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Old 12-28-2017, 09:10 AM   #1
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Generator wiring advice


I've ordered a 3500/4000 watt portable inverter generator and I'm planning how to wire it to my house. This generator comes with a 30 amp RV (TT-30) outlet.

I'm planning to use the RV outlet on the generator to cable to a Generac locking power inlet on the outside wall of the house. Inside the house, I will place a small subpanel with a few breakers. This subpanel will not attach to house wiring anywhere and will not be bonded to the main service panel.

I will run some dedicated generator power outlets from the subpanel and I'll plug in whatever appliances I need into these outlets.

Inside the subpanel, I'm assuming that I should wire the neutrals and the equipment ground from the outlets to the neutral bus. Then, both the neutral and ground going back to the generator would also be wired to the neutral bus.

Back at the generator, I'm assuming that the neutral and ground will be bonded to the frame (I will check to make sure this is the case).

Is this essentially the same configuration that would be used with an RV connected to a generator? Does anybody see a problem with this arrangement?
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Old 12-28-2017, 09:19 AM   #2
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Re: Generator wiring advice


Sure would be easier to install a GenTran transfer switch, and wire it to the generator and to specific circuits in the panel. That way you have a definite demarcation from the grid to the generator. However, your generator will be woefully inadequate to handle large loads other than lighting and a few receptacles.
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Old 12-28-2017, 09:43 AM   #3
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Re: Generator wiring advice


Yes, I understand. The problem is that I have an old home and the service panel and some of the wiring is "grandfathered". If I wanted to put in a real transfer panel, I'd need to get a permit. The AHJ might very well cause me real grief and force a $15,000 rewire of my house. I don't really want to get into that just to add a small generator.

My solution is to add a completely separate panel which I won't get permitted. I just want to make sure that my installation is safe.

One question I have is whether I should keep neutrals and grounds separate at the subpanel. Does it matter?
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Old 12-28-2017, 09:50 AM   #4
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I agree with chandler. A transfer switch will be a lot less work. Even less work is a generator interlock for your main panel. They are designed for specific panels. You install a 30 amp two pole breaker at the top of the panel. The generator back feeds into the breaker. The interlock prevents you from turning on the generator breaker while the main breaker is on hence preventing backfeed into the power grid. They however are not legal in some jurisdications. If you cannot do an interlock then A conventional transfer switch will be easier and cheaper than your proposal . That however is a pretty small generator a refrigerator , microwave and a couple of lights are going to come close to maxing it out
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Old 12-28-2017, 10:05 AM   #5
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Re: Generator wiring advice


An interlock is not available for my panel (it's an old split panel). As I stated above, in order to make substantial changes to my service, such as a transfer switch, I'd need to substantially update my wiring, upgrade some circuits and generally get into an expensive and complicated situation. It's hard to see how that would be cheaper than $30 for a subpanel and breakers.
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Old 12-28-2017, 10:40 AM   #6
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Re: Generator wiring advice


With a TT-30 receptacle, the generator is most likely 120v only.
It's also likely that the inverter is a "floating neutral" design, so it makes sense to keep it isolated from the existing house wiring.

Don't be surprised if the hot and neutral both measure 60v to ground.
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Old 12-28-2017, 10:49 AM   #7
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Re: Generator wiring advice


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Originally Posted by Oso954 View Post
With a TT-30 receptacle, the generator is most likely 120v only.
It's also likely that the inverter is a "floating neutral" design, so it makes sense to keep it isolated from the existing house wiring.

Don't be surprised if the hot and neutral both measure 60v to ground.
I thought that might be the case. After some other reading, I'm thinking maybe it would be wise to keep the equipment ground and neutrals separate at the panel and to take them back to the generator separately, too. I think that's the way an RV would be wired.
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Old 12-28-2017, 11:25 AM   #8
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Re: Generator wiring advice


Just a FYI for the reader's on this OP... I would not advise the OP or anyone else of doing this wiring project as it is being proposed. Following is why I state this opinion of mine. Take it for what it is worth.

