# THD Filter



## WronGun (Oct 18, 2013)

I have a client who’s generator blew all the electrical components of his furnace. 

He was told by someone he needs to filter the THD on the furnace line...

Is this even possible on a small scale ?

I’ve used standard line filters before but a filter for THD? 




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## nrp3 (Jan 24, 2009)

What type of generator, how old and was it ever maintained? What kind of heating equipment?


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## drsparky (Nov 13, 2008)

Transanal Hemorrhoidal Dearterialization? Bet that hurts.


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## macmikeman (Jan 23, 2007)

How about total harmonic distortion? Not if it is a single phase unit......


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## drsparky (Nov 13, 2008)

Total Harmonic Distortion is a measurement of distortion. Normally used to test how accurately an amplifier reproduces a wave form in audio systems. A distortion analyzer injects a clean 1K signal into the amplifier input then samples the amplifier output, it then filters the 1K signal and what ever audio signal remains is THD. 
That about as closely related to generator and furnace problems as the above mentioned hemorrhoid treatment.
Sounds like some one is using jargon to look impressive. 
You can have nasty looking 60hz coming out of a generator if it not sinusoidal and a distorted wave form but the term THD just doesn't apply.


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## WronGun (Oct 18, 2013)

Let me ask this a different way. 

Is there a way to clean generator power ? 



Seems like this can be solved with an inverter generator. 

I know this can be an issue with regular portable generators. For instance, I have a few generators and have tried them all at my home. 

I have 2 rack mounted power conditioners on my home theater. These will only function from my Honda Inverter Generator Which puts out “cleaner power”

When Ive use my Briggs or Generac generators my power conditioners will not allow anything in the home theater to turn on. 

Apparently, my client is having an issue with furnace electronics operating correctly from generator power. 


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## WronGun (Oct 18, 2013)

Article I found 

When using an AC-power commercial portable generator, the consistency of the electric current is specifically important. On most generators, this is listed as total harmonic distortion (THD). The higher the THD, the greater the fluctuations in current flow. If THD is too high, it will overheat critical components, and if it is too low, it will negatively impact performance.

In this post, we will explain total harmonic distortion’s impact on power equipment, and detail what you need to consider when purchasing a commercial portable generator.

What is Total Harmonic Distortion?

Alternating current (AC) gets its name from the fact that the electronic particles within the current regularly fluctuate polarity from positive to negative. This gives the flow of electricity the appearance of a sine wave 


In ideal conditions, the sine wave alternates between positive and negative consistently over a specific time period. However, a variety of factors can cause small distortions or irregularities, which show themselves as spikes and dents (see below).


In the most basic terms, total harmonic distortion is the average percentage of how much an electrical current’s sine wave differs from what it would be under ideal conditions.

So in essence, the lower the THD, the more consistent and clean the power supply.

What Does This Mean to Your Power Equipment?

Power sources with higher harmonic distortion overheat, short out and damage the internal electrical components of power equipment.

According to IEEE Standard 519, Recommended Practices and Requirements for Harmonic Control in Electrical Power Systems, when a power source has higher levels of harmonic distortion the result is subtle malfunctions in the equipment that in some cases may have serious consequences.

To further emphasize the point, Associated Power Technologies in their paper, Total Harmonic Distortion and Effects in Electrical Power Systems, states that, “Unwanted distortion can increase the current in power systems, which results in higher temperatures in neutral conductors and distribution transformers... If left unchecked, increased temperatures and interference can greatly shorten the life of electronic equipment and cause damage to power systems.”

While this may not be a big deal for your basic power tools, a tool with a digital interface and advanced circuitry could:

Experience minor malfunctions that affect performance, such as inconsistent heat output from an automatic welder.
Shut down to protect itself against large spikes, resulting in brief work stoppage and possible delays.
Break down sooner than it would otherwise, causing avoidable downtime and costly repairs.
Ultimately, the quality of your work will be impacted, and repeatedly poor power will cost you hundreds or thousands of dollars in repairs and replacement parts.

Main Takeaway

When shopping for a commercial portable generator, most manufacturers will list the THD on the product specification table or on a label.

The IEEE Standard 519 recommends that computers and allied equipment, such as programmable controllers, use an AC power source with no more than 5% harmonic voltage distortion, with no single harmonic being more than 3%.

By making the investment in a clean, consistent power generator today, you will end up saving yourself time and money down the road. 


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## MikeFL (Apr 16, 2016)

How do you know it was not the lightning strike or surge which necessitated the generator in the first place? Tree crosses primaries, causes surge, power out, genset on, and furnace doesn't work. Blame the genset?


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## WronGun (Oct 18, 2013)

MikeFL said:


> How do you know it was not the lightning strike or surge which necessitated the generator in the first place? Tree crosses primaries, causes surge, power out, genset on, and furnace doesn't work. Blame the genset?




We don’t know... I mentioned this to him it could be a surge.

It could also be a loose neutral. 
I recently had to replace every single LED bulb , every transformer (total of 7) and other items with electronic displays caused by a loose factory Main neutral bar in a panel. 





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## telsa (May 22, 2015)

Rotten neutral strikes again.

Start there.

Never believe weirdo civilian instant technical expert opinions.


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## splatz (May 23, 2015)

I personally would very careful about second guessing the person that told them it was THD. Even if THD is not the exact right term, they might have the right idea, the generator's power is not the pure sine wave the furnace needs. It might also be a surge or something else. 

But if you say that guy's wrong, and you aren't right, in that customer's eyes, you're on the hook if it fries the electronics again. Are you prepared to give him the right answer? 

The right way to do that would be a bit of a project, test the generator output, check with the furnace manufacturer, see what the real problem is, propose a fix. Why stick your neck out if you don't have to, let the other guy be the expert. 

I'd tell him IF we take that person's diagnosis, and ASSUME that dirty power is the problem, installing a power conditioner should fix it. If he wants to be sure, tell him to run it by his expert. 

I have been working with the Sola Hevi-Duty for a long time, and I have to say electronics do seem to last longer where they use them. But they're pretty expensive. I don't know of an inexpensive hard wired power conditioner. 

Still it should be a lot cheaper than replacing the generator with one that's more electronics-friendly. And way cheaper than freezing your ass off when the power goes out, and getting the furnace fixed when it comes back on. 

In any case I'd install surge protectors on both the main panel and the generator panel, and on the furnace circuit. That's with or without the power conditioner, although they say the power conditioner provides pretty good surge protection on it's own. Tell the customer it's a smart way to hedge your bet. And of course you're going to want to check all the connections and make sure everything's as it should be.


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