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Old 04-16-2008, 11:56 PM   #16
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Originally Posted by jrclen View Post
I was hoping you weren't going to do that. For aluminum you will need a #1 wire.

Your the first one that has said 2-2-4-6 AL wont hold my 100amp sub. Everyone else says that I am ok in doing this. PLUS with everything ON in my shed I MIGHT draw 45 amp IF im lucky

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Old 04-17-2008, 12:31 AM   #17
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The conductors aren't being upsized due to voltage drop or any reason related to proper circuit operation. So I wouldn't apply that here. Good point though. Are you talking about a service with aluminum 2-2-4-8? We are talking about a copper feeder with 2-2-2-8. I doubt the inspector will even blink at your wire size if it is a service. That is very common.
This is a subpanel feeder in a church, copper. I was joking about the inspector catching it, no one seems to use #3. I don't see any exceptions to 250.122(B), I bet it applies but is not enforced.

MR500, I'll be the second person to tell you, you need #1 aluminum. There are charts in the codebook showing wire ampacities for different situations. In this instance, #2 aluminum is only good for 90 amps.
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Old 04-17-2008, 09:59 AM   #18
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Originally Posted by mr500 View Post
Your the first one that has said 2-2-4-6 AL wont hold my 100amp sub. Everyone else says that I am ok in doing this. PLUS with everything ON in my shed I MIGHT draw 45 amp IF im lucky

Mike
Did you explain that you are installing a feeder for a sub panel? These people you mentioned are probably thinking you are installing a service. There is a difference in the code. You can install the 2-2-4-6 aluminum if you want. If the inspector approves the installation, you have it made. If he red tags it, you get to pull out that wire and replace it with conductors which comply with the code. All I am trying to do is give you the facts and cite the National Electric Code. I cannot force anyone here to do things correctly. That is your inspectors job. But I will not advise you to install something which does not comply with the code. That would not be ethical.

There is a way around this. Install a 90 amp circuit breaker to protect the 2-2-4-6 aluminum wire. Then convince the inspector with calculations showing the #4 neutral will be large enough to handle any load imposed on it in the future.

Call your inspector and ask him what he will accept and approve.
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Old 04-17-2008, 10:17 AM   #19
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This is a subpanel feeder in a church, copper. I was joking about the inspector catching it, no one seems to use #3. I don't see any exceptions to 250.122(B), I bet it applies but is not enforced.
I was going out on a bit of a limb with my statement, and citing the intent of the code. (and the text in my 2008 handbook) 250.122B is enforced. If we must increase the size of the ungrounded conductors due to voltage drop or to comply with some other article of the code, we then have to apply 250.122B. I run across this in industrial location feeders pretty often.

But in my opinion, increasing the size of the ungrounded conductor simply to buy a size which is available, would not present any reason for a larger grounding conductor on a circuit which doesn't require a larger conductor.

Of course you and I both know, an inspector could refuse to see things my way and make me pull a new EGC.

Good catch though Cow, and I'm glad you brought it up.

Petey, how about a second or third opinion?
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Old 04-17-2008, 12:27 PM   #20
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Don't you just love this stuff? I'm not sure there is a freakin electrician on the planet that agrees on how 250.122(B) is applied. I would like to think there has to be some math principle that can be shown as to why there would be any change required for the egc if a larger conductor is used on a circuit that would normally be served by the next size down. If your feeding a 100 amp rated sub-panel.. then 100 amps is the maximum ocpd allowed. If there are no conduit derations, no ambient deration and no voltage drop considerations, no impedance considerations so an so forth then as far as the egc is concerned it would seem to me it would have no logical or mathmatical or safety reason to be upsized.
If you come along someday and hang a 125 amp sub you could breaker the #2 at 110 amps or next size up 125 amps and this would require an obvious upsize to #6 egc in accordance with T250.122. All is well provided we pull a new egc. 250.122(B) is pretty much non issue under this type circumstance.

250.122(B) is for those situations where an upsize in ungrounded conductors is a result of some other factor like high deration applications or voltage drop to name a few.

As an example if I'm running a feeder for a 100 amp sub-panel and the length of the feeder requires me to consider voltage drop... then I will be looking at 250.122(B).

A 100 amp feeder normally takes a #8 copper conductor at 16,510 cmil.

If I am choosing to maintain a 2% voltage drop on my feeder and my source voltage is 240 volts then at 100 ft I can use #3 copper ungrounded conductors and #8 copper egc.

But at 130 feet to maintain 2% I need #2 copper... still 100 amp rated sub-panel and 100 amp ocpd.

#2 copper is 66,360 cmil and #3 copper is 52,620 cmil....so 66,360/52,620 is a multiplier of 1.29

Since my egc would normally be #8 copper using table 250.122 I would need to multiply the cmil of #8 copper by 1.29.

1.29 x 16,510 cmil = 20,821 cmil this would require upsizing the #8 egc to #6 egc. and a different result from the egc table.
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Old 04-17-2008, 03:36 PM   #21
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I think I can answer this pretty simply. 122b is telling us that if the impedance of our #3 is to high over a given distance and we need to use say, #1. Then the impedance of our #8 over that distance will also be to high, so 122b tells us to upsize the EGC also.

