Backfeeding one subpanel via the main from another subpanel

I've got a metered main panel which feeds a small subpanel in my pumphouse with 10-3 via a 30 amp breaker in the meter main panel. I also feed a 200
amp house subpanel with 2/0 lugged to the busses in the meter main and the subpanel with a 200 amp main disconnect in the subpanel.
Can I backfeed the 200 amp subpanel from the pumphouse subpanel by switching the main breakers in the meter main panel to off and connecting a generator to the pumphouse panel? It seems like the electrical connection is there and flipping the meter main breaker off would disconnect the meter from the main panel buss.
This is not a question of whether this is NEC permissable, just whether its electrically possible. The purpose of this is to quickly power the pumphouse and also power selected low-load circuits (e.g., 2 amps or less) in the house subpanel with a small generator in the short-term before I properly interconnect a back-up generator with the meter main panel.
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MOST subpanels cannot be safely backfed (as I am sure you gathered from the other posts.)
BUT there are subpanels which are approved for: 1) have a 2 pole slot be used as a service feed; 2) havinging a second 2 pole slot be used as an alternative (e.g.: generator) feed; and 3) the manufacturer will sell or install an interlock so that only one of the two breakers is closed at the same time.
If you don't have such a panel, forget it. You might consider replacing it with a panel that can incorporated the interlocked feed breakers.
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snipped-for-privacy@crosslink.net says...

"Backfed", or "fed twice"? It's very common to "backfeed" a subpanel. .I.e. feed via a breaker in the normal breaker positions and leave the "main" slot missing. I did this when building a garage moons ago and the inspector was quite impressed with the workmanship.

Ah, you are talking about feeding a panel twice. No, I'm not that stupid either. I kinda like the guys (who are freezing their asses off) servicing my power system. ;-)

Agreed! ...assuming we're talking about feeding a panel from two sources.
--
Keith

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pumphouse
200
the
the
The panel has to be approved for that application. (It ain't much: the extra main breaker should require a screwdriver to remove it. Just a reminder to the electrician that it isn't a just another 240 circuit.)
vinging a second 2 pole slot be used as an

the
replacing it

Well, "they" make panels that just don't have a main breaker. With the prevision for making a particular two pole breaker difficult to remove, these can be used as service panels or branch panels or whatever.
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snipped-for-privacy@crosslink.net says...

That's good to know. It wasn't rated for any such thing, but passed the inspection with flying colors. This was in the mod '80s so perhaps the code anticipates such things better now?

...good to know. Thanks!
--
Keith

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Keith R. Williams wrote:

This isn't common in my area. I'm surprised this passes code. Did you identify this "normal" breaker as being the feed so that someone working on the panel knows how to de-energize it? I don't have a current NEC, but I'd like to see the section reference that allows this practice. I'm also surprised that all circuit breakers would function properly in this configuration. I think most are still thermally activated so they likely don't care which direction the current is flowing, but I could imagine a design that was current direction sensitive and might not work properly if backfed.
Matt
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says...

That was the only requirement; a sticker identifying the disconnect breaker (IIRC, the sticker said "OFF" ;-).
BTW, the reason it was done this way is I wanted to use a 100A box for a 40A service to a subpanel in my garage. 40A boxes didn't have enough slots and 100A service was way more (and expensive) than I needed.

I believe they're generally thermal and magnetic. How would the breaker know which direction the current was flowing? It's AC.
--
Keith

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Keith R. Williams wrote:

You can't buy a 40 or 50A main breaker for a larger panel?

If the breaker is thermal only, it won't know which direction. If it is magnetic (has a coil) or a capacitor, the phase difference will indicate direction. I don't know if this matters as I'm not familiar with the innards of a modern circuit breaker, but I certainly wouldn't automatically assume that polarity is immaterial.
Matt
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says...

Not at least at the time (mid '80s). A 100A panel required a 100A breaker.

