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TL;DR: If you can afford a low-THD generator, go for it. Otherwise, it's apparent that 10-12% is still widely acceptable unless you have equipment that specifically states that it needs <5% THD.

It's a never ending debate. If you want a black and white answer, then go for an inverter generator so you can get the coveted 3-5% THD and you no longer have to worry about whether or not it's safe for use with your appliances. A pair of either the Genmax 9000W or Predator 9500W inverter generators in parallel configuration will give you all the capacity you need.

But you have to pay the piper.

If you're like me and all you can afford to pony up is for a loud, open-frame, 3600 RPM screamer, then you're definitely not alone. They're not good at being silent or being clean (output-wise). What they are known for is that they're inexpensive. But inexpensive doesn't always mean it's cheap or bad. And "some" THD is not always going to be a deal-breaker. Here's what Champion had to say... take it with a grain of salt: Total Harmonic Distortion.

Champion portable generators will output an industry standard total harmonic distortion (THD) rating of about 12%-20% depending on load applied. They will produce a sine wave, not a modified or square wave. This is perfectly acceptable for running common commodities found in your home such as TVs, computers, your appliances, etc.

THD is a measure of the deviation of a sine wave from a "perfect" sine wave. All electricity, including line electricity, has measurable THD.

If you have a specific item that requires less than 5% THD such as a UPS style battery backup, a pellet stove, or high efficiency furnace control board, we recommend purchasing a Champion Inverter Generator (sizes from 1600W to 3500W); Champion DH Series Open Frame Inverter (sizes from 3500W to 8750W) or a Champion Home Standby Generator (range from 8.5KW to 14KW); all units provide a less than 5% THD.

Please consult your specific appliance manufacturer to determine if the appliance requires low THD (less than 5%) to operate properly.
So unless you have very specific equipment or electronics that require 5% or less THD, you should be fine with the 10-12% THD on the generator you were looking at for most of the appliances you will use in an emergency. It's still way lower than Champion's 12-20% THD claim. And if you read between the lines, if Champion was wrong in their stipulation and equipment started breaking left and right because of their gen's "dirty power", by claiming the above, they're opening themselves up for litigation.

To close, go with an inverter if you can afford it. They have gotten a lot cheaper in recent years but they're still at least 3-4x more expensive than conventional generators in the same wattage.. at least that's the case where I live.
 

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Indeed, 10-12% THD isn't really bad and most anything will run fine on it. When you get up above 20%, you're getting into some distorted waveforms. I have a performance series Firman generator, It's rated at around 25% THD. I've scoped it a few times and the waveform isn't pretty. I use it for things like a hot plate, fans, and an electric percolator, but I'm not comfortable using it for anything else.

Inverters have come down in price pretty nicely. I'd highly recommend one if you need clean power.
 

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Inverters have come down in price pretty nicely. I'd highly recommend one if you need clean power.
Agreed. But if we are responding to the @truedatnola post above, then he is wanting to supply his tenants with power. So, there would likely not be a way for him to know what they are plugging into his gen. If something failed as a result of the power he provided to them, then they might try to hold him liable. It's not uncommon for a fridge to cost $2,000-$3,000 nowadays! A landlord supplying power to a tenant can be a sticky situation.
 

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Agreed. But if we are responding to the @truedatnola post above, then he is wanting to supply his tenants with power. So, there would likely not be a way for him to know what they are plugging into his gen. If something failed as a result of the power he provided to them, then they might try to hold him liable. It's not uncommon for a fridge to cost $2,000-$3,000 nowadays! A landlord supplying power to a tenant can be a sticky situation.
Yeah, it creates a bit of a conundrum. There's a need to fairly high wattage but also a need to keep THD low to reduce risk of damage to anything plugged into to it. I don't know what kind of liability he would have for power provided to his tenants during an outage. As far as I know, he has no legal obligation to provide power at all unless it's part of the lease. But I have never seen power production as a part of any lease, especially residential. It sounds like it would be provided as a courtesy. If I were him, I'd definitely find out if there is any legal exposure with that arrangement.
 

