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Originally posted by Excam_Man:

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Originally posted by Skins2881:

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Skins, you obviously didn't think about what you suggested to the OP, on the use of an extension cord for diagnostic testing.
(I know you know better, as I know where you stand on the use of electric heaters and overloaded circuits)

What? I do it all the time. Especially for telling if a fridge is broken and tripping a GFI or if a GFI is broken. There is no danger to plugging a furnace into a extension cord for 20-30 minutes. Most furnaces only draw 5-7A.

Recommending anyone to plug an appliance (which contains a motor) into an (unknown) extension cord is recklous.
You know most people are going to have standard 50-100' cords in the 16ga range.
16ga at 6-50' 3-wire is 10 amps, loaded to 80% is 8 amps.
16ga at 51-100' 3-wire is 7 amps, loaded to 80% is 5.6 amps.

There's reasons for selling short 3-6' appliance specific, heavy duty 14-12ga extension cords.

You also didn't state to just plug ONE furnace into the extension cord (of unknown specs/length/gauge), but TWO furnaces, each containing a blower motor.

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would be to run an extension cord to the attic and plug both units into a circuit

Now, you can't believe the OP's 20+ yr old, 111,000 btu furnace, has a blower only pulling 5-7 amps?
In fact, the old beast happens to have a 3/4 hp PSC blower motor, pulling 11.1 (RLA) running load amps.
Furnace is rated at 14.4 maximum load amps and requires 12ga wiring.
This is all for ONE furnace.

So,if that's not bad enough, multiply the specs x 2.
22.2 running load amps??? on an extension cord???

Nothing states testing for only 20-30 mins.
Run it that way to see if it trips, could mean days depending on frequency of the tripping.

Now, if you come across this installation;
Are you going to recommend changes or are you on the same page as his previous HVAC tech, seeing nothing wrong with the wiring/installation?

Man you are worked up over this. Sorry for not being clearer. Two extension cords 16awg bare minium, preferably 14 or 12awg. 80% doesn't matter here, we aren't talking about a continuous load. Since the OP stated that it trips after 10-20 minutes, there would be no reason to extend the test past 30 minutes. Obviously this would be something that was done as a diagnostic. I wouldn't even do this if I was trouble shooting this. I would just amp clamp and compare to name plate. OP, please don't go on vacation or even grocery shopping with the extension cords hooked up. This is intended for a brief step in the process of elimination and should be attended to the entire time during testing.

As far as if I came across this installation, I'd figure out what I am actually dealing with and make suggestions on that. Since I can only see a keyhole version of what he's dealing with, it's hard to tell. First thing I would do would be to remove the outlet they are plugged into and see if it's a three wire circuit and check both hots were connected with the tab broken between the hots. If I found that someone had replaced the outlet not realizing that it was intended to be two circuits, then I'd hook up second feed and break the tab on it. I don't know his comfort with removing an outlet, especially one that could be energized from multiple sources, so I'm not going to suggest that. I also said "At this point I'm probably in this for my own curiosity, if I was there I could narrow it down in just a few minutes to HVAC or electrical and which system by process of elimination, but it would be hard for me to convey the process over a paragraph or two and without seeing everything."

OP says it worked at some point, it also passed an inspection. So something in the system has changed. My guess is that it was a three wire circuit and someone didn't know what they were dealing with when replacing the outlet. I'd want to establish what exactly we are dealing with and correct it, if it's actually two furnaces on one circuit then I would run a new home run and have one circuit per furnace.

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Originally posted by Skins2881:
Man you are worked up over this. Sorry for not being clearer. Two extension cords 16awg bare minium, preferably 14 or 12awg. 80% doesn't matter here, we aren't talking about a continuous load. Since the OP stated that it trips after 10-20 minutes, there would be no reason to extend the test past 30 minutes. Obviously this would be something that was done as a diagnostic. I wouldn't even do this if I was trouble shooting this. I would just amp clamp and compare to name plate. OP, please don't go on vacation or even grocery shopping with the extension cords hooked up. This is intended for a brief step in the process of elimination and should be attended to the entire time during testing.

As far as if I came across this installation, I'd figure out what I am actually dealing with and make suggestions on that. Since I can only see a keyhole version of what he's dealing with, it's hard to tell. First thing I would do would be to remove the outlet they are plugged into and see if it's a three wire circuit and check both hots were connected with the tab broken between the hots. If I found that someone had replaced the outlet not realizing that it was intended to be two circuits, then I'd hook up second feed and break the tab on it. I don't know his comfort with removing an outlet, especially one that could be energized from multiple sources, so I'm not going to suggest that. I also said "At this point I'm probably in this for my own curiosity, if I was there I could narrow it down in just a few minutes to HVAC or electrical and which system by process of elimination, but it would be hard for me to convey the process over a paragraph or two and without seeing everything."

