Electrical/generator.furnace question?

[Kevin Beitz]

You need a line conditioner.... Like this...

https://www.ebay.com/itm/ACME-T-1-69...hQX:rk:49:pf:0

[Frank Pratt]

A line conditioner will take care of noisy power, but won't correct a bad sine wave.

[John Schtrumpf]

Did you try it with the generator's economy control switch set to Off?
Note: "O" is off, "|" is on

Out of curiosity, do the furnace's electronic controls freeze or reset/recycle when this happens. Wondering if maybe a motor is starting at that point causing a power dip or noise spike.

Note: I have no training in this area, so take my speculations with a grain of salt.

[David L Morse]

Larry, from your description it sounds like the main burner comes on for a short period before it shuts off. If that's the case you may have a grounding problem.

There's a flame sensor on the main burner. It send a very low level signal to the control board. Part of the signal path includes the metal parts of the furnace. These parts are normally grounded.

An inverter generator generates a lot of high frequency noise, This noise is mostly filtered from the output. The filtering involves shunting some of that noise to ground. The exact path taken by the noise current depends upon, among other things, exactly how you have grounded the generator.

It's very possible that you have the furnace parts as a part of this path. The noise current would cause a voltage drop in that path which could interfere with the low level signal from the flame sensor.

Can you provide a description of how the generator is connected to the furnace and how you have grounded it?

[Frank Pratt]

I think David is on to something.

[Larry Edgerton]

Larry, from your description it sounds like the main burner comes on for a short period before it shuts off. If that's the case you may have a grounding problem.

There's a flame sensor on the main burner. It send a very low level signal to the control board. Part of the signal path includes the metal parts of the furnace. These parts are normally grounded.

An inverter generator generates a lot of high frequency noise, This noise is mostly filtered from the output. The filtering involves shunting some of that noise to ground. The exact path taken by the noise current depends upon, among other things, exactly how you have grounded the generator.

It's very possible that you have the furnace parts as a part of this path. The noise current would cause a voltage drop in that path which could interfere with the low level signal from the flame sensor.

Can you provide a description of how the generator is connected to the furnace and how you have grounded it?

Ok, this is good! I ground the generator to the same ground that is used for the panel in the house, 1/2" rod 8' in the ground. The cord is the main cord for my motorhome, the heaviest one I have.

Soooo.... I went out to the barn and grabbed the cord, took it in the shop tested continuity. There was a ground problem. Molded in caps, so I guessed it would be the male end as that gets the most abuse and cut it off, installed a new cord cap. Has ground. I never suspected the cord as it was such a nice heavy cord with little use. I will try it when it warms up a tad, -12 this morning.

Also considering installing a Vermont Castings gas stove that has no electronics at all. All I am really after is making sure the house does not freeze up and that solution will work if I am here or not. I am not going to invest in an expensive standby generator that may or may not work when called upon, if needed at all. I have restored two houses now that have had backups that did not work when needed[Vacation homes] and flooded.

Thanks David. I will test in a couple of days when it warms up.

Larry

[Arthur Fleming]

I am always loath to respond to electrical issues on forums, because you have no idea of whether you are 100% understanding the issues, and if they are 100% understanding your reply, but I had this problem, and followed the advice I got from others and it worked. I have a Honda 2000 watt inverter generator, clean sine wave. As it was explained to me was the neutral is an electronically generated neutral, and not the same potential as the ground. Some of the newer furnaces use the ground for a measuring/calibrating point. The furnace shuts off right at the point of supplying heat. The fix for me was to take a three prong extension cord, cut the female end off, splice the neutral and ground wire together, thus making them the same potential. The hot wire WILL be live, TAPE it off so no-one gets shocked. I made this cord up, and whenever we have a power failure, and need the furnace, it works fine. I have the water heater, (which works fine on the generator with no adaptations needed. I have a power vent, so the water heater needs power) . I have my water heater and furnace wired on cords so they are removed from the utility grid when they are powered by the generator. They plug directly into the generator. There are various code issues with this. One being the output of my generator is not GFI protected. My place is old enough that my water heater and furnace are not arc faulted, or GFI protected under normal use, either. I am not an engineer, and can not explain scientifically why this happens, and why the neutral/ground cord trick works, but it does. The funny part is a dirty power, non inverter generator will probably run the furnace with no issues, but I wouldn’t recommend a real cheap one with a too large distortion/voltage /frequency fluctuation, on any sensitive electronics. I have heard that this is a fairly common issue on gas furnaces, and inverter style generators. You may be able to get more information by Googling gas furnaces, inverter generator issues. I would be interested in hearing how this proceeds, Thank you, Artie

