I intend to run an underground feeder wire (approximately 150') from my home
service panel to a subpanel for a shop that I'm building in my back yard.
The question is...do I have to get a special service panel to allow for the
connection of the new wire for the shop or can I just piggy back (attach to
the same terminals) the new wires to the existing service coming in ?
If I understand your question, the "connection" you want is a big breaker
in your service panel; for that kind of distance, I'd use a 60A 2-pole
breaker and run #4 wire. You can use a 100A breaker with #4 wire, but 100A
breakers are expensive. If 60A turns out to be not enough (are you running
a TIG welder *and* a big air compressor at the same time?) you can replace
the 60A breaker with a 100A without having to replace the wires.
I haven't looked up the wire size/voltage drop chart for that distance; I
don't know what your load is. You might want to run #3 or #2 wire.
If you have more than 6 switches (breakers) in the subpanel in the shop, it
needs to have a main disconnect. If it has six or fewer switches, you can
get by without a main disconnect.
Can you document that? My subpanel has room for 16 breakers (I am using 7
of them) but nowhere for a main disconnect.
I don't know why you would even want a main disconnect; doesn't the breaker
in main panel do that?
A subpanel *in a separate building* is treated like a service entrance.
Service entrances must have 6 or fewer switches to totally disconnect the
power to the building. If your subpanel is in the same building as the
service panel, this (NEC) rule doesn't apply. I don't know about the CEC.
Here are the sections of the US NEC that require you to have a building
disconnecting means. The usual way to accomplish that in a main lug
only panel is to install a double pole breaker with a kit that holds it
into the panel so that it cannot be readily removed. The feeder
conductors are than connected to the terminals of that breaker which
feeds the power into the buss bars via the breakers push on contacts.
225.31 Disconnecting Means.
Means shall be provided for disconnecting all ungrounded conductors that
supply or pass through the building or structure.
225.33 Maximum Number of Disconnects.
(A) General. The disconnecting means for each supply permitted by 225.30
shall consist of not more than six switches or six circuit breakers
mounted in a single enclosure, in a group of separate enclosures, or in
or on a switchboard. There shall be no more than six disconnects per
supply grouped in any one location.
Exception: For the purposes of this section, disconnecting means used
solely for the control circuit of the ground-fault protection system, or
the control circuit of the power-operated supply disconnecting means,
installed as part of the listed equipment, shall not be considered a
supply disconnecting means.
(B) Single-Pole Units. Two or three single-pole switches or breakers
capable of individual operation shall be permitted on multiwire
circuits, one pole for each ungrounded conductor, as one multipole
disconnect, provided they are equipped with handle ties or a master
handle to disconnect all ungrounded conductors with no more than six
operations of the hand.
If the subpanel has room for 16 breakers then it has room for a main
disconnect. Assuming 220V service you will use 2 of the available
positions for the main (subpanel) disconnect. Again, it would be
really really good to have a printed reference book with you when
doing this reather than relying on usenet!
Not compared to the wire. Price out 150' of #4 and be prepared for quite
a shock. This is one of the (few) times to consider aluminum wire[+]. When
installed properly (with appropriate connectors and grease), it's perfectly
safe. But check with a inspector.
At this ampacity range and for this purpose/length, there's not a lot of
point to oversizing the wire and _not_ having the breaker match it. In other
words, if you only need 60A, but you're gonna run #4, you might as well
put a 100A breaker in even if it costs a bit more.
[+] in a similar situation a slightly shorter length of #4 copper feeder
would have cost me almost $800CDN. In #3 aluminum, it was ~$400.
Chris Lewis, Una confibula non set est
It's not just anyone who gets a Starship Cruiser class named after them.
If you want to run a set of service conductors to your shop as permitted by
"230.40 Number of Service-Entrance Conductor Sets.
Each service drop or lateral shall supply only one set of
Exception No. 3: A single-family dwelling unit and a separate structure
shall be permitted to have one set of service-entrance conductors run to
each from a single service drop or lateral."
You would install a meter can that will contain double barreled lugs on
the load terminations. If you run a set of conductors to the shop that
originate in the homes indoor service equipment that would be in
"230.3 One Building or Other Structure Not to Be Supplied Through Another.
Service conductors supplying a building or other structure shall not
pass through the interior of another building or other structure."
If the panel is an exterior surface mount than your only challenge will
be to obtain a panel with double barreled main lugs.
