Ah, Electricity

Matthew K

Matthew K

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Georgia
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Broke Engineer
Hello all, so you know with all this hurricane stuff, it is probably time to wire our generator to run some things in our house:p.

I'm obviously not an electrician, but our home has TWO 200 AMP Panels fed by one main line. We had someone come out today that is more heavily focused on construction rather than wiring things, although they are licensed to do so. So I'm taking what their saying as somewhat of a grain of salt...

If possibly, I'd like to have both panels fed by the generator and it be up to me which loads I have turned on. Our generator is only 6500 watts, and it is my understanding some areas code may specify that we only have circuits wired up to the max output of the geny, meaning I couldn't legally wire up two whole panels with a measly 6500 watts. I'm not sure if that is the case here, but I was wondering if 1) its not super illegal to do it & 2)How would I go about sharing one generator with two panels, I'm fairly certain it is possible, but I'm fuzy on the details. Along with this I'd presume I can have 240v to run an air conditioner if I wanted. That's something the guy that came out said we couldn't do...
 
Matthew K said:
... Along with this I'd presume I can have 240v to run an air conditioner if I wanted. That's something the guy that came out said we couldn't do...
Click to expand...

I can speak to the air only...my last house had a 9000 watt generator, and it had instructions that it could power anything in the house, BUT THE AIR CONDITIONING! Me, being the fool that I am, thought, "9000 watts should power my air just fine." Soooo, I tried it once....ONCE. It was immediately apparent that it was a bad idea! Air tried to come on, generator tried to die, lights dimmed, horrible sounds were made by the air, the generator, and me, all during the few seconds that I tried it...
But I'm also no electrician, so I can't say WHY it didn't work, just that it didn't.
 
I assume that you have only one meter, and that from that, you have two separate breaker panels fed.

You will need to have a transfer switch between the meter and the panels, such that if, at any time, you are going to use the generator, then the power lines from the meter are completely, physically, disconnected from your home's electrical system. It is critical because, if this is not done, you could back feed power into the grid, and create a hazardous condition for lineman.

You should be able to buy a whole-home generator which could run on either natural gas or diesel, and these are routinely available in 240 V models.

This outfit has a very good array of generators, and frequently has very good pricing with free shipping, as well. In addition, the owner is a pilot (for what that's worth). You can actually get a remarkably capable generator for a not-ridiculous amount of money.

https://wholesalepowertools.com/generators?generator_type=139
 
tawood said:
I can speak to the air only...my last house had a 9000 watt generator, and it had instructions that it could power anything in the house, BUT THE AIR CONDITIONING! Me, being the fool that I am, thought, "9000 watts should power my air just fine." Soooo, I tried it once....ONCE. It was immediately apparent that it was a bad idea! Air tried to come on, generator tried to die, lights dimmed, horrible sounds were made by the air, the generator, and me, all during the few seconds that I tried it...
But I'm also no electrician, so I can't say WHY it didn't work, just that it didn't.
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Sounds like maybe it wasn't wired for 240v? Unless you have a very large a/c 9000w should easily run at least one floor of air conditioning
SCCutler said:
I assume that you have only one meter, and that from that, you have two separate breaker panels fed.

You will need to have a transfer switch between the meter and the panels, such that if, at any time, you are going to use the generator, then the power lines from the meter are completely, physically, disconnected from your home's electrical system. It is critical because, if this is not done, you could back feed power into the grid, and create a hazardous condition for lineman.

You should be able to buy a whole-home generator which could run on either natural gas or diesel, and these are routinely available in 240 V models.

This outfit has a very good array of generators, and frequently has very good pricing with free shipping, as well. In addition, the owner is a pilot (for what that's worth). You can actually get a remarkably capable generator for a not-ridiculous amount of money.

https://wholesalepowertools.com/generators?generator_type=139
Click to expand...
Agreed on the transfer switch. My generator can put out 240v. I was more curious as to how the system would break it down to 120v for the regular outlets...I just found out my neighbors house is wired so that their 8000w generator can power both of their breakers if they want to. I may be going over to see how theirs is set up.
 
