Back Up Generator ?

velvetfoot

Minister of Fire
Dec 5, 2005
10,006
Sand Lake, NY
What you linked says it "bridges", or ties the two hots together on the 3 prong. On the 4 prong they're separated
No. 3 prong is hot, neutral, ground. Hots joined on 4 prong side of adapter. See HD Adapter. Cause genny only delivers 125v. Note that its described: the NEMA L14-30R is a 30 Amp, 125/250-Volt, 4-prong female connector.
 

jatoxico

Minister of Fire
Aug 8, 2011
4,218
Long Island NY
No. 3 prong is hot, neutral, ground. Hots joined on 4 prong side of adapter. See HD Adapter. Cause genny only delivers 125v. Note that its described: the NEMA L14-30R is a 30 Amp, 125/250-Volt, 4-prong female connector.
You have it backwards. The 3 prong goes into your inverter which is only capable of putting out 120 v in a single phase. The x and y that are normally separate are tied together in the one hot on the three prong. With the adapter the 2 hots run then through the extension cord as separate wires but they are in phase. So you are feeding your 2 pole panel with a single phase source.
 
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velvetfoot

Minister of Fire
Dec 5, 2005
10,006
Sand Lake, NY
It's semantics. This is all single phase. Two legs for 240, one and a neutral for 120. The two wires in the connection cable designated as 'hots' are joined together in the 4-prong side of the adapter.
 

jatoxico

Minister of Fire
Aug 8, 2011
4,218
Long Island NY
I'm only trying to alert you to a potential problem/danger so don't take my persistence as being a PITA. It may be semantics but no question you can overload the neutral if you try running a circuit wired as an MWBC. It takes a couple minutes to check for them.
 

Highbeam

Minister of Fire
Dec 28, 2006
17,028
Mt. Rainier Foothills, WA
It is extremely rare and weird, though possible, to have any multi wire branch circuits in a residence.

Be careful not to confuse illegal backfeeding of a panel with legal (in the us) backfeeding of a panel equipped with the proper interlock device.
 
It is extremely rare and weird, though possible, to have any multi wire branch circuits in a residence.

Be careful not to confuse illegal backfeeding of a panel with legal (in the us) backfeeding of a panel equipped with the proper interlock device.
I guess depending on situation and location. Almost every 120 volt 15 amp circuit in my house is a multiwire branch circuit. Our house was built in 2014. It saves a lot of money for the electrical contractor, they have to pull half as many cables, and uses 2/3 the copper.
 
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Sodbuster

Minister of Fire
Sep 22, 2012
1,335
Michigan
It is extremely rare and weird, though possible, to have any multi wire branch circuits in a residence.

Be careful not to confuse illegal backfeeding of a panel with legal (in the us) backfeeding of a panel equipped with the proper interlock device.

That sheet metal back-feed device that you have to manually throw, before you start to backfeed? I don't see much of a difference.
 

WinterinWI

Member
Dec 6, 2018
162
Wisconsin
That sheet metal back-feed device that you have to manually throw, before you start to backfeed? I don't see much of a difference.
It physically prevents the main and the backfeed from being on at the same time. So when the power goes out on a Saturday night after you've had one too many, the panel can't be accidentally energized by the backfeed breaker while the main is on.

It just forces you to remember to turn off the main first.
 

semipro

Minister of Fire
Jan 12, 2009
3,749
SW Virginia
It physically prevents the main and the backfeed from being on at the same time. So when the power goes out on a Saturday night after you've had one too many, the panel can't be accidentally energized by the backfeed breaker while the main is on.

It just forces you to remember to turn off the main first.
Our generator is easy enough to start that my wife could probably do it if I wasn't home to do it.
The interference interlock makes it a lot easier to tell her how to configure the electrical connections safely and keeps me from botching the same.
Its cheap insurance to save some lineman's life.
 

Highbeam

Minister of Fire
Dec 28, 2006
17,028
Mt. Rainier Foothills, WA
It physically prevents the main and the backfeed from being on at the same time. So when the power goes out on a Saturday night after you've had one too many, the panel can't be accidentally energized by the backfeed breaker while the main is on.

