I found 3 pieces x 60 feet each of 2 ga aluminum XHHW-2 (90 degree C) wire. I plan to run this on a 100 amp CB in the shop. Is there any issues with AL wire? Thanks!
Aluminum 2ga wire Q
- Thread starter 930dreamer
- Start date
porschedude996TT
Well-known member
No problem as long as the new panel and the breaker are ok with the alu wire. The power companies use it all the time. XHHW-2 90C 2 gauge is exactly what you will need.
OP
The mains are fed with AL wire, so I'm assuming the CB won't be an issue?
rabidsquirrel
Well-known member
The CB needs to be marked in order for it to be ok. AL/CU usually.
OP
I'd have to check that the CB is rated for AL/CU, thanks.
pattenp
Well-known member
#2 Al should be over current protected to no more than 90 amps when used as a branch or feeder circuit. When used as service entrance for a dwelling it can be protected at 100 amps.
Just what are you going to feed with this wire?
Just what are you going to feed with this wire?
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Bold underline by me.
(7) 120/240-Volt, 3-Wire, Single-Phase Dwelling Services
and Feeders. For individual dwelling units of onefamily,
two-family, and multifamily dwellings, conductors,
as listed in Table 310.15(B)(7), shall be permitted as
120/240-volt, 3-wire, single-phase service-entrance conductors,
service-lateral conductors, and feeder conductors
that serve as the main power feeder to each dwelling unit
and are installed in raceway or cable with or without an
equipment grounding conductor. For application of this section,
the main power feeder shall be the feeder between the
main disconnect and the panelboard that supplies, either by
branch circuits or by feeders, or both, all loads that are part
or associated with the dwelling unit. The feeder conductors
to a dwelling unit shall not be required to have an allowable
ampacity rating greater than their service-entrance conductors.
The grounded conductor shall be permitted to be
smaller than the ungrounded conductors, provided the requirements
of 215.2, 220.61, and 230.42 are met.
Table 310.15(B)(7) Conductor Types and Sizes for
120/240-Volt, 3-Wire, Single-Phase Dwelling Services and
Feeders. Conductor Types RHH, RHW, RHW-2, THHN,
THHW, THW, THW-2, THWN, THWN-2, XHHW,
XHHW-2, SE, USE, USE-2
Conductor (AWG or kcmil)
Service or Feeder
Rating (Amperes) Copper
Aluminum or
Copper-Clad
Aluminum
100,4, 2
110, 3 ,1
125, 2 ,1/0
150, 1, 2/0
175 ,1/0, 3/0
200, 2/0, 4/0
225 ,3/0, 250
250 ,4/0, 300
300, 250, 350
350, 350, 500
400,400, 600
The 1st number is the ampere rating, 2nd number is the wire size using copper, 3rd number is the wire size using aluminum conductors, this is a copy & paste from the 2011 NEC, sorry that the chart did not copy in the same format it was copied from.
OP
30 hp 3 phase motor.
Gooch
Well-known member
what voltage? 208 or 240?
if 208, you need #2 copper or #1/0 Alum 75* rated insulation or greater.
if 240, you need #3 copper or #1 Alum 75* rated insulation or greater.
you can NOT apply table 310.15(B)(7)
208 can be protected with up to a 225A Breaker or 175A TD Fuses
240 can be protected with up to a 200A Breaker or 150A TD Fuses
Then size your overloads based on the chart with your starter.
100 amp breaker seems too small, you will probably run into nusiance tripping when starting(unless you have some form of soft starter)
OP
It's going to be a rotary phase converter idler @ 240 V. I spin it up to speed to reduce to inrush current.
wyliesdiesels
Well-known member
So then you're not feeding a motor, you're feeding a rotary phase converter? The circuit requirements are different then!
rabidsquirrel
Well-known member
Sounds like he's spinning up a larger motor with another smaller motor to me.
OP
Spudland_Dave
Well-known member
So, just like a 3 year old...I like to know why...
