Using a cheater 3-prong to 2-prong adapter

[uscpsycho]

I have read about the pros and cons of using a cheater adapter like this. But I have a unique situation that isn't covered in anything I've read.

I have a 3-prong grounded outlet and a 3-prong AV device. The problem is I am getting a ground loop buzz in my speakers. Using the cheater adapter eliminates the buzz.

I know that it is not recommended to use a cheater adapter to plug a 3-prong device into an ungrounded 2-prong outlet. But what if it is a grounded 3-prong outlet and you are just bypassing the ground prong? Is that safe/OK?

If that is not OK, would it be safe/OK to:

1) Plug a 3-prong surge protector into the outlet and then plug the cheater into the surge protector

2) Replace the outlet with a GFCI outlet and plug the cheater into the GFCI outlet

3) Keep using the cheater plug with my grounded outlet but connect a wire from the tab in the cheater plug to the faceplate screw (as intended) which should be grounded in this case since it is a 3-prong outlet. But I wonder if this would just reintroduce the ground loop buzz?

 

[Stuff]

This has come up on other forums over the years and usually involves a lot of finger pointing. In the end something is wired wrong but can be close to impossible to find. Good read here: https://web.mit.edu/jhawk/tmp/p/EST016_Ground_Loops_handout.pdf

Do not get rid of the ground as that provides personal safety protection. They make "ground loop hum eliminators"to replace the 3 prong adapter but I don't believe any are UL listed which means not safety tested. They also make isolators that you put in line between equipment.

 

[Sponsor]

 

[Reach4]

1) Plug a 3-prong surge protector into the outlet and then plug the cheater into the surge protector

The device you would want to try would not be a surge protector, but rather some other device such as an isolation transformer or a noise filter or an EMI filter.

2) Replace the outlet with a GFCI outlet and plug the cheater into the GFCI outlet

That would be safe. Not addressing permissibly.

3) Keep using the cheater plug with my grounded outlet but connect a wire from the tab in the cheater plug to the faceplate screw (as intended) which should be grounded in this case since it is a 3-prong outlet. But I wonder if this would just reintroduce the ground loop buzz?

If it did not reintroduce the buzz, that would imply the faceplate screw was not grounded.

 

[wwhitney]

I have a 3-prong grounded outlet and a 3-prong AV device. The problem is I am getting a ground loop buzz in my speakers. Using the cheater adapter eliminates the buzz.

That's a reasonable diagnostic method, but not an acceptable long term solution.

The next test I suggest is to temporarily arrange that all the equipment that has any connection to the speakers in any way at all is powered from a single receptacle. That may involve some extension cords and power strips, but the idea is to have only one connection to the house wiring, and to have no ground loops in your extension cords/power strips.

That should eliminate the buzz. If it doesn't, then some piece of equipment you have is responsible for the buzz, and you can try by process of elimination to identify it. If it does, then something is going on in your house wiring that is causing the ground loop, and you either need to find and fix it, or work around it in a more permanent fashion. [When everything is close enough together, the simplest thing is to power everything from a single power strip.]

Cheers, Wayne

 

[uscpsycho]

The device you would want to try would not be a surge protector, but rather some other device such as an isolation transformer or a noise filter or an EMI filter.

The cheater plug is doing the trick, so I don't need additional isolation/filtering if I use it. Just trying to figure out if there is a way to safely use the cheater plug.

That would be safe. Not addressing permissibly.

I know that in situations where there is a 2-prong outlet with no ground available, you can install an ungrounded GFCI outlet if you need to use a device with a 3-prong plug. That is permissible.

If I put a GFCI outlet in and use the cheater plug in between the device and the outlet, are you saying that is safe for me and for the device? Would putting a surge protector in the chain help? And if so, should it go before the cheater plug or after?

That's a reasonable diagnostic method, but not an acceptable long term solution.

The next test I suggest is to temporarily arrange that all the equipment that has any connection to the speakers in any way at all is powered from a single receptacle. That may involve some extension cords and power strips, but the idea is to have only one connection to the house wiring, and to have no ground loops in your extension cords/power strips.

