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 ?
Does the subpanel you're installing not already have a "main"
breaker in it? The disconnect doesn't have to be separate.
Use an ordinary house main panel "package", not a main-breaker-less
subpanel for the subpanel.
Further, in the CEC, you can use a main panel breaker pair
as a disconnect for the subpanel - you don't have to have
the disconnect at the sub. This may be true in the NEC also.
[I _prefer_ to be able to kill the subpanel from the main
without killing the main. But, if there's a long distance
between the two, having a second breaker in the sub
[Mine has breakers at both ends. A Siemans main panel "package"
with 100A main in the garage, and a Sylvania Commander 100A feeding
it from the main.]
Large breakers (eg: > 60A) are certainly available, but usually
not at places like HD except as part of a "panel pack". Large
breakers for old panels are getting _very_ expensive. Just
paid $80 for a 30A Commander dual. Ick. Fortunately the 100A
feed breaker was given to me free from a friend.
4ga sounds right, but you'll actually need a total of four
conductors. Ground and neutral have to be separate in the subpanel
(remove the bonding jumpers).
Age and Treachery will Triumph over Youth and Skill
Electrical supply can undoubtedly help, but I'd question whether the
service feed is sized adequately to handle the total service first.
In conduit 4 isn't large enough, my table says 2, and that's copper.
Somebody w/ updated/full code table handy can supply better data, but
I'm pretty sure 4 isn't adequate by code.
Methinks this needs more thought and input before you jump in here...
Something else to consider in addition to what others have said is the
temperature of the conduit and wire up on the roof. I think that it is
necessary to upgrade the wire size to compensate for the possible extreme
heat that the conductors may be subject to. Of course this depends on where
you are located. See if you can get wire with insulation rated for 105
degrees Celsius instead of 90 degrees. Regardless, number 4 is not rated for
Personally I am not a big fan of using EMT in wet conditions, although it is
permitted. After several years of long term exposure the conduit can get
No one will make you use a 125 ampere feeder merely because your panel
can carry that load. The size of the feeder is based on the actual load
to be served. Then an overcurrent protective device is selected to
protect the feeder. You need to do a load calculation based on the
loads to be served and adding any allowance you want for future
expansion of the use of electricity.
"This alternating current stuff is just a fad. It is much too dangerous
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