The transfer switch powers individual circuits, not the panel. There is a series of switches on the transfer labeled "line" or "Gen", meaning the circuit is powered by either/or. When your power comes back on, you have to throw the switch back to "line", unless of course you spring big bucks for an auyomatic system. The transfer switch takes the panel breaker out of service when the switch is on "Gen", so it's impossible to backfeed the service line.

Your genset can power 240 volt circuits, like a well pump, by strapping two of the switches together, and having each 120v leg powered by one gen circuit, balancing the load on the switch. I would check the start draw on your a/c. I can easilly see it bring your portable genny to it 's knees.
 
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Your typical 240 is really two 120v legs out of phase, with a neutral "in the middle."

Hence, you get 120 from each leg to neutral, and 240 from leg to leg.
 
Well, V x A=Watts so, 240 x 200 = 96000 watts. That assumes you are loading the system to maximum. Seems you need to isolate a few circuits you wish to power via generator, or get a much bigger generator.
 
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You can do it but when you turn it on, you will get a 3' long blue flame :)
 
Reason won't run AC is compressor is on 40 amp circuit at a minimum, 240x40 = 9600.... Add in the air handler and you are way over the limit. That is reason the genset won't run AC.
 
Matthew K said:
Hello all, so you know with all this hurricane stuff, it is probably time to wire our generator to run some things in our house:p.

I'm obviously not an electrician, but our home has TWO 200 AMP Panels fed by one main line. We had someone come out today that is more heavily focused on construction rather than wiring things, although they are licensed to do so. So I'm taking what their saying as somewhat of a grain of salt...

If possibly, I'd like to have both panels fed by the generator and it be up to me which loads I have turned on. Our generator is only 6500 watts, and it is my understanding some areas code may specify that we only have circuits wired up to the max output of the geny, meaning I couldn't legally wire up two whole panels with a measly 6500 watts. I'm not sure if that is the case here, but I was wondering if 1) its not super illegal to do it & 2)How would I go about sharing one generator with two panels, I'm fairly certain it is possible, but I'm fuzy on the details. Along with this I'd presume I can have 240v to run an air conditioner if I wanted. That's something the guy that came out said we couldn't do...
Click to expand...
Do you have 2 meters? Are the two panels right next to each other or is one of them somewhere else in the house? Is there a breaker in one of them, that would be the one with the meter if a one Meter service, that "feeds" the other one, the "sub panel?" It would be like a big one, 100amps or so? How legal do you need to be? Of course you want to be safe. Do you need it to kick in automatically, or are you ok with spending a few minutes throwing some breakers before you fire up the generator? I dont know exactly what the issue with the airconditioner is other than any thing with a motor needs a big burst of juice to "start."
 
Matthew K said:
Hello all, so you know with all this hurricane stuff, it is probably time to wire our generator to run some things in our house:p.

I'm obviously not an electrician, but our home has TWO 200 AMP Panels fed by one main line. We had someone come out today that is more heavily focused on construction rather than wiring things, although they are licensed to do so. So I'm taking what their saying as somewhat of a grain of salt...

If possibly, I'd like to have both panels fed by the generator and it be up to me which loads I have turned on. Our generator is only 6500 watts, and it is my understanding some areas code may specify that we only have circuits wired up to the max output of the geny, meaning I couldn't legally wire up two whole panels with a measly 6500 watts. I'm not sure if that is the case here, but I was wondering if 1) its not super illegal to do it & 2)How would I go about sharing one generator with two panels, I'm fairly certain it is possible, but I'm fuzy on the details. Along with this I'd presume I can have 240v to run an air conditioner if I wanted. That's something the guy that came out said we couldn't do...
Click to expand...

I don't have a transfer switch my generator feeds directly into my panel and I choose what circuits to run...
 
Chip Sylverne said:
The transfer switch powers individual circuits, not the panel. There is a series of switches on the transfer labeled "line" or "Gen", meaning the circuit is powered by either/or. When your power comes back on, you have to throw the switch back to "line", unless of course you spring big bucks for an auyomatic system. The transfer switch takes the panel breaker out of service when the switch is on "Gen", so it's impossible to backfeed the service line.

Your genset can power 240 volt circuits, like a well pump, by strapping two of the switches together, and having each 120v leg powered by one gen circuit, balancing the load on the switch. I would check the start draw on your a/c. I can easilly see it bring your portable genny to it 's knees.
Click to expand...

