On May 16, 1:28 pm, "RBM" rbm2(remove wrote:
As the others have indicated, you need to rethink this. 125 amp sub panel in
the same building as the main panel doesn't require a disconnect in it or at
it. If you need a 125 amp feeder, I believe it's 1/0 copper, which you can't
pull three plus ground through a 1 inch conduit

"tr" wrote in message

oups.com...

I am adding a 125 amp subpanel to the far side of my house. I need to
add a disconnect breaker near the new subpanel...but...I can not find
anything rated at 125 amps at either Home Deport or Lowes. The
largest they have for disconnect is 70 amps for a spa setup.?

Do I need to find a electrical supply house for this...or is there
something I am missing at Home Depot ?

Also...I am running a feeder line from the main panel to this
subpanel...the run is about 100 ft...can someone tell me what the code
is regarding the size of wire needed for this run. The retired
electrician at Home Depot says a 4awg three connector cable will be
fine...it is being run through 1" EMT across a flat roof with rain
tight compression connectors ?

Thanks, Tim

Tim-

4 Gage is fine IF you're running in air.........

in conduit you need to bump up to at least 2 gage

& you're allowed three of them in a 1" conduit but you need a ground
as well.....you "might" be able to sneak a smaller ground conductor in
there (if allowable) but you'll have to do the fill calc

Double check your ampacity (in a conduit) & make sure you spec the
correct wire .......to get the highest ampacity you'll need THHN rated
conductor

do you really need 125 amps? 95 amps could be done with 4 gage THHN
in a 1" conduit but than would be a tough pull.

if the 1" conduit is already in, sounds like you're going to be
conduit limited on your ampacity


For a sub panel like you're talking about......I'd use 1.25 or 1.5"
conduit to make my life easier

double check my info before cutting any cable

cheers
Bob

BobK207 wrote:

On May 16, 1:28 pm, "RBM" rbm2(remove wrote:

As the others have indicated, you need to rethink this. 125 amp sub panel in
the same building as the main panel doesn't require a disconnect in it or at
it. If you need a 125 amp feeder, I believe it's 1/0 copper, which you can't
pull three plus ground through a 1 inch conduit

"tr" wrote in message

groups.com...


I am adding a 125 amp subpanel to the far side of my house. I need to
add a disconnect breaker near the new subpanel...but...I can not find
anything rated at 125 amps at either Home Deport or Lowes. The
largest they have for disconnect is 70 amps for a spa setup.?

Do I need to find a electrical supply house for this...or is there
something I am missing at Home Depot ?

Also...I am running a feeder line from the main panel to this
subpanel...the run is about 100 ft...can someone tell me what the code
is regarding the size of wire needed for this run. The retired
electrician at Home Depot says a 4awg three connector cable will be
fine...it is being run through 1" EMT across a flat roof with rain
tight compression connectors ?

Thanks, Tim


Tim-

4 Gage is fine IF you're running in air.........

in conduit you need to bump up to at least 2 gage

& you're allowed three of them in a 1" conduit but you need a ground
as well.....you "might" be able to sneak a smaller ground conductor in
there (if allowable) but you'll have to do the fill calc

Double check your ampacity (in a conduit) & make sure you spec the
correct wire .......to get the highest ampacity you'll need THHN rated
conductor

do you really need 125 amps? 95 amps could be done with 4 gage THHN
in a 1" conduit but than would be a tough pull.


At connections rated 100A and less (like circuit breakers) you can only
use wire at its 60° ampacity rating.

At connections rated over 100A (or marked for wire larger than #1) you
can only use the wire at its 75° ampacity, maximum. For 125A that is
minimum size #1 with 75° insulation (like THWN). I agree with John that
you also need to consider the hot roof.

[Do you have that connection/ampacity rule in Canada Chris?]

As everyone agrees, #4 is totally inadequate. Maybe there is a reason
the "retired electrician at Home Depot" is retired.

You need a 125A disconnect at the source end which you don't mention
(but not at the subpanel). You may not find one that fits your source
panel. If you are adding load, your service may not be adequate as dpb said.

--
bud--

According to Bud-- :

At connections rated 100A and less (like circuit breakers) you can only
use wire at its 60° ampacity rating.

At connections rated over 100A (or marked for wire larger than #1) you
can only use the wire at its 75° ampacity, maximum. For 125A that is
minimum size #1 with 75° insulation (like THWN). I agree with John that
you also need to consider the hot roof.

[Do you have that connection/ampacity rule in Canada Chris?]

I don't recall seeing a rule just like that, but I don't have occasion
to look at sort of thing very much, and my CEC book is quite old now...

I _suspect_ our code doesn't shift temperature ratings based
purely on the ampacity. More based on _use_ (feed vs. circuit,
motor vs. resistive etc), conditions (eg: length, conduit,
burial, conduit fill etc) and cable type of course.

My vague comment re #4 was for 100A indoors, not in conduit etc.
I missed the significance of the routing, and I should have been
clearer it was for 100A not 125A... Oops.

My 100A garage feed is underground - 110'. Direct-burial-rated
Al #3 triplex. Would have been #4 if copper. The cable was
chosen by the electrician thru discussion with the inspector
when I balked at the price of #4 copper.
--
Chris Lewis,

Age and Treachery will Triumph over Youth and Skill
It's not just anyone who gets a Starship Cruiser class named after them.