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Not sure what happened

PrinceOfAnarchy

New Member
Hello all. I've been a digital musician hobbyist for about 6 years. I'm just now considering elements related to powering devices and speakers.

I'm renting an older house. I started using a 3 light indicator to check the outlets. Some are grounded, while others test as up open ground. Although I'm still trying to learn how electricity works and how it impacts audio systems, it seems like my best bet will to be to run my audio equipment off grounded connections and try to avoid 3 prong devices on the open ground receptacles. My plan is to move out of this house, so I'm not too concerned about updating the open ground outlets.

Here's where I got totally confused, though. I have an outlet reading "open ground" on the 3 light tester. But, when I plug in a PDU into the circuit the lights change to show correctly grounded wiring. I have different brands of PDUs. The outlets remain showing open ground when I plug in my Tripp-Lite PDUMH15. But, the lights change to show grounded wiring when I hook my Synaccess MP-1001E into the circuit.

So, what is this telling me about my Synaccess PDU? I noticed it has a ground symbol on the front with a small hole. I am so confused as to what is going on. I thought the only way to be grounded was to be linked to a grounding rod outside the home. Why are the outlets testing as grounded when I plug in the Synaccess PDU? Why do they still show open ground when I plug in the Tripp-Lite PDU?
 

sagor1

Active Member
When you plug equipment into the socket, the equipment is probably providing a ground between neutral and ground, assuming you are using a 3 pin plug (North America). The outlet is still faulty...
 

PrinceOfAnarchy

New Member
When you plug equipment into the socket, the equipment is probably providing a ground between neutral and ground, assuming you are using a 3 pin plug (North America). The outlet is still faulty...
I assumed the outlet was still faulty and the circuit was not truly grounded. Can you explain what you mean by "the equipment is probably providing a ground between neutral and ground"? What would be the application of this feature?
 

sagor1

Active Member
Both of those PDU have current measurement devices inside - electronics that are using the outlet for power. It is possible one of those devices has some link to ground via that measuring device, hard to tell for sure. The link to ground could be very weak, like a 1Megaohm resistor (like some powerline filters). That may be enough that the device thinks the ground is good. That is all a wild guess, but bottom line is the outlet is faulty to start with and you should not be using a faulty outlet for electronics (or anything for that matter). Also, I would trust the PSU that shows the open ground indicator, not the one that thinks it is good.
 

Tony Stewart

Well-Known Member
Most Helpful Member
The PDU will contain two Common Mode choke caps to the PE ground ( 1 to 4.7 nF) that act as a bidirectional low pass filter. They draw much less than 1 mA for UL or <2.5 mA for CE ( I recall) but that is enough to make a primitive ground tester give this result. I expect it is looking for a low voltage difference between N & Gnd when injecting say 100 uA of current with some other signal from the tester. Since one expects ground and neutral to be < 100 ohms back to the PE connection or the sub-distribution transformer, it is a false reading.

In theory "ground" is wherever you define 0V and extend that elsewhere with some tolerances for noise or current and resistance. Protective Earth, PE aka "ground pin" follows the same reasoning, so since your tester measured near 0V on the ground relative to Neutral, it assumed the ground was connected but didn't test it with 10A but rather something much smaller to check for low voltage difference.

However, this is a false reading.
 

PrinceOfAnarchy

New Member
I think you should watch YT tutorials regarding this issue. It would help.
I've never seen a YT video explaining how plugging in a PDU will change the reading on an outlet tester. I'm sure Tony Stewart has it correct in his explanation. The only problem is it's too over my head. Open Ground on the tester made sense to me - no connection to the EGC. Plugging in equipment and seeing the test results changed is where I got lost.
I've been doing kind of a deep dive into electricity, currents, voltage, breakers, ground faults, noise filters, etc. I've been learning a lot, but it's also been a lot of learning how much there is to learn and how much I don't know. I've gained a ton of respect for electricians. I'm going to keep learning, but ultimately the main thing I've learned is I'm probably never going to be a DIY electricity guy. But, I still think it's good for me to understand some of the general concepts.

One of my goals is to get good power quality for audio. I'm planning to move out of my current home, so I'm not concerned with my open grounds. I've been here for 7 years and never realized I had them. I'm wondering a bit though now if the open grounds actually improve my audio quality. I've heard a lot of noise can travel along the ground wire.

I was curious about the behavior where the tester changed when plugging in a PDU. I thought I would ask about it and maybe learn something. But, mainly, I'm trying to plan for my next home. It sounds like the #1 thing I can do is have an electrician wire me up with a dedicated line to my recording studio as well as my hi-fi room. I've also read that the dedicated lines should be on a separate phase as major appliances and GFCI outlets. I might not have too much control over that, though. But, I do plan on going with dedicated lines, and possibly isolated grounds as well.
 

Nigel Goodwin

Super Moderator
Most Helpful Member
I've never seen a YT video explaining how plugging in a PDU will change the reading on an outlet tester. I'm sure Tony Stewart has it correct in his explanation. The only problem is it's too over my head. Open Ground on the tester made sense to me - no connection to the EGC. Plugging in equipment and seeing the test results changed is where I got lost.
I've been doing kind of a deep dive into electricity, currents, voltage, breakers, ground faults, noise filters, etc. I've been learning a lot, but it's also been a lot of learning how much there is to learn and how much I don't know. I've gained a ton of respect for electricians. I'm going to keep learning, but ultimately the main thing I've learned is I'm probably never going to be a DIY electricity guy. But, I still think it's good for me to understand some of the general concepts.

One of my goals is to get good power quality for audio. I'm planning to move out of my current home, so I'm not concerned with my open grounds. I've been here for 7 years and never realized I had them. I'm wondering a bit though now if the open grounds actually improve my audio quality. I've heard a lot of noise can travel along the ground wire.

I was curious about the behavior where the tester changed when plugging in a PDU. I thought I would ask about it and maybe learn something. But, mainly, I'm trying to plan for my next home. It sounds like the #1 thing I can do is have an electrician wire me up with a dedicated line to my recording studio as well as my hi-fi room. I've also read that the dedicated lines should be on a separate phase as major appliances and GFCI outlets. I might not have too much control over that, though. But, I do plan on going with dedicated lines, and possibly isolated grounds as well.
I suggest you move your concerns to something else - the mains supply is almost certainly not going to affect audio quality - unless you've got massive noise coming up it, which your system can't cope with (which is extremely unlikely).
 

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