Having went through a major power outage here in 2003 and my wife and I just barely staying warm with a KeroSun heater and having no hot water to shower with for 5 days in our ALL electric home, I knew our next home that I wanted to be prepared...

So when we bought another home with gas heat, I did as the OP is proposing. While I was updating our 1960 model home from a 100 amp to a 200 amp service, I went ahead while I had the wall open and set a 12 circuit Sq.D. breaker box to be powered by my genset. (to the left in the pic behind the orange hanging leaf blower) NOT one piece of wire in our home was connected to my emergency wiring.

I ran dedicated wire from the small emergency generator powered breaker box to the dedicated receptacles I installed for the gas furnace, refrigerator, and electric water heater. Fed the emergency panel with a conduit buried UG with # 6 copper conductors from my 5500 W genset that I put in my garden shed.

Provided a pigtail set to plug in from a 4" sq. box that I set in the shed to the genset's 30 amp 240 volt outlet. Provided a vent in the shed wall for the genset exhaust to ventilate out of.

I put red cover plates on all my gen powered receptacles marking them with my P- label maker " emergency power only" and their cir #. I marked the emergency breaker box " Powered by Generator Only" .

We lived in the house for 7 years and never once did I have to use my emergency power system. When we sold the home and had 30 days to get moved out, I knew I had a problem. How would the new home owner EVER figure out my emergency power system ?

So I sat down and typed up a bulleted operation manual for how the new owner could operate my system. When I finished it, I read it and tossed it in the trash. A person would have to be an electrician to grasp and adhere to my instructions.

When we bought this house, it was to be our LAST home, so I spared no money or time making the home the way we wanted it. Why NOT put in my own genset system ? But most will find, peoples intentions = bad philosophy, as our lives get changed in short time any day for health reasons, financial.... and then we have to move.


My thoughts were, how would the home inspector coming that is representing our buyer, handle my handiwork on his inspection report ? Would he flip out when seeing my system of emergency power ? If I was home inspector, I know that I would flip out... I knew that we may even lose the sale on our home, because of my genset system.

So before the home inspector came, I sold the genset, removed all the red plates and receptacles and blank cover plated them. I put a sheet metal plate over the emergency breaker box and painted it with the wall paint. I removed the garden sheds genset wiring. If the new owner wants to dig out all of my handy work and make it functional again, then it is on them. I disabled it ALL, before we moved.

We property owners have to consider what our handy dandy electrical projects may do to our homeowners insurance in case of a fire(even if the source of ignition is NOT the emergency wiring, the fire investigator always looks to the electrical wiring in the home FIRST)

So, do your emergency system as the pros here are recommending, and do it right and get it inspected. Keep that approved inspection certificate in a safe place. And for nothing else, we property owners need to be considerate of the new owners of our properties...well being. JMO
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Last edited by Gregsoldtruck79; 12-29-2017 at 04:06 PM.
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Old 12-28-2017, 12:30 PM   #9
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Re: Generator wiring advice


@Gregsoldtruck79

I appreciate your sharing your experience. You're quite right, I might never have a need for the generator. But even if I never use it, my investment in the the generator + wiring will be around $600 - $700. I could easily undo all of the wiring in a couple of hours and make it vanish into the night.

On the other hand, I could do the whole thing "right", which probably means getting a serious generator for $5000 and then paying an electrician $15,000 to $20,000 to rewire my house to bring it up to code and install a proper transfer switch. And then, it's possible that I would spend $25,000 and I still might never need the generator.

When I get ready to sell my 70 year old house, it's possible that I'll have to do a lot of upgrades to sell the house. That would be the time to upgrade everything at once. Less cost and less disruption than doing it piecemeal. Given that I live in an old house in a desirable neighborhood, it's quite possible that someone will buy the house, tear it down and build a newer and larger one.

