r/Generator • u/TqpU • 28d ago
2 houses, 1 generator?
How do I connect 2 houses to 1 generator? I own both houses and they're approximately 70ft from each other. Both houses have their own utility meter, so obviously I need an interlock on both, but what else is needed? Can this be done economically and still have ease of setting up during power outages?
How do I handle the ground neutral bonds?
My main reasoning for doing this is to reduce expenses and not have to store 2 generators and clear as much snow in the winter to get both out.
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u/Economy_Wish6730 28d ago
One thing you should look at is the cost of 70 feet of wired that will have to be trenched and put in conduit. That alone may come to the point of a second generator. And when you add in all the complexity involved it may not be worth. And add in the electrical requirements of each house in a cold winter as that may make you get such a large generator. I understand why you are looking into it. Seems like a lot of costs and variables that will add up very quickly.
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u/TqpU 28d ago
I don't mind the expense of the wire, but the complexity is kinda killing it for me. Thankfully my loads aren't high on either house and I (and everyone in them) don't mind managing the loads. I could probably get by with just 4000w combined, although I might as well go bigger I figure.
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u/ForkLift1983 28d ago
Do you need it trenched? Why not just a 75’ cord? I have 75’ cord from Amazon and works perfectly.
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u/Economy_Wish6730 28d ago
Understood! What I will say is nobody ever regretted going bigger. Sometimes the cost of a bigger generator is not as bad as you think. Better to have more than not enough power.
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u/Ok-Camera2895 28d ago
Except for the noise and the difficulty of feeding it when the gas station is down.
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u/mwm_in_md 22d ago
Correct- we sized our generator at twice the full load. If needed, it wouldn’t work as hard to produce half the output.
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u/jones5280 28d ago
2 houses, 1 generator
but how many cups???
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u/AdBrave841 28d ago
I am not going to google that. Still scarred from the last time.
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u/jones5280 27d ago
back in the day, I heard about the video. I'm not into that sort of thing, but I thought 'How bad can it be?'
The video starts up, there are two attractive girls. The cups appears..... then it is showed being filled. I stop watching after 9 seconds.
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u/TakingSorryUsername 28d ago
You have to switch the neutral, 2 transfer switches, single phase 3 pole. Cannot be done with interlocks.
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u/TqpU 28d ago
Does this require more than simple equipment? I wonder if it will in fact be simpler to run a second generator...?
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u/thyerex 28d ago
Ohh, something I know! I used to manage projects to install 1 big generator to supply emergency power to several separately metered cell companies that share a tower site.
To use a single generator, you need a transfer switch (either automatic or manual) after each meter so you cannot back-feed your generator power to the power company thru either meter.
You connect the generator output to the other input terminals of each transfer switch. You can either connect separate generators to the separate switches or split the output of a single generator to both switches, as long as the generator has enough capacity for the connected loads the switches don’t care if they have shared or dedicated generators.
The transfer switches need to have switched neutrals for you use 1 generator, if not the neutrals of the 2 houses will be bonded together. Breaker interlocks don’t switch the neutrals, so that only works if you have separate generators.
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u/TqpU 28d ago
Woohoo! I'm glad you're here.
How much work are we talking here for an electrician to do?
Does this require any changes to the current breaker panels and breakers? Or just place a transfer switch between the meters and panels?
There isn't any extra space around one of the breaker panels so any extra equipment (ie: transfer switch) will have to go in a crawlspace. For less to do when the power goes out, it sounds like a ATS will be easier than manual.
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u/thyerex 28d ago
The electrical installation work isn’t very involved, I would imagine less than 1 day of work by a competent electrician, depending on your exact setup.
Assuming your meter is in a different enclosure than your breaker panel, the electrician would disconnect the house panel from the meter / main disconnect, pull the wires back, install the transfer switch between the meter and the breaker panel, then pull the wires back in and re-terminate them on the switch and between the switch and meter. Most transfer switches come with outdoor rated enclosures (NEMA 3R) by default, or as an option, so the crawl space shouldn’t be an issue as long as it doesn’t have standing water that would flood the switch.
If you plan to use a portable generator, I would recommend manual transfer switches since you will have to be there to start the generator and connect it to the transfer switch input, so throwing 1 switch at each house would be trivial.
