# 60V on HDMI?



## canbug (Dec 31, 2015)

I am troubleshooting why a homeowner is getting 60V on his HDMI cable from his computer to his receiver.
Older 1950s house. 2 wire with and added bare ground, basement is an apartment , so no access. the receptacles are on a GFCI. I metered 
H-N, 117v
H-G, 56v
N-G, 5v

I checked the wiring of the receptacle, redid a splice in one box, checked bonding in the panel, wiring of the GFCI. It appears to me that the added ground my be a loop with T splices, therefore high resistance on some bad T splices? Only 1 grd wire per box. I removed the grd wire, and now my readings are,
H-N, 117
H-G, 117
N-G, 0

The two locations, computer and receiver are on the same cct. The two outlets are 15' apart. Here's the odd thing, we ran an extension cord so that the receiver is plugged into the same receptacle as the computer and 0V on the HDMI.
It was getting late and the only thing I didn't do was to drop off the remaining down stream loads, upstairs bedrooms. Next trip.

Any ideas guys?

Thanks.

Tim.


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## splatz (May 23, 2015)

When you say 60V am I right you mean to the HDMI shield? It's pretty close to the 56V you're getting from hot to ground, which is a pretty strong clue.  

My guess would be one of the circuits has a neutral issue, unless there's a service neutral problem, with H-N readings on one leg that are high, and on the other leg, low by the same amount. But that doesn't sound like it fits. 

If you see voltage on the ground you also want to consider issues with a neighbor's service but I think that would affect both your circuits.


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## canbug (Dec 31, 2015)

Yes, on the shield. I removed the ground because the GFCI will protect the cct but I'm still getting the 60v from the HDMI shield that is plugged into the computer to the receiver chassis. If both pieces of equipment are plugged into the same receptacle the issue goes away. 0 volts. Just a head scratcher.

Tim.


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## Southeast Power (Jan 18, 2009)

Can you safely measure if you have any current flow from Ground to Neutral both at the receptacle and at the panel?


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## canbug (Dec 31, 2015)

I can and will try to during my next visit. I won't be back now for a couple of weeks but I'll update when I do.

Thanks.

Tim.


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## paulengr (Oct 8, 2017)

Removing grounds is terrible from a safety point of view. After you removed it, you now have 120 V neutral-to-ground so that should give you a huge hint what's going on. Imagine somewhere else in the circuit that is "grounded" if someone now touches a metal housing and they are anywhere close to grounded...I know you said you added a GFCI but let me ask you this...if you have a GFCI will it trip without a circuit to ground? Of course not. The idea of a GFCI isn't to prevent an electrocution...the idea is to hopefully stop one in progress before the victim is dead. It really only works correctly WHILE the electrocution is in progress. There is no prevention whatsoever except when the outdoor ones trip every time it gets damp outside.

What you are most likely seeing is that the ground is broken somewhere so effectively your ground is "floating". When this happens imagine that you have two conductors passing really close to each other, like in the the wiring. The magnetic field of the hot induces a magnetic field in the ground so now you have a really crappy transformer and if we have a meter with a high input resistance (which most of them do), we can actually measure it. If you short it out in this condition, it disappears again. The fact that it is only about 60 V says that there might be a connection somewhere but it is so crappy that it doesn't actually quite work. Usually we see this in industrial settings too except that in those conditions if the wire is fully disconnected, it forms a capacitor (two conductors separated by an insulator). Particularly in vacuum breakers and starters, it is very common to measure almost full line voltage on an "open" circuit because the breaker/starter acts like a capacitor and passes voltage right through it. No current but enough voltage to give you a pretty nasty zap.

Final possibility is that you have an actual short circuit from the hot to ground somewhere but the resistance through the connection and/or the ground is so crappy that it doesn't actually give you a solid connection. I've even seen this happen with intentional line-ground circuits. I ran into an illuminated light switch in New Jersey once that had the little lamp in it connected to ground. With the ground disconnected, the lamp quit working. Either way again the current is almost zero so if you go looking for voltage you will see it but if you look for current, it disappears MOST of the time. 