That should eliminate the buzz. If it doesn't, then some piece of equipment you have is responsible for the buzz, and you can try by process of elimination to identify it. If it does, then something is going on in your house wiring that is causing the ground loop, and you either need to find and fix it, or work around it in a more permanent fashion. [When everything is close enough together, the simplest thing is to power everything from a single power strip.]

Cheers, Wayne

I am pretty sure the problem is the wiring. I have done a fair amount of troubleshooting already just to identify the source of the hum (did not yet plug everything into one outlet). Since a cheater plug on one single device solves the problem I believe that indicates the problem is the wiring. And this device is the only one on a different outlet which is more support to my conclusion.

So the easy fix is figuring out a safe way to use the cheater plug. Maybe replacing the existing 3-prong outlet with a GFCI outlet + cheater plug might be the answer.

 

[Drick]

Wayne is on the right track. Its most likely something connected to that component that is causing the problem. Try the process of elimination method. Once you find it try; 1) Plugging in the component as close as possible to your grounded component. 2) Replacing the cable connecting the two components. 3)Creating a ground path between the two components by a.) Loosening a screw on the frame of each component. b.) Cutting a single strand of wire long enough to run between the components and strip off about a half inch on insulation on each end. c.) Loosen a screw on the back metal frame of each component, wrap the wire around each screw, and tighten. You may need to sand off a small spot of paint to guarantee a good connection to the frame.

I had this same problem years ago between a grounded power amplifier and a ungrounded preamp. Running a wire between the phono ground screw and chassis of the amp fixed it. Looking back I wonder if it was a bad RCA patch cord, but I didn't think to try that at the time.

NMV, just saw your last post. being plugged into a different outlet is your problem. Running a wire between the two components may still solve it if plugging them into the same outlet is problematic.

 

[wwhitney]

And this device is the only one on a different outlet which is more support to my conclusion.

So the easy fix is figuring out a safe way to use the cheater plug. Maybe replacing the existing 3-prong outlet with a GFCI outlet + cheater plug might be the answer.

How far is it from the "different outlet" (#2) to the other one (#1)? Are they currently on different breakers?

If putting everything on one receptacle resolves the hum, then running a quality extension cord from #1 to #2 may be a better solution than the GFCI/cheater. If #1 and #2 are currently on different breakers, then extending the circuit in the walls from the #1 to a new outlet near #2 would be the proper solution. Assuming that isn't prohibited, e.g. because #1 is in the living room and #2 is in the dining room.

Cheers, Wayne

 

[Reach4]

I know that in situations where there is a 2-prong outlet with no ground available, you can install an ungrounded GFCI outlet if you need to use a device with a 3-prong plug. That is permissible.

If I put a GFCI outlet in and use the cheater plug in between the device and the outlet, are you saying that is safe for me and for the device? Would putting a surge protector in the chain help? And if so, should it go before the cheater plug or after?

In my opinion, it is safe. But if lightning strikes and there is injury not caused by what you did, could a plaintiff's lawyer argue that what you did caused the injury, could a jury hold you liable? Sadly, yes.

If I put a GFCI outlet in and use the cheater plug in between the device and the outlet, are you saying that is safe for me and for the device? Would putting a surge protector in the chain help? And if so, should it go before the cheater plug or after?

The device you would want to try is not a simple surge suppressor. But if you use a filter or suppressor, I would put it before the cheater.

 

[uscpsycho]

The device you would want to try would not be a surge protector, but rather some other device such as an isolation transformer or a noise filter or an EMI filter.

Just to be clear, I'm not looking at a surge protector to eliminate the hum, I know a surge protector won't do that. The cheater plug is doing a fine job of eliminating the hum.

I'm wondering if I put the surge protector between the existing grounded 3-prong AC outlet and the cheater plug, if that will address the safety concern? I'd rather do this than replace the outlet with a GFCI which would be complicated at this point.

How far is it from the "different outlet" (#2) to the other one (#1)? Are they currently on different breakers?


If putting everything on one receptacle resolves the hum, then running a quality extension cord from #1 to #2 may be a better solution than the GFCI/cheater. If #1 and #2 are currently on different breakers, then extending the circuit in the walls from the #1 to a new outlet near #2 would be the proper solution. Assuming that isn't prohibited, e.g. because #1 is in the living room and #2 is in the dining room.