Chip is correct. Residential transfer switches are designed to isolate individual circuits not an entire panel. It is a function of the loads you want to run while using the generator. There are a number of guides to indicate the load each device will draw or you can calculate using volts X amps = watts.. Also, you need to factor in the start up load of each device, which can be 2-3x the normal operating load. So, to answer your questions:

#1 - Yes, it probably is "illegal" to wire your portable generator to run the entire panel(s). If it isn't "illegal" it most certainly isn't very safe and won't meet building code.
#2 - There are transfer switches that are designed to feed multiple circuits (such as a full panel), but now you are getting into industrial equipment.
 
luvflyin said:
Do you have 2 meters? Are the two panels right next to each other or is one of them somewhere else in the house? Is there a breaker in one of them, that would be the one with the meter if a one Meter service, that "feeds" the other one, the "sub panel?" It would be like a big one, 100amps or so? How legal do you need to be? Of course you want to be safe. Do you need it to kick in automatically, or are you ok with spending a few minutes throwing some breakers before you fire up the generator? I dont know exactly what the issue with the airconditioner is other than any thing with a motor needs a big burst of juice to "start."
Click to expand...
1 meter, the two panels are right next to each other. Both have a breaker main if that is what your talking about. And just for anyone reading, I didn't bring up the air conditioner part. I'm not concerned about whether the generator will handle it, I've had experience with similar sized generators being able to run at least one of the central a/c systems just fine.
Luigi said:
Well, V x A=Watts so, 240 x 200 = 96000 watts. That assumes you are loading the system to maximum. Seems you need to isolate a few circuits you wish to power via generator, or get a much bigger generator.
Click to expand...
That's why I was asking about legalities. I'm aware my generator outputs very little compared to the overall capability of the grid tied system. And the circuits would be under strict control by me. Instead of choosing and installing a few main circuits, I'd rather have the ability to choose and or adapt what circuits I want on. I know of residential systems like this, I was just looking for detail into that system.
 
Matthew K said:
1 meter, the two panels are right next to each other. Both have a breaker main if that is what your talking about. And just for anyone reading, I didn't bring up the air conditioner part. I'm not concerned about whether the generator will handle it, I've had experience with similar sized generators being able to run at least one of the central a/c systems just fine.

That's why I was asking about legalities. I'm aware my generator outputs very little compared to the overall capability of the grid tied system. And the circuits would be under strict control by me. Instead of choosing and installing a few main circuits, I'd rather have the ability to choose and or adapt what circuits I want on. I know of residential systems like this, I was just looking for detail into that system.
Click to expand...


I have this lockout switch that prevents back feed..

upload_2017-9-5_21-23-49.png
 
Gary said:
Chip is correct. Residential transfer switches are designed to isolate individual circuits not an entire panel. It is a function of the loads you want to run while using the generator. There are a number of guides to indicate the load each device will draw or you can calculate using volts X amps = watts.. Also, you need to factor in the start up load of each device, which can be 2-3x the normal operating load. So, to answer your questions:

#1 - Yes, it probably is "illegal" to wire your portable generator to run the entire panel(s). If it isn't "illegal" it most certainly isn't very safe and won't meet building code.
#2 - There are transfer switches that are designed to feed multiple circuits (such as a full panel), but now you are getting into industrial equipment.
Click to expand...
You can get either for residential. Or a load-shed transfer switch. A few of the houses around here have 24 KW generators that will run the whole house including a smaller AC unit. They have whole-panel transfer (the original houses had 100A service, many have been upgraded.

For a portable generator, USUALLY a transfer switch is used that isolates various circuits.

You will need to see what local codes require. In some places work on the panel - including transfer switches - require a licensed electrician. Around here, a local inspection is required (and is essentially enforced by the power company.
 
The easy answer is that you can't do it without violating the NEC (National Electric Code), and you don't have the knowledge to do it safely.

So don't. Please.

As for the reference in the post above to local codes, every local code without exception has adopted the NEC as that code. So when I say "you're violating the NEC", it also means you're violating local codes.
 
