure you get 4 wire. Protect with a 50 amp breaker unless running through walls, then got with 40. Or just go with 2 gauge. It runs about $2.75 a foot for 2 gauge, $1.30 a foot for 6 gauge.

If the distance is short you could also do copper, more expensive but you'll get more amps in a smaller wire gauge than aluminum.

 

[maxspeed96ct]

Great info everyone, the wire will be running through my attic , or if I can manage to snake through my ceiling in the laundry / half bath room it will be a shorter route. I just have to do alittle more investigating.

attic route would be about 100ft long, while routing through my laundry room would shorten it to about 60ft.

As far as amp draw, right now it will be minimal . But I do plan on adding a outlet for a welder. And one day id love a automotive lift but thats more of a dream . The welder is realistic.

How many amps would be sufficient for a avg 240v welder ( I think most of them draw about 30amps ), some lights and outlets and 2 garage door openers . I think 60 should be just enough.
How much would be required if I did want to leave room for a auto lift ?

 

[JakeKohl]

60 would probably do it...but consider the result if it didn't. Pay me a little now or a whole lot later! 90 gives you plenty of overhead.

 

[pattenp]

Matt, would you please explain what you're saying. You lost me on the 50 vs. 40 if run in walls. Also are your sizes of 6, 4 or 2 aluminum, because later you say he could use copper.

If you know how to run wiring, you can easily do this. Run SER cable... 6 gauge should work just fine unless you plan on super heavy current useage. Make sure you get 4 wire. Protect with a 50 amp breaker unless running through walls, then got with 40. Or just go with 2 gauge. It runs about $2.75 a foot for 2 gauge, $1.30 a foot for 6 gauge.

If the distance is short you could also do copper, more expensive but you'll get more amps in a smaller wire gauge than aluminum.

 

[theoldwizard1]

I know enough about electricity to be dangerous.

If you have to ask, maybe you shouldn't try doing it yourself !

The process is the same regardless of the size of subpanel you are adding. The only difference is the size of the wire.

Grounding is different for attached versus detached building as was pointed out.

 

[Norcal]

Depending on the type of panel you have most likely you have to special order a 90A breaker. I think you'll find that 90A to a typical DIY'er garage is not needed. If you can find a 75A or 80A breaker I think you'll be good to go. I have the capability to go to 90A in my garage/shop but I elected to just use a 60A breaker and have had no problems. The 60A breaker was $13 compared to $50-$60 for a 90A.

75A is not a standard breaker or fuse size, 70A is.

 

[pattenp]

I don't know why I typed 75A, I think I had 75 degrees C on my brain thinking about wire amp capacity. He would be hard pressed to find a 2 pole 75A circuit breaker.

75A is not a standard breaker or fuse size, 70A is.

 

[matt151617]

Matt, would you please explain what you're saying. You lost me on the 50 vs. 40 if run in walls. Also are your sizes of 6, 4 or 2 aluminum, because later you say he could use copper.

Aluminum (I haven't really seen copper bigger than 8 gauge in Home Depot; even that was NM). And the breaker difference was the wiring run out in the open vs inside walls (C temp rating). The SER cable is rated at 40 amps (60C) if inside walls, 50 amps (75C) open space. I only mention it because my install had the SER in an unfinished basement along the ceiling and not through any insulation.

 

[maxspeed96ct]

If you have to ask, maybe you shouldn't try doing it yourself !

.

You sound like a women lol ! I rather struggle and have the satisfaction of doing it myself and know its done right rather then pay someone else.

If you know how to run wiring, you can easily do this. Run SER cable... 6 gauge should work just fine unless you plan on super heavy current useage. Make sure you get 4 wire. Protect with a 50 amp breaker unless running through walls, then got with 40. Or just go with 2 gauge. It runs about $2.75 a foot for 2 gauge, $1.30 a foot for 6 gauge.

If the distance is short you could also do copper, more expensive but you'll get more amps in a smaller wire gauge than aluminum.

I dont mind paying alittle extra, I do need a wire thats safe for being next to insulation.

 

[eljefino]

I'm running your typical "tombstone" welder on a 40 amp/ 240V breaker that goes to a subpanel with another 40 amp breaker. Code says since welders are intermittent loads (unless doing production work) you can use thinner wire/ smaller breakers. Naturally if you want more, go for it. I would cut through the laundry room too; a shorter run is always better.

What I would do is run a subpanel but also run a 14 gauge/ 15 amp wire for general overhead lights only, and maybe the garage door opener. Then if you blow the breaker for the subpanel and/or light a fire while welding you won't be fumbling in the dark.

 

[pattenp]

This is why I asked for you to clarify. Simply running the cable within a wall does not require the amp rating to be reduced to the 60C rating. The reduction is required if the wire is run within insulation.

