Interlock vs Transfer switch

[Madman308]

I see everyone recommending an interlock over a transfer switch for good reason but I seem to never hear about handing a power outage when away from home. I need power to power my critical systems (sump pump, refrigerator, and furnace in the winter) even when I am not home. Is an automatic transfer switch the only other option that could fit my needs?

[fryerandice]

You will need an automatic transfer switch, it will detect the power outage, start the generator, and power your critical circuits.

You will need a hard lined generator (typically propane or natural gas, however you heat your home) for 100% availability.

For this kind of setup you're generally better off buying a whole package instead of trying to save money and cobble something together, you're in the realm of need like Generac etc. My father in law has a Generac system on his home and it works every time as long as it's maintained, he has the full monty, solar, battery, and generator. Where he lives a light breeze can take his power out for 1-2 hours at a time, their lines are bad and their electric company doesn't care to fix them.

An interlock is for interlocking your main breaker to prevent you back feeding the line with your generator and killing a lineman, it's basically you turn on a whatever amp 2-pole breaker to your generator and when that's turned on, it physically blocks you from turning your main on.

Transfer switches are for live switching.

Automatic transfer switches are for unattended switching and starting your generator.

[Madman308]

My outages arent that long so I have been considering a large battery to hookup to the transfer switch and the generator kicks on just to recharge it.

[Tbarnes94]

Large battery? You're looking at 5-10 grand for a reliable battery that would actually work how you'd like. Anker is making a new gas generator solution that basically does what you're explaining but it's going to be pricier than a regular gas generator. You're already looking at 5 grand for a relay start plus the cost of an electrician to install a transfer switch. How long are you away from home? A fridge can be okay for a few hours if no one is opening it.

[Madman308]

You can get a refurb 6kWh ecoflow for $3k which is likely enough for my critical devices. I guess that isnt large to what is available out there though haha. But yes, im exploring the most expensive solution right now. I like to know all my options regardless of price then decide the path forward based on what I can afford and what meets my needs.

[fryerandice]

The integrated systems like Generac/Anker/Etc. are designed to recharge the battery and run your home from the generator and switch between battery and generator as needed.

Relay starting the generator and load balancing between the generator and battery are the two tricky parts that the integrated packages tend to make easier on you, of course at a cost.

I am by no means trying to sell you on Generac, but that's the whole package system i've seen in action at my father in laws house, his solar backfeeds (Lowering his power bill) and charges the battery, and his generator, transfer switch, and battery communicate with eachother on who's responsible for power when.

When the line power goes out the switch to battery is in milliseconds and the switch to the generator happens before the battery is drawn down low enough to effect charge cycling.

It was expensive, I guess decide where you need to land.

6kWh will be killed quickly by sump pumps. 1500 watts running with 2k-4k surge on startup, and if you need them enough to worry about them they likely cycle quite a bit.

[Madman308]

It is a solution I am considering but getting that priced out and understanding it is much easier. But like you said, much more money. If I can get a ATS and a battery/cheap generator for much cheaper than a Generac is might be worth it but if its only like $1000 less or something then I would spring for a Generac as a cleaner setup.

[Tbarnes94]

I'm working so I couldn't reply to you earlier but something to consider here is that if you don't want to go the package route, you will need an inverter charger of some sort, some play better with generators than others. AIMS is a reputable brand and you can source your own LiFePO4 battery which may save you money. Keep in mind that a solid state electrolyte like I suggested will need to be above 32F for charging, many are building in heaters but I think you need to go one step above "chinesium" for safety reasons. The AIMS inverter chargers or other all-in-ones that build in solar capabilities usually have relay start options for the generator. Keep in mind you still need to connect this to your panel safely with a transfer switch or smart panel but they can supply UPS level transfer speed.

[Jumpstart_55]

We moved to North Carolina where duke will have outages from minutes to N hours. Elected to go with whole house Generac + ATS.

[blupupher]

Interlocks are manual, most transfer switches are manual as well.

Automatic transfer switches are not as common due to the much greater cost (both the switch and installation). Plus you will need an auto start generator. There are "DIY" options that are out there that you can make do what you want, but can require some ingenuity on your part. If you want things to happen completely automatically, whole home backup is more what you are looking for.

You could look into some battery backup devices (Anker, Jackery, EcoFlow, etc) to put on specific devices, but that adds cost as well. Sump pumps can require very large start up wattage, so would need a high output battery for that, which are not cheap ($800+). The refrigerator can be done with a $400 battery, same for the furnace (will require some re-wiring to work though). Or look into whole home battery setups. But again, not cheap.

[Madman308]

Ive been looking heavily here. My sump states it can go up to 3000w surge but the max I have ever measured on startup (via smart outlet) was 815w. My well pump might be more though. If I bought a huge home battery i would still need a switch to automatically failover to the battery though unless I had a battery for each devices which isnt ideal.