[David L Morse]

Arthur,

Your comment made me look up that generator. Turns out it has a floating neutral. As you know, neutral and ground have to be bonded at some point in the system. Normally that is at the service entrance. Your extension cord trick is the bonding point. If the generator is used at a campsite for direct connections then that or similar is the way to do it.

If the generator is used for backup power to an existing service then the bonding point in the service entrance must be used. That is, four wires from the generator to the panel. Ground and neutral are separately connected to the service equipment, like a subpanel.

So now, Larry, exactly what is this RV cable you're using, how does it connect to the generator, and how does it connect to your electrical system? Wire by wire, if you would please.

It will be interesting to see what happens with your added ground connection. Generally, more than one ground path ("ground loops") will cause more noise problems than a single path.

My biggest concern right now though is that you might be using that 240V receptacle and not have a neutral connection.

[Wade Lippman]

Arthur,

Your comment made me look up that generator. Turns out it has a floating neutral. As you know, neutral and ground have to be bonded at some point in the system. Normally that is at the service entrance. Your extension cord trick is the bonding point. If the generator is used at a campsite for direct connections then that or similar is the way to do it.

Consumer generators are not bonded; commercial generators are to comply with OSHA; they are also required to be grounded.
I have no idea if bonded/grounded generator will run your generator better. Try it; I still think the generator is defective.

[Arthur Fleming]

That’s why whenI use it, I bring in an extension cord, off a 20 amp receptacle on the generator, and have the furnace, and water heater on cords. I live in a townhouse, to use a generator during power failures it MUST be quiet. For the money the inverter type generator cost, I coulda bought one that would pretty much run an entire house (using some panel management, of course) When this first happened, I looked it up online, it seems to be quite common for inverter style generators, and gas furnaces.

Arthur,

Your comment made me look up that generator. Turns out it has a floating neutral. As you know, neutral and ground have to be bonded at some point in the system. Normally that is at the service entrance. Your extension cord trick is the bonding point. If the generator is used at a campsite for direct connections then that or similar is the way to do it.

If the generator is used for backup power to an existing service then the bonding point in the service entrance must be used. That is, four wires from the generator to the panel. Ground and neutral are separately connected to the service equipment, like a subpanel.

So now, Larry, exactly what is this RV cable you're using, how does it connect to the generator, and how does it connect to your electrical system? Wire by wire, if you would please.

It will be interesting to see what happens with your added ground connection. Generally, more than one ground path ("ground loops") will cause more noise problems than a single path.

My biggest concern right now though is that you might be using that 240V receptacle and not have a neutral connection.

[Mike Cutler]

Consumer generators are not bonded; commercial generators are to comply with OSHA; they are also required to be grounded.
I have no idea if bonded/grounded generator will run your generator better. Try it; I still think the generator is defective.

Wade
All portablegenerators sold on the market as OSHA Compliant, which iOS most of them, must now have "Neutral Bonded to Frame" connections. This began in 2010, started in 2012, and was finalized as of 2015.
What does this mean?
It means that the frame of the generator and the neutral out conductor are the same potential electrically, and touching the frame of the generator should now be safe as the neutral reference is no longer floating. Prior to 2010 generators were not required to be wired this way. Currently, to the best of my knowledge, only Honda and Yamaha, have a switchable neutral to Frame bond at the generator.
What does this mean if a newly purchased portable OSHA compliant generator is used as back up power for a house?
It means that there are now TWO points in the system that ground and neutral are reference to. The Main Service Panel, and now the generator frame.
If this condition is not abated, it means that there is now "potential" on the ground wires of the house electrical system, if the generator bond is at a different potential that house bond, which it will be. By default this turns the ground wires of the system into "conductors". Ground is never a "conductor".
How does a person prevent this issue?
A "Neutral" disconnect is required. In other words, the Neutral must be disconnected form the service panel entrance so that there is now only one, the generator, neutral to bond connection.
If the generator Neutral to frame bond is present, and the Service Panel Neutral to Ground bond id present, this can cause issues with sensitive electronics that rely on a stable ground reference and GFCI's, most notably the GFCI outputs on the generator itself.
There is a "hack: to get around all of this if someone wants to research it long enough on the 'net. I won't post it here. It would definitely not be NEC Compliant!