It just forces you to remember to turn off the main first.
Yes! It is how the way to make backfeeding safe and legal. Mine was permitted and inspected.

You, @Sodbuster , are correct that it is functionally the same except the lockout eliminates the possibility that you forget about shutting off the main first.

A couple of things could happen if you forgot to throw the main because you failed to install an interlock. One, your poor generator tries to energize the whole city. Bam! the generator's breaker pops. Or two, say the powerline between your home and the transformer is broken, then you have just created a hot line laying on the ground that could actually zap someone.
 

Sodbuster

Minister of Fire
Sep 22, 2012
1,335
Michigan
Yes! It is how the way to make backfeeding safe and legal. Mine was permitted and inspected.

You, @Sodbuster , are correct that it is functionally the same except the lockout eliminates the possibility that you forget about shutting off the main first.

A couple of things could happen if you forgot to throw the main because you failed to install an interlock. One, your poor generator tries to energize the whole city. Bam! the generator's breaker pops. Or two, say the powerline between your home and the transformer is broken, then you have just created a hot line laying on the ground that could actually zap someone.
Around here, when you call in a power outage they ask you if you'll have a generator running, I always say yes. I assume as computerized things are theses days that the information goes right to the lineman's computer letting the crew know their is a chance of a hot wire.
 

jatoxico

Minister of Fire
Aug 8, 2011
4,218
Long Island NY
It is extremely rare and weird, though possible, to have any multi wire branch circuits in a residence.
No evidence to prove it but I wouldn't be surprised to find it's regional. I looked and sure enough I have a couple. Installed incorrectly too. The breakers are supposed to be connected (that's what those holes are for) when wired as an MWBC so they throw together.
 
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maple1

Minister of Fire
Sep 15, 2011
10,382
Nova Scotia
I have MWBCs also. Never knew what they were until reading about them in this place. Explained that issue that time when I tried to feed 120 to both sides of my panel.

Wish Interlocs were legal here. Sure would make things simple. I think their logic is, that it isn't 'fool proof', because the hardware is attached to the panel cover (or at least the ones I looked at were that way), so if the panel cover is removed, there goes your safety device. Which I guess they may have a point on, but seems silly to me. Are there that many people who take their panel cover off? There are likely many fold more people who just throw the main (as long as they remember - and also remember to unplug the genny before they unthrow it again) & do it a more 'wrong way'. Which come to think of, I don't think I have ever heard of anyone actually getting in serious trouble for somehow.

EDIT: And another thing - why aren't there more 240v inverter gennies on the market? One of those would be sweet. I stumbled on a nice looking Champion 6000w open frame one last night on the net. Not available in Canada. Huh, OK. So it's a $5000 Honda, or a $3000+ B&S that has mixed reviews and not sure is available here or not either.
 
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peakbagger

Minister of Fire
Jul 11, 2008
5,138
Northern NH
I have known several folks who pull the panel cover and just plug in a 240 dual breaker to backfeed a panel. The rational from one friend (an electrician) was during an extended power outage they were driving around the neighborhood with a generator to allows several homes to have power for a few hours to run their heat and keep the freezers running. The houses did not necessarily have standard dryer plugs or secondary panels with the right breakers so to them it was easier to open a basement window , drag a cord in, pop the panel cover and plug in an appropriate sized breaker. It usually took the people he was helping having the breaker trip out once or twice until they figured that the power from the generator was not unlimited.
 

begreen

Mooderator
Staff member
Nov 18, 2005
81,785
South Puget Sound, WA
I have known several folks who pull the panel cover and just plug in a 240 dual breaker to backfeed a panel. The rational from one friend (an electrician) was during an extended power outage they were driving around the neighborhood with a generator to allows several homes to have power for a few hours to run their heat and keep the freezers running. The houses did not necessarily have standard dryer plugs or secondary panels with the right breakers so to them it was easier to open a basement window , drag a cord in, pop the panel cover and plug in an appropriate sized breaker. It usually took the people he was helping having the breaker trip out once or twice until they figured that the power from the generator was not unlimited.
That's how I had to power the house during an extended outage when we first moved in. We had a Coleman contractor generator that had 240v out. I knew what i was doing but still wouldn't trust myself and triple checked to make sure there was no backfeeding.