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Old 13th October 2012, 04:29 PM   #1
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Default neutral to ground voltage?

Hello,

i want to build a GC amp and want to use the wall outlet as my AC source. so i thought i check the outlet with a multi-meter and i wrote down the results of my findings:

H(Hot), N(Nuetral), G(Ground).

H to N = 219.6-221 V
H to G = 126.2 V
G to N = 127 V

we have dual voltage system around here, the socket is the 3 wire receptacle

i have some photos for the wiring inside the wall if needed

i tried searching around the net. but i'm lost and don't know the effects of these results that will have on my safety grounding design, because that assumes the Nuetral wire is at 0 volts

Is this a normal results(having two hot wires, N-G voltage of 127VAC?). and if not its effects on the cuircit and if it adds any distortion/noise to the power supply?

thanks
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Last edited by Burnincoils; 13th October 2012 at 04:33 PM.
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Old 13th October 2012, 05:09 PM   #2
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It sounds like the neutral in your country is really a H, similar to the US 240V outlets. There is plenty on the net about US 240V outlets
It is not a problem as long the amplifier power supply provides primary to secondary isolation which most do for safety reasons. Do not connect the neutral to ground at the amplifier. The neutral and H should connect only to a double pole power switch which connects to the power transformer.
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Old 13th October 2012, 05:12 PM   #3
AndrewT is online now AndrewT  Scotland
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Live and Neutral are both consodered as LIVE and as such both are dangerous.

Your Live and Neutral are both @ ~120Vac relative to Earth.
i.e. both are dangerous.

This is very similar to the way North America distributes power into domestic households. The big difference is that the NA generally only use one feed for 120Vac whereas you have both feeds for 240Vac.

Earth is supposed to be safe.
Your Earth will measure very close to Zero Volts relative to the ground you stand on. In that respect it will not kill you.
It does not matter that you have two Live feeds to your power socket. The third wire is your Safety, or Protective Earth (PE).

Wire up any isolating transformer to the two feeds and the secondary output is isolated from the mains feeds and is considered safe.
Connect the PE to your chassis and that ensures you cannot be killed by internal faults in your home built equipment as long as the PE continuity is maintained until the fuse blows to isolate your equipment.

here I see a problem. You have two feeds, you need to fuse both of these Live feeds.
But I don't know what happens if only one fuse blows. Yes the equipment stops operating because there is no "circuit" around the Primary. But one end of the primary is still connected to the Live mains feed that has an intact fuse.

Can someone explain how we make this arrangement safe?
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Old 13th October 2012, 05:31 PM   #4
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Quote:
Originally Posted by Burnincoils View Post
Hello,

i want to build a GC amp and want to use the wall outlet as my AC source. so i thought i check the outlet with a multi-meter and i wrote down the results of my findings:

H(Hot), N(Nuetral), G(Ground).

H to N = 219.6-221 V
H to G = 126.2 V
G to N = 127 V

we have dual voltage system around here, the socket is the 3 wire receptacle

i have some photos for the wiring inside the wall if needed

i tried searching around the net. but i'm lost and don't know the effects of these results that will have on my safety grounding design, because that assumes the Nuetral wire is at 0 volts

Is this a normal results(having two hot wires, N-G voltage of 127VAC?). and if not its effects on the cuircit and if it adds any distortion/noise to the power supply?

thanks
First, disconnect all devices or home appliances that are connected to electrical outlets and remeasured tensions above.

Those voltages of 127V and 126.2 V arose because you have devices in the house, which are connected between phase (H) - grounding (G), and neutral (N) - grounding (G), some capacitors (see EMI filter from the image above).
Click the image to open in full size.

Disconnect all equipments from all outlets and re-performed measurements.
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Last edited by donpetru; 13th October 2012 at 05:34 PM.
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Old 13th October 2012, 08:50 PM   #5
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Quote:
Originally Posted by AndrewT View Post
here I see a problem. You have two feeds, you need to fuse both of these Live feeds.
But I don't know what happens if only one fuse blows. Yes the equipment stops operating because there is no "circuit" around the Primary. But one end of the primary is still connected to the Live mains feed that has an intact fuse.

Can someone explain how we make this arrangement safe?
The system is not unsafe if only one fuse blows, the case is connected to the PE. Many 3 phase systems rely on fuses and often only one fuse blows, the system does not become unsafe as a result.

On an industrial system we would use a ganged double pole circuit breaker rather than a fuse, but these are a bit bulky to fit in an appliance
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Old 13th October 2012, 09:29 PM   #6
imix500 is offline imix500  United States
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Quote:
Originally Posted by AndrewT View Post
Can someone explain how we make this arrangement safe?
On commercial equipment that is designed to operate anywhere in the world, I have seen a DPST relay after the overload protection as part of the auto-sensing PSU. This would certainly isolate both sides assuming the contacts don't fuse together.
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Old 15th October 2012, 02:46 AM   #7
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thanks to everyone for their inputs

please let me know how does this attached grounding schematic look like



*where do i locate the fuses? on both hot and nuetral wires at the output of the IT?
Attached Images
File Type: jpg 169 templatetext.jpg (49.6 KB, 101 views)
File Type: jpg 169 templatefused.jpg (53.0 KB, 97 views)
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Last edited by Burnincoils; 15th October 2012 at 03:04 AM. Reason: added schematic
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Old 15th October 2012, 04:23 AM   #8
AJT is offline AJT  Philippines
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Quote:
Originally Posted by Burnincoils View Post
Hello,

i want to build a GC amp and want to use the wall outlet as my AC source. so i thought i check the outlet with a multi-meter and i wrote down the results of my findings:

H(Hot), N(Nuetral), G(Ground).

H to N = 219.6-221 V
H to G = 126.2 V
G to N = 127 V

we have dual voltage system around here, the socket is the 3 wire receptacle

i have some photos for the wiring inside the wall if needed

i tried searching around the net. but i'm lost and don't know the effects of these results that will have on my safety grounding design, because that assumes the Neutral wire is at 0 volts

Is this a normal results(having two hot wires, N-G voltage of 127VAC?). and if not its effects on the circuit and if it adds any distortion/noise to the power supply?

thanks
looks like you have a balanced line there...the secondary of the distribution transformer has 240 volts split with a center tap....

line to neutral systems are derived from 3 phase lines, one phase to neural...so that a 240 volt service is derived from 3phase 400volt line to line system....the neutral point is earthed at the transformer side, but neutral lines are also run together with the other 3 phases, in some power cables you will find that there are 5 cores, 3 cores for the phases, one core each for neutral and ground....
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Old 15th October 2012, 04:25 AM   #9
AJT is offline AJT  Philippines
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Quote:
Originally Posted by Burnincoils View Post
thanks to everyone for their inputs

please let me know how does this attached grounding schematic look like



*where do i locate the fuses? on both hot and neutral wires at the output of the IT?
you have to consult your "local" electrical codes for that...
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Old 15th October 2012, 10:21 AM   #10
AndrewT is online now AndrewT  Scotland
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re post7

the PE is the third wire in the mains cable.
It is not the secondary wire connected to the gain clone.

If you want mains fault protection in the gain clone, then wire a connection from gain clone chassis to PSU chassis. This connection will take mains fault current from gain clone chassis to PSU chassis to PE and then blow the mains fuse.

The second 120Vac feed to the primary must also be fused. Just like the upper mains feed.
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