Aluminum (I haven't really seen copper bigger than 8 gauge in Home Depot; even that was NM). And the breaker difference was the wiring run out in the open vs inside walls (C temp rating). The SER cable is rated at 40 amps (60C) if inside walls, 50 amps (75C) open space. I only mention it because my install had the SER in an unfinished basement along the ceiling and not through any insulation.

 

[matt151617]

This is why I asked for you to clarify. Simply running the cable within a wall does not require the amp rating to be reduced to the 60C rating. The reduction is required if the wire is run within insulation.

I'm very unfamiliar with the overly intricate NEC... is the temperature reduction required if it simply passes through a wall with insulation? If this is true, basically any garage panel install would have to have the reduction because the wire would pass through an external wall at some point. Unless it was transitioned.

 

[pattenp]

That's a good question and only the local AHJ can answer that. You would think if the cable only passed through a few inches of insulation it would not be required to meet the reduced temp. But if it has to travel through several feet of insulation then that's a whole different matter.

I'm very unfamiliar with the overly intricate NEC... is the temperature reduction required if it simply passes through a wall with insulation? If this is true, basically any garage panel install would have to have the reduction because the wire would pass through an external wall at some point. Unless it was transitioned.

 

[Aceman]

That's a good question and only the local AHJ can answer that. You would think if the cable only passed through a few inches of insulation it would not be required to meet the reduced temp. But if it has to travel through several feet of insulation then that's a whole different matter.

Keep in mind 310.15(A)2 Exception. Sometimes that'll give you a little wiggle room.

 

[Charles (in GA)]

Don't forget possible derating issues for an attic installation, due to the heat.

Charles

 

[matt151617]

OP, if you elect to go with #2 wire, you won't have to worry about the derating if you get the cheaper 70 or 60 amp breaker.

 

[Norcal]

SER cable has to be sized at the 60 degree rating now, for example for 100A using AL 1/0 is required, oversizing a cable wiring method means you have to upsize the grounding conductor, making the install non-code compliant....

 

[pattenp]

Where are you getting this requirement from? SER is only required to be sized based on 60C if run within insulation. 2011 NEC 338.10 (B) (4) (a)

SER cable has to be sized at the 60 degree rating now, for example for 100A using AL 1/0 is required, oversizing a cable wiring method means you have to upsize the grounding conductor, making the install non-code compliant....

 

[oleguy]

SER cable has to be sized at the 60 degree rating now, for example for 100A using AL 1/0 is required, oversizing a cable wiring method means you have to upsize the grounding conductor, making the install non-code compliant....

don't think so.a factory cable assembly grounding conductor is sized to max ocpd.if it were in conduit then you would have to.yes?

 

[maxspeed96ct]

OP, if you elect to go with #2 wire, you won't have to worry about the derating if you get the cheaper 70 or 60 amp breaker.

Ok , even through insulation ?

SER cable has to be sized at the 60 degree rating now, for example for 100A using AL 1/0 is required, oversizing a cable wiring method means you have to upsize the grounding conductor, making the install non-code compliant....

Sorry buddie , but im lost in what your saying. Can you lame it up for me .

 

[Norcal]

don't think so.a factory cable assembly grounding conductor is sized to max ocpd.if it were in conduit then you would have to.yes?

See 250.122(B) there are NO exceptions, unless you use a metalllic conduit & use it as the EGC.

250.122(B)

(B) Increased in Size. Where ungrounded conductors are
increased in size, equipment grounding conductors, where
installed, shall be increased in size proportionately according
to the circular mil area of the ungrounded conductors.


This supercedes other ECG sizing sections.

 

[Norcal]

Where are you getting this requirement from? SER is only required to be sized based on 60C if run within insulation. 2011 NEC 338.10 (B) (4) (a)

See 338.10(B)4(a) which takes you to art 334.

(4) Installation Methods for Branch Circuits and
Feeders.
(a) Interior Installations. In addition to the provisions
of this article, Type SE service-entrance cable used for interior
wiring shall comply with the installation requirements
of Part II of Article 334.
FPN: See 310.10 for temperature limitation of conductors.

334.80 which is in part II.

334.80 Ampacity. The ampacity of Types NM, NMC, and
NMS cable shall be determined in accordance with 310.15.
The ampacity shall be in accordance with the 60°C (140°F)
conductor temperature rating. The 90°C (194°F) rating
shall be permitted to be used for ampacity derating purposes,
provided the final derated ampacity does not exceed
that for a 60°C (140°F) rated conductor. The ampacity of
Types NM, NMC, and NMS cable installed in cable tray
shall be determined in accordance with 392.11.
Where more than two NM cables containing two or
more current-carrying conductors are installed, without
maintaining spacing between the cables, through the same
opening in wood framing that is to be fire- or draft-stopped
using thermal insulation, caulk, or sealing foam, the allowable
ampacity of each conductor shall be adjusted in accordance
with Table 310.15(B)(2)(a) and the provisions of
310.15(A)(2), Exception, shall not apply.
Where more than two NM cables containing two or
more current-carrying conductors are installed in contact
with thermal insulation without maintaining spacing between
cables, the allowable ampacity of each conductor
shall be adjusted in accordance with Table 310.15(B)(2)(a).