Gary said:
Chip is correct. Residential transfer switches are designed to isolate individual circuits not an entire panel. It is a function of the loads you want to run while using the generator. There are a number of guides to indicate the load each device will draw or you can calculate using volts X amps = watts.. Also, you need to factor in the start up load of each device, which can be 2-3x the normal operating load. So, to answer your questions:

#1 - Yes, it probably is "illegal" to wire your portable generator to run the entire panel(s). If it isn't "illegal" it most certainly isn't very safe and won't meet building code.
#2 - There are transfer switches that are designed to feed multiple circuits (such as a full panel), but now you are getting into industrial equipment.
Click to expand...
Yes and no. I have two 200 amp transfer switches feeding two 200 amp panels. Load-shedding devices can take out a few of the larger loads, but otherwise all circuits are powered when the gennie is running.

For a permanent installation, local codes required me to install a generator capable of simultaneously powering 85% of the connected circuits (i.e., the whole house). There's likely no such requirement for a temporary installation that only feeds certain circuits.

This page gives a few options for how you could hook up a portable generator to power your house, either through the main panel by adding an interlock, or through a subpanel with select circuits. You could run the generator into two panels the same way that your single meter feeds both panels. But you'd bring the generator into each interlock instead of the main bus. These configurations many or may not all be strictly legal in your jurisdiction. Whatever you go with, make absolutely certain that there is no way of inadvertently backfeeding the outside wiring.

http://www.generatorsforhomeuse.us/transfer-switch/
 
Matthew K said:
1 meter, the two panels are right next to each other. Both have a breaker main if that is what your talking about. And just for anyone reading, I didn't bring up the air conditioner part. I'm not concerned about whether the generator will handle it, I've had experience with similar sized generators being able to run at least one of the central a/c systems just fine.

That's why I was asking about legalities. I'm aware my generator outputs very little compared to the overall capability of the grid tied system. And the circuits would be under strict control by me. Instead of choosing and installing a few main circuits, I'd rather have the ability to choose and or adapt what circuits I want on. I know of residential systems like this, I was just looking for detail into that system.
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Ok. You definetly have to have the mains off to prevent back feeding the grid. If the panels are in series, one panel getting fed from the other panel which gets the original feed from the meter it is easily doable. I don't have experience with this type of "dual" panel so my advice would be in the grain of salt category.
 
SCCutler said:
You will need to have a transfer switch between the meter and the panels, such that if, at any time, you are going to use the generator, then the power lines from the meter are completely, physically, disconnected from your home's electrical system. It is critical because, if this is not done, you could back feed power into the grid, and create a hazardous condition for lineman.
Click to expand...

I have to strongly second this warning!

I backfed my home succesfully through a few bad storms, but please! It isn't worth it! I soon went the whole house xfer switch route. What's at stake? That grey transformer out on the pole is a two-way device. If it normally steps 3,000 volts down to 240, backfeeding it will boost your genset output from 240v to 3,000v! That will give your repairman at the top of some pole maybe many blocks away a potentially lethal surprise! DON'T DO IT!

-Skip
 
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SCCutler said:
Your typical 240 is really two 120v legs out of phase, with a neutral "in the middle."

Hence, you get 120 from each leg to neutral, and 240 from leg to leg.
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Disagree, not out of phase. The primary side of the transformer is single phase.
 
EppyGA said:
Disagree, not out of phase. The primary side of the transformer is single phase.
Click to expand...

I am more than a little out of practice and, to be honest, I am a little embarrassed. Two legs off of a center-tapped transformer, not out of phase at all.

---

Edit:

Picturing oscilloscope traces.
 
luvflyin said:
Ok. You definetly have to have the mains off to prevent back feeding the grid. If the panels are in series, one panel getting fed from the other panel which gets the original feed from the meter it is easily doable. I don't have experience with this type of "dual" panel so my advice would be in the grain of salt category.
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Two main panels would likely be in paralel, fed by a single meter.
 
Lindberg said:
Two main panels would likely be in paralel, fed by a single meter.
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Yeah. That would make it unable to feed the busses on both sides by feeding the generator through a breaker on one of the sides without leaving the mains open and maybe zapping a lineman down the road.
 
luvflyin said:
Yeah. That would make it unable to feed the busses on both sides by feeding the generator through a breaker on one of the sides without leaving the mains open and maybe zapping a lineman down the road.
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Not if you parallel the input and have a transfer switch or interlock for each panel.
 
