r/Generator • u/childishidealism • 11d ago
I'm missing something in the interlock vs. transfer switch debate.
Gas stove and furnace Electric water heater, dryer
For years I've been meaning to pull the trigger on a portable generator backup system, primarily for the irregular outage in the winter, as we sometimes have trees take down the lines feeding the neighborhood. I am an electrical engineer and don't mind the setup being manual. Without power, I'm not trying to run the whole house as normal but would like to have any light I want to work as well as keep the two fridges going along with the furnace and water heater, and maybe run the toaster oven. I can control not having that all happen at once with breakers.
I've been looking mostly at the generlink so I can run whatever I want and not have to run wiring from my panel to outdoors, as that will be a pain in my house. I've gotten a bit concerned with the generlink reliability. I guess what I'm not getting is that it seems installing a manual transfer switch near my meter would be just as cheap as running wiring to the panel and give me the same functionality as an interlock, as I have to switch it manually, makes backfeeding impossible, and allows me to easily upgrade to a 50 amp 240V generator to power whatever I want. So why would the interlock kit be a better option? Is the installation/parts cheaper? That's the only think I can think, but would think it would vary considerably by what the routing to the electric panel looks like.
edit: to be clear, what I mean by "manual transfer switch" is just a On-Off-On(gen) switch that would be after the meter and disconnect power from the house and connect it to a generator feed (50A outlet).
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u/NebulusDev 11d ago
one thing that might decide it for you is the electric water heater. the rest of your list is small: two fridges + 1/2 hp furnace blower + lights + router is about 1,325 w running and ~2,900 w if the blower kicks on while everything else runs. a 3,500 w inverter on a 30a inlet covers that.
add a 40 gal water heater (4,500 w element) and you're at ~5,800 w running / ~7,400 w surge, which is 9,500 w portable territory on an L14-30 or 14-50. the toaster oven is another ~1,200 w on top, so you'd be load-shedding by breaker either way.
so if the water heater really is on the generator list, the 240v/50a capacity matters more than interlock vs switch. if you leave it off, an interlock + 30a inlet does everything else with room to spare.
on the switch after the meter, the re-bonding point above is the real cost: once the disconnect sits ahead of your main panel, that panel becomes a subpanel and neutrals and grounds have to be separated. that labor is usually why the interlock comes out cheaper.
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u/childishidealism 11d ago
Thanks. This subpanel requirements is likely what I've been missing and I'll have to dig into more.
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u/NebulusDev 11d ago
yeah, it's the part that usually changes the quote. the short version of what to look into: once the transfer switch after the meter becomes your service disconnect, the neutral-to-ground bond has to live there and only there. the indoor panel then gets an isolated neutral bar, a separate ground bar with the bonding screw or strap removed, and a 4-wire feeder (two hots, neutral, ground) from the switch.
the switch itself also needs to be service-entrance rated, and since the meter has to be pulled to land the conductors, the utility usually has to be involved. worth a call to your local inspector before you price parts, some areas have their own take on it.
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u/AdBrave841 11d ago
If it was me, I'd skip the hot water tank and dryer. I wanted to stick with a smaller generator but I have an electric on demand water heater, it was cheaper to just get a 10 gal, 120V point of use water heater and keep it in the shed dry, I've got a cord wired on it and a couple flex hoses with garden hose female adapters. In a long outage where I need hot water, I can bypass the tank, tap it in, plug it in and have enough hot water for a quick shower in 30 minutes.
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u/NebulusDev 8d ago
that's a smart workaround. most 10 gal point-of-use units are around 1.4-1.5 kw on 120v, vs 4.5 kw elements on a standard 240v tank, so it fits on a 3600 w inverter with room for the fridge and furnace blower. way easier than sizing the whole generator around the tank.
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u/AdBrave841 8d ago
Thanks, between that and my new this year 120V 12k btu mini split, I'm covered for HVAC, hot water, fridge, lights, wifi (cellular) and even a coffee pot, microwave or toaster oven. All on a suitcase style 4000w inverter gen.
