sync40
Newbie level 2

Hi to everyone,
I am not new to electronics, in special working with lower than 24 volts DC, or with mains 127 VAC (always by using optocouplers to driving triacs and so), but now I a have a great doubt regarding my Tektronix 465 purchased yesterday.
In the past I have been using isolated hand-held scopes that could connect to just every point without any issues. However, I had never liked the limited pixel resolution, so I was looking for a big deal on an analog scope, and purchased the 100 MHz (almost 30 years old) Tektronix 465, just to know after reading the first chapter of its user manual, that the ground signal terminal (that is, the outer BNC probes from the two input channels, and of course the metal case) is tied permanently to the third terminal of a polarized mains plug (the ground or "earth" on the power cable). I know that this could be for safety reasons, but my main concern is that my house (and almost none in the neighbor has the third "earth" connector installed). Of course the appliances are connected through "3 connector outlets" but only the live and neutral are implemented; the earth circular connector is simply not connected.
So I am now in paranoia just checking all the voltages in the house and with the oscilloscope on and off, and I am very confused:
(remember that the third "earth" connector is not implemented in my installation):
1) the scope is plugged into the mains but with the power switch off; I put my DVM to read AC voltage between the shorter (live) mains jack and the scope case (that is the same that the BNC probes ground) and reads about 74 volts.
2) the same as (1) but the DVM between the larger (neutral) mains jack and the scope case, and reads about 37 volts.
3) the same as (1) but with the scope powered and it reads about 60 volts.
4) the same as (4) but with the scope powered and it reads about 50 volts.
I am planning to use my scope in 5 volt digital circuitry, always isolated by a wallmart transformer, or a linear power supply (transformer, bridge, regulator), and attach the BNC outer ground to my 5 volts ground, and the BNC center to the point that I want to measure (just the traditional way). Should I worry about the 60 volts present at the BNC outer ground when the scope is on, to induce overvoltages in my 5 volts circuit? I believe that no matter what, that 60 volts are just the reference for the scope, and if my 5 volts circuit is really 65 volts for the scope, that should not interfere with my circuit. Am I right?
Could I suffer from an AC shock hazard of the 60 volts in the BNC connectors, even by touching it?
Thank you very much for any help.
I am not new to electronics, in special working with lower than 24 volts DC, or with mains 127 VAC (always by using optocouplers to driving triacs and so), but now I a have a great doubt regarding my Tektronix 465 purchased yesterday.
In the past I have been using isolated hand-held scopes that could connect to just every point without any issues. However, I had never liked the limited pixel resolution, so I was looking for a big deal on an analog scope, and purchased the 100 MHz (almost 30 years old) Tektronix 465, just to know after reading the first chapter of its user manual, that the ground signal terminal (that is, the outer BNC probes from the two input channels, and of course the metal case) is tied permanently to the third terminal of a polarized mains plug (the ground or "earth" on the power cable). I know that this could be for safety reasons, but my main concern is that my house (and almost none in the neighbor has the third "earth" connector installed). Of course the appliances are connected through "3 connector outlets" but only the live and neutral are implemented; the earth circular connector is simply not connected.
So I am now in paranoia just checking all the voltages in the house and with the oscilloscope on and off, and I am very confused:
(remember that the third "earth" connector is not implemented in my installation):
1) the scope is plugged into the mains but with the power switch off; I put my DVM to read AC voltage between the shorter (live) mains jack and the scope case (that is the same that the BNC probes ground) and reads about 74 volts.
2) the same as (1) but the DVM between the larger (neutral) mains jack and the scope case, and reads about 37 volts.
3) the same as (1) but with the scope powered and it reads about 60 volts.
4) the same as (4) but with the scope powered and it reads about 50 volts.
I am planning to use my scope in 5 volt digital circuitry, always isolated by a wallmart transformer, or a linear power supply (transformer, bridge, regulator), and attach the BNC outer ground to my 5 volts ground, and the BNC center to the point that I want to measure (just the traditional way). Should I worry about the 60 volts present at the BNC outer ground when the scope is on, to induce overvoltages in my 5 volts circuit? I believe that no matter what, that 60 volts are just the reference for the scope, and if my 5 volts circuit is really 65 volts for the scope, that should not interfere with my circuit. Am I right?
Could I suffer from an AC shock hazard of the 60 volts in the BNC connectors, even by touching it?
Thank you very much for any help.