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Old 07-17-2012, 03:30 PM   #1
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my hvac ducts are showing 120 volts!


I have isolated the breaker, but can't find any wires touching the charged duct. It is isolated from the main unit by a baffle, no grounding strap. Main unit housing not energized.

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Old 07-17-2012, 05:03 PM   #2
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my hvac ducts are showing 120 volts!


120 volts to ground? If so, you should stop what you're doing and contact an electrician - this is dangerous territory. If you have voltage flowing to the ductwork, you obviosly have grounding issues somewhere and need to figure those out ASAP.

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Old 07-17-2012, 05:17 PM   #3
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my hvac ducts are showing 120 volts!


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Last edited by Yoyizit; 07-17-2012 at 05:22 PM.
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Old 07-17-2012, 10:13 PM   #4
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my hvac ducts are showing 120 volts!


What does the breaker feed?
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Old 07-18-2012, 08:22 AM   #5
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my hvac ducts are showing 120 volts!


Run a 7-1/2 w bulb from the duct to ground.
If the bulb doesn't light it's a phantom voltage or a very flimsy connection.

If it does light, have an assistant watch the bulb while you push, pull and bang on the duct to try to find a place that makes the bulb flicker.

Depending on your results there are more options, here.
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Old 07-18-2012, 10:34 AM   #6
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my hvac ducts are showing 120 volts!


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Originally Posted by Yoyizit View Post
Run a 7-1/2 w bulb from the duct to ground.
If the bulb doesn't light it's a phantom voltage or a very flimsy connection.

If it does light, have an assistant watch the bulb while you push, pull and bang on the duct to try to find a place that makes the bulb flicker.

Depending on your results there are more options, here.
Telling someone to physically interact with energized ductwork sounds like a great way to kill someone.

To the OP; you're either going to need to identify everything on that circuit and start tracing it out, or call an electrician. In situations like this, I recommend the latter.
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Old 07-18-2012, 11:06 AM   #7
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my hvac ducts are showing 120 volts!


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Originally Posted by Yoyizit View Post
Run a 7-1/2 w bulb from the duct to ground.
If the bulb doesn't light it's a phantom voltage or a very flimsy connection.

If it does light, have an assistant watch the bulb while you push, pull and bang on the duct to try to find a place that makes the bulb flicker.

Depending on your results there are more options, here.
That's just dangerous. Chrisjones, please don't do this. Messing with issues like this needs to be done by a qualified person. Unless you're a licensed electrician, or have an extensive background in that area, I'd strongly suggest that you get a qualified professional to troubleshoot this.
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Old 07-18-2012, 11:24 AM   #8
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my hvac ducts are showing 120 volts!


How are you checking voltage? Duct work is grounded through the air handler.
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Old 07-18-2012, 12:03 PM   #9
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my hvac ducts are showing 120 volts!


Today, the average North American traditional funeral costs between $7,000 and $10,000.


You may pay $200 to have an electrician come out and fix it; $6,800 - $9,800 savings…and …umm… you won’t be dead.



Keep the breaker off and call a pro.
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Old 07-18-2012, 12:29 PM   #10
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my hvac ducts are showing 120 volts!


set the meter to read the 120v then shut the servcie switch off on the side of the furnace....if it doesn't drop the volts have somebody go to the breaker panel and shut each one wait yes/no leaving off onesoff for 5 minutes...don't want toshort cycle refrig....
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Old 07-18-2012, 01:45 PM   #11
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my hvac ducts are showing 120 volts!


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Today, the average North American traditional funeral costs between $7,000 and $10,000.


You may pay $200 to have an electrician come out and fix it; $6,800 - $9,800 savings…and …umm… you won’t be dead.



Keep the breaker off and call a pro.
You forgot likelihoods.
The chance of dying from electricity for a non-electrician is about 600/100,000,000, per year.
This times $10,000 = $0.06, way cheaper than an electrician.

Driving a vehicle is 50x more dangerous than messing with electricity, per year.

Hardly anyone outside of actuaries seems to understand risk.
Yet, anytime you walk from your house to your car in a thunderstorm you are making a risk/cost/benefit calculation, even if you don't know it.
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Old 07-18-2012, 07:58 PM   #12
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my hvac ducts are showing 120 volts!


More people die from low voltage (120 volt) shocks then any other voltage. And the majority of those people are not electricians.

Many older people die from the fibrillation 120 volts causes, and often die in their sleep, and re mis classified as natural causes deaths.
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Old 07-18-2012, 09:46 PM   #13
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my hvac ducts are showing 120 volts!


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How are you checking voltage? Duct work is grounded through the air handler.

Although I agree with you, very often both return and supply ducts are isolated from the air handler via a rubber anti-vibration transition piece.
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Old 07-19-2012, 03:51 AM   #14
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The chance of dying from electricity for a non-electrician is about 600/100,000,000, per year.
Unless, of course, you're trying to troubleshoot an electrical condition without the proper knowledge and equipment. Then those chances go way, way up.

Knowing your limits is very important in the DIY game. While I think most people here could reasonably troubleshoot a blown fuse, or burnt wire (with our assistance, of course), trying to figure out what is causing a very dangerous ground condition goes too far IMO. At what point do we tell them "call the professionals"?
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Old 07-19-2012, 02:47 PM   #15
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my hvac ducts are showing 120 volts!


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Unless, of course, you're trying to troubleshoot an electrical condition without the proper knowledge and equipment. Then those chances go way, way up.

Knowing your limits is very important in the DIY game. While I think most people here could reasonably troubleshoot a blown fuse, or burnt wire (with our assistance, of course), trying to figure out what is causing a very dangerous ground condition goes too far IMO. At what point do we tell them "call the professionals"?
No, this is from all reasons: accidents, bad test equipment, operator error, etc.. If you're knowledgeable your chances are way better than this average.

At what point do we tell them "call the professionals"?
>For me, it's when the longer the DIYer works, the worse things get.
Of course, people who work with, e.g., explosives, gas pipes, more than 240v, etc., cannot use this rule.

@BeenThere, EC & M mag just had an article about a guy who got a 120v shock and was fine at first but then developed disturbing symptoms.
I thought he was malingering but he did get a settlement, and the expert witness said you can get 500 mA from 120v with sweaty hands (about twice what is the nominal, accepted max level from 120v, from the GFCI people).


Last edited by Yoyizit; 07-19-2012 at 03:00 PM.
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