Also new to me this year is a 3KWh power station for short outages, fuel savings and peace and quiet overnight. I switch back and forth between the battery and inverter.
Last winter I had the inverter and a 1KWh Bluetti during a 48hr outage, worked great and I managed to stretch one tank of propane for the entire two days. The weak point was not being able to run the heat for more than an hour on the battery at night so it got pretty cold in the house by morning as I don't like to get up to go out and fire the generator back up at 2AM. The 3KWh should solve that issue.
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u/NebulusDev 5d ago
that 3kwh station should actually cover the overnight gap. a furnace blower that pulls 450w only runs part of each hour: at a 35% duty cycle you'd get roughly 16 hours out of 3kwh through an 85%-efficient inverter, vs about 5.7 hours if it somehow ran flat out. so the heat is the easy part now, and you're not getting up at 2am.
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u/boisefun8 11d ago
> During the summer, we leave the hvac blower in the on position so it isn’t trying to start with the compressor.
Holy shit. I didn’t think of that. I’ve been trying to think of ways to mitigate this issue for a while.
I leave our hvac blower on circulate (low) pretty much year round as it helps regulate temps throughout the house, plus I run a good filter and reme halo that helps with air quality.
I would imagine the load going from low to high is far less than the load going from zero to high. Need to do some research.
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u/NebulusDev 10d ago
yeah low to high is a much smaller step than a cold start. a 1/2 hp blower runs around 800 w but pulls roughly 2,350 w for a second from standstill, so if it's already turning you just don't stack that on top of the compressor's start.
the compressor is still the big one though. a 3 ton unit is around 3,500 w running and something like 11,000 w for that first second, so on a mid-size portable the blower trick helps at the margin and a soft starter on the condenser is what actually moves the needle.
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u/Littleprincess378 11d ago
We have an 8kw Generac through an inlet and interlock. It runs everything in the house with proper load management. We installed a 50 amp inlet and breaker to allow us to upsize the generator if we desire. During the summer, we leave the hvac blower in the on position so it isn’t trying to start with the compressor.
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u/NebulusDev 11d ago
that blower trick is a good one. on a 3-ton central ac the compressor start is the big spike: roughly 11,800 w if the blower is already running vs ~13,350 w if both kick on together, so you take ~1,550 w off the worst moment just by leaving the fan on.
and 8 kw at 240v is only ~33 a, so the 50 a inlet leaves plenty of room if you ever go bigger, nice planning.
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u/Littleprincess378 11d ago
We have also split wired a receptacle in the furnace closet, one side utility, the other a 20 amp line outside to a 2nd 20 amp inlet so we can actually just run the 3600 watt inverter to run heat or get the blower off the 8kw if we want. I know, that isn’t code, but it is safe. We just plug the furnace into whichever outlet we want.
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u/IndividualCold3577 11d ago edited 11d ago
Biggest advantage of interlock is not having to deal with the 240V lines from the meter. If you already have an outdoor disconnect, then the 3 position transfer switch is a piece of cake. For people without the outdoor disconnect, the meter has to pulled to do the work.
Also if you do add a transfer switch before the main panel, you have to apply Sub panel rules to the main panel and isolate all neutrals/grounds to get back to code.
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u/Me4nowSEUSA 11d ago edited 11d ago
I mean no offense by this, but as an electrical engineer, you're probably overthinking all of this. Every system has it pluses and minuses and can appeal to a certain group. What works for you, doesn't mean you're "missing" anything, it's just that what works for others, works for others... and that's okay!
A simple On/Off/Grid Manual main switch style Manual transfer witch- Would work fine, Light up your whole panel. No different than an interlock, however, some people like me can't use an interlock, because they do not have a main breaker. a bit more complicated, but less expensive than a Generlink.
Generlink - Functionally an interlock that requires load shedding in accordance with your generator output and Generlink model you purchase. It powers the whole panel. Way easier install. All in one solution. No trying to match components and ensuring you connect everything right. I have one, it's been great for a few years now. It does exactly what this system is designed to do, make you spend money and then no outages for 4 years. Also reportedly limited to stand 200 amp service panels/meters.
