Ground to Neutral Voltage Problem

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I have a copier manufacturer requiring less than 2 Volts between neutral and ground at the receptacle. Receptacle is dedicated and only 1.5 volts between ground and neutral with no load. When copier makes copy it jumps to 7 Volts. Tech tells me this is unacceptable and causes copier to malfunction. I have tried Iso ground receptacle and regular. Also tried only using the conduit (EMT) as only ground path. I checked connections in sub panel and tested between ground and neutral buss. No voltage difference at panel busses, even when copier makes copy. I did find a 25 Volt reading between Ground conductor and Ground Buss when removed and nothing plugged in at receptacle. It appears to be inductance from phase conductor and disappears when breaker is off. Is this normal. Any ideas would be greatly appreciated.
 

don_resqcapt19

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Staff member
Location
Illinois
Occupation
retired electrician
The voltage between the grounded conductor and the EGC is really a measurement of the voltage drop on the grounded conductor on the load side of the main or system bonding jumper. You need to check for excessive current on the grounded conductor or a poor connection on the grounded conductor.
 

brian john

Senior Member
Location
Leesburg, VA
What you can do if the are willing to pay for it is over size the conductors.
Install an isolation transformer at the copier.
Install a true on line UPS at the copier.

BUT I had a site that was 3-phase 4-wire, ungrounded, at some point A phase shorted to ground The site had 120 VAC between neutral and ground and ALL equipment operated fine this was very sensitive equipment. IN addition there was a study some years ago where sensitive electronic equipment was operated at varying voltages between neutral and ground with no malfunctions. But arguing with the manufacture is usually a waste of breath.
 

hurk27

Senior Member
The sooner these manufactures quite using the chassis and EGC as signal return paths the faster this problem will go away, most copiers and printers are now wired by Ethernet, but many of the internal bus's are still bonded to the chassis, so noise on the system grounding (EGC) will affect them, almost impossible for us to eliminate (except in the case of bootlegged grounds and or neutral current on the system grounds) also sometimes one printer/copier might be networked between computers all across a building, and some of these computers are fed from different services, no way to fix that!

I have never had a problem with a stand alone copier, just ones networked.

one thing to check is to see if any current is flowing on the grounding, but like you said you tried an isolated ground and still had the problem.

without having a super conductor wire at hand to prevent voltage drop in the neutral, over sizing the neutral is about the only way to lessen the VD.

I have a problem with poor designed equipment when they try to put the blame on us.
 

don_resqcapt19

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Staff member
Location
Illinois
Occupation
retired electrician
7 volts between the grounded conductor and the EGC under load is excessive to me and, and assuming a correctly sized conductor, suggests a connection problem with the grounded conductor.

Take a look at the ungrounded conductor to the EGC under load. If that voltage drop is a lot less than that of the grounded conductor, you will know that it is a grounded conductor problem. if the voltage drop on the ungrounded conductor is about the same as that of the grounded conductor, then you will need to upsize the conductors to reduce the voltage drop.
 
I agree 100% about using the chassis as signal ground. I have tried explaining to tech but as Brian said waste of breath. I didn't mention it is a copier/printer/fax and is networked. They also seem to have most problems when a job is sent via PC over netwok. I apoligize for the lack of details.
 
Thanks guys for your help. I haven't checked the load on the feeder grounded conductor at the sub panel. I did check for voltage between the Neutral and Equipment Ground Busses this read 0 even when copier is operating. The dedicated copier circuit is #12 THHN and 50' Max. I didn't check for voltage drops due to the short distance. I will do some more tests and let you know what I find.
Thanks again.
 

gar

Senior Member
Location
Ann Arbor, Michigan
Occupation
EE
101130-1508 EST

AVSparky:

I did check for voltage between the Neutral and Equipment Ground Busses this read 0 even when copier is operating.
If this measurement is at the sub-panel, then connect a test wire, can be an extension cord, from neutral at the sub-panel and run this to the copier area. This test wire (lead) connects to one input of the meter. I am assuming the meter is a good high input impedance digital with resolution to at least 0.1 V on a 120 V range.

From the sub-panel neutral monitor the voltage to the neutral at the copier while the copier is operating. #12 wire is about 1.6 ohms/1000 ft. 20 amps thru 50 ft of #12 copper wire would produce a drop of about 1.6 V.

Separately monitor the voltage from the sub-panel neutral to the EGC at the copier while the copier is operating. Voltage should be near zero. There should be no current flow in the EGC.

These measurements should lead you in the direction of the problem.

.
 

dereckbc

Moderator
Staff member
Location
Plano, TX
Receptacle is dedicated and only 1.5 volts between ground and neutral with no load.
Why? with no current flowing there should be 0 volts. Voltage between N-G at the load device is really measuring the voltage drop developed on the grounded circuit conductor, or the IR product. If current =0 and resistance is reasonable low like .1 ohms or less, there should be no voltage difference with no load current.


When copier makes copy it jumps to 7 Volts.
Again why? How much current? How long a length? What size conductor? With a 10 amp load with a conductor impedance of .1 ohm should only develop 1 volt.

This tells me you have either a connection problem, too small of a grounded circuit conductor, extremely long or all the above. I agree with Hurk equipment manufactures need to move away from ground reference signals, but 2 volts of less drop N-G is really easy to obtain.

As a design rule, not code requirement, feeders are allowed 2% VD, and branch circuits 3% for a total of 5% overall voltage drop. So at 120 that works out to 6 volts, and 3 volts N-G at load device. Sound like your feeder is fine to the sub panel. Problem appears to be in the branch circuit. Using a # 12 AWG on a 20 amp breaker, with a maximum 16 amp load current, you should be good out to 65 feet one way cable distance.
 
