Electrical Subpanel

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 ?
Thanks, Ray
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Ray wrote:

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.
Bob
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it
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?
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can
breaker
The disconnect rule is not a requirement for a sub-panel, it is a requirement for a separate structure.
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Toller wrote:

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.
Bob
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I believe there's something similar, but less than 6, and/or it doesn't apply to pure residential.
--
Chris Lewis, Una confibula non set est
It's not just anyone who gets a Starship Cruiser class named after them.
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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. -- Tom H
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.
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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!
--

Larry Wasserman Baltimore, Maryland
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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
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Ray 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 service-entrance conductors. 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 violation of "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 circuit breaker. -- Tom H
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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 well.
--

Larry Wasserman Baltimore, Maryland
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Thanks to all for your input ! Ray
> 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 ? > > Thanks, > Ray > >
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my
for
(attach
require you to install a ground rod, and bond the neutral and ground bars in your sub panel. Double check the exact NEC, though.
Dave

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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.
Jeff Dantzler Seattle, WA
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Jeff Dantzler wrote:

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 grounding electrode.
Best regards, Bob
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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.
-- Mark Kent, WA
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wrote:

bars in

conductors:
the
bond them

safe,
meter.
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. Dave
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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, up-to-code panel.
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
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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.
-- Mark Kent, WA
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home
the
to
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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