Can't tell,if my house is properly grounded

last_lemming OP 275 posts 02-21-2017 3:22pm


Will do - just so I’m clear:

hot = smaller blade
neutral = larger blade
ground = small round hole below the two blade holes.

I know I sound like a simpleton here, but I don’t want to shock myself or damage the equipment. Also I’m assuming I will not damage the equipment as long as I follow the above procedure - for instance testing hot and neutral at the same time while equipment is on.

I made several edits in my last post. You might want to reread it again.

hot = smaller blade
neutral = larger blade
ground = small round hole below the two blade holes.

Hole slot sizes on the receptacle face itself. The hot and neutral blades on the 3 wire grounding plug are the same size.

I know I sound like a simpleton here, but I don’t want to shock myself or damage the equipment.

Don’t touch the metal probes with your fingers. Just make sure to touch the far outside sides of the plug blades. When touching the safety equipment ground pin touch it from the bottom side of the pin. You can also use the metal screw that holds the duplex cover plate on.

If it makes you feel safer wrap some electrical vinyl tape around most of the metal of the probes of the meter test lead probes leaving only the metal tips exposed.

Finally If you still do not feel safe measuring the AC voltages, Don’t do it! Safety first.

Also I’m assuming I will not damage the equipment as long as I follow the above procedure - for instance testing hot and neutral at the same time while equipment is on.

No, it will not damage any of your equipment. The multimeter is a high resistance meter. The branch circuit won’t even know you are checking it out.

Take your time. Again, if you do not feel safe don’t do it!
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That clarifies everything.  I'm not too scared of it, i've done a little bit of electrical  investigation on cars and a little on homes but  I just like being very clear when I do stuff with it!

Ok here is the results with power of preamp and amp on:

hot + neutral = 120.5V+/-

hot + ground = 120.5V +/-

neutral + ground = .05V steady

GOOD NEWS!!!

So I found a proper cheater plug and tried putting it on the tube amp only - buzz completely gone whether the phono pre was on or off.  So it appears the amp was to blame and the phono preamp just amplified the problem.

So now, hopefully, when my new Decware integrated tube amp comes in it wont exhibit this buzz/hum, if it does at least I know its not the AC line.

I want to thank everyone who spent their time an energy helping me out!  I learned a bunch and tracked down my problem.

last_lemming OP 277 posts                                               02-21-2017 5:47pm

Ok here is the results with power of preamp and amp on:

hot + neutral = 120.5V+/-

hot + ground = 120.5V +/-

neutral + ground = .05V steady

The voltage measurements look great.
Neutral to ground AC voltage of 50 millivolts is ok.
With that said though IF there is an internal problem with the preamp and the neutral conductor is bleeding off somehow to the equipment ground conductor would a 50mv difference of potential, voltage, cause the hum you are hearing?

Per NEC code the safety equipment ground and service entrance neutral conductor is intentionally bonded, connected, together at the main electrical service panel and not at point there after.

If a difference of potential is present, (50mv), and a closed circuit exists, will current travel through the circuit? Yes, imo.

Someone like Al, ( almarg ), could answer that question. Hopefully maybe Al is following this thread and will chime in.

Curious what scale on the multimeter did you use when you checked the neutral to equipment ground voltage? The lower the scale the more accurate the reading.

//

How about the other test?

With the preamp plugged into the AC outlet but powered off, not in standby if it has a standby feature, do you get hum/buzz through the amp/speakers?
I believe if the preamp has AC line filtering it is done near the IEC inlet connector ahead of the main power on/off switch. I am not 100% sure of that though.

Check to see if you get the hum with the main power switch turned off on the preamp.
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