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Thanks for that info. I guess if I can't modify a generator with high THD, I'll just have to keep looking for a tri-fuel with low THD.

So far, this is the only tri-fuel model I've found with THD of <5%: Winco Tri-Fuel Generator - HPS12000HE, 10800 Watt, Honda, Electric Start

It's $5,600, so I'm going to keep looking for a cheaper alternative.
truedat, where y'at?? and how's ya momma??

You can add on tri-fuel conversion kits to many generators. The downside though, it you'll void any warranties. That said, most warranties are not but for a year, maybe three. So if you're in it for the long haul, you'll have the generator much longer then any warranty.

The Northern Tool in Metaire has a Powerhorse 13000es with a claimed THD under 5% in stock for $1,900, though you'ld want to add on a snorkel to run NG. Powerhorse Portable Generator 13,000 Surge Watts, 10,000 Rated Watts, Electric Start | Northern Tool

Additionally, they have what many would consider a better option, with a Honda Engine for $3,200, also with low THD. At least they offer free shipping NorthStar Portable Generator with Honda GX630 OHV Engine 13,000 Surge Watts, 10,500 Rated Watts, Electric Start, CARB Compliant | Northern Tool

Finally, if I were to have any plans on offering generator power to tenets, first, I would have some sort of Hold Harmless Agreement drafted up for them to sign that would at least be a buffer to help keep you out of trouble, and would also line out how the power gets to the tenet and what they can connect too (who is supplying the extension cord, and is the cord UL listed to run that much power for such a long run [a 10/3 cord would probably be needed to hold the 20amps] and maybe a tagging system where you put a sticker on things they can pug in).

But good luck and know there are lots of options out there!
 

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Agreed. But if we are responding to the @truedatnola post above, then he is wanting to supply his tenants with power.
Ideally, I'd like to supply my tenants with power during an outage as a courtesy (the one we had after Hurricane Ida lasted weeks), but that's only an option if I can afford it. Estimates on a Generac whole-house system were $24K for just my unit, and >$30K for the all 4 units. If I did have a system that could power their units, I'd first have them sign hold harmless agreements.
 

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Ideally, I'd like to supply my tenants with power during an outage as a courtesy (the one we had after Hurricane Ida lasted weeks), but that's only an option if I can afford it.
Got it.

Your earlier posts indicated that you are looking at 10,000W+ gens that run on NG. Maybe it would help us if we understood how much and what kind of power you would like to supply your tenants. For example, are you wanting to run 120V extension cords or 120/240V cords? And how many amps would you allow each tenant to have available for use? Then would you be on the same gen also and, if so, how much power would you like to have?

After doing the math for all of that it might narrow down which generator would be the best fit.
 

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Maybe it would help us if we understood how much and what kind of power you would like to supply your tenants.
Thanks for your reply.

From what I think I know, I can't expect to find any portable generator powerful enough to fully supply all 4 units of my 4plex at our normal levels of usage (and can't afford the whole-house standby systems that could).

If that's correct, then I'm hoping that I could find one that would keep me at normal usage (I don't think I have anything out of the ordinary: 2 fridges, 1 freezer, 2 window units, washer/dryer, tankless water heater, a computer and various computer equipment, average household appliances and lights), and then if there was any power beyond that, I'd want to power at least the 3 fridges in my tenants' units. 2 of my apartments have window units with heaters, another has mini-splits; I'm guessing it would be overly optimistic to think I could find a generator that could encompass their AC as well.

I am not obligated to supply power to them, but the difference between being able to stay in one's home or not during New Orleans' extended outages is whether one has at least power for refrigeration and AC.

As for my concerns with THD, in theory, I suppose I could get a "dirty" energy generator for my basic usage (fridge, AC), and then get a smaller inverter specifically for my computer and other "sensitive electronics."

Someone suggested that instead of a fuel-based generator, that I instead get a solar set-up. When I asked the Generac guy (who quoted me $24K for a system that just covered my unit) if he installed solar, he said, "no. They are very expensive and will not power your AC units for very long."