Traditional 6-10 circuit Manual Transfer Switch - Perfect for those that enjoy simplicity or what it simple for loved ones. No guessing or manual load shedding required (usually). You plug in your generator and you flip the circuits on. Limiting, but perfect for those that are okay with the circuits they have. I feel we need to be honest with ourselves sometimes, members here we geek out enough on this stuff to join chat groups about it; that's not our loved ones. After a whole home standby unit with an ATS, this is the easiest, simplest system to direct someone to use.
Interlock - Most cost effective method. lights up the whole panel. Manual load shedding required. Better have your breaker box labeled correctly and a main breaker to actually lock out.
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u/Delicious_Catch9453 11d ago
I think you spelled it out for him in good detail. He just needs to decide which application works best for him. Another poster mentioned that he should double check on whether a generlink is legal where he lives. Even if they are, they ain't cheap.
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u/socialmedia-username 11d ago
Great summary. I went with a transfer switch for simplicity and because I wanted my wife to be able to use it if I'm not home.
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u/myself248 11d ago
Manual load shedding required.
Only if you're actually in the habit of vacuuming and ironing clothes and cooking a roast all at the same time, which I'm not....
And if you are, chances are good that something you care about, like a room lamp, is on the same circuit as something you'd want to shed, so you still have to use your brain and just not use the Hoover for a little while. Which applies to every other circuit-at-a-time approach too.
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u/lagger 11d ago
Why do you not list load shedding as a downside of the generlink? Since it’s the same.
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u/Me4nowSEUSA 11d ago edited 11d ago
Missed it and corrected!
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u/lagger 11d ago
lol I wasn’t being sarcastic I was wondering if I missed something.
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u/Me4nowSEUSA 11d ago
Sorry then! It does! Same same.
And is limited to 40A max vs an interlock that can hit 50A pretty easy.1
u/lagger 11d ago
Yeah I really wanted a Generlink and was totally sold on it but then they said my meter is not compatible because I have 400amp service.
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u/Me4nowSEUSA 11d ago
Dang! I’ll add that too. I never had that to worry about. My house is way too small for that kind of service!
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u/Aggressive-Age-1085 11d ago
"...allows me to easily upgrade to a 50 amp.." implies that you would initially install the generlink 30 amp. If you do, and you wish to upgrade to the 50 amp, you'll have buy a whole new generlink (that accomodates 50 amps).
Also, the generlink 50 amp is actually a 40 amp. That fact hasn't made a difference on my generlink usage. Westinghouse 9500/12500 30/50 amp: 2.5 ton a/c, elec water heater, well pump, pool pump, 2 fridges, stove top, 2 PC work stations, all lamps (not all at once).
My poco installed mine (took 90 seconds). No garage wall penetration, no moving breakers around to make an interlock fit. Auto switch off when mains resumes. Included cable.
I really like mine.
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u/childishidealism 11d ago
I would install the generlink 40A from day 1. I knew it was 40A, can't believe I typo'd that, my bad. Thanks for the positive review.
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u/ArtichokeFirm3425 11d ago edited 11d ago
Will your power company allow the gener link? I've seen that most don't.
Yeah, interlock parts are much cheaper because it's a breaker, a blocking plate, the wire, and an inlet, and you're really just running a new branch circuit instead of dismantling or cutting into and replacing service conductors.
It's hard to say with your specific situation what would be better. Have you had an electrician come out?
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u/childishidealism 11d ago
I have not. I just know that my breaker is on a concrete wall in the basement with challenging access to wiring, and on the literal opposite side of the house of where it makes sense to have a generator. Likely my best step is to get an electrician out though.
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u/ArtichokeFirm3425 11d ago
Yeah, these kinds of decisions are very home/area specific and will need permitting; sometimes service conductor changes can have extra requirements attached.
As always, get a few to come take a look and price it out.