But that would not apply to simply running a #2 just because the supply house doesn't carry #3. So we would be allowed to ignore 122b in this case.

The explanation in the handbook points this out pretty well. Of course the handbook notes, like fine print notes, are not code.

Of course, the further I crawl out on this limb, the more I look down to see if Petey is coming with his chain saw.
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Old 04-17-2008, 05:22 PM   #22
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Did you explain that you are installing a feeder for a sub panel? These people you mentioned are probably thinking you are installing a service. There is a difference in the code. You can install the 2-2-4-6 aluminum if you want. If the inspector approves the installation, you have it made. If he red tags it, you get to pull out that wire and replace it with conductors which comply with the code. All I am trying to do is give you the facts and cite the National Electric Code. I cannot force anyone here to do things correctly. That is your inspectors job. But I will not advise you to install something which does not comply with the code. That would not be ethical.

There is a way around this. Install a 90 amp circuit breaker to protect the 2-2-4-6 aluminum wire. Then convince the inspector with calculations showing the #4 neutral will be large enough to handle any load imposed on it in the future.

Call your inspector and ask him what he will accept and approve.

OK. Not trying to ruffle feathers, Im just trying to learn how to do all this. SO, I guess it would be best if I just ran copper #3 in conduit??and a #8 for eq gnd following what you guys say about the AL wire. What size conduit will hold all this wire?
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Old 04-18-2008, 10:42 AM   #23
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OK. Not trying to ruffle feathers, Im just trying to learn how to do all this. SO, I guess it would be best if I just ran copper #3 in conduit??and a #8 for eq gnd following what you guys say about the AL wire. What size conduit will hold all this wire?
There is nothing wrong with aluminum wire. You just need to use the correct size for the circuit breaker you want to install on the circuit. For 100 amps use 1-1-1-6 aluminum or 3-3-3-8 copper wire. Make sure the wire has a W in the type, for your underground conduit. Such as THWN or XHHW. Use a minimum size of 1 1/2 sch 40 PVC conduit for the 1-1-1-6, and minimum 1 1/4 sch 40 PVC for the 3-3-3-8 copper. If this service is to a separate building such as a garage or shed, don't forget a ground rod.

I just checked, feathers are ok.
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Old 04-18-2008, 06:08 PM   #24
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I don't like any direct burial. If anything ever happens to it your S O L.

Please don't tell the utilities this. They would need to install millions of poles and many millions of miles of overhead to replace all the direct burial.
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Old 04-18-2008, 06:20 PM   #25
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Please don't tell the utilities this. They would need to install millions of poles and many millions of miles of overhead to replace all the direct burial.
No just put it in pipe and its all good.
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Old 04-18-2008, 08:39 PM   #26
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There is nothing wrong with aluminum wire. You just need to use the correct size for the circuit breaker you want to install on the circuit. For 100 amps use 1-1-1-6 aluminum or 3-3-3-8 copper wire. Make sure the wire has a W in the type, for your underground conduit. Such as THWN or XHHW. Use a minimum size of 1 1/2 sch 40 PVC conduit for the 1-1-1-6, and minimum 1 1/4 sch 40 PVC for the 3-3-3-8 copper. If this service is to a separate building such as a garage or shed, don't forget a ground rod.

I just checked, feathers are ok.
Well good. We need our feathers don't we. I'm just going with the 3-3-3-8 and get it over with and ill use 2" for the piping. A lot of the wire i find is only that THHN ...Then I see some that has THHN THWN as well. I am assuming they are NOT the same. All that has to do with the sheathing and I need the W for wet locations correct?? CAN a wire be THHN and THWN?? that problay makes NO damn sense at all huh. hahahah
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Old 04-18-2008, 08:51 PM   #27
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Well good. We need our feathers don't we. I'm just going with the 3-3-3-8 and get it over with and ill use 2" for the piping. A lot of the wire i find is only that THHN ...Then I see some that has THHN THWN as well. I am assuming they are NOT the same. All that has to do with the sheathing and I need the W for wet locations correct?? CAN a wire be THHN and THWN?? that problay makes NO damn sense at all huh. hahahah
It's dual rated. I've yet to see a piece of THHN that wasn't also THWN.
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Old 04-18-2008, 08:53 PM   #28
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OK GREAT. So if I buy off ebay and it says THHN I assume then it will work for wet locations THWN Good stuff!!!!!!!!!!!!!!
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Old 04-19-2008, 09:45 AM   #29
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I agree with cow, most THHN is dual rated THWN now days. But I wouldn't pull it in an underground conduit without seeing that W. I have a thing about not doing things twice. So look to make sure.
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Old 04-19-2008, 05:21 PM   #30
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Great. Fantastic answerers just what I was looking for on this. Ill be sure and read the cover BEFore he cuts it and i slap it in conduit!!

Off the spend money

Mike

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