I haven't been able to sift through all these variables and find any definitive answers on how I should move forward.

I hope that answers your question. I know next to nothing about any of this stuff.
 

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I haven't been able to sift through all these variables and find any definitive answers on how I should move forward.
I'm not sure which one you have but electric tankless water heaters draw a ton of power. The general statement from google "One whole-house tankless water heater has four 7,000-watt elements, for a total electrical load of 28,000 watts. This load requires wire and a circuit breaker that will handle at least 120 amps " So if yours is electric, while likely not that large of a unit it might still be off the table. Different story if it runs on natural gas. Far as the rest of the stuff it can vary a LOT based on exactly what you have down the model of each appliance etc. But in general this could be helpful.

I'm sure folks can poke plenty of holes in this but as I said it really just depends on what exactly you have. Also how much you expect to be running at one time.

TypicalHigher End
Window AC7501500
Fridge500800
Chest Freezer300600
Washer6001400
Electric Dryer21005000
Computer400800
Incandescent Lights (ea)60100
LED Lights (ea)415
Misc Appliances (ea)2001500
 

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👆 Yeah, that water heater could be an issue for sure and needs to be investigated as to its power requirements. The dryers are hopefully running on natural gas. All the A/C power requirements needs to be totaled up also (don't forget the heat mode on those that have it if you plan to run it).

There are two schools of thought when it comes to generators as I see it. One method is to run everything normally as if on grid power (that would definitely need to be a big gen for 4 households). In areas where power outages are frequent and long, that is the preferred method for a lot of people, but it comes at a price.
The other method is to use load management and only run what is necessary while keeping the amperage within the limits of what is available. This is what I do since our outages are rare. I have a WEN GN625i inverter gen that I run in 120V mode only. This gives me about 40 amps of 120V power to use selectively to run things like my inverter window A/C, natural gas furnace, fridge, freezer, natural gas water heater ignitor, microwave, toaster oven, and then a few other small things like lamps, phone chargers, etc. I try not run the gen over 30 amps continuously just to extend its life. I do not use my central air unit or any other 240V appliance because the gen would simply not be big enough. The idea is to just get by using a small gen until grid power returns.

I think you really need to add up all the loads and see what you are dealing with. You can usually get the amps or watts off the labels or use a meter to actually measure the load. And which items are 240V (like possibly that water heater) because that would change things. Without knowing for sure what the loads actually are you will be shooting from the hip and more likely to make a bad decision.
 

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Thanks for that info. I guess if I can't modify a generator with high THD, I'll just have to keep looking for a tri-fuel with low THD.

So far, this is the only tri-fuel model I've found with THD of <5%: Winco Tri-Fuel Generator - HPS12000HE, 10800 Watt, Honda, Electric Start

It's $5,600, so I'm going to keep looking for a cheaper alternative.
good solid power will cost good money.
6 k for 10 kw is a good deal if the power is super clean.
honda or an honda eu series of gen set is the gold standard.
ask lot's and lot's of questions before you buy!
you can add tri fuel to any gasoline gen set.
some are easy and are in kit form.

for me i prefer the eu7000is honda as it is inverter class and super clean and a good solid gen setup.
and you can stack them for more power as needed.
 

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oh yea if you are thinking of running a tankless electric hot water heater on a gen...
you are better off doing a cut to the chase and use an LP or NG hot water heater when on gen...
it saves all of the energy conversion loss.
you can run several hot water heaters on the same system.
i use bi fuel on hot water as a solution.
NG as primary, electric as back up in case the NG is out.
 

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As Genknot mentioned, load management... key takeaway there. That's how I would do it. Since you're not under obligation to provide power anyway, just budget enough for them to use their lights, fridge, TV, computers, internet, a way to charge their phones and run maybe no more than a small window A/C, etc... none of the heavy stuff.

The challenge is how to impose that condition. Individual breakers and/or power meters to each apartment?