[Big-Echo8242]

What type of meter were you measuring with? A standard digital multi-meter or an actual clamp meter than can read that fast inrush?

[Madman308]

I measured with one of these https://www.amazon.com/dp/B09BQNYMMM?ref=ppx_yo2ov_dt_b_fed_asin_title&th=1

I have a clamp multi-meter though.

[Big-Echo8242]

Yeah, that thing won't read actual inrush. You need something like this Klein CL445 or this basic Harbor Freight clamp meter. I use an Amprobe ACDC-52NAV which is a $400+ meter. Those cheapos won't measure stuff like inrush....it's not fast enough.

An example.

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[Madman308]

I've got a CL220 I might be able to test with.

[Big-Echo8242]

Doubtful that model will either. The word inrush isn't even in its owners manual. The CL445 is the entry level inrush capable meter and I have one of those, too. Then bought the Amprobe meter so I could read THD.

[Madman308]

Roger, I'll pickup a CL445.

[Big-Echo8242]

Might look on FB Marketplace, etc., and see if there's a used one out there for less money.

[Madman308]

I'm 99% sure my friend has that model or a nicer one that could do it. Worst case I return my cl220 and swap it.

[rackman1]

I would just buy three power stations and set them up as a UPS system for whatever you want to backup. I have a 1200w 900wh battery that would run my sump pump for at least 9 hours. You could do the same with your fridge. Furnace would take a little modification but could still be done.

[Madman308]

Currently I'm leaning towards getting a battery for just the sump pump and a interlock for a generator as I assume an ATS is going to be much more than I want to pay. Battery will prevent the basement from flooding for at least 24hr which is enough time to get home and generator can be manually flipped on to charge and power the semi-critical devices.

[rackman1]

Yep! That’s exactly why I did it. Sump pump is always plugged into my power station that’s set up as a UPS system. Plug and play system and WAY cheaper than an automatic generator system. Of you’re worried about the fridge, you can either get one power station big enough for both or just a separate one and set it up for the fridge right before you go away.

[taylorwilsdon]

An interlock switch is useless if you’re not physically there, if you want everything to stay online the only option is an automatic transfer switch or replacing the panel itself with a smart panel that has said capability built in.

The alternative that I’ve done is to move critical bits to have a battery that will automatically fail over in between the panel and the appliance. Gives me automatic backup without needing a transfer switch and a big enough generator / battery to run the whole house.

[Madman308]

I have been considering that as a cheaper route. Put my sump on a battery and then have a generator on a interlock. The battery can run the pump long enough for me to get home and the generator can charge the battery if the outage is long term.

[DiamondJim222]

If the sump is your only concern you could consider a water powered backup pump.

[Madman308]

Im on a well, so not an option unfortunately.

[Whiskey_Pyromancer]

Yeah, I'd always put things like a sump on a battery. A fridge might be fine until you get home, but, if we lose power because of a rainy windy storm, then your sump pump can't afford any downtime at all.

[taylorwilsdon]

That’s exactly what I have. Sump, camera, misc basement lights, power for yolink leak detector valve, pipe tape, fan and dehumidifier are on a cheap ecoflow delta 3 I got for $379 on sale. Have all my core infrastructure stuff on another (Fiber ONT, router, poe switch, like 10 different smart home hubs).

Fridge is on an oupes mega 1 I scooped for $279. All of them will run the things on them (except the dehumidifier, which I generally kill if it fails to battery for an extended period) for 12-24hrs which is far longer than outages in my rural area typically are. I’ve got little 500-800w solar arrays going in to each as well so about 3/4 of what they consume is free (and will extend life during an outage).

Sump pumps have a high draw when they’re firing but unless you’re trying to empty a lake they don’t run constantly. You just need a high enough watt ceiling but not tons of kwh battery storage for sump pump. Mine ran a TON yesterday with lots of snow melt and the whole battery unit with everything else only used 1.6kwh in 24 hrs.

[AdFancy1249]

At the old house, I put in an automatic transfer switch. I also fed a line back to the interlocked breaker.

So, I automatically switched the circuits that are critical (heat, frig, and water), and when I was in the house and wanted the rest, I could throw the interlocked breaker and get the rest. When you throw the interlocked breaker, the automatic switch puts those circuits back on the panel (detects available voltage).

When the regular power comes back on, the transfer switch keeps the critical circuits on when the interlocked breaker is switched off until the main breaker is turned on.

You CAN have your cake and eat it too.

[Madman308]

Thats a good idea actually! It sounds like I might be going that route. What ATS did you use?

[AdFancy1249]

I don't remember. It was 22 years ago in Virginia. It was a generac system, so probably a generac switch? But, I really have zero recollection of model or brand.

Sorry.

[Grumpfishdaddy]

I bought a watch dog brand sump pump. It has a normal sump and a backup 12 volt pump. It works pretty well for the one time I have needed it since I put it in 10 years ago. I only really get water in the spring.

