Neutral & Earth bonding in Sub-panel

kannan07c

Member
Hello All

Bonding of Earth and neutral in machine subpanels will cause a problem, but I want to know how it would affect PLC & VFD, etc.

The machine has 2 panels one for heaters (uneven load in each phase) another has VFD (250 kW) for the motor. since the last 4 months continuously facing a problem with drive most of the time control board failed without any error replaced with new VFD but no improvement. Also found some liquid from boards maybe electrolyte.

While checking found both panel earth & neutral & bonded together. I removed the bonding but want know to make sure it was the root cause of all the time drive failure.

Also After removing bonding in the sub-panel between earth & neutral showing some 100kohms. The main panel (transformer room) & subpanel earth are not connected then how showing some ohms and it keeps varying. In a cable have 4 wire i.e 3 phase & 1 neutral.

Please advice..
 

petersonra

Senior Member
for NEC compliant systems:

bonding of earth and neutral causes current to flow on the equipment ground conductor, sometimes called PE in some parts of the world. it probably won't have any negative impact on controls for the most part, even though it is undesirable.

if there is liquid in the cabinets it may be condensation and that could lead to damage of circuit boards.

it is hard to give you much help from so far away.

the neutral-earth bond should be made at only one place, usually the service point.

having said all this there are other electrical systems different from the NEC.
 

kannan07c

Member
for NEC compliant systems:

bonding of earth and neutral causes current to flow on the equipment ground conductor, sometimes called PE in some parts of the world. it probably won't have any negative impact on controls for the most part, even though it is undesirable.

if there is liquid in the cabinets it may be condensation and that could lead to damage of circuit boards.

it is hard to give you much help from so far away.

the neutral-earth bond should be made at only one place, usually the service point.

having said all this there are other electrical systems different from the NEC.
Thanks for a reply........

Neutral current won't affect to the control boards?
Its not a condensation its oily .....
 

petersonra

Senior Member
I don't see how current flowing through the EGC external to the VFD would cause a capacitor to leak.

I will suggest this. Many VFDs are designed for solidly grounded wye power. If you don't have this, it can create havoc.
 

kwired

Electron manager
Drive power circuit likely doesn't have a connection to the neutral conductor, so neutral current will have no impact on the drive power circuit.

Stray currents on EGC and equipment frames can possibly cause problems if that current gets onto any grounded control circuit conductors though, but the control circuit about has to be grounded more than once for this to be much of a possibility.
 

kannan07c

Member
"If you don't have this, it can create havoc."

I did not understand this...please let me know what should I introduce.
 

Jraef

Moderator
Staff member
That's a DC drive, not a VFD, and it's an SCR (thyristor) based topology so there are no large DC bus caps like there are in a PWM based VFD or DC drive. So that's not likely capacitor electrolyte from a large bus cap, it's something else. It might be coming in on conduit or cable connections or it might be from a power supply or something, which might better explain your anomalies.
 

kannan07c

Member
That's a DC drive, not a VFD, and it's an SCR (thyristor) based topology so there are no large DC bus caps like there are in a PWM based VFD or DC drive. So that's not likely capacitor electrolyte from a large bus cap, it's something else. It might be coming in on conduit or cable connections or it might be from a power supply or something, which might better explain your anomalies.
Yes , image attached is of DCS550 more than 5 control board failed we replaced with Parker 591, its board also failed.
we replaced with AC drive ACS800 and motor but its RDCU failed, ABB team worked near about a month but they are clue less. They said power problem but,Our factory have other machines (CNC machine, small drives in different machines) but no any affect there.

So, I m looking for what will be other causes, only i saw this neutral & earth bonding is out of standard.

Below images of Paker DC dear mother board, its metal part have some oxidation type dont know what & how its coming & ICs terminals also..
 

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kannan07c

Member
Drive power circuit likely doesn't have a connection to the neutral conductor, so neutral current will have no impact on the drive power circuit.

Stray currents on EGC and equipment frames can possibly cause problems if that current gets onto any grounded control circuit conductors though, but the control circuit about has to be grounded more than once for this to be much of a possibility.
I'm also suspecting that as Neutral & earth bonded. As two-panel (one panel with heaters & another with Drive)have common earthing & neutral are bonded with that, also after removing bond measured AMPERE in neutral conductor found 30A and its varying as heaters ON/ OFF.

But not sure how much neutral current can effect control boards.
 

synchro

Senior Member
I'm also suspecting that as Neutral & earth bonded. As two-panel (one panel with heaters & another with Drive)have common earthing & neutral are bonded with that, also after removing bond measured AMPERE in neutral conductor found 30A and its varying as heaters ON/ OFF.

But not sure how much neutral current can effect control boards.
Does the Drive have a connection to the neutral, or is the neutral only there for the heaters?
As kwired said, if currents from the neutral flow through the ground/earth connections to the control board it could cause problems (especially if there are multiple earth connections like there often are).
If the neutral and earth (PE) are bonded then this should be done in one place well before the conductors connect to the drive and machine. That way there should be not be any significant current through the PE connections to the control board that could damage it.
 

kannan07c

Member
Does the Drive have a connection to the neutral, or is the neutral only there for the heaters?
As kwired said, if currents from the neutral flow through the ground/earth connections to the control board it could cause problems (especially if there are multiple earth connections like there often are).
If the neutral and earth (PE) are bonded then this should be done in one place well before the conductors connect to the drive and machine. That way there should be not be any significant current through the PE connections to the control board that could damage it.
Neutral only for heaters........both had the same earth & neutral has bonded in it.

But After removing the bonding still neutral & Earth showing continuity some time 500 ohms & varies. Neutral bonded to earth in a transformer room & its earth point is different, whole plant (panels, machines) have another earthing point. Both the transformer room & Plant Earthing point are isolated.
 

synchro

Senior Member
Neutral only for heaters........both had the same earth & neutral has bonded in it.

But After removing the bonding still neutral & Earth showing continuity some time 500 ohms & varies. Neutral bonded to earth in a transformer room & its earth point is different, whole plant (panels, machines) have another earthing point. Both the transformer room & Plant Earthing point are isolated.
I can only speculate at this end. But if the neutral has a poor or intermittent connection along the way from the transformer, and the neutral is bonded to earth at the panels, then heater current will flow through the earth conductors. In this case if the earthing conductor path to the transformer room also has a high resistance as you mention, then the voltage at the PE (protective earth) connections to the drive boards could be elevated and possibly cause damage.
 

kannan07c

Member
Dear All


Adding some more points here. We have done a power quality analysis and recorded data for a week & found Voltage Unbalance in the primary & secondary side of the transformer.
Please suggest how much this will affect to drive & drive control card failure any link.

Attached reports for reference.
 

Attachments

kwired

Electron manager
Dear All


Adding some more points here. We have done a power quality analysis and recorded data for a week & found Voltage Unbalance in the primary & secondary side of the transformer.
Please suggest how much this will affect to drive & drive control card failure any link.

Attached reports for reference.
I did not look at any of your reports, but for a typical VFD I don't think you wil have much issue with mild voltage imbalance. The AC input goes directly to a rectifier and all it will effect is how much current draw comes from each input leg. Everything after that point comes from a two wire DC bus, starve the input too much on one leg and you will reduce the output ability of that bus though. In fact you can use a drive as a single phase to three phase converter because of how this works, though you do have to derate the input rating of the drive if you are using it this way.
 

synchro

Senior Member
Since multiple control boards have failed on the DC drives and variable frequency AC drive, it's possible that there could be issues on the voltage levels, ground return, etc. of external I/O lines connecting to the control boards that are damaging them.
 
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