Lindberg said:
Not if you parallel the input and have a transfer switch or interlock for each panel.
Click to expand...
Yeah. That'd work. He should be able find some one to do it. Whoever told him it can't be be done was speaking with forked tongue. All ya needs is a "fork" in the output from the generator
 
EppyGA said:
Disagree, not out of phase. The primary side of the transformer is single phase.
Click to expand...

Yeah, I was going to say something, but thought it too pedantic. Single split-phase, each leg 120v potential to common.
 
The code is that you can't have an AUTOMATIC transfer unless the transfer keeps you from overloading the generator (either the generator is big enough or it only switches circuits that won't overload it). You also need some way to NOT energize the utility mains. What you don't want to do is just connect thngs by a suicide cord.

The answers are a mechanical lockout as previous shown (they make these as after markets for a variety of panels). Note also that the breaker that you are back feeding MUST be secured from inadvertent removal (either a bolt down breaker or a specific hold down designed for such purpose).

The other are the small panels designed to be transfer panels.

I actually have an 80 KVA generator and a 400A automatic transfer switch on my house.
 
I have your same set up, two 200 amp main panels. I have a 50 amp sub panel fed by either the main panel, or a propane fueled auto-start generator, via an automatic transfer switch. I put all the critical loads there. For me, that is heat, sewer pump, water well pump, sump pumps, kitchen (less oven), and strategic lighting / plugs (to include media / internet). This gets us through short outages, and keeps the house from freezing / flooding / losing food when we are not around. Your limiting factor is the generator, I have 17KVA. No shot at all running any of the A/C systems. When we had a summer outage for a week, we ran window units in two rooms, though. Also, during that week, I did some highly non-NEC compliant but technically sound patch cord work to the main panels to get some more functionality, not as a licensed electrician, but as an experienced General Contractor.
 
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3393RP said:
As for the reference in the post above to local codes, every local code without exception has adopted the NEC as that code. So when I say "you're violating the NEC", it also means you're violating local codes.
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Not quite accurate according to NEMA. And it gets more murky from there as different jurisdictions that have adopted it have adopted different versions.

Further, some jurisdictions have adopted codes that go far beyond the NEC requirements. I am aware of at least one jurisdiction that will not even issue an electrical permit except to an electrician licensed in that jurisdiction, with all work required to be performed by licensed electricians or apprentices under their direct and immediate supervision. My current local jurisdiction will issue a permit to the homeowner or a licensed contractor, and will inspect work done by either (but homeowner can only do work in his/her own home).

https://www.nema.org/Technical/FieldReps/Documents/NEC-Adoption-Map-PDF.pdf
 
Tell me about the automatic switches:
-does the generator detect an outage and start automatically?
-how does it handle repeated 1 sec outages? 10 sec outages?
-can you override the switching system and run on generator only to prevent repeated restarts?
-what is the delay from outage to back online when generator starts? (assume no storage)
-if not whole-building generator then probably it switches some sections off, powers pre-determined things/areas?
 
Let'sgoflying! said:
Tell me about the automatic switches:
-does the generator detect an outage and start automatically?
Click to expand...
The switch notes the loss of the mains power and fires up the generator and when the generator comes on line it moves the switch to the generator.
-how does it handle repeated 1 sec outages? 10 sec outages?
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Even one second is a long time. Once the generator comes on line, it continues to run for 10-20 minutes even if the mains come back.
-can you override the switching system and run on generator only to prevent repeated restarts?
Click to expand...
Yes, I can leave it on the generator even if the main comes back. I can also inhibit the automatic start up/switch over. I can also fire up the generator even without the mains failing.
-what is the delay from outage to back online when generator starts? (assume no storage)
Click to expand...
About 3 seconds, no more than 5. You hear the generator crank pretty much as soon as the power drops. It runs for about two seconds before the switch moves the load over.
-if not whole-building generator then probably it switches some sections off, powers pre-determined things/areas?
Click to expand...
As I mentioned earlier, if the transfer is automatic, then the load transferred has to be sized for the generator. If you don't have enough for the whole house, the usual way is to have a second panel that only has your "essential" loads on it that gets switched to the generator.

Many of the smaller automatic switches actually build the "essential" panel into them. You pig tail those circuits over from your main panel.
 
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