Or, would you like to take a gander at a pre-owned but unused 22kW whole-house unit? NEW Generac 22kw generator w/switch & battery, private owner. Never uncrated. $6000 FIRM CASH
 

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Curious though, typically each unit has its own panel inside so how would you ensure each tenant doesnt use more than they should? I suppose you can manage this with transfer switches limiting what's on each but this sounds far more complicated and costly than simply hooking up a generator to cover everyone's basics. I did once live in a 5 unit building that had all the breakers in the basement but still no way to prevent someone from walking down and flipping things back on without maybe putting a padlock on it.
 

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Here's an idea of how I might approach this... Use a branch panel with an extension cord going to each home. A simple UK-style DIN consumer unit that can house individual MCBs as well as WiFi smart power meters going to each tenant. You can configure the power meters to cut power to a tenant if they go beyond the allowable wattage and/or current allotted to them. It's draconian but I don't see any other way to prevent one or more tenants from overloading the gen.

As the owner, you can monitor all four meters on your phone. It tells you how much current and power each tenant is drawing. It also measures energy consumption (kWh) so you can work out a charging scheme if you want to bill them for the power they used during the outage.
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This is all 120V-only (L1-N and L2-N). Offering 120/240V (L1-N-L2) will require some changes.
 

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Harmonic distortion

Hi jas42,

It is not a simple problem, the Generac XG series has a total harmonic distortion from 4.7 t0 25% , the XP series, less than 5%. But what is THD?.

The AC voltage supplied by the grid has a sinusoidal form (as shown in the next post) , very near to the ideal smooth curve represented by the math function sine. The main characteristic of this ideal curve is that it has not sharp changes in its trajectory. When this curve is converted in voltage, and is fed to a resistive device, such as an incandescent lamp, it impulses a current with the same wave form, a smooth variable current waveform.

Any deviation from this ideal sine waveform is called distortion. In the AC supplied by the grid, there are many big generators carefully designed to produce the best waveform and quality electrical power. In a 60 cycles per second (60 Hz) system, this frequency is named the fundamental frequency.

Due to design difficulties and costs, many portable generators produce not only a non sinusoidal waveform but more than the funamental frequency; along with the 60Hz, there are multiples of this freq., double, triple etc and they are called harmonics.

If the fundamental frequency is 60 cycles per second, at to say 120 volts, the other unwanted frequencies, especially the third harmonic (180 Hz), are present in a variable amount, to say 5volts, 12 volts etc. the fifth may be 3 volts in example. The sum up of the total amount of unwanted voltages, generated at frequencies different to 60 Hz, expressed as a percentage of the the fundamental 60 Hz 120 volts, is called Total Harmonic Distortion.

This THD, is fed mixed with the 60 Hz, deforming the smooth curve, and depending of the load, may or may not be too harmful. An incandescet lamp or a portable drill are not affected, but a sofisticated electronic control may be alterated in its functions seriously, induction motors may overheat, as power transformers.

To filter this harmonics, there are special harmonic filters. Most common filters or economic line conditioners, merely filter out spikes or noise, regulators mantain line voltage inside safe margins, but to avoid harmonics out of your delicate electronics, you will need dedicated harmonic filters, that will control spikes too.

An UPS (uninterruptible power supply), may or not may solve the problem.
Be aware of simple UPS that will provide an horrible "square" wave full of power spikes and deformations ( see the photo) that will harm anything but an incandescent lamp. There are other that provide a "modified sine wave", similar to the produced by the common inverters, better than square . The pure sine wave inverters or UPS produce a clean, distortless voltage wave appropiate for all kind of equipment.

But, UPSs and inverters (domestic) run on low voltage DC current. UPSs have an internal battery, used only when normal AC supply is cut. Most of them (the small ones ) have a by pass relay to feed directly the protected equipment with the AC mains. The true online UPSs convert the AC supply to DC and then generates an AC sinusoidal, clean voltage wave, independent of the incomming supply. This is a solution, costly but solution.

The other solution would be exchange your generator for an XP10000.

In few words:

Harmonic filter, true online UPS, XP10000 genset, or take the risk to damage your equipment.