Cheers, Wayne

The two outlets are on different breakers and in different rooms. I could run an extension cable from #1 to #2 for purely testing purposes but I can't have an extension cord permanently running across the house. Going into the walls isn't an option either.

In my opinion, it is safe. But if lightning strikes and there is injury not caused by what you did, could a plaintiff's lawyer argue that what you did caused the injury, could a jury hold you liable? Sadly, yes.

What about what I mentioned above? Would it be safe to leave the existing grounded 3-prong outlet and use a surge protector instead of installing a new GFCI?

The device you would want to try is not a simple surge suppressor. But if you use a filter or suppressor, I would put it before the cheater.

I'm not using a filter or suppressor for the hum. The cheater totally eliminates the hum. The "device" I'm referring to is my HT projector which I'm plugging into the cheater.

The solution to my hum is the cheater plug. My goal is now to figure out a safe way to use it. As you said, replacing the existing plug with a GFCI is one way. What about leaving the existing plug and adding a surge protector?

 

[wwhitney]

The two outlets are on different breakers and in different rooms. I could run an extension cable from #1 to #2 for purely testing purposes but I can't have an extension cord permanently running across the house. Going into the walls isn't an option either.

Using the cheater is not a safe long term solution, although the GFCI+cheater is safer than cheater alone.

So do the test with the extension cord and see if it works. If it does, you either have to do one of the two things you say aren't options, or diagnose your in wall wiring to see what the problem is.

My first suggestion on diagnosing the in wall wiring would be to kill those two breakers, unplug everything that is dead, and then restore power and just plug in your audio equipment, to see if the hum goes away. If it does, figure out what item that was plugged in is causing the hum. If it doesn't, my second suggestion would be to look for a place where both circuits are in the same box, e.g. if both circuits are mixed lights and receptacles, and one switching location has switches for lights on each circuit.

Cheers, Wayne

 

[Reach4]

I'm wondering if I put the surge protector between the existing grounded 3-prong AC outlet and the cheater plug, if that will address the safety concern?

Not in my opinion.

 

[uscpsycho]

In my opinion, it is safe. But if lightning strikes and there is injury not caused by what you did, could a plaintiff's lawyer argue that what you did caused the injury, could a jury hold you liable? Sadly, yes.

I think I found the solution!

You say a GFCI plug with the cheater will be safe, but I don't want to replace the outlet because the current situation makes it difficult. I was wondering if GFCI could be added to an existing plug and I discovered there is, and this is an example.

So I think I can plug this GFCI wall adapter into my existing grounded outlet, plug the cheater into the GFCI and then plug my projector into the cheater. Same as replacing the outlet. Right?!

Now, I do want surge protection so should the surge protector go between the GFCI and the cheater? Or should it go between the cheater and the projector? Or does it not matter?

 

[wwhitney]

Your long term solution should not involve intentionally defeating the ground connection on any piece of equipment that comes with a 3 prong plug.

Cheers, Wayne

 

[Reach4]

Now, I do want surge protection so should the surge protector go between the GFCI and the cheater? Or should it go between the cheater and the projector? Or does it not matter?

Surge supressors are to protect equipment, no people. They would be best with a real ground.

GFCI breakers are a possiblity, but cost more. Your inline device sounds good to me, until somebody else is doing the plugging-in, or you forget what you were up to.

 

[uscpsycho]

My first suggestion on diagnosing the in wall wiring would be to kill those two breakers, unplug everything that is dead, and then restore power and just plug in your audio equipment, to see if the hum goes away. If it does, figure out what item that was plugged in is causing the hum. If it doesn't, my second suggestion would be to look for a place where both circuits are in the same box, e.g. if both circuits are mixed lights and receptacles, and one switching location has switches for lights on each circuit.

Cheers, Wayne

I feel like I've already done this. Everything related to my AV is on one outlet except for the projector in the remote room. And I have no buzz until the projector is plugged in then the buzzing starts.

If I unplug the HDMI cable from the projector, which breaks the projector's link to the other AV equipment, the buzz goes away. Then the second the HDMI cable touches the HDMI input on the projector, before the HDMI cable is even inserted, the buzz comes back. So I think I am in your second scenario. Right?