Why is it the #2 AL can carry 100A sometimes and only 90A other times?
Seems silly a cable capacity is detetmined by the application vs the materials it was made with? Its like saying 12-2 Romex is good for 20A for recepticles in your living room, but only good for 15A in your kitchen...BTW I was cable shopping last Friday and HD has a chart of conductors and ampacity...the chart there shows #2 AL as 100A...
wyliesdiesels
Well-known member
I too have wondered about this in the past. I've done some digging in my NEC and other code reference books but couldn't find the reason for this! Thx for bringing it up Dave.
pattenp
Well-known member
Branch circuits are sized by 310.15(B)(16) whereas Service entrance as the main power feed to a building is sized by 310.15(B)(7) 2011 NEC. It is what it is.
wyliesdiesels
Well-known member
Yes, I'm aware of both those tables and have both of them in front of me. I realize "It is, what it is" but
that's not the answer to the question. The question is, what's the science or engineering behind this?
that's not the answer to the question. The question is, what's the science or engineering behind this?
pattenp
Well-known member
wyliesdiesels
Well-known member
LoL!
Harleyguy
Active member
I will never use aluminum wire again. Due to the heat and expansion and contraction of aluminum wire it has a tendency to get loose at the lug. Loose connections will arc and burn. Just my 2 cents.
Thats why they require a de-oxidizer on all the connections and have a lug that is rated for al-cu connections, if you size wire properly to a load it will never heat up. I agree though, aluminum is just a good way to save money and I would never recommend it over copper.
wyliesdiesels
Well-known member
Copper expands, contracts and heats up as well, though not as bad as aluminum. If aluminum is terminated and installed correctly, it works just fine for decades of service with no problems. U have to make sure of a few things including that the terminals are rated for al, put anti-ox on the bare ends and make sure to torque them down the proper amount! Aluminum wire is used for primary wire on poles- ACSR, and to feed all types of customers including residential, commercial and industrial.
Spudland_Dave
Well-known member
I haven't a clue. But, I can tell you why water is wet.
LOL...Sounds like the NEC is like my mom when I was 5...."if you dont get to bed, the boogey man will come"....
Again...So I spoke with an electrician about this over a coffee...and he said if I hooked my garage feed to the meter, It would be ok to use a 100A breaker in the Garage Panel..but if I hook it up to my Main Panel, it technically 90A... makes no scientific sense to me.
I suppose thats probably why he told me to get 100A Breaker for my panel and not worry about it.
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porschedude996TT
Well-known member
The 100amp main in your new sub-panel is more of disconnect than a breaker.
I don't find much science in the whole NEC, looks like a pile of band-aids to me... Just my opinion.
I don't find much science in the whole NEC, looks like a pile of band-aids to me... Just my opinion.
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Spudland_Dave
Well-known member
I agree about the "Disconnect" statement...he actually used the word "Disconnect" as the determining factor... IN other words, if theres a breaker "feeding" the 2ga, that breaker SHOULD be 90A, if there is no "feed breaker" as in it comes in "off the pole" you can protect that same wire with a 100A main in the panel.
My point of contention is why should it be any different either way? 100A is 100A no matter where the power is coming from or going to.
Professur
Well-known member
I'm no electrician .. but it seems obvious to me why it would only have a 90 on the sub panel ... it's coming off a 100A on the main, correct? Well, if I'm working in the garage pulling 90A at the sub, add in loss for the stretch between sub and main ... I'm over 90 at the main now ... no? So the likelihood of me popping a breaker is high at this point .. yes? So ... where do I want the breaker to pop? Here at the sub (where the draw is) or way over at the main ... well away from where I'm working (if it wasn't ... I wouldn't need a sub in the first place)? Just seems common sense to me.
wyliesdiesels
Well-known member
Since you're not an electrician, let me fill u in. In the NEC, there is 2 ampacity tables- 1 for service conductors, the other for branch circuits and feeders. A 2ga AL wire has an ampacity of 100amps when used as a service conductor. However, the same exact wire, when used as a branch circuit feeder, MUST be protected with a 90amp breaker! So, the wire is either classified as a service conductor or a branch feeder. Breakers are sized based on the wire they're protecting. Its not about what breaker location is more convenient for the user, or what size is needed to compensate for losses! You don't install a higher amperage breaker to compensate for distance or voltage losses, either! That's a no no! What you're suppose to do is increase the wire gauge to compensate for losses!