If you are actually running a feeder than it will have to be protected
by an Over Current Protective Device (OCPD) such as a set of fuses or a
Standard & approved practice would be to install a breaker in your main
panel and connect the subpanel feed to that breaker. It would be a
very good idea to research this at your local library rather than on
usenet, and speak to your local building inspector & permit office as
Thanks to all for your input !
> I intend to run an underground feeder wire (approximately 150') from my
> service panel to a subpanel for a shop that I'm building in my back
> The question is...do I have to get a special service panel to allow for
> connection of the new wire for the shop or can I just piggy back (attach
> the same terminals) the new wires to the existing service coming in ?
This is not true. The right way to run a subpanel is to run four conductors:
2 hots, 1 neutral, and 1 ground. Buy a good panel and also buy a separate
ground bus for that model panel. SquareD QO is good quality.
Bond the incoming ground to the ground bus (and the case of the panel.)
Do NOT bond the ground to the neutral in a subpanel. It is okay to bond the
subpanel ground to a proper grounding rod located close to the subpanel,
but it also must be bonded to the incoming ground.
The neutral should be kept separate from the ground in subpanels. Only bond them
at the service entrance.
People will disagree what constitutes a "service entrance". To play it safe,
consider the service entrance to be the one main panel connected to the meter.
I think the subpanel in the original post was to be in a separate building
(a detached garage 150' from the house.) So bonding the ground and neutral
at the subpanel and having a ground electrode is correct.
If the subpanel is in another building, *and* if there are water pipes or
telephone wires or CATV (etc.) connecting the two buildings, I'm not sure
how it's supposed to be done. I think in that case you'd run 4 wires,
isolate the ground from the neutral in the subpanel, and would add a
Yes, you must run 4 wires in that case. This is the better way to do it so you
have the option of
adding a metallic path to the outbuilding in the future. You'll kick yourself
when you want a CATV
cable in the outbuilding and you didn't run a 4th wire with the building feeder.
In fact, here in Washington, you now must use the 4 wire method to all
subpanels, even to detached
structures with no grounded metallic paths.
I think it is true, he appears to be installing a sub panel in a building
which is unattached to the building that houses the main panel, and these
buildings do not have anything like metal pipes running between them. If
this assumption is true, then the NEC requires the installation of a ground
rod, and requires the neutral bus be bonded to the ground bus.
If my assumption on the setup of these 2 building is wrong, then I stand
corrected. This is why the original poster needs to check with the local
electrical authority in his area. Get the right info based on your
particular situation, and go from there.
Local codes vary. I'm in Seattle, and when I bought this place, my
inspector didn't like the cheesy little subpanel in the garage, where
neutral and ground were bonded. He said is was a code violation. That
detached building also has other 120V circuits to it that aren't on that
panel, as well as phone, copper water supply, and cable. It has ground
rod. I plan to fix it eventually by running a larger feeder with a bigger,
Dave--I'm pretty sure it used to be okay to bond G-N as long as there
were no other conductors and as long as a good ground rod was in place.
Codes change quickly and geographically so it pays to check with an
inspector or local electrican.
My point was just that it is always safe to run the 4 wire feeder, a
ground rod (or 2) and then use a separate ground bus in the subpanel.
There may also be an issue with needing a service disconnet depending on
the number of curcuits served by the panel.
This subject has been discussed at length in this and other forums.
Any one curious what sort of "bad things" can happen when your neutral
and safety ground (i.e. equipment cases) become live due to a fault can
find out from those more knowledgable than myself.
Cheers All--Jeff Dantzler
I don't believe this to be true. The NEC ALLOWS either a 3-wire or 4-wire feeder
in this case. A
3-wire service (as opposed to feeder)would also be allowed in this case. It does
not require a
3-wire feeder, you get to choose the method you want. Regardless of the feeder
chosen, the building
must have a grounding electrode system and that system connected to the
grounding bus. In a 3-wire
feeder or service, the neutral/grounded bus and the grounding bus are one and
the same. In a 4-wire
feeder, they are isolated.
Always a good idea, as the NEC may not apply.
run a 2" underground pipe for the electrical wires
and a 1 1/2" underground pipe for the telephone and cable.
NEVER run electrical wires and cable tele. wires in the same pipe.
install a 100A sub panel in the "new garage"
install a 100A breaker in service entrance Main panel.
also you should run 2 exterior grounding rods (for the Main panel).
1 near the meter socket and the other aprox. 6' from the 1st. one.
and also ground the main panel to the cold water main pipe.
(be sure to clamp the grounding wire on BOTH sides of the water meter).
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