Grounded Neutral condition detection.

MisterBill2

Joined Jan 23, 2018
19,422
Even going into a building, IF, and ONLY IF, the transformer actually provides real isolation, "grounding the neutral" does nothing to insure "balanced power" (whatever that means). because the neutral being at the center point provides a centered pair of voltages. One more case of doing something "because everybody else does it."
 

nsaspook

Joined Aug 27, 2009
13,553
If the circuit is actually isolated, as shown, then what advantage is provided by connecting one side to any common point shared with the non-isolated system??
The explanation that I have received before is "that everybody does it", and that is not very effective in describing any benefit for either safety or noise reduction.
An adequately isolated system, with a correctly "grounded" electrostatic shield between transformer primary and secondary, should not have any common-mode noise or disturbances coupled in from outside.

Are you talking about the separately derived system bond and grounding?
https://www.fluke.com/en-us/learn/blog/grounding/grounding-separately-derived-systems


You don't seem to have any expertise on that subject. The transformer I used has a properly connected "grounded" electrostatic shield to reduce common-mode noise or disturbances . You don't seem to understand the importance of hum and noise floor reduction by the elimination of neutral and ground loops (small noise currents caused mainly by motors and large load connects/disconnect surges) by breaking the galvanic connection using a isolation transformer for sensitive audio (recording studios, complex media rooms and home theaters) and instrumentation systems.
 

nsaspook

Joined Aug 27, 2009
13,553
Even going into a building, IF, and ONLY IF, the transformer actually provides real isolation, "grounding the neutral" does nothing to insure "balanced power" (whatever that means). because the neutral being at the center point provides a centered pair of voltages. One more case of doing something "because everybody else does it."
Balanced power is IMO mainly a fad with some usefulness in sensitive audio applications. Using separately derived power transformers to break main panel galvanic ground loops is not,
as it's used intensively in industry and audio.
1711735134062.png
 

MisterBill2

Joined Jan 23, 2018
19,422
Are you talking about the separately derived system bond and grounding?
https://www.fluke.com/en-us/learn/blog/grounding/grounding-separately-derived-systems


You don't seem to have any expertise on that subject. The transformer I used has a properly connected "grounded" electrostatic shield to reduce common-mode noise or disturbances . You don't seem to understand the importance of hum and noise floor reduction by the elimination of neutral and ground loops (small noise currents caused mainly by motors and large load connects/disconnect surges) by breaking the galvanic connection using a isolation transformer for sensitive audio (recording studios, complex media rooms and home theaters) and instrumentation systems.
I CERTAINLY am familiar with and understand the benefits of isolation by means of an isolation transformer. My question was about the benefit of then tying the isolated portion back to a noisy environment. Note that usually when folks go to the effort of adding an isolation transformer, they are very careful about what gets connected to the isolated side. That means no motors or large loads, AND NO GROUND LOOPS, because of no grounds.
 

nsaspook

Joined Aug 27, 2009
13,553
I CERTAINLY am familiar with and understand the benefits of isolation by means of an isolation transformer. My question was about the benefit of then tying the isolated portion back to a noisy environment. Note that usually when folks go to the effort of adding an isolation transformer, they are very careful about what gets connected to the isolated side. That means no motors or large loads, AND NO GROUND LOOPS, because of no grounds.
It's not being tied back to the noisy environment. The fact the isolated system has a proper safety ground does NOT mean it shares the source of noise from the primary side. You use another ground rod (EARTHING) system to connect to the secondary ground/neutral bond. The separate rod (EARTHING) system MUST (life safety and the protection of both property and equipment) be bonded to the primary grounding system outside of the scope of normal energy paths. Your comments CERTAINLY do seem to mean you're not familiar with this common configuration of TECHNICAL GROUND SYSTEMS.
Note that a transformer does not isolate grounds on one side for the transformer from those on the other side. That’s because safety codes also require that all grounded objects (and all grounded Systems) in a facility must be bonded together.
https://www.fullcompass.com/common/files/5644-PowerandGroundingforAudioandAudioVisualSystems.pdf

1711743099012.png
1711743126523.png
 
Last edited:

MaxHeadRoom

Joined Jul 18, 2013
28,827
The industrial side of thinks is opposite, when ever I have made up cabinets or completed CNC retrofits, I have used the control circuit recommendations in NFPA79 where the 120v control circuitry is fed from a step down/isolation transformer and a neutral is created by earth grounding one side of the secondary.
Also equi-potential bonding together with central earth GND termination point is carried out in order to eliminate GND loops.
Per the Siemens publication on the subject.
 

LadySpark

Joined Feb 7, 2024
194
The industrial side of thinks is opposite, when ever I have made up cabinets or completed CNC retrofits, I have used the control circuit recommendations in NFPA79 where the 120v control circuitry is fed from a step down/isolation transformer and a neutral is created by earth grounding one side of the secondary.
Also equi-potential bonding together with central earth GND termination point is carried out in order to eliminate GND loops.
Per the Siemens publication on the subject.
There is a few extra things to consider like power correction that goes into that as well. Like common returns.
 

MisterBill2

Joined Jan 23, 2018
19,422
The industrial side of thinks is opposite, when ever I have made up cabinets or completed CNC retrofits, I have used the control circuit recommendations in NFPA79 where the 120v control circuitry is fed from a step down/isolation transformer and a neutral is created by earth grounding one side of the secondary.
Also equi-potential bonding together with central earth GND termination point is carried out in order to eliminate GND loops.
Per the Siemens publication on the subject.
The systems we installed for GM used an ungrounded secondary of the isolation transformer. The sole ground reference was at the junction of two 120 volt "ground detect" lights. So those were at half voltage as long as the system was powered. And a connection to ground of any portion of the control system would illuminate one to full intensity and darken the other, The benefit was that the system could continue to function correctly even with an unintentional ground connection. The same scheme meant that any such ground connection could not deliver much current to start a fire or cause damage. AND the shock hazard was less. So there was a real benefit to having an isolated system. And nobody got zapped.
AND, when working with those hot-chassis radios and televisions, powering them from an isolated source avoided not only a shock hazard but also avoided damage to the various test equipment, such as scopes and alignment generators.
 

nsaspook

Joined Aug 27, 2009
13,553
The systems we installed for GM used an ungrounded secondary of the isolation transformer. The sole ground reference was at the junction of two 120 volt "ground detect" lights. So those were at half voltage as long as the system was powered. And a connection to ground of any portion of the control system would illuminate one to full intensity and darken the other, The benefit was that the system could continue to function correctly even with an unintentional ground connection. The same scheme meant that any such ground connection could not deliver much current to start a fire or cause damage. AND the shock hazard was less. So there was a real benefit to having an isolated system. And nobody got zapped.
AND, when working with those hot-chassis radios and televisions, powering them from an isolated source avoided not only a shock hazard but also avoided damage to the various test equipment, such as scopes and alignment generators.
Same as on any US Navy ship. The standard is “floating neutral” power from the generator to the 110 AC socket. The ships hull was ground with two hots and no neutral from 110VAC delta systems from transformers powered by the main 440/255V delta.

We had line grounded indicators to isolate shorts for most rooms with dedicated emergency power capability like radio, radar, and important electronic/electrical spaces.
 
Last edited:
Top