Now if I plug my projector into the cheater there is no hum at all.

 

[uscpsycho]

If it doesn't, my second suggestion would be to look for a place where both circuits are in the same box, e.g. if both circuits are mixed lights and receptacles, and one switching location has switches for lights on each circuit.

Cheers, Wayne

Point of clarification please. Are you saying the problem would be that the circuit from outlet #1 and outlet #2 are in the same box somewhere? Or are you saying that if outlet #2 is mixed up with any other circuit (not necessarily outlet #1) then this could cause the ground loop problem? I don't think #1 and #2 could be mixed together but I can see #2 (the projector) being mixed up with something else. For some reason the breaker for this outlet has a bar on it that ties three breakers together so they all have to come on and off at the same time. No idea why it is like that.

Your long term solution should not involve intentionally defeating the ground connection on any piece of equipment that comes with a 3 prong plug.

Cheers, Wayne

I know... Is this kind of troubleshooting something any licensed electrician should be able to figure out? Or do I need to find one with specialized experience dealing with things like this?

 

[Jadnashua]

Have you tried to actually check that the ground wires on the receptacles are tightly attached? It could be as simple as verifying and tightening the screw(s). You'd want to also check back at the panel on the CBs feeding those circuits to ensure they are tight.

While less likely, when you insert the plug, is there significant resistance? An old one, where the spring tension has been lost, won't be making good connections.

 

[wwhitney]

If I unplug the HDMI cable from the projector, which breaks the projector's link to the other AV equipment, the buzz goes away.

Is there such a thing as an HDMI isolator? Maybe a device that takes HDMI and converts it to an optical format? Or maybe the HDMI shield only has to be grounded on one end (I'm unclear on when it's enough to ground a cable shield at one end, and when it has to be grounded on both ends), in which case you could just use the equivalent of a "cheater HDMI connector". Much better to break the ground loop at the HDMI cable than at the EGC of the projector.

If you can get an HDMI cable to the remote projector location, why can't you get an extension cord to it? [I don't really like the idea, but it would be enough to run a separate EGC alongside the HDMI cable and connect it to the grounding prong on the cheater. That way all the equipment EGCs come from the common point of receptacle #1.]

Point of clarification please. Are you saying the problem would be that the circuit from outlet #1 and outlet #2 are in the same box somewhere?

I don't really know much about ground loops. But:

As soon as you have two pieces of equipment plugged into the same receptacle, and an HDMI cable that connects them with a shield grounded at both ends, then you have a ground loop. Now in the case of a single receptacle, it's a simple loop outside of the walls, and as you should confirm by testing with an extension cord, I think that has no negative consequence.

But if you're on two different receptacles, then there's some in wall wiring involved in the ground loop. And if those receptacles are on different circuits, then the in wall wiring will include a path back to the main panel, which implies proximity to much other electrical equipment.

So I infer the problem is that when the ground loop is big and passes near other power wiring and grounds connected to other equipment, it picks up conducted or radiated interference that causes the unwanted hum. Now if a figure 8 loop is worse for some reason than a simple loop, then the issue of EGCs from circuit #1 and circuit #2 being interconnected could matter. But now that I think about it, I don't really see why that would make a difference.

Another test you could try is shutting off everything except circuits #1 and #2. Certainly I would expect that if the only powered equipment in the whole building is the AV equipment and projector, then in-wall ground loop won't be picking up any interference, and there won't be a hum.

Cheers, Wayne

 

[Drick]

The HDMI cable needs to be shielded, but not from both ends. Remove an inch of jacket from one end of the HDMI cable and carefully cut/peel the shield off.

 

[wwhitney]

I can't tell what it does because of all the marketing speak, but I guess that this protect may do the equivalent, if you want something neater looking and reversible:

https://www.amazon.com/Protector-Lighting-AIMOS-Portable-Supports/dp/B07TYLZS1K/

Because I don't see what else it could be doing other than interrupting the continuity of the shield to keep it from being a current path. But that's may also reflect my lack of training in electronics engineering. : - )

Cheers, Wayne