Not sure what happened

[PrinceOfAnarchy]

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?

 

[PrinceOfAnarchy]

Three pin plugs 'can' be a safety feature, assuming it's all properly wired etc. But three pin plugs and earthing don't automatically make anything 'safer', in some circumstances it makes it more dangerous.

As to the effectiveness of so called 'surge protectors', I would imagine proper grounding would be essential to make them work as well as they can - but cheap ones are probably mostly useless anyway.



It's all very confusing - mostly because there's lot's of confusing and pointless terms used.

Just think class I and class II - earthed or not, that covers everything without confusion.

As for isolation transformers - again, they have their uses, but still don't make everything 'safe' - basically all they do is effectively disconnect the neutral wire from earth. So you've now got two power wires, neither of which is live or neutral.

Really you need to understand why things are done certain ways, and making it safer in one respect makes it more dangerous in another.

From a service point of view (with 50+ years experience), I spent most of it in an 'earth free environment' as far as could sensibly be done. As with most of the service trade, I wouldn't have dreaming of using an earthed oscilloscope - incredibly dangerous in a service environment. But if you don't know (and understand) why, then you're probably safer keeping it earthed.

I read that surge protectors protect between Line and Neutral, Line and Ground, and Neutral to Ground. Mike Holt was saying it's a myth that you need a grounded connection for them to work. He was explaining that it's really about diverting the surge from hot to neutral via the MOVs. I have also read about "Series mode" protectors like Surgex, Brickwall, Zerosurge that are non sacrificial. They cost more. I currently have some Tripp-Lite isobars set up on both grounded and non grounded outlets. But, my goal is to relocate to a new house and have all grounded outlets. I also read that the breaker box surge protector is something good to add as another layer of protection.

I think I have a pretty good understanding of the class I devices and the equipment grounding conductor. Then from your post I'm understanding that all class II is "double insulated" to provide the safety. So, something like a cell phone can't shock you. The floating neutral part is a little confusing if the two-prong is connected to the mains. It makes sense with a battery as the 0V is reference is related to the battery and not earth. I guess with portable electronics it is a battery. So, the battery charger is what is class II double insulated. Or would you also say that the laptop computer or mobile phone is also double insulated?

Would the class II 0V reference still technically be referenced to Earth if the hot and neutral are coming from the wall? Without a transformer, wouldn't the neutral still be referenced to earth? But, after a transformer you have an isolated 0V reference?

Also, what about leakage current and static discharge? Isn't that another reason for the class I design?

I think I do understand the isolation transformers pretty well. Like you say, the neutral is no longer connected to earth. Then, in some cases there is also no EGC, which would make working with an earthed oscilloscope safer. Less chance to blow up your scope by misplacing a probe. But, that wouldn't be up to code if you were actually using the iso transformer in production to reduce noise. I also read about differential probes and oscilloscopes with isolated connections as well as battery operated oscilloscopes.

This has all been quite a lot of information to take in for someone that doesn't even own a multimeter! Somehow I ended up on this path through my background in audio, researching floating neutral vs neutral bonded generators, and discovering that I have ungrounded outlets in my home. It all seems very dangerous, and I'm not planning to mess with electricity very much. If I need something electrical, I will call an electrician. I've gained a lot of respect for the profession. I'm just trying to educate myself a little regarding how it all works both in general and related to audio. Some of the concepts are sinking in a little, but some if it is still confusing. Concepts like ground loops still make my head spin.

 

[Nigel Goodwin]

I have learned about the difference between unbalanced and balanced with the concept being to eliminate ground noise. I also recall in the past when we had DJ turntables connected to a mixer with RCA cables we had to also connect the the grounding wire to a lug on the mixer. So, I guess those RCA cables did not provide a ground link? I've read about whether shields are grounded and got a bit confused.

It was optional - and depended entirely on the specific manufacturer, many (most?) had the option to connect or disconnect the chassis/earth connection under the turntable.

Basically the phono cables connected to the pickup cartridge, and the earth wire connected to the chassis of the turntable. These neeeded to be connected together, and you could do it either at the turntable end (and use just the phonos) or at the amplifier end, by using both phonos and the earth wire. You shouldn't use both, as that can potentially cause an earth loop.