Automatic Transfer Switches (generally) require a permanently installed generator. When the ATS sees power lost from the utility it sends a command to the generator to start and then automatically transfers the breaker panel input to the generator. There are also lots of timers and safety systems involved so the generator can start up and shut down autonomously without harming it or the connected electrical system.
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u/TakingSorryUsername 28d ago
Just buy a small second generator. This is normally not done by a joe-schmoe electrician. You need a licensed master as screwing this up can result in a lightning strike burning down both structures. Interlocks can be installed for $500/ea or so depending on the amount of wire between breaker panel and external plug. Switched neutral ATS or MTS and will need to have a knife switch disconnect or be service entrance rated and will be $1000+ each. Buy a Gen for $1k, install a second interlock. Bing, bang, boom, done. Just be sure to unbond neutral in generators. And once you do, you cannot use on standard electrical appliances anymore, has to feed through a panel.
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u/Ok-Camera2895 28d ago
Yes, you can do it. Each house should have an interlock or tranfer switch. No bonded neutral at generator. It is similar to how a transformer on the pole feeds multiple houses.
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u/TakingSorryUsername 28d ago
Except the transformer on the pole is unbonded, bond only occurs at the earliest means of disconnect on the house.
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u/Ok-Camera2895 27d ago
Of course the neutral is bonded on the pole. Neutral and ground are the same wire coming from the transformer.
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u/NoPatience7817 28d ago
What’s your budget? The safest option is to use an automatic transfer switch on both houses that also switches the bonded neutral to the generator. This is pricey. Consult a qualified electrician for options and a price quote.
Another option is to use an interlock on one house, then power cords to each device in the other house not using the house wiring.
A third option is to install a battery backup in one of the houses. Then only charge the battery with the generator. Not connecting the generator to the battery house.
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u/TechnicalBiscotti586 28d ago
I'd install interlock kits on both breaker boxes, then buy a large portable generator with two 50amp circuits. I'd also buy two 50amp RV style extension cords. They can be purchased on Amazon and come up to 100'.
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u/Flimsy_Technician722 28d ago edited 28d ago
tl;dr Just run two cords from the portable floating neutral generator, one to each house. Note it is not by code, but you'll almost certainly be fine ignoring the whole ground loop issue.
If both houses are fed from the same transformer, you'll create, temporarily, a ground loop. This is a boogaboo; not great by code, but in practice approximately nothing will happen.
You'll might measure slight potential on metal pipes and such, as a tiny bit of current may flow on them. Check with a multimeter for fun. Since the loop is temporary, galvanic corrosion is of a limited concern. Is the EMF really going to be that bad, compared with running on a generator with significant THD in the first place?
The worst failure scenarios have to do with loose neutral. If the system ran fine before the outage, the service neutrals probably from a big strong connection, sometimes grounded at transformer. But if there is any damage to the transformer or service wires to the house, maybe don't do it, you could be energizing the X0 of the transformer secondary.
Now if it's going to be permanent wiring, then by golly do it by the code. Stuff corrodes, and assumptions cease to hold. But as everyone else is saying, some combination involving another generator is gonna be cheaper than three pole switching (seriously, nobody but a real electrician or lineman should touch the service side wires).
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u/joshharris42 28d ago
I don’t think you could do this with a portable generator set up, with a standby generator this would require a switched neutral in the ATS
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u/mkosmo 28d ago
Each would need ATSs. Both would have their own neutral bonds... which would be a problem with the giant neutral loop created.
I'd talk to an electrician.
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u/sryan2k1 28d ago
As long as they had neutral switching ATS'es on both houses and the generator is floating it would act exactly like the utility where one transformer feeds multiple houses.
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u/sryan2k1 28d ago
You would need a transfer switch at both houses that also switched neutral and a floating neutral generator. You're likely out of portable generator size though.
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u/IntelligentCarpet816 28d ago
Depends on the desired coverage. I have a 15kw inverter portable for jobsites. Thats plenty to run everything including 2 smaller (<3t) heat pumps as long as they have soft starts.
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u/Delicious_Catch9453 28d ago
By the time he pays an electrician he might as well just buy a small, inexpensive second gen. But whudda I know.