Sub panel ground wire size ?

I'm going to put a subpanel in a garage. I'm going to run #4 copper off a 70 amp breaker for the hots and neutral. It's about 70 feet and #6 would probably do but I picked up a partial roll of #4 cheap. But what I don't know is what the rules are for the ground wire size?
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On Apr 7, 7:32 am, snipped-for-privacy@gmail.com wrote:

I never found anyone with an answer for this. How do you figure out the ground wire size for a subpanel?
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On May 4, 3:36 pm, snipped-for-privacy@gmail.com wrote:

Did you look? I DAG'd http://www.google.com/#hl=en&q=what+size+ground+wire+subpanel and the first hit answers your question and tells you the relevant code. The Terry Love forum hit near the top is also pertinent, as is this: http://www.codebookcity.com/codearticles/nec/necarticle310.htm R
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Neither one really answers my question for a 70 amp circuit. I saw it said #8 for 100amp. I've stumbled across other posts that refer to tables. I'm guessing it's decided by the supply size breaker, not the breakers in the sub panel. Given #8 for 100amp I'm guessing maybe I could use #10 for 70 amp? I've got to go about 70 ft so I don't want to buy any bigger wire than I have to.
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snipped-for-privacy@gmail.com wrote: ...

Code Sec 250-94 limits minimum size to no less than #8.
Voltage drop tables indicate for 240V you need T rated temperature to make 75 ft ampacity rating for 70A/2% voltage drop w/ #8 anyway.
I'd pull #6; the initial cost differential is a one-time thing; the voltage drop savings and peace of mind are forever.
--
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On May 5, 12:15 pm, snipped-for-privacy@gmail.com wrote:

If it's a cost question, sell the #4 you got for cheap and buy #6 with #8 ground. I'd figure the #4 is about twice the price of the #6 so you probably wouldn't have to go back into your pocket.
The NEC is copyrighted, as are most codes out there. You won't find them online - just snippets here and there. Even if you had the book in front of you, it still won't address every situation. That's where the inspectors come in as they're the guys in the trenches interpreting the code...for good or bad.
R
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Yes, I've noticed that about the code. Seems stupid, it should just be on the internet. Sounds like I need to use #8 for my ground to meet the code I'd rather just go ahead and do that than try to "trade in" the #4 I have now for different wire. I'm not getting this inspected but the various building codes are generally good sense so I try to follow them.
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On May 5, 2:32 pm, snipped-for-privacy@gmail.com wrote:

Agreed. It's as stupid as if you had to BUY your 1040 forms. I would also think that someone could mount a Freedom Of Information act class- action suit and spank the fookers into open-sourcing code.

The NEC, while arcane at times, is much more rationale and arbitrary than a lot of the building code. Some of the local villages around here adopt modifications to the state code that are so stupid that you want to cry. 'Luckily' they have part-time building inspectors who aren't up on the code themselves, so everyone starts in the same place - in a hole!
I actually had one inspector show up after framing was completed on a small remodeling job, and ask where the window header was! The structure was all exposed and there was only one window opening in the project... I stood there with my mouth literally hanging open and pointed wordlessly to the area over the window.
R
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Actually, the NEC is available in two places on line:
At <http://www.nfpa.org>, if you register for a free account. The NEC is known as NFPA 70. If you search their site and go to the web page for NFPA 70, at the bottom are links for "View this document" for the 2002, 2005, and 2008 versions.
At <http://resource.org/bsc.ca.gov/index.html , you can find the California State building codes. The California Electrical Code is the 2005 NEC with some amendments.
Cheers, Wayne
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Thanks for that info. I registered for the free account and viewed it. Not a very user-friendly way of accessing it - I hate the Java applet, but, hey, it's free and right from the horse's mouth.
R
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responding to http://www.homeownershub.com/construction/sub-panel-ground-wire-size-16972-.htm archibald tuttle wrote:
Wayne Whitney wrote:

nfpa was a bust. they seemed to want $165 for a membership, couldn't find a link to get a free account. maybe I didn't prospect long enough.

Bingo- gotta respect those legislatures retentive enough to enact this stuff as statute. I don't think it is legitimate for the the electric industry to withhold from people rules to which they are subjected. To me the battle to free the code is like that to free legal decisions which used to closely held in cyberspace by westlaw and lexis. Thank god for Findlaw, an early pioneer and google scholar which got many of the older decisions by OCR I'll guess.
The legislators in california did precisely what I believe the constitution requires - enact into law those rules which we must follow rather than delegate to unelected 'experts' what rules we must follow.
Meantime, most electrically focused forums fall all overthemselves to ban helping homeowners. I'm surprised that none of their fellow electricians are homeowners. here I thought that was a decent paying blue collar job. What a great attitude. A help site with no help. Like not helping homeowners, i.e. nonprofessionals, will make them safer. I have no problem if professionals choose not to spend their time answering simple questions over and over for folks who can't google. I have no problem if the nature of a question reveals that the poster is likely completely out of their depth that professionals simply suggest - get a professional. I have no problem if sites want to differentiate between professionals so you know whether a particular piece of advice is coming from a credentialed person.
But this snotty protectionist barrier to entry kind of stuff where you can't even see a code table unless you have a secret decoder ring has got to stop:
Table 150.122 California Electric Code         Equipment Grounding Conductor         circuit breaker    copper    aluminum 15    14    12 20    12    10 30    10    8 40    10    8 60    10    8 100    8    6 200    6    4 300    4    2 400    3    1 500    2    1/0 600    1    2/0 800    1/0    3/0 1000    2/0    4/0 1200    3/0    250 1600    4/0    350 2000    250    400 2500    350    600 3000    400    600 4000    500    800 5000    700    1200 6000    800    1200

cheerio
-------------------------------------
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The "National Electrical Code" is a copyrighted document and cannot be reproduced without permission from the NFPA who publishes it. There is no conspiracy to withhold information from the general public. I encourage do-it-yourselfers to learn the parts of the code that applies to the particular job that they are working on.
On my web site I reference the particular articles that apply to the work that I am discussing. I also have links to purchase the code book and other code reference short cut books as well.
John Grabowski http://www.MrElectrician.tv
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snipped-for-privacy@gmail.com wrote:

6ga is pretty much the standard for panel grounding up to 200a.
There's a reason that 6ga bare copper comes in a box of 25'.
s
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