Neutral to ground voltage
- Thread starter aaqib
- Start date
- Status
- Location
- Massachusetts
- Increase the conductor size of the neutral
- Decrease the distance between the systems bonding jumper and the point your taking the reading.
- Reduce the current on the neutral
The difference in voltage between neutral and ground is caused by voltage drop on the neutral.
Can I ask why your concerned with 3 volts?
Pierre C Belarge
Senior Member
- Location
- Westchester County, New York
Adding to Bob's response.
It may not be a code/electrical issue, depending on the installation. The factors Bob posted are the "usual suspects" to the voltage reading you are experiencing.
If the voltage between neutral - ground are affecting the load equipment, you may have to redesign the circuit/feeder or change equipment.
It may not be a code/electrical issue, depending on the installation. The factors Bob posted are the "usual suspects" to the voltage reading you are experiencing.
If the voltage between neutral - ground are affecting the load equipment, you may have to redesign the circuit/feeder or change equipment.
mivey
Senior Member
I would like to know the same as Bob: why are you concerned about the voltage difference between the neutral and ground?
The neutral is a current-carrying conductor just like the line conductor and will experience similar voltage drops. And like he said, a bigger conductor = less voltage drop.
The neutral is a current-carrying conductor just like the line conductor and will experience similar voltage drops. And like he said, a bigger conductor = less voltage drop.
gar
Senior Member
- Location
- Ann Arbor, Michigan
- Occupation
- EE
080705-1414 EST
mivey:
Here is a reason to be concerned with 3 V.
A CNC machine is connected to a computer. Both the machine and computer have their RS232 common referenced to the respective chassis. The common wire in the RS232 cable is small, maybe #24 or #22, and both probably have line filters from the hot lines to the chassis and the EGC wires. Some of this voltage difference may result from noise currents thru the EGC wires. The common wire in the RS232 cable is of no significance in comparison to #12 or larger wires in the EGC path.
The RS232 specification requires the signal to swing between levels above +3 V and below -3 V at the receiving end. However, not all receivers have a large input hysteresis. A gaussian noise voltage will easily have peak voltages 3 times the RMS value of that gaussian noise signal. Thus, a 3 V meter reading could indicate a possible data error problem.
I would solve this kind of problem with an isolated RS232 path.
.
mivey:
Here is a reason to be concerned with 3 V.
A CNC machine is connected to a computer. Both the machine and computer have their RS232 common referenced to the respective chassis. The common wire in the RS232 cable is small, maybe #24 or #22, and both probably have line filters from the hot lines to the chassis and the EGC wires. Some of this voltage difference may result from noise currents thru the EGC wires. The common wire in the RS232 cable is of no significance in comparison to #12 or larger wires in the EGC path.
The RS232 specification requires the signal to swing between levels above +3 V and below -3 V at the receiving end. However, not all receivers have a large input hysteresis. A gaussian noise voltage will easily have peak voltages 3 times the RMS value of that gaussian noise signal. Thus, a 3 V meter reading could indicate a possible data error problem.
I would solve this kind of problem with an isolated RS232 path.
.
Yeah! What he said.dereckbc said:
I don't follow advances in CNC machining but happen to be looking at some just yesterday on the internet. I found it strange that almost all of the systems I saw were still using RS-232 (or a parallel printer port
). I ran across only one using USB.gar
Senior Member
- Location
- Ann Arbor, Michigan
- Occupation
- EE
080605-2122 EST
dereckbc:
I really do not know to what you were referring. Ethernet, 422, 485, or what.
I believe Smart $ interpreted your comment as USB.
USB as used on CNC machines seems to be designed around reading memory cards and not for communication with computers.
People in the CNC industry tend use RS232 to describe both the signal level interface and async serial communication. RS232 when applied with suitable isolation can provided simple, reliable, secure, moderately long cable length (4000 ft), and 115.2 kbaud capability.
I expect async communication thru RS232 ports will around for quite a while.
.
dereckbc:
I really do not know to what you were referring. Ethernet, 422, 485, or what.
I believe Smart $ interpreted your comment as USB.
USB as used on CNC machines seems to be designed around reading memory cards and not for communication with computers.
People in the CNC industry tend use RS232 to describe both the signal level interface and async serial communication. RS232 when applied with suitable isolation can provided simple, reliable, secure, moderately long cable length (4000 ft), and 115.2 kbaud capability.
I expect async communication thru RS232 ports will around for quite a while.
.
tryinghard
Senior Member
- Location
- California
Eye yi, yi! The neutral is a current carrying conductor; it?s supposed to have current. The ground is not a current carrying conductor; it?s not supposed to have current. Therefore there will be a difference at any given moment between them.
Do not misuse the ground, it has nothing to do with returning current, AC or DC, if a return path is needed bring a conductor along for this purpose.
Conversely to this the neutral (grounded conductor) is not ground it only happens to be connected to the ground at the source, it should not be connected to ground past the source again to eliminate any parallel neutral current.
The neutral has a duel purpose at the source, 1) to enable returning current of its circuit, and 2) to enable a ground fault path from non-current carrying items (metal frames) to source, it enables extremely high current that will in turn operate overcurrent protection. Past the source the bonding enables ground fault path not the neutral.
Do not misuse the ground, it has nothing to do with returning current, AC or DC, if a return path is needed bring a conductor along for this purpose.
Conversely to this the neutral (grounded conductor) is not ground it only happens to be connected to the ground at the source, it should not be connected to ground past the source again to eliminate any parallel neutral current.
The neutral has a duel purpose at the source, 1) to enable returning current of its circuit, and 2) to enable a ground fault path from non-current carrying items (metal frames) to source, it enables extremely high current that will in turn operate overcurrent protection. Past the source the bonding enables ground fault path not the neutral.
brian john
Senior Member
- Location
- Leesburg, VA
I have seen lots of information about limiting N-G voltage. I have seen voltage at 7.5 VAC with no issues on equipment guaranteed to fail by the manufacture above 1.5 VAC.
I (as posted numerous times) had a case where neutral to ground voltage was 120 VAC. VERY SENSITIVE electronics with an elaborate grounding system. This system was operating for a long time ungrounded (no N-G bond) and operated with a phase to ground bond for an unknown period of time.
I am not an engineer, I have no clue how "this equipment" that needs the low N-G levels operates, I just know what I have seen.
BUT and I mean a HUGE BUT, I have no problem meeting manufactures specs and do sell ISO transformers regularly.
I (as posted numerous times) had a case where neutral to ground voltage was 120 VAC. VERY SENSITIVE electronics with an elaborate grounding system. This system was operating for a long time ungrounded (no N-G bond) and operated with a phase to ground bond for an unknown period of time.
I am not an engineer, I have no clue how "this equipment" that needs the low N-G levels operates, I just know what I have seen.
BUT and I mean a HUGE BUT, I have no problem meeting manufactures specs and do sell ISO transformers regularly.
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