No, they're *both* magnetic and thermal (thermal for long time- constant events and magnetic for gross overloads). Either way, the breaker has no idea where the source and where the load is. Only the current matters, since the breaker doesn't even know about ground (ground isn't connected to the breaker at all). The breaker *cannot* know which end is which.
--
Keith

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Its electrically possible, but potentially deadly. You really need to put in an approriate bypass switch so there is NO chance that you will backfeed from the generator back to the utility.
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I was wondering why you need a separate panel with a manual transfer switch (this is the way they seem to be configured)? Couldn't you just hook up the generator to the main panel through a transfer switch (i.e line - off - generator, no subpanel)?
I know the danger of doing it this way is that you might pull too much current if all the circuits are on, but the generator has its own overload protection (and the circuits are still protected by the breakers). This would save on a lot of additional wiring, plus you could still overload the generator even if it is only powering specific circuits.
Thanks, Budman
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Why not just do it right the first time? How much is this chunk of wire your trying to avoid buying?
If you want 'short term', run extension cords from the gen set to the house.
( That's the extent of my back-up power system, and I haven't needed it yet ... knock wood )
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When the power is out, it is easy to become fairly desperate. DAMHIK. The manual or automatic transfer switch is the best solution.
Locating the generator at the pump house should work just fine. It will be a bit quieter than having the generator out the back door.
I WOULD PULL THE METER WHILE USING THE GENERATOR.
When the power company crews come through there would be no chance of feeding the service lines. It would be a simple matter of disconnecting the generator and reinstalling the meter.
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ Keep the whole world singing. . . . DanG

pumphouse
feed a 200

main and the

by switching

a generator

is there and

from the main

whether its

the pumphouse

in the

properly
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DanG wrote:

Where I live they put a seal tag on the meter housing. You can't pull the meter without breaking the seal. I don't know if pulling it is illegal or not, but I'm sure the power company would be rather unhappy if they saw the seal broken and would likely investigate you for power theft.
Matt
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We had an interesting effect of back-feeding in this area recently when the 11kV underground cable shorted out _AGAIN_. (The 5th patch to a 400 yard length in 18 months)
The SEB were backfeeding the 11kV local sub-network via some 240V pole-mounted cables. The cable sagged under the load and clashed together. Local residents were subject to cascades of molten copper dropping down onto the pavement!

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N7RX wrote:

Friend of yours that's not very bright (we all have at least one): "Gee, the power is out."
<sound of generator starting up>
Friend: "Hmm, someone's mowing the lawn."
<friend opens panel>
Friend: "Oooh, the main circuit breaker tripped. I better reset it."
>ker<*CHUNK*
<moments later, smell of cooked utility worker and sound of ambulances arriving>
Friend: "Gee, I wonder what happened..."
-Z
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switching
generator
and
main
its
pumphouse
Check with your electrical utility. They probably have a policy and diagrams for using standby generators for premise electrical systems that are connected to their power grid. Most are going to require an approved transfer switch and an inspection. These requirements are probably going to force you to comply with the current adopted version of the National Electrical Code and National Electrical Safety Code.
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switching
generator
and
main
its
pumphouse
Purposefully not an answer to your question.
NEC is a safety code. Like all codes is sometimes goes too far. In your scenario, however, the potential risk of a lot of very bad things happening far outweighs your desire for a quick fix.
Look to the code and act responsibly for your family's sake and the public in general.
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someonesimple posted for all of us....

I like that!!! Good job!
--
Tekkie

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switching
generator
and
main
I'm confused on the "meter main panel". Typically when you open the main breaker it disconnects the load side of the meter (not the line side). When you say metered main panel I'm thinking this is a combination panel with a few breakers and a ring base meter in the same panel. The utility connects to the line side of the meterbase.
If this is true you risk backfeeding the utility via and meter. This of course is a potential safety hazard for any fellow lineman, or if power is restored when the generator is on line you risk "launching" your generator thru the pump house. I take it the 10-3 is fed to the pump house is on a 2 pole 30 A breaker, and that your generator is a 240 V type. Depending on distance voltage drop may be a problem.

its
pumphouse
If you risk backfeeding the utility as describe above then don't do it until you properly interconnect a backup generator with a manual transfer switch (double throw safety switch).
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