[Wade Lippman]

Wade
All portablegenerators sold on the market as OSHA Compliant, which iOS most of them, must now have "Neutral Bonded to Frame" connections. This began in 2010, started in 2012, and was finalized as of 2015.

My Champion 73536i purchased 2 years ago has a floating neutral. At least I thought it did, so I googled and found the following:
http://help.championpowerequipment.c...generator-mean
Apparently Champions are still floating neutral.

HD says that 5 of the 150 generators they sell are OSHA compliant.
Honda says their EB (industrial) generators are OSHA compliant; the implication being that their consumer generators aren't.
This 2017 article seems reasonably authoritative and says that few generators under 5kw have bonded neutrals.
https://www.rvtravel.com/how-generat...r-an-rv-works/

I agree that OSHA compliant generators must have bonded neutral, but it appears that consumer generators are rarely OSHA compliant.
Note the word "appears". I don't actually know, but am just going by what I am finding on the internet which might be misleading.

[Mike Cutler]

Wade

I stand corrected. Thank you for clarifying the issue. I haven't seen any new ones that aren't neutral bonded to frame, but I would only really see them at work in an an industrial environment. That'll teach me to make assumptions.
I wonder if the manufacturers have responded to the market demand, or some just don't produce generators that aren't targeted at work site use????
My2017 Generac 17.5KW "portable" is neutral bonded to frame, but I also have a "vintage" 4KW Coleman Power Mate that is not.
What is important is that a person needs to understand what kind of generator they have before they back feed a house electrical system with it.
There are many, many discussions on generator forums, and Mike Holt's site about the issue. I've also given feedback to Generac that they should consider explaining the difference between the two concepts more succinctly in their instruction manuals.
It's an interesting topic. However, I do think it a little odd that in the year 2019, people still need to consider having an emergency back up generator. And I work for a major electrical utility.

[Larry Edgerton]

I am always loath to respond to electrical issues on forums, because you have no idea of whether you are 100% understanding the issues, and if they are 100% understanding your reply, but I had this problem, and followed the advice I got from others and it worked. I have a Honda 2000 watt inverter generator, clean sine wave. As it was explained to me was the neutral is an electronically generated neutral, and not the same potential as the ground. Some of the newer furnaces use the ground for a measuring/calibrating point. The furnace shuts off right at the point of supplying heat. The fix for me was to take a three prong extension cord, cut the female end off, splice the neutral and ground wire together, thus making them the same potential. The hot wire WILL be live, TAPE it off so no-one gets shocked. I made this cord up, and whenever we have a power failure, and need the furnace, it works fine. I have the water heater, (which works fine on the generator with no adaptations needed. I have a power vent, so the water heater needs power) . I have my water heater and furnace wired on cords so they are removed from the utility grid when they are powered by the generator. They plug directly into the generator. There are various code issues with this. One being the output of my generator is not GFI protected. My place is old enough that my water heater and furnace are not arc faulted, or GFI protected under normal use, either. I am not an engineer, and can not explain scientifically why this happens, and why the neutral/ground cord trick works, but it does. The funny part is a dirty power, non inverter generator will probably run the furnace with no issues, but I wouldn’t recommend a real cheap one with a too large distortion/voltage /frequency fluctuation, on any sensitive electronics. I have heard that this is a fairly common issue on gas furnaces, and inverter style generators. You may be able to get more information by Googling gas furnaces, inverter generator issues. I would be interested in hearing how this proceeds, Thank you, Artie

I am doing this with a cord as well. Investing in a standby and automatic switch is not in the cards for me. I had the two furnaces wired with twistlock outlets when I built the house for this reason. I had the electricians make up a twistlock adapter for a normal cord end to be used when the power is out. I don't worry about the water heater, its electric, but if push came to shove I have a welder that could run the well and the water heater.

Sub Zero this morning, no testing yet.

[Kevin Beitz]

I use whats called a line conditioner... Not cheap... But works good.