I don't know who you think your trying to convince with your new magician's career, but I see though all the smoke and mirrors from a mile away.

Worked up? No, just combating the constant BS from people who should know better.

Just how many people do you think read your reply and thought to themselves;
"We need to get TWO extension cords, plug them into the same outlet and run both of them to the attic for testing"?
Afterall, you stated they only pull 5-7 amps, so it's no big deal.

Even now, your ok with using TWO 16ga extension cords plugged in same circuit for testing.
And it's been posted that these blower motors are rated at 11.1 RLA and the furnace has a maximum 14.4 amps.
The manufacture requires 12ga wiring. If you're going to test something, why not use a setup that will provide you with useful information? These two furnaces together on one circuit isn't useful, it's WRONG.

And why in the hell would you suggest trying something that you wouldn't even do during troubleshooting?

Did you miss the fact that just one blower motor is rated at 11.1 RLA?
WHY is it so hard to tell the OP has an electrical problem and not an equipment problem?

Here's the information again, two furnaces ((11.1 RLA blower motor + additional loads)x2) on one 20 amp breaker.

Is WRONG.


Now let's address your "bait and switch".

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First thing I would do would be to remove the outlet they are plugged into and see if it's a three wire circuit and check both hots were connected with the tab broken between the hots.

Are you fucking serious?
Just how in the hell could two electrical feeds be connected to the outlet with the jumper cut and have a tripping breaker taking out both outlets (HVAC systems)?

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If I found that someone had replaced the outlet not realizing that it was intended to be two circuits, then I'd hook up second feed and break the tab on it.

Now we have an incompetent person replacing an outlet and just randomly leaving one wire unhooked.
As a note, the OP says nothing about having an extra breaker or one being off (Not saying it can't be true).

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if I was there I could narrow it down in just a few minutes to HVAC or electrical and which system by process of elimination, but it would be hard for me to convey the process over a paragraph or two and without seeing everything.

WTF?
If you was there? Narrow it down between equipment or electrical? Process of elimination? Hard to convey process in a paragraph or two?

Let me make it simple (in one long sentence):
These two furnaces plugged into one receptacle, being feed from one 20 amp circuit is not only against code, against the manufactures specifications, but is flat ass wrong from the word go.

Why is that so hard to accept, comprehend and put into words that the OP has electrical issues?

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OP says it worked at some point, it also passed an inspection. So something in the system has changed. My guess is that it was a three wire circuit and someone didn't know what they were dealing with when replacing the outlet. I'd want to establish what exactly we are dealing with and correct it, if it's actually two furnaces on one circuit then I would run a new home run and have one circuit per furnace.

OP posted they assume it worked at one time, but doesn't know.
Passed an inspection... lmao... you have faith in inspectors? lol Too funny!

Somethings changed(?), maybe/maybe not. One thing is for sure, everything is old, stressed and weak.

"If it's actually two furnaces on one circuit..."(?)
They have to be, since one tripping breaker takes out both furnaces.

No matter what is taking place, the two systems are on one circuit, which needs to be corrected. That is simply an electrical issue and CAN NOT be an equipment problem.

Unless, some backwards hillbilly did an awesome job hacking it all together.

Jesus Excam, deep breaths man, deep breaths. I don't have the energy to fight with you over something this silly. I retract all previous statements. Hire a competent electrician.

OP, my only guess on how this was working and is now not working is as I said earlier it's possible a HVAC tech or homeowner replaced the outlet and didn't know it was a three wire circuit and only hooked up one feed. Also it's possible that someone disconnected the second feed in the panel, then one furnace stopped working so someone else replaced the outlet in the attic and hooked up the only hot wire when replacing. All conjecture because I can't see what is there and have no clue what was done in the 20 years that could have lead to the issues you got my best guess. I'd suggest looking in panel and outlet to see what's there, but I don't like to have people poking around live energy if they don't do it regularly.

Best of luck, as I said earlier in the thread there's nothing I can do from here. I've seen people screw things up a million ways from Sunday with no explanation why'd they would do it. There's enough about this installation from what you have conveyed that I'm 99.9% there is no failure of equipment, just human error involved.

OK fellas, remember your pressure points......