Best regards.
Has anyone been provided with, or found, any documentation from their Power Supplier that indicates what quality of power they provide? Including THD?
My home is fed from Ontario Hydro (Canada). Getting THD numbers from them, or the local distributor, is like pulling teeth. The range of "allowable" amounts of THD in the documents I've found includes 3%, 5%, 8%, 11% and 12% and refer to both short term and long term as well as full load and partial load conditions. I get that there are several factors that influence THD, but it seems to me that there should be a worst case scenario. E.g. stable state goal of <5%. Worst case = 12%.
I'm curious as to whether anyone has ever tested the power supply to their home to see what kind of THD they are getting. I'd like to do this with my own home, but a good clamp meters, with THD measuring capabilities, run from about $500-$1,600 USD. Kinda steep for a one time use and I can't find anyone nearby who rents them.
My goal in all of this is to find out what I'm being supplied and try and match this in the genny that I buy. I have alot of sensitive electronics and none have been affected by the power that I have been provided by our utility provider for 20+ years.
Thx
 

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Has anyone been provided with, or found, any documentation from their Power Supplier that indicates what quality of power they provide? Including THD?
My home is fed from Ontario Hydro (Canada). Getting THD numbers from them, or the local distributor, is like pulling teeth. The range of "allowable" amounts of THD in the documents I've found includes 3%, 5%, 8%, 11% and 12% and refer to both short term and long term as well as full load and partial load conditions. I get that there are several factors that influence THD, but it seems to me that there should be a worst case scenario. E.g. stable state goal of <5%. Worst case = 12%.
I'm curious as to whether anyone has ever tested the power supply to their home to see what kind of THD they are getting. I'd like to do this with my own home, but a good clamp meters, with THD measuring capabilities, run from about $500-$1,600 USD. Kinda steep for a one time use and I can't find anyone nearby who rents them.
My goal in all of this is to find out what I'm being supplied and try and match this in the genny that I buy. I have alot of sensitive electronics and none have been affected by the power that I have been provided by our utility provider for 20+ years.
Thx
Two words: Inverter Generator.

If I may be so blunt, you seem to be overthinking it. If nothing has been damaged in the last two plus decades, I wouldn't worry about the quality of the AC your utility company provides.

But if power quality is paramount, get a dual-conversion UPS to power your sensitive electronics. For longer outages, an inverter generator would be your best bet. It will provide even better AC power quality compared to utility power.

Out of curiosity, what sort of "sensitive electronics" do you have?
 

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My goal in all of this is to find out what I'm being supplied and try and match this in the genny that I buy. I have alot of sensitive electronics and none have been affected by the power that I have been provided by our utility provider for 20+ years.
I have been told that our grid runs up to about 3-4% THD worst case, but I have no way to measure it. I have looked at it with my scope and I can see some distortion in the waveform. My WEN GN625i inverter has a much better looking waveform than my grid power.

On grid power I worry more about surges and spikes than THD.
 

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Where I live, the max allowable TDD and THD is 5%.

3.2.4 Harmonics

3.2.4.1 For the purpose of this Section, Harmonics shall be defined as sinusoidal voltages and currents having Frequencies that are integral multiples of the fundamental Frequency.

3.2.4.2 The Total Harmonic Distortion (THD) shall be defined as the ratio of the RMS value of the harmonic content to the RMS value of the fundamental quantity, expressed in percent.

3.2.4.3 The Total Demand Distortion (TDD) shall be defined as the ratio of the RMS value of the harmonic content to the RMS value of the rated or maximum fundamental quantity, expressed in percent.

3.2.4.4 At any User System, the THD of the voltage shall not exceed five percent (5%) during normal operating conditions.

3.2.4.5 At any User System, the TDD of the current shall not exceed five percent (5%) during normal operating conditions.
Like Genknot, I'm also worried more about voltage surges and spikes from things like nearby lightning strikes.
 

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Our grid power vs PM0126000 generator...

Grid - Kind of flat on top right now...
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