Do not use a ground rod with the subpanel; aside from being a NEC
code violation, it can induce current in the grounding conductor.
There should only be one grounding point in the system, and that
should be at the service entrance.
Could you please cite the code reference that says that you cannot install a ground rod on a sub-panel. They are required for separate buildings and are used for lightning protection. They cannot be bonded to the neutral in a sub-panel.
On Fri, 20 May 2016 13:09:00 GMT, firstname.lastname@example.org (Scott Lurndal)
There is no limit to the number of rods or other electrodes you use,
only a limit of one main bonding jumper where the neutral gets tied to
the grounding electrode system. In fact, if this sub panel is in a
separate structure, another electrode is required.
On Friday, May 20, 2016 at 11:56:53 AM UTC-5, email@example.com wrote:
ire to supply a panel with 4 breakers (20A each)? Do you have to consider t
he possible use of all of the circuits carrying the maximum load? Thanks!
y given time. Will you be running machines constantly or intermittently?
You do not have to total up the rating of the individual circuit breakers.
ning protection is a good idea.
It is an attached garage (poorly wired) sharing a circuit with living, and
dining. I want to extent (6-6-6-8) about 35' and use a 4-breaker box. Put e
xisting receptacles on their own, and add a couple circuits for power tools
. Cheapest source for cable was .80/ft, but they wanted $18 shipping! I thi
nk HD is a little over $...I'll have to check them out.
If you have extra slots in your main panel, you might want to compare the
costs of just running four individual circuits from the main panel. Four 12
gauge Romex cables would probably accomodate what you're needing.
You might pay slightly more for the cables, but you wouldn't need a
subpanel, or the extra breaker in the main panel.
Just something to consider.
Copper is heavy, so it's usually cheaper to buy it locally. Home Depot has
a more limited selection, but their prices are hard to beat if they have
what you need.
A subpanel should be connected with FOUR wires (two hots, separate neutral,
The neutral bar in the subpanel must be isolated from the ground bar (the
ground and neutral must not be connected in the subpanel).
You can use as many breakers in the subpanel as you wish (as many as the
panel supports anyway). However, you need to determine what the typical
total load of all those branches will be. For example, will you be running
two or three machines at the same time?
If your expected load is less than 60 amps, you can use 6 gauge wire to
supply your subpanel. It should be protected by a 60 amp breaker in the
In the subpanel, you would protect each individual branch with
appropriately sized breakers (15 amp for 14-gauge wire, 20 amp for 12 gauge
If you overload an individual branch, the corresponding breaker in the
subpanel will trip.
If you load multiple branches at once (i.e. 18 amps on four branches),
you'll trip the breaker back in the main panel, even if you don't
necessarily overload an individual branch in the subpanel.
If the subpanel is in a detached building, you must add a grounding rod at
that building (NEC 250.32(a) I believe).
Multiple grounds are fine (ground rods, buried metal water pipe, rebar in
the foundation, etc.) but all grounds must be bonded together with wiring.
A main breaker is required in a detached structure if there are more than
six breakers in the panel.
If the subpanel is in the same building as the main panel, I believe the
breaker in the main panel qualifies as the disconnect even if you have more
than six breakers in the subpanel.
Regardless, I prefer having a main breaker in a panel. If there's an
electrical issue, or you want to make changes, you can just kill the whole
panel instead of trying to figure out which circuit you're on. It's also
safer working in a panel when you can kill the main breaker and disconnect
all power from the panel.
When I built my pump house back in 1991, I thought the electrical inspector
said the limit was four breakers max without a main. Either he was wrong or
the codes have changed. In any case, I have a small panel in the pumphouse
that connect directly to the meter (not a subpanel). It has a double-pole
breaker for the pump, and a couple small breakers for lights and outlets.
There's no way to cut power to the panel if I need to replace a breaker or
something. I've done work in the live panel, but it's not something I would
recommend. If you slip with a screwdriver or something you have NO
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