Subpanel with main breaker for barn

I've been shopping online, the box stores, and hardware stores for a small breaker panel to update my pole barn's wiring.

Right now I have a #8 wire running to the shed, and a 2-circuit main lug panel with one 15A circuit for lighting, and one 20A circuit for a plug in the front corner of the barn.

I think I would rather have a Main Breaker panel so I can cut power in the barn by pulling one switch.

All I really need is a panel with 6-8 circuits and a 40A main breaker. Mostly I would like to install outlets around the barn on 2 or 3 separate circuits, and maybe add a floodlight for the yard.

The smallest main breaker panels I can find are 100A with 16-20 circuits. Way more than I need, way more than I want to spend.

Anybody know of a smaller main breaker panel?

You will most likely not find a smaller panel with a main breaker but on a #8 240 I believe code allows for a 60 amp disconnect feeding a subpanel which will allow you to use a smaller panel and still disconnect it at the barn. Once again check code before changing it. Jeff

You can buy a small subpanel and stick a double breaker in it as a "main switch." You run your main power wires into the terminals screws of the breaker instead of the main lugs on the panel. This way, the breaker becomes a "main disconnect."

Many areas require that the "back-fed" breaker have a hold-down kit installed so it cannot be yanked out easily.

You can get what you need at Home Depot cheap - either with Square D type QO, or Homeline. Sneider Electric sells a cheap "backfeed breaker kit." They have it for the Square D and Homeline boxes.

That would have to be a short run of wire to the barn to run 60 amp on #8 wire.

I have a few buildings with 6 hole panels with a 240v main breaker put in it, then you have 4 holes left for feeding the building.

--->Paul

The #8 wire needs to be protected with a 40 amp feeder
breaker. I also presume you understand the grounding and
bonding requirements that are discussed a lot on YT forums.

Here's some recent "opinions and comments" from the code people. National Electric Code is not law - but good reading anyway.

Intalling a double-breaker in a small panel as a main is very common and allowed - even with the latest NEC "recommendations."

The write-up:

Backfed Breakers
The National Fire Protection Association (NFPA) has
issued an informal opinion that
backfed circuit breakers used to connect to a load center must be clamped.
“Clamped” means that the individual circuit breaker
must be attached to the load center back plane with a
screw or other device specifically made for the purpose
of preventing the breaker from being inadvertently
pulled loose from the bus bars of the load center. The
screw or other device is supplied by the manufacturer of
the load center. Many load centers have no provisions
for clamping, and therefore are not suitable for
backfeeding.
NEC 690.64(B)(5) requires that such breakers be
“identified” for backfeeding. According to Underwriters
Laboratories (UL), an identified breaker is one that does
not have terminals marked “line” and “load.” The
clamping requirement comes from NEC 408.16(F) in
Chapter 4 of the code, one of the general chapters. A
proposal to modify Article 690 will be submitted for
changes to the 2005 NEC. But until then, the Chapter 4
requirement is the governing requirement, since nothing
in Article 690 overrides it or even conflicts with it.
Most inspectors will accept the following reasons for not
clamping a breaker being backfed from a utilityinteractive
inverter:
• The plug-in breaker will immediately become deenergized
(dead) when the breaker is accidentally
unplugged from the load center because of the antiislanding
circuits built into the listed inverter under UL
Standard 1741.
• The front panel on most load centers actually clamps
all circuit breakers to the bus bars, and this panel
cannot be removed without a tool.
• Access to the inside of any load center connected to a
utility feeder allows an unqualified person to easily
come into contact with any exposed bus bar and the
main feeder wires.
Here are several solutions if the inspector requires that
the backfed breaker be clamped:
• Determine whether the existing load center has a kit
that can be used to clamp breakers into position, and
use that kit.
• Install a second service panel disconnect that
bypasses the existing load center, as described in
HP89. This service panel can be purchased from a
number of vendors, and has only a single breaker that is bolted in place.

Prices for the hold-down kit to make a regular breaker your main-breaker in a small panel.

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You can usually get a 100 amp panel at Menards for $50-$60 along with many breakers. The wiring running to your barn isn't heavy enough for a 100 amp main. It cost me a pant load just for the materials to run 175 ft to my pole barn when I install a 100 amp panel. A union electrician did my job for free. It's always nice to have friends in high places.

If you don't want to pay that much, get a $50 100 amp panel and feed your existing main wires into a 40 amp breaker. The 40 amp 220 v breaker will become your new main breaker and it will back feed your box. May not be done according to a building inspector's liking or NEA code, but it will be better than connection 8 g wires to a 100 amp main. That said, I'm guessing your feed to the barn is protected by a 40 amp breaker from your house. So, what's the safety concern? Yea, it may not meet NEA code but you use breakers to protect your wires from overload.