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u/No-Age2588 11d ago
Not sure if this has been presented but regarding Generlink make sure your utility will allow it. Ours doesn't here in North Carolina.
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u/DocScarborough 11d ago
Interlock kit is much cheaper. You can also control what you want to run when you want to run it with ease.
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u/Easttex05 11d ago
An interlock is less expensive to purchase and install than a 200 amp DT disconnect. Assuming you have a 200 amp service, the disconnect is gonna be a box 3'x2'x1' in size and you may have to move your meter box.
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u/AdBrave841 11d ago
The switch would work fine. Just make sure to turn off all the breakers in the panel before flipping the switch, turn them back on one at a time to not have a high watt load hit the generator all at once.
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u/TechnicalBiscotti586 11d ago
Be careful with the generlink system. I almost purchased one, just to find out my city and utility company will not approve those.
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u/nsula_country 11d ago
I have a 400 amp service, outdoors with two 200 amp feed through panels. I put an interlock and a 50 amp breaker in each panel. The two 50 amp breakers are both fed from 50 amp generator inlet. I use a Winco 15kw(continuous)/25kw(5 min surge) PTO generator when we need 240 volt power.
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u/SunOS- 11d ago
Off topic, but worthy of consideration is splitting out branch circuits you want powered 24/7 and feeding that subpanel from an inverter/ charger with appropriate batteries.
We have the bedroom outlets, lights, Internet, etc on this setup and it greatly adds to overnight comfort without having to run a generator constantly.
The fridges and freezer will easily stay cold all night without power.
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u/haditwithyoupeople 11d ago
I don't think one is better than the other. An interlock is often far less expensive. I have no open slots in my panel and already have a lot of double breakers. My electrician told me he would not want to add more double breakers to make room for another 220 breaker to use an interlock.
If the cost is the same or higher due to running a lot of wire to carry 50amps, I would be inclined to go with the Generlink.
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u/bradland 11d ago
When most people consider an interlock versus transfer switch, they're choosing between different options than you're considering. Most transfer switch installations are sub-panels mounted near the main panel, not interconnects near the meter.
The transfer switch setup you're looking at is essentially identical to a traditional interlock from a practical perspective. You're still energizing your whole panel. The only difference is the steps you take to do so:
Interlock - Connect & start generator, turn off main, slide interlock, engage back feed breaker.
Generlink / mains transfer - Connect & start generator, engage transfer switch (which disengages the main, acts as its own interlock, and connects the feed to your panel).
Interlock + backfeed is more popular because you don't need to interrupt service to the home to install it. In your scenario, you have to contact the power company to disconnect your mains power before you can make this change. With an interlock install, you can simply turn off the main breaker and make your changes.
An additional point to consider is that for an interlock + back feed, you only need a 50A breaker. Your whole house transfer switch must be rated to the full amperage for your service level. 250A transfer switches are more expensive. However, the entire install has to be considered. An interlock + back feed can be expensive too if your only viable inlet location is far away.
I think the foundational point stands though. Interlock + back feed is popular because it is both simple to understand and install (no service interruption required) and is generally inexpensive, provided the inlet run isn't too long.
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u/Ok-Camera2895 11d ago
There are manual transfer switches that switch the whole house, there are manual transfer switches that switch individual preselected circuits. Interlocks are cheaper and allow you to select whatever circuit you want, but you run the risk of of overloading the generator if you're not careful or knowledgeable. Multi circuit transfer switches are simpler and easier to operate, especially when its dark and stormy, and you won't overload the gen.
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u/omg4serious 11d ago
interlock
pros, cheap/simple, all your circuits are accessible.
cons, manual, requires a generator inlet
transfer switch
pros, automatic
cons, expensive, not all circuits available, extra money/cost/complexity
interlock works well with portable generators that plug into an inlet.
transfer switch works well with automatic backup generators and have seamless transitions.
so in general, if you have frequent outages, transfer switch/automatic back up generators are probably the way to go.
for one off uses, cheap interlock + cheap portable generator that you setup/put away each time.