feeder wire for a subpanel
ben...@pookmail.com
main in the basement. I'm guessing it's about a 40' run. The panel
will be 100A or 125A. The reading I've done so far suggested I need
SER type cable for the feeder run. I couldn't find this cable at any
local home store. One store had SER aluminum listed as special order,
but they couldn't get it anyway.
Any idea what the right cable is for this? I also hope this comes as
a sheathed cable, or would it be 4 separate cables?
J.A. Michel
<ben...@pookmail.com> wrote in message
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You can't run conduit? I'd use conduit and THHN conductors.
S. Barker
is 4/3 with ground. And it does come in romex if you go to the electrical
supply house.
s
<ben...@pookmail.com> wrote in message
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ben...@pookmail.com
> If it's 4 seperate cables, they'll have to be in a conduit. What you need
> is 4/3 with ground. And it does come in romex if you go to the electrical
> supply house.
They make romex in a large enough gauge for this? I was guessing it
must be huge (e.g. 4 or 6 gauge)...
ben...@pookmail.com
>
> You can't run conduit? I'd use conduit and THHN conductors.
Not unless I can get some kind of thin flexible conduit. I'll be
running this across the basement (through the floor joists), up the
inside of the wall, into an attic space, along a roof joist and down a
wall stud into the new panel.
ben...@pookmail.com
> You may have to go to a real electrical supply. #1 SER is probably way
> out of the "hobby" class that the home stores cater to.
> The other question is, are you sure you really need 100a? Are you
> using electric strip heat or a tankless water heater?
So #1 SER is what I need?
I'm running a ton of stuff. I'll install 7 20A circuits. I calc the
max simultaneous draw will be in the 70A range. It includes a couple
space heaters, two electric griddles, a heat gun (the latter two for
encaustic painting), computers, lighting, some tools. Part of what's
going on is I'm making up for some homeowner installed way
undersuitable wiring. My entire 2nd floor (about 500 sf) is tied into
1 first floor 20A circuit. So I can barely draw from the existing
wiring for my needs.
Big_Jake
I ran a feeder for an addition on my house, very similar to what you
are talking about. It is SE cable or "Service Entrance" cable, and
not exactly romex, but the same idea. I bought mine around the time
copper was at the all time high, so we went with aluminum. It is
2-2-2-4 cable, with three 2 gauge conductors and one 4 gauge conductor
for the ground. I think it was around $1.50 / foot, from a supply
house. This was for 100 amps. I assume the copper equivalent would
be one gauge smaller, but I don't have my code book in my hands.
My cable is about 1" in diameter, so the copper equivalent would be a
little smaller, but still really substantial. You also want to be
VERY sure that you don't run in where you might shoot a drywall screw
or a nail into it. With 100A going through it, you could have a
really bad day.
JK
RBM
volt. The feeder you intend to run is 100 amp @ 240 volt. That's 200 amps @
120 Volt. What gfretwell suggested #6 copper, is 60 amp @ 240 volt or 120
amp @ 120 volt. More than enough for your load
<ben...@pookmail.com> wrote in message
news:d09973d6-f528-47dd...@l1g2000hsa.googlegroups.com...
Big_Jake
> On Mon, 10 Dec 2007 20:51:16 -0800 (PST), benj...@pookmail.com wrote:
> >So #1 SER is what I need?
>
I'm not completely up on my code, but apparently there is an exception
which allowed me to have 100A breaker with the 2-2-2-4 Aluminum SE
cable. All the work was down under permit and has been inspected.
JK
RickH
Can you use one inch rigid exterior conduit and go up the outside of
the house then back into the house on the top floor? Running it along
a downspout maybe so it's not conspicuous. Then it will be easy to
just pull whatever wire you want.
HerHusband
> main in the basement. I'm guessing it's about a 40' run. The panel
> will be 100A or 125A.