BYW, you would most likely not save any money trying to find a smaller box, because where I live, you can't install anything less than 100 amp service.
George

Yup, the #8 wire is protected by a 40A feeder breaker in the main panel in the house.

Lets explore a few different options:

Ive seen some 100 amp 120/240 volt panels with a main breaker that arent all that expensive at the big box stores, thats one way to handle it.

If you dont want to upgrade your wiring to 100 amps just install a smaller 40 amp breaker (Or do a backfeed if such isnt possible)

Another option is a small sub panel in which you use a proper 40 amp branch breaker to backfeed the rest of the buss.

If youre going to supply 120/240 volt single phase three wire service (i.e. more then just say an outlet) at the pole barn DONT FORGET EACH BUILDINGS ELECTRICAL SERVICE REQUIRES CONNECTION TO A GROUNDING ELECTRODE

The old system allowed you (if no other electrical paths) to run out only 3 wires (2 Hots and a Neutral) while the modern system requires 4 wires out to the pole barn (2 hots, Neutral, Equipment Ground). Under the new 4 wire system out at the pole barn DO NOT I REPEAT DO NOTTTTTT BOND THE EQUIPMENT GROUND BUSS TO THE NEUTRAL BUSS AS DONE AT THE MAIN SERVICE ENTRANCE

NOTE check with your local authority as requirements (if any in your area) vary city to city and county and state to state DO AS THEY REQUIRE NOTTTTTTTTTTTTTT ANY OPINIONS HERE BE THEY LAY OR PROFERSSIONAL

If in doubt I in good faith and conscience have to recommend you consult with a licensed professional qualified electrician if youre not competent to make decisions or do the work safely yourself DONT FORGET THE GROUNDING ELECTRODE

John T Long retired EE and rusty on the NEC so no warranty

I'd love a 100 Amp service out to the barn. Maybe I should just break down and put in the smallest 100A main panel I can find, and replace the main with a 40A breaker to make it legal...

Then later, if/when I save up for it, hire someone to bury a #4 cable back there, and figure out how to avoid the septic system and tree roots.

I agree a 100 amp service at shop would be good for future expansion. In the meantime either backfeed a panel with a proper 40 amp breaker or use a 40 amp main breaker IFFFFFFFFFFFFFFFF thats possible in the panel. See my post below about the number of wires out to the shop and having a Grounding Electrode out there

Keep safe

John T

Lets not forget about ground rods and ground-
neutral isolation here. Vital when livestock are
involved.

My electrician, a union electrician, said you don't use a grounding rod on a sub panel, only the main panel is grounded. He ran 4 wires to the sub panel, two hot, one neutral and one ground. Bar connecting ground and neutral was removed in the sub panel.
George

I try not to follow this electrical stuff to much, but it's my understanding that you don't want to tie neutral and ground together at a subpanel but it's okay to ground a subpanel with a seperate ground rod. Somebody correct me if I'm wrong.

If the sub panel is at a separate building it certainly does require a ground rod system.

I have been retired for a while and am not up on the current codes but 6 or 7 years ago we could use a ground rod at a sub panel as long as there was no other conductor running between the building containing the main service and the outbuilding that could act as a ground fault path. In other words if there was a metal gas pipe, metal water pipe, metal conduit, or according to our local state inspector even a telephone line, you had to pull a 4th conductor for a ground fault conductor. In the 2002 code that was spelled out in the code section 250:32

Whether you use a ground rod or a 4th conductor as a grounding conductor (NEC calls this the Equipment Grounding Conductor) the ground and the neutral (NEC calls this the grounded conductor) have to be isolated in the subpanel.

How would it work to flip the breaker feeding the #8 at the source end?

HTH, Dave

The fourth conductor was so the neutral and
ground bars could remain isolated from each other
in the sub-panel. And a ground rod could be used
without neutral current being carried back though
earth and the grounding conductors.

The overhead three wire triplex service supplies
cause some real problems. With elevated grounding
system potential when livestock are involved.
If no livestock or swimming pools etc are
involved. Then nobody notices ground system being
hot with 1 to 10 volts.

Not so long ago we had a municipal public pool
shutdown because the swimmers were getting shocks.
Neutral current returning through the earth. The
faults were out on the street on opposite sides of
the pool.
Had to call in consultants as even the PUC
staff couldn't tell the difference between neutral
and grounding systems.
There used to be a metal property line fence
around the same recreational facility. People were
getting shocks off the fence. So rather than
figure out the problem. The municipality replaced
the metal fence with a wooden fence.