I don't believe in sinking money into a house that might not provide a good payback. For now, I think my plan is a pretty good solution for my situation.
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Last edited by woodyl; 12-28-2017 at 12:36 PM.
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Old 12-28-2017, 12:44 PM   #10
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Re: Generator wiring advice


Quote:
Originally Posted by woodyl View Post
@Gregsoldtruck79

I appreciate your sharing your experience. You're quite right, I might never have a need for the generator. But even if I never use it, my investment in the the generator + wiring will be around $600 - $700. I could easily undo all of the wiring in a couple of hours and make it vanish into the night.

On the other hand, I could do the whole thing "right", which probably means getting a serious generator for $5000 and then paying an electrician $15,000 to $20,000 to rewire my house to bring it up to code and install a proper transfer switch. And then, it's possible that I would spend $25,000 and I still might never need the generator.

When I get ready to sell my 70 year old house, it's possible that I'll have to do a lot of upgrades to sell the house. That would be the time to upgrade everything at once. Less cost and less disruption than doing it piecemeal. Given that I live in an old house in a desirable neighborhood, it's quite possible that someone will buy the house, tear it down and build a newer and larger one.

I don't believe in sinking money into a house that might not provide a good payback. For now, I think my plan is a pretty good solution for my situation.

I think your estimates for being able to use a generator as backup power being JUST large enough for your homes essentials, IE: Ref, heat, showers.... may be high.

https://www.amazon.com/Reliance-Corp...ransfer+switch
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Old 12-28-2017, 02:27 PM   #11
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Re: Generator wiring advice


A generator equipped with a TT40 receptacle has to be special purpose meant for RVs. It is only 120 volts. If you wire to a sub panel you will only be able to use half the slots unless you jury rig it


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Old 12-28-2017, 02:35 PM   #12
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Re: Generator wiring advice


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Originally Posted by rjniles View Post
A generator equipped with a TT40 receptacle has to be special purpose meant for RVs. It is only 120 volts. If you wire to a sub panel you will only be able to use half the slots unless you jury rig it


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The subpanel I ordered is very small. It's a single-side 120V panel with 4 slots. We're talking about a small generator here. A larger panel would be overkill.
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Old 12-28-2017, 02:48 PM   #13
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Re: Generator wiring advice


Quote:
Originally Posted by woodyl View Post
An interlock is not available for my panel (it's an old split panel). As I stated above, in order to make substantial changes to my service, such as a transfer switch, I'd need to substantially update my wiring, upgrade some circuits and generally get into an expensive and complicated situation. It's hard to see how that would be cheaper than $30 for a subpanel and breakers.
I see the logic of this. All you want to do is basically lengthen and "T" the
extension cord that would normally run from the generator.
Keep ground* and neutral separate.
Don't use any MWBC's, they rely on current cancelling in the neutral.
You'll have to decide how to power both "legs" of the 120/240V panel
from a 120V source, or, use a 120V panel. They're not too common these
days.

*Calling it ground is even more of a stretch than usual. It's purpose will be to provide a return path for fault current to trigger the OCD. Nothing
more.
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Old 12-28-2017, 03:14 PM   #14
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Re: Generator wiring advice


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Originally Posted by CodeMatters View Post
I see the logic of this. All you want to do is basically lengthen and "T" the
extension cord that would normally run from the generator.
Keep ground* and neutral separate.
Don't use any MWBC's, they rely on current cancelling in the neutral.
You'll have to decide how to power both "legs" of the 120/240V panel
from a 120V source, or, use a 120V panel. They're not too common these
days.

*Calling it ground is even more of a stretch than usual. It's purpose will be to provide a return path for fault current to trigger the OCD. Nothing
more.
You've got it. I want to set up a more robust solution than just running extension cords all over the place. I will run 2-3 outlets around the house for refrigerator and lights and a dedicated separate outlet for my gas furnace. As far as multi-wire branch circuits, no chance of that because the panel is 120v with only 4 slots (up to 8 branch circuits). This will reduce the chances of overloading the generator and will provide good control of what's running.

It's a low-cost solution that should be adequate for what I'm planning. I think keeping the grounds and neutrals separate is a good idea.
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Old 12-28-2017, 03:26 PM   #15
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Re: Generator wiring advice


Never seen a single sided 120 panel. You have a link to the product.

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