If you want to install a 100A breaker for your subpanel, you'll need to
run four #2 copper wires (or 1/0 aluminum). I've never seen sheathed
cable this large, even at my local electrical supply stores, so you'll
probably have to run individual conductors in conduit.
> Not unless I can get some kind of thin flexible conduit.
You'll need at least 1-1/4" PVC conduit for the four #2 wires, though I'd
go with 1-1/2" as it's a lot more common and would be easier to pull
wires through.
The largest flexible conduit I've seen is 1", so you'll probably need to
use rigid conduit.
> I'll be running this across the basement (through the floor joists),
> up the inside of the wall, into an attic space, along a roof joist
> and down a wall stud into the new panel.
You could run rigid conduit along the underside of the joists if
appearance isn't an issue. Otherwise, if the conduit has to run
perpendicular to the joists, you'll need to use lots of short sections
with couplings. A lot more work, but doable. Plumbers do it all the time.
Keep in mind, the holes you drill for the conduit can't be any larger
than 1/3 the depth of the joist, and must be at least 2" from the top and
bottom edge of the joist. A 2" hole for the conduit would be too big to
fit in a 2x6 joist, but you should be fine if you drill your holes in the
center of 2x8 or larger joists. I'd still choose surface mounting if
that's an option.
You'll need pulling elbows where you change directions (basically an
angle with a removable cover).
Installing conduit would be a lot of work, but it would offer better
protection and make changes easier in the future.
However, if you think you can get by with a 60Amp panel, you could use
6/3 romex cable which is commonly available at most home centers (it's
frequently used for installing kitchen ranges).
If you really think you'll need 100 amps or larger, maybe you could
install two 60A subpanels, fed with two separate 6/3 cables? That would
be a lot easier to install, and give you 120A total, assuming you have
space for two 60A breaker pairs in your main panel.
> The reading I've done so far
I recommend you pick up a copy of "Code Check Electrical". It condenses
all the various code requirements for cable sizes, conduits, derating
requirements, etc. Be warned though, it's not a "how-to" book, it's more
reference material. You'll probably have to read through the important
sections multiple times to catch everything.
Anthony
S. Barker
an NM-B 4/3 with ground.
s
<ben...@pookmail.com> wrote in message
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S. Barker
s
<gfre...@aol.com> wrote in message
news:mnasl3tvddsut21ed...@4ax.com...
> On Mon, 10 Dec 2007 20:42:49 -0800 (PST), ben...@pookmail.com wrote:
>
>>They make romex in a large enough gauge for this? I was guessing it
>>must be huge (e.g. 4 or 6 gauge)...
>
> Romex tops out in #2 that would work for 100a if it was copper but he
> said aluminum.
S. Barker
s
<gfre...@aol.com> wrote in message
news:vsasl39bk2dpu7meo...@4ax.com...
> On Mon, 10 Dec 2007 20:51:16 -0800 (PST), ben...@pookmail.com wrote:
>
>>So #1 SER is what I need?
>
fg
> If you are really using that much up there I doubt you really need any
> space heaters. I bet you would do fine with 60a. That is a lot. That
> is 14,400 watts. How big are these griddles?
Good point. I won't need one of the space heaters whenever I'm using
the griddles. The griddles draw 12A each, and do release a lot of
their heat into the room. The other heater is needed, though, as it's
in a different room.
fg
> You are calculating your demand incorrectly. You're max draw is 70 amp @ 120
> volt. The feeder you intend to run is 100 amp @ 240 volt. That's 200 amps @
> 120 Volt. What gfretwell suggested #6 copper, is 60 amp @ 240 volt or 120
> amp @ 120 volt. More than enough for your load
You're right, I think my max is around 70A at 120 volt. I guess I was
presuming you feed a subpanel with 240V so that it provides a balanced
load to both bus bars. So you're saying I could feed the panel with a
60A 240V breaker using 6/3 romex, and then pull more than 60A at 120V
(e.g. install 7 20A 120V circuits with a max simultaneous draw around
70A)?
