AVS Forum banner
1 - 20 of 28 Posts

·
Registered
Joined
·
3 Posts
Discussion Starter · #1 ·
Please help!



I build a home theater room utilizing a isolated cabinet for all of the home theater equipment. All of the equipment is on its on 20A circuit. The equipment in the cabinet includes;


1x Onkyo TX-NR515 Reciever

1x PS3

1x HTPC

1x AT&T U-Verse Internet and Cable

3x Monoprice 1x2 HDMI Powered splitters

1x Monoprice 4x4 HDMI to Cat5e/Cat 6 Matrix with IR


The PS3, HTPC, and U-Verse cable are all connected to the HMDI splitters so that the signal can be split and and sent either to the Matrix or to the Onkyo receiver. The matrix is currently running 2 TVs in other areas of the house via HDMI over Ethernet capabilities over Cat6. The Onkyo receiver is running one 60" LG plasma TV in the home theater room over another separate HDMI to Ethernet with IR extender. The LG TV is on a completely separate 15Amp circuit that only shares a ground and neutral back at the breaker.


My issue is I have a grounding issue between the ground and neutral when the Onkyo receiver and the LG TV are connected via HDMI. When connected I get anywhere from 15 to 120Ohms at my outlet furthest from the breaker. As you would expect this is a problem and causes voltage to build up between the two and when I touch anything metal that is a part of the circuit (TV, screw on an outlet, etc) there is a small arc. Flipping a light switch that is on that same circuit as the TV can cause the HDMI signal to flicker or black out for a few seconds.


I have tried and checked various things.

- There isn't a grounding issue on the 20Amp circuit when this problem is occurring on the 15Amp circuit.

- When the HDMI is unhooked from anywhere between the Onkyo Receiver and the TV the ground to neutral resistance drops to less than 1ohm.

- I have replaced the HDMI to ethernet extender.

- I have checked all of the grounds in all of the outlets and switches on the 15amp circuit.

- When the volume is turned up on the Onkyo reciever the resistance from neutral to ground is higher.


I don't really know what else to do. I would like to find a lower cost option (I don't want to replace the TV and/or receiver).
 

·
Registered
Joined
·
2,189 Posts
You can't use a meter to measure Ohms when any of the circuits are connected to the AC power system (Hot, Neutral or Ground). Are you sure that the meter was measuring Ohms? But arcs & sparks mean that you (or the cable co.) have a power wiring error.
 

·
Registered
Joined
·
3 Posts
Discussion Starter · #3 ·
Yes the meter was measuring resistance from ground to neutral. There should and is conductivity between the two. In what way could there be power wiring error? All of the systems work and the only bridge between the two is the HDMI over Ethernet and when the connection is not made it has a very low resistance. The only resistance between neutral and ground should be the amount wire from the outlet to the grounding bar. I am guessing that because of the resistance of the wire and some amount of resistance in the receiver that it is adding to the resistance of the wire because the circuits are in parallel. The only thing that doesn't make sense is that the resistances should be equal on both the 20amp and 15amp circuits.


I really appreciate the feedback as I am really stumped and could spend a lot more time and money on this than I already have.
 

·
Registered
Joined
·
2,853 Posts
It sounds like a serious problem. If it is arcing to you then it would seem your equipment grounding conductor is not working properly. This is obviously a bad thing. You might be ok now, but you don't want a large fault to find it's path to ground through you.


You should not have more than a couple ohms resistance (like 1 or 2) between a grounded conductor and the equipment grounding conductor.


How old is the house? Who wired it? What's the panelboard look like?


My first recommendation is call an electrician because I think you have a serious problem. Ignoring that advice I would buy a 3-prong test cube and see if the receptacles all check out.


Tim
 

·
Registered
Joined
·
3 Posts
Discussion Starter · #5 ·
I have checked out all of the wiring and it all is to code and checks out... the only thing I can think of is that the receiver doesn't have a ground plug for the receptacle. The last option would be to ground the cat6 to HDMI shield which would be a pain. The arc (more like a static shock) is very small and only happens when I touch the metal frame of the TV.
 

·
Registered
Joined
·
2,853 Posts
120 ohms from neutral to ground is not something wired to code. I could see where if you had a bad path to ground and then connected the tv to the receiver via HDMI the resistance might go DOWN.. But an increase in resistance makes no sense. As you stated, they are parallel paths-- the path to ground would never get longer.


What kind of meter are you using?


Is the TV double insulated, or is it a 3-prong plug? If 3-prong, you shouldn't be getting a shock from the TV. Is it possible that you are getting charged (ie socks on a wool carpet) and discharging into the tv?


Is anything else connected to the TV besides power and HDMI (CATV for example?)


Are either of these circuits landed in a subpanel?




Tim
 

·
Registered
Joined
·
4,233 Posts
Arcing happens on DC power not AC, but you should not be measuring ohms with hot wires. First you need to cut the power from the breaker and then measure. From your description (I have not read any further) it sounds like you are shorting to ground. You should not be at 150 ohms. Anything in kilo or mega ohms is fine.
 

·
Registered
Joined
·
4,538 Posts

Quote:
Arcing can occur with AC or DC.
Quote:
Originally Posted by Pain Infliction  /t/1469125/home-theater-grounding-issue/0_40#post_23228197


At a much higher voltage than what he is using. I should not have said that it happens in DC and not AC, but instead have said in his application. Either way, if he is getting sparks when touch tools to screws, he is obviously grounding out on something.
What about arc welders? They operate at about 25 volts AC and put out one hell of an arc. Current matters too!
 