But remember that in residential wiring (and most commercial and industrial) the idea is that the breaker is doing triple duty. It is supposed to trip if we have a short circuit, an overload, or a ground fault. The breaker is going to be rated for 15 or 20 A in residential systems. We say everything has to be bonded but bonding is treated as basically anything that might happen to conduct electricity...the ground wire in a roll of Romex, maybe a couple rusty screws, an old rusted out piece of conduit, a strip of aluminum spiral wound around real conductors (aka liquid tight or flex), you name it. Then it has to conduct electricity through a loose connection that is crudded up with dirt or maybe a broken wire that is loosely touching the side of a painted metal box...it's no wonder that ground fault protection works at all.

So like the others I agree...measure the current on your ground first. Let's eliminate any possibility of an actual fault to ground so that we can avoid the obvious safety risk. Then the hard part comes...trying to find a loose/broken connection in a system that normally doesn't carry any current or voltage whatsoever, or possibly a short between the ground and neutral. Best way I know of is to take a spare roll of THHN and connect it to the ground bar right at the system bonding jumper. Spool off enough wire (a couple hundred feet) so you can freely drag it anywhere around the house. Measure the resistance across this wire and that is now your reference ground. Take it to your receptacle. Measure from the reference ground to the ground pin and also to the neutral. Measure resistance from neutral to ground pin. You should see close to the same resistance on all 3 wires back to the system bonding jumper, and roughly twice that resistance from neutral to ground pin. If you get open circuit or very high resistance, obviously you have an open somewhere. If you get a lot less than you expect then you have a short somewhere. Repeat the measurements at different points in the system until you narrow down the problem.

The BEST way to do this uses a milliohm meter. These aren't terribly expensive but it's not a common tool that most electricians have. Most of the time you can get by with a standard multimeter that reads down to 0.1 ohms but it works a lot better with the milliohm meter. As a motor guy I do this all the time testing three phase motors for internal shorts. But my micro-ohm meter (for testing motors over about 100 HP, and testing contact resistance in breakers and starters) is a big bulky Megger thing that takes up its own tool bag so I use the multimeter any time I can avoid the big momma micro-ohm meter. So the text book answer is you need a milliohm meter to do this kind of work but frankly 95% of the time I get by without it, and for me it's a standard tool of the trade. If you have the chance to buy the milliohm meter though, do it. Breaker and starter contacts are typically around 50 microohms or less, and the specs always call for 1 milliohm or less, and motors measure in the milliohm range. So you can quickly tell if the contacts or springs are shot in breaker/starter or test for damaged coils in a motor beyond the basic megger insulation test using one. They will set you back around $100-$200 for an Amprobe or Extech, or over a thousand if you go Biddle or Hioki brand. Low ohm bridge testing isn't something Fluke does well. We have both at the shop...the Biddle is spot on every time but a pain in the rear size wise and the fact that the batteries are always flaky and falling off, and the probes are so huge they are almost impossible to use on anything smaller than utility-size equipment, and they want $200 just for a charger where the AEMC's, Amprobes, etc., are nice and compact and the probes are very easy to get onto smaller equipment.


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## canbug (Dec 31, 2015)

Thanks for the response Paul. 
If you notice, after I remove the ground from the receptacle, I end up with 0 volts H-G. The house is completely finished with a renter in the basement, where the panel is of course. I suspect that when the grd wire was installed into the old 2 wire system, it was T tapped below each receptacle and these splices are where I'm running into trouble. A high resistance connection. The GFCI was already installed into the cct. We are allowed to protect an old 2 wire ccts with a GFCI and wiring in a separate ground wire is not required in an older house.
Repairing the , I'll call it a grd grid, is not something the homeowner is willing to do at this time. I did explain that a whole house rewire would be the safest way to resolve the floating ground.
He did mention a couple of times that he had used a "cheap" electrician for some upgrading and now he regrets it.
You get what you pay for.

Tim.

I will test for amperage when I go back and update.


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## paulengr (Oct 8, 2017)

I noticed you said disconnecting neutral bonding jumper raises ground to 120 V. So it suggests that either there is a real ground fault or just a really good induced voltage path and either way the ground is floating. My gut feeling is real ground fault.


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