That would make this all easier.
Doug Miller
>On Dec 11, 5:58 am, "RBM" <rbm2(remove this)@optonline.net> wrote:
>> You are calculating your demand incorrectly. You're max draw is 70 amp @ 120
>> volt. The feeder you intend to run is 100 amp @ 240 volt. That's 200 amps @
>> 120 Volt. What gfretwell suggested #6 copper, is 60 amp @ 240 volt or 120
>> amp @ 120 volt. More than enough for your load
>
>You're right, I think my max is around 70A at 120 volt. I guess I was
>presuming you feed a subpanel with 240V so that it provides a balanced
>load to both bus bars.
That's one reason. The other reason is to supply 240V loads.
> So you're saying I could feed the panel with a
>60A 240V breaker using 6/3 romex, and then pull more than 60A at 120V
>(e.g. install 7 20A 120V circuits with a max simultaneous draw around
>70A)?
Absolutely -- as long as you don't pull more than 60A on any one leg at any
time. 30 on one leg, 40 on the other, will be just fine.
>
>That would make this all easier.
Yep.
--
Regards,
Doug Miller (alphageek at milmac dot com)
It's time to throw all their damned tea in the harbor again.
Big_Jake
> WHO said alum?
>
> s
>
> <gfretw...@aol.com> wrote in message
>
> news:mnasl3tvddsut21ed...@4ax.com...
>
> > On Mon, 10 Dec 2007 20:42:49 -0800 (PST), benj...@pookmail.com wrote:
>
> >>They make romex in a large enough gauge for this? I was guessing it
> >>must be huge (e.g. 4 or 6 gauge)...
>
> > Romex tops out in #2 that would work for 100a if it was copper but he
> > said aluminum.
I think I started the talk of aluminum, saying that I had used it for
the cost savings over copper.
JK
Big_Jake
> On Tue, 11 Dec 2007 10:58:22 -0600, "S. Barker"> cite that, it sure isn't what 310.15(B)(6) says
The Table in 310.15(B)(6) says, for a dwelling, which we are assuming
this is, for a "Service or Feeder", which this sounds like, the rating
in amps for a #4 copper or #2 aluminum shall be 100A. Are you saying
that the problem is that it isn't a service but a subpanel? This
should fall under the definition of "feeder" and I'm sure that my AHJ
and electrician had that in mind when they allowed & ran my feeder,
protected by a 100A breaker, through a piece of 2-2-2-4 Aluminum SE
cable.
If I'm wrong, tell me how.
JK
S. Barker
Big_Jake
> On Tue, 11 Dec 2007 17:48:25 -0800 (PST), Big_Jake
> as the main power feeder to a dwelling unit". That means if this is
> the feeder to the main breaker you can use the table. This assumes the
> diversity of the total house load. You won't be using everything at
> once. That may not be true in a feeder to a sub panel since we don't
> know what the sub panel serves.
> Don't feel bad. A lot of people get confused by this, even inspectors
> who should know better.
Here's a couple more for you - (I don't do this for a living)
According to another table in 310-16, my SE cable would have been ok
for 100 amps if the wire was rated for 90c. and #4 Copper ok for 95
amps, which would can be "rounded up" to the next common breaker size,
no?
JK
Big_Jake
> On Wed, 12 Dec 2007 18:48:45 -0800 (PST), Big_Jake
> listed for 90c. The 90c column is really just there for derating
> purposes. An example is if you had 8 THHN conductors in a pipe you
> have to derate them down to 70% of their ampacity 310.15(B)(2) but
> since THHN is a 90c conductor you can start derating from the 90c
> ampacity. So for a #12 you would start derating from 30a, get 21a but
> you are still limited by 240.4(D) that makes it 20.
So the termination at the breaker of the main panel and the connection
to the buss at the other end aren't rated for 90c?