·
Registered
Joined
·
4,538 Posts

Quote:
Originally Posted by Pain Infliction  /t/1469125/home-theater-grounding-issue/0_40#post_23229733


Sure they do and when you are getting into welders you are talking about a lot of amps compared to about 1 amp that an avr pulls. If even that much.
The current draw of the receiver is irrelevant. If things are badly wired enough, a breaker will trip. That's 20+ Amps. Have you checked that all the outlets and switches on both circuits are properly wired (no crossed hot/neutral, no loose ground splices, wires wrapped around screw terminals instead of 'stabbed', etc.)?
 

·
Registered
Joined
·
4,233 Posts
Actually its not irrelevant. If he had a short in his receptacles the breaker would have already tripped and tripped every time he reset it. Not to mention sparks and possibly some burn spots where the short is. Now if there is a short from the receiver (which there might be) this would explain the arc from the DC power from the receiver. Also in AC, it does not matter if the hot and neutral wires are crossed. It does in DC but not AC. If there was something wrong with how his house is wired he would have known by now.
 

·
Registered
Joined
·
4,538 Posts

Quote:
Originally Posted by Pain Infliction  /t/1469125/home-theater-grounding-issue/0_40#post_23230133


Actually its not irrelevant. If he had a short in his receptacles the breaker would have already tripped and tripped every time he reset it. Not to mention sparks and possibly some burn spots where the short is. Now if there is a short from the receiver (which there might be) this would explain the arc from the DC power from the receiver. Also in AC, it does not matter if the hot and neutral wires are crossed. It does in DC but not AC. If there was something wrong with how his house is wired he would have known by now.
I agree that a dead short will cause a breaker to trip. But a short isn't the only possible problem. A loose, corroded or other high resistance connection is a more likely cause of trouble. Could you please explain what you mean by a short in the receiver and why it would be limited to the amount of current the receiver draws? And as to the crossed wires, all I can say is we've wasted a buttload of money on polarized plugs if it didn't matter. It actually does matter, if for no other reason than safety. Most electronic devices with two wire cords create a semblance of ground by coupling the neutral to the chassis by way of a high value resistor or a capacitor or both. If this pseudo ground is referenced to the hot wire and not the neutral than there could very well be voltage present on the chassis. The current, however would be limited by the resistance used in coupling to the chassis.
 

·
Registered
Joined
·
4,233 Posts
Dude there is no such thing as polarity in AC! So yes you did waste your money. In a house the neutral is tied to the ground so if yours was backwards, you would have popped the breaker every time you plugged something in the wall. That is the only case though. If you plug in an AC converter (small transformer) you can plug it in right side up or down. It does not matter because there is no polarity in AC like I have said. Only DC has polarity.


As far as me saying the receiver was the issue....I never said that it was the issue other than it could be the issue. The issue could be with his switch box or other components, and I would not no what the problem is without looking at it.


DC voltage will arc and continue to arc until the power is cut or the source is taken away. That is because of how the voltage flows. It does not flow like a sine wave which is what AC voltage doe,s and there for if it does arc it would be for a split second and then stop. If the arc welder is an AC welder it has to have something to continue the spark because the is no way to hold an arc with AC power. I do not know much about welders but that is how AC works.
 

·
Registered
Joined
·
4,538 Posts
Who said there was polarity in AC? The two wires that comprise an AC source are referred to as 'hot' (or line) and 'neutral' (or return). This has nothing to do with 'positive' and 'negative' which are terms of polarity. In case you haven't bought a device with a two wire power cord in the past 20 years, here's a bit of info from WikiPedia about polarized AC plugs: https://en.wikipedia.org/wiki/AC_power_plugs_and_sockets#Polarization (notice that one blade is wider than the other - you can only plug it in one way). It is true that most 'wall wart' transformers aren't polarized but that's because their output is electrically isolated from the input. And yes, the 'neutral' and 'earth' (or 'ground') are tied together at the source (breaker box) but that is the only place they are typically joined. Therefore an outlet with the hot and neutral reversed will not cause a breaker to trip. It will, however, defeat the safety of a polarized plug.



Oh, and by the way...If AC doesn't arc, explain this to me:

or this:

also, here's a piece on AC welding:
 

·
Registered
Joined
·
4,649 Posts

Quote:
Originally Posted by Pain Infliction  /t/1469125/home-theater-grounding-issue#post_23237272


If the arc welder is an AC welder it has to have something to continue the spark because the is no way to hold an arc with AC power
Not necessary. AC or DC, you will get an arc when the voltage exceeds the breakdown voltage of the gap. AC will extinguish at the zero crossing (although inductance in the circuit can prevent that). But it will reignite as soo as the breakdown voltage is exceeded again on the next half cycle.
 

·
Registered
Joined
·
4,233 Posts
I going to tell you this one last time. There is no such thing as polarity in AC! Yes in a house the neutral is tied to the ground but other than that it does not matter if you cross lines. Houses are not the only source of ac power. Look at 3 phase AC! There is no neutral wire! All three wires are hot!
 
1 - 20 of 28 Posts
Top