Underline by me.

 

[Aceman]

See 338.10(B)4(a) which takes you to art 334.

(4) Installation Methods for Branch Circuits and
Feeders.
(a) Interior Installations. In addition to the provisions
of this article, Type SE service-entrance cable used for interior
wiring shall comply with the installation requirements
of Part II of Article 334, excluding 334.80.
FPN: See 310.10 for temperature limitation of conductors.

334.80 which is in part II.

334.80 Ampacity. The ampacity of Types NM, NMC, and
NMS cable shall be determined in accordance with 310.15.
The ampacity shall be in accordance with the 60°C (140°F)
conductor temperature rating. The 90°C (194°F) rating
shall be permitted to be used for ampacity derating purposes,
provided the final derated ampacity does not exceed
that for a 60°C (140°F) rated conductor. The ampacity of
Types NM, NMC, and NMS cable installed in cable tray
shall be determined in accordance with 392.11.
Where more than two NM cables containing two or
more current-carrying conductors are installed, without
maintaining spacing between the cables, through the same
opening in wood framing that is to be fire- or draft-stopped
using thermal insulation, caulk, or sealing foam, the allowable
ampacity of each conductor shall be adjusted in accordance
with Table 310.15(B)(2)(a) and the provisions of
310.15(A)(2), Exception, shall not apply.
Where more than two NM cables containing two or
more current-carrying conductors are installed in contact
with thermal insulation without maintaining spacing between
cables, the allowable ampacity of each conductor
shall be adjusted in accordance with Table 310.15(B)(2)(a).

Underline by me.

The bold I added is in the 2011.

 

[Norcal]

The bold I added is in the 2011.

If one has the misfortune of being on the '08. Glad they corrected that mistake, too bad they would not delete the AFCI mistake..... Effing snakeoil.


There has been a lot of SER installed to the 75 degree ampacity including a subpanel in my own house which has been safe for many years, so any corrections are welcome. The correction does not apply to CA yet as we are on 2008, they are speeding up the adoption of codes a lot compared to 10 years or so ago.

.

 

[oleguy]

See 250.122(B) there are NO exceptions, unless you use a metalllic conduit & use it as the EGC.

250.122(B)

(B) Increased in Size. Where ungrounded conductors are
increased in size, equipment grounding conductors, where
installed, shall be increased in size proportionately according
to the circular mil area of the ungrounded conductors.


This supercedes other ECG sizing sections.

how do you change the egc in cable?he says ser correct?when you go to diff gauge ungrounded conductors,the egc is sized accordingly.in cable.the key here is WHERE INSTALLED.I WILL AGGREE IF CONDUIT WAS USED.JUST NOT SER.

 

[oleguy]

also nothing has been installed yet.i bellive he is asking for opinions on wire size.when a feeder size is decided on,and installed,if upsizeing is done then what you say is correct.

 

[Norcal]

how do you change the egc in cable?he says ser correct?when you go to diff gauge ungrounded conductors,the egc is sized accordingly.in cable.the key here is WHERE INSTALLED.I WILL AGGREE IF CONDUIT WAS USED.JUST NOT SER.

You don't, the SER becomes non-compliant. Conduit would be required, this only applies when oversizing. It's just another one of those time where no good deed goes unpunished, a few code cycles back it was only required when upsized for voltage drop, but that exception was removed.

 

[pattenp]

2011 NEC 250.122 (A) now only requires multiconductor cable to comply with table 250.122, so 250.122 (B) doesn't apply.

See 250.122(B) there are NO exceptions, unless you use a metalllic conduit & use it as the EGC.

250.122(B)

(B) Increased in Size. Where ungrounded conductors are
increased in size, equipment grounding conductors, where
installed, shall be increased in size proportionately according
to the circular mil area of the ungrounded conductors.


This supercedes other ECG sizing sections.

 

[oleguy]

You don't, the SER becomes non-compliant. Conduit would be required, this only applies when oversizing. It's just another one of those time where no good deed goes unpunished, a few code cycles back it was only required when upsized for voltage drop, but that exception was removed.

roger that..thanks for your view...

 

[matt151617]

Ok , even through insulation ?



Sorry buddie , but im lost in what your saying. Can you lame it up for me .

Yes, even through insulation, it's rated higher than the breaker you'll be putting in even with the reduction.

 

[pattenp]

As a multiconductor cable, SER is compiant under 2011 NEC.

roger that..thanks for your view...

Originally Posted by Norcal
You don't, the SER becomes non-compliant. Conduit would be required, this only applies when oversizing. It's just another one of those time where no good deed goes unpunished, a few code cycles back it was only required when upsized for voltage drop, but that exception was removed.