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But why?!?!
Proposal to delete it:
http://www.necplus.org/Features/Pages/SomeProposedChangestothe2014NEC.aspx?sso=0
I wish I knew more about this stuff.
Proposal to delete it:
http://www.necplus.org/Features/Pages/SomeProposedChangestothe2014NEC.aspx?sso=0
I wish I knew more about this stuff.
I spin the 30hp with a 5 hp gas motor and throw the switch.
Can we see a video of this? And what the heck are you powering with that much motor!?
Spudland_Dave
Well-known member
Close but you got it backwards...
100A in the Sub-Panel, which essentially becomes a Shut-Off at that point and its fed with a 90A in a Main Panel.
since everyone on here is so hard up on everything being 100% code compliant, lets get it correct.
Size wire based on 310.15b16 for conductors in a raceway (almost all except triplex, or conductors in free air)
Derate it based on ambiant temperature, what the lugs your terminating on are rated for as far as temperature, how many conductors in a raceway, how far above a rooftop it is, ect... then that is the ampicty. Unless it is a dwelling unit service conductor feeder then its table 310.15b7
#2 is good for 100amps in a non residenial service feeder application according to the ampacity table of 310.15b16 if its rated for 90*c but I will bet you can't find a lug rated for 90*c so you move over a column to the 75*c column and it 90 amps. But for example if its in a boiler room thats 130*f and its in a raceway with 5 different current carrying conductors you would apply both of those deration factors with the starting point of 90*c if your wire is rated for that in the first place.
The NEC is kinda dumb.
Size wire based on 310.15b16 for conductors in a raceway (almost all except triplex, or conductors in free air)
Derate it based on ambiant temperature, what the lugs your terminating on are rated for as far as temperature, how many conductors in a raceway, how far above a rooftop it is, ect... then that is the ampicty. Unless it is a dwelling unit service conductor feeder then its table 310.15b7
#2 is good for 100amps in a non residenial service feeder application according to the ampacity table of 310.15b16 if its rated for 90*c but I will bet you can't find a lug rated for 90*c so you move over a column to the 75*c column and it 90 amps. But for example if its in a boiler room thats 130*f and its in a raceway with 5 different current carrying conductors you would apply both of those deration factors with the starting point of 90*c if your wire is rated for that in the first place.
The NEC is kinda dumb.
wyliesdiesels
Well-known member
Yes, we(all sparkies on here, I hope) are well aware of the deration factors.
But, that still doesn't answer the question of WHY is the same piece of wire limited to 90a when used in certain applications!
Because residential loads are limited it is allowed to UNDERSIZE the SE conductors & they chose to draw the line somewhere, but there are still the illiterate who think that 2AWG aluminum is OK for 100A everywhere.
Spudland_Dave
Well-known member
So the NEC from my point of view...tends to err on the side of extreme caution...and rightfully so...It still doesnt explain why or how the NEC would allow 100A on 2ga if it would cause problems in ANY application. Just because its an SE & Residental, doesnt mean the metallurgical properties of aluminum change.
In theory, the cable IS the SE for the garage...as I mentioned it would be legal to run 2GA from the pole to my panel, but its not legal from panel to panel.
wyliesdiesels
Well-known member
Good insight.
Agreed! I guess we'll never really know the science! In my code book in front of me, I see the same applies to copper service conductors. So this isn't limited to al!
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