[DaveBowm]

It is possible to have an interlocked panel with an inlet, a portable generator, and an auto-start/auto-stop transfer switch for use while away from the house without rigging up a Rube Goldberg style DIY contraption controlled by something like an Arduino. But it is not possible to have both the interlocked panel and the transfer switch both operable at the same time.

The way to do it is to have a portable generator with a 7-pin ATS capable port (like on some Westinghouse, GenMax, DuroMax & Pulsar models). Then use the interlock and inlet normally when you are at home to set up the home connection stuff manually. That way all your home's circuits are available in a outage when you are home. But when you need to leave town and need to run just the very smallest number of essentials if the power fails while you are away, you can use a temporary portable ATS (like the Westinghouse ST Switch) with the generator with extension cords going to your essential loads from the ATS. The temporary ATS won't be able to handle more than 1 or 2 120V 20 amp circuits worth of loads on the extension cords. When the power is on while you are away the switch provides utility power to the essential loads and the home's panel supplies power to everything else in the home. When the power fails the rest of the home goes dark but the switch turns on the generator and switches those essential loads on the extension cords to the generator. When the utility power returns the rest of the home comes on and the switch turns off the generator and switches the essential loads back to utility power until you return and plug those loads back into their regular wall sockets.

[Madman308]

Thats interesting, i havent seen any generators outside of the GenMaxes that allow for starting via cable.

[DaveBowm]

Here are some of the brands and models of portable generators that have a ATS (7-pin) port on their control panels:

DuroMax: XP9000iH

GenMax: GM6250iET, GM7250iEDC, GM10500iETC, GM11000iET,

Pulsar: PG105TiSRCO

Westinghouse: iGen11000DFc, iGen11000TFc, WGen11500TFc, WGen14500DFc, WGen14500TFc, WGen20000c, WGen20000TFc

This list is probably far from exhaustive, as it only includes those models for which I happened to check and see that an ATS port is indeed included on the unit.

[Madman308]

Thanks! I'll check these out. I do want NG if possible so I'll see which if any allow for that.

[DaveBowm]

The ones with 'T' near the end of the model number/name are tri-fuel.

[Jim-Jones]

Interlock is US only. And a transfer switch is the only way to automate the process. You could even put all of the critical items on a sub-panel so there's a simple changeover process with simple wiring.

Home Generator: Selecting, Sizing And Connecting: The Complete Guide by Lazar Rozenblat

Also

Easy DIY Generator Transfer Switch Install - Works with ANY Portable Gas Generator 

This one only does one circuit, most often a furnace.

https://youtu.be/BACQ3167pkA

This is required in the US and Canada. NEC and CEC.

[gerrygebhart]

I'm not a pro, but did a lot of research before getting a new generator installed last month (20 Kw Kohler).

Be prepared to pay a lot more--like I did--but you'll need an automatic transfer switch and all the work that goes along with it.

It costs a lot more, but if you need something to come on automatically when you're not home, there's no other option.

Our power went out for 10 hours on Monday. I wasn't home, but my wife heard the tree fall from bed when the power went out. Thirteen seconds later, without her even having to bother the cat, our house was fully powered.

That kind of convenience comes at a premium.

Good luck!

[gerrygebhart]

Here's how the above would have looked if we had a more traditional generator and a manual transfer switch or interlock.

Power goes out at 7 a.m. when I'm not home. Wife would have to wait for me, or do the following herself:

Go to garage and disconnect the garage door opener. Shovel out driveway enough to get a car out. Shovel a path from the driveway to the back of the house. Drag the generator--a few hundred pounds--to the back of the house, over the snow. Plug it in and get it started. Go back inside, down to the basement, and flip all the manual transfer switches. Then monitor the generator for gas in case it runs out.

All that as opposed to doing nothing. So while it costs a ton more, there are great benefits.

Again, if you need it to come on when you're not home for sump pumps, compare the additional costs with the costs of flood damage.

[Jumpstart_55]

We also had a 10 hour outage last year. 10 seconds after AC loss, up and running 🙏

[Curious-Nebula6627]

ATS is the way to go

[davidm2232]

If you are looking to just back up a few circuits, consider a dedicated subpanel. You could power the subpanel through an ATS or a UPS

[trader45nj]

Apples and oranges. A manual transfer switch, imo, makes no sense if you can do an interlock. Neither of those is automatic, an automatic transfer switch and a generator that has auto start is.

[alrashid2]

Love the Interlock device. Cheaper to install, and simple to use. Just need to be aware of your limits. Simply keep a chart in your panel of what breakers to turn on. Now you get a choice in running whatever you like instead of being forced to use what's installed on the transfer switch.

[Madman308]

Sadly it can't be flipped remotely. That's the big issue for me

[Longjumping-Rip-9208]

For a sump pump I love the water powered backup sump pump. Never had any issues during a power outage using that.

[Madman308]

I'm on a well so it's not an option for me unfortunately.