JK
ben...@pookmail.com
> On Tue, 11 Dec 2007 09:24:46 -0800 (PST), fg <bgros...@gmail.com>
> wrote:
>
> >On Dec 11, 5:58 am, "RBM" <rbm2(remove this)@optonline.net> wrote:
> >> You are calculating your demand incorrectly. You're max draw is 70 amp @ 120
> >> volt. The feeder you intend to run is 100 amp @ 240 volt. That's 200 amps @
> >> 120 Volt. What gfretwell suggested #6 copper, is 60 amp @ 240 volt or 120
> >> amp @ 120 volt. More than enough for your load
>
>
> will balance 80a across the 2 hot legs but going 60a is just a few
> bucks more for 6/3. The breakers and panel will probably be the same.
So does that mean I would only need a 60A double-pole breaker in the
main to feed the subpanel? This breaker will feed two hots (240v) to
the subpanel bus bars, and then I can pull up to 96A (80% of 120) of
120v from that subpanel?
Doug Miller
>
>So the termination at the breaker of the main panel and the connection
>to the buss at the other end aren't rated for 90c?
Almost certainly not -- but they're marked. Check 'em.
Doug Miller
>On Dec 11, 4:32 pm, gfretw...@aol.com wrote:
>> On Tue, 11 Dec 2007 09:24:46 -0800 (PST), fg <bgros...@gmail.com>
>> wrote:
>>
>> >On Dec 11, 5:58 am, "RBM" <rbm2(remove this)@optonline.net> wrote:
>> >> You are calculating your demand incorrectly. You're max draw is 70 amp @
> 120
>> >> volt. The feeder you intend to run is 100 amp @ 240 volt. That's 200 amps
> @
>> >> 120 Volt. What gfretwell suggested #6 copper, is 60 amp @ 240 volt or 120
>> >> amp @ 120 volt. More than enough for your load
>>
>>
>> From what you say there 40a with #8/3 would be more than enough. You
>> will balance 80a across the 2 hot legs but going 60a is just a few
>> bucks more for 6/3. The breakers and panel will probably be the same.
>
>So does that mean I would only need a 60A double-pole breaker in the
>main to feed the subpanel?
Yes.
>This breaker will feed two hots (240v) to
>the subpanel bus bars,
Yes.
>and then I can pull up to 96A (80% of 120) of
>120v from that subpanel?
The 80% rule applies to continuous loads -- defined as maximum current for
more than three hours.
You only identified about 70A of load anyway...
RBM
or 120 amps @ 120 volts
<ben...@pookmail.com> wrote in message
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ben...@pookmail.com
> So does that mean I would only need a 60A double-pole breaker in the
> main to feed the subpanel? This breaker will feed two hots (240v) to
> the subpanel bus bars, and then I can pull up to 96A (80% of 120) of
> 120v from that subpanel?
Should that 60A double-pole breaker be a 120/240v or just a 240v? I
would presume the latter, but I see both at the store so thought I'd
ask.
Thanks to *everyone* who has been so generous with their time and
expertise!
HerHusband
>> main to feed the subpanel? This breaker will feed two hots (240v) to
>> the subpanel bus bars, and then I can pull up to 96A (80% of 120) of
>> 120v from that subpanel?
> Should that 60A double-pole breaker be a 120/240v or just a 240v? I
> would presume the latter, but I see both at the store so thought I'd
> ask.
You want a 240V breaker that has two breakers tied together with a common
bar. When you turn the breaker off, you want to turn off BOTH legs of the
240V supply.
You DO NOT want the double breakers with two individual switches, as that
could still leave one half of the supply powered if you didn't flip both
switches.
Just to clarify, if you run 6/3 wire with a 60A breaker, that's 60 amps on
EACH side of neutral (60 on the black wire, 60 on the red wire).
If you balance half of your 120V loads on one side, and the other half of
your 120V loads on the other, it should support close to 120Amps total. I'm
not sure what the derating requirements are, but it should be more than
enough to support the 70A loads you are planning.
Anthony