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ghostbuster

Senior Member
Hang on a second guys,this copier(if 10 amps rated) will create surge currents every 20-30 seconds approx. 80-100 amps for 5-10 power cycles,EVEN WHEN THE COPIER IS IN IDLE MODE.If your metering is fast enough it may be picking up part of this normal copier electrical transient activity .:)
 

gar

Senior Member
Location
Ann Arbor, Michigan
Occupation
EE
101201-1015 EST

ghostbuster:

Was the model number or any information provided on the copier. How do you know there are 80 to 100 A pulses of current?

.
 

ghostbuster

Senior Member
All photocopiers/laser printers we have measured over the last 10 years contain fuser bulbs that keep hot (for instant copy mode) by cycling.Worst case scenario,we have seen them create 20-30% voltage sags on the line each time they cycle.:)
 

don_resqcapt19

Moderator
Staff member
Location
Illinois
Occupation
retired electrician
Why? with no current flowing there should be 0 volts. Voltage between N-G at the load device is really measuring the voltage drop developed on the grounded circuit conductor, or the IR product. If current =0 and resistance is reasonable low like .1 ohms or less, there should be no voltage difference with no load current. ...
That is correct assuming that the neural originates at the point in the system where the main or system bonding jumper is located at. If this a sub-panel, you will see the voltage drop of the feeder grounded conductor.
 

gar

Senior Member
Location
Ann Arbor, Michigan
Occupation
EE
101201-1356 EST

ghostbuster:

I just do not believe your 80 to 100 A comment for multiple cycles of the AC line..

The fusing element is basically a resistor. There will be a variation in resistance from cold to hot. The amount will be a function of the temperature difference. If it is something like Nichrome heated to orange, then maybe 10 to 15% change. If it was an incandescent filament, then possibly a 1000%, but this would be for less than 8 MS.

See my photo P3 at http://beta-a2.com/EE-photos.html for the maximum inrush for a 100 W 120 tungsten filament turned on at the 170 V point in the cycle, worst case phase angle. Much less than 8 MS.

Using a Fluke 27 and a Y8100 the following measurements were made.

My HP 5SI MX laser printer without using a scope has two current levels in standby of about 0.2 A and 4 A. The duty cycle is about 4 to 6 seconds on and about 8 seconds off. My total change in voltage at the plug terminals to the HP between these two states is about 2 V at 120 V nominal. This is after a couple outlet strips and a noise filter, not a low impedance. Calculated source impedance is 2/4 = 0.5 ohms.

At the same point looking at the EGC to neutral I get about a change from a residual of 0.5 to 1.5 V. Thus a 1 V change from the HP fuser. This is half of the hot to neutral change and thus a good correlation.


To answer the question on the original post there needs to be more quantitative information. With a good DVM much more can be learned about the cause without additional test equipment.

.
 

wirenut1980

Senior Member
Location
Plainfield, IN
Thanks guys for your help. I haven't checked the load on the feeder grounded conductor at the sub panel. I did check for voltage between the Neutral and Equipment Ground Busses this read 0 even when copier is operating. The dedicated copier circuit is #12 THHN and 50' Max. I didn't check for voltage drops due to the short distance. I will do some more tests and let you know what I find.
Thanks again.

If you are reading 0 V between neutral and ground bus at a subpanel, I think that means the two busswes are bonded together, which is incorrect.
 

wirenut1980

Senior Member
Location
Plainfield, IN
101201-1356 EST

ghostbuster:

I just do not believe your 80 to 100 A comment for multiple cycles of the AC line..

The fusing element is basically a resistor. There will be a variation in resistance from cold to hot. The amount will be a function of the temperature difference. If it is something like Nichrome heated to orange, then maybe 10 to 15% change. If it was an incandescent filament, then possibly a 1000%, but this would be for less than 8 MS.

See my photo P3 at http://beta-a2.com/EE-photos.html for the maximum inrush for a 100 W 120 tungsten filament turned on at the 170 V point in the cycle, worst case phase angle. Much less than 8 MS.

Using a Fluke 27 and a Y8100 the following measurements were made.

My HP 5SI MX laser printer without using a scope has two current levels in standby of about 0.2 A and 4 A. The duty cycle is about 4 to 6 seconds on and about 8 seconds off. My total change in voltage at the plug terminals to the HP between these two states is about 2 V at 120 V nominal. This is after a couple outlet strips and a noise filter, not a low impedance. Calculated source impedance is 2/4 = 0.5 ohms.

At the same point looking at the EGC to neutral I get about a change from a residual of 0.5 to 1.5 V. Thus a 1 V change from the HP fuser. This is half of the hot to neutral change and thus a good correlation.


To answer the question on the original post there needs to be more quantitative information. With a good DVM much more can be learned about the cause without additional test equipment.

.

I've never seen a 20% V drop from a copier, but it can be significant. It would be next week, but I might be able to get some data from the copier in the office and post what the current inrush is and for how long if anyone is interested.
 

Cow

Senior Member
Location
Eastern Oregon
Occupation
Electrician
All photocopiers/laser printers we have measured over the last 10 years contain fuser bulbs that keep hot (for instant copy mode) by cycling.Worst case scenario,we have seen them create 20-30% voltage sags on the line each time they cycle.:)

I've witnessed the same thing. We have a customer that turned a residence into an office. With a copy machine in the bedroom idling the lights would dim every once in a while when something would kick on briefly in the copy machine.
 
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