help on strange voltages

[Riograndeelectric]

I received this email today form one of my customers ( Doctors office)facility was built in 2007. wired with MC cable. I have done a couple of service call here in the past to add a couple of Receptacle.

I am not sure but I believe all circuit are MWBC.any input in this would be help helpfull. I have to go out tomorrow and look at this problem


Thanks.
Cameron

Here is the power report that we ran on Friday. We recorded 4000 events in about an hour ( this is the max our monitor will record.) We do expect to see some activity when we run a power monitor like this, however this is really excessive. There are Neutral to Ground swells up to 7 volts, and voltage sags down to 105 volts. This many events in such a short amount of time can play havoc on the machines logic, and can damage several key components in the machine itself. From the looks of this I think that you might have a loose or poor ground on this circuit.
Please let me know when your electrician is done so that I can have my tech return and check the machine over for any other issues that might have been caused by this. Thanks,

 

[LarryFine]

There are Neutral to Ground swells up to 7 volts, and voltage sags down to 105 volts.

That sounds like good ol' voltage drop to me, with both conductors dropping about the same amount.

 

[George Stolz]

With that in mind, can you give us some more backstory? What's the machine, how many amps, length of run, etc.

 

[charlietuna]

This monitor was installed at the equipment which means the problem could be anywhere, not just in this circuit. It could be another part of this circuit, or any common neutral on this circuit, on the feeder or even off the property in the service.
Nothing was said about the monitor - type or manufacturer? The reading of 105 volts is not excessive and well within most power company specs. A system with a lot of computers can easily have 5 to 7 volts between the ground and the neutral due to harmonics?? This is a typical manufacturer's rep blaming his equipment problems on the power source. What you need to do i install YOUR power monitor at the panel serving this circuit and then you'll begin to be able to put your finger on the problem--if there is one.

 

[Riograndeelectric]

With that in mind, can you give us some more backstory? What's the machine, how many amps, length of run, etc.

I have not been to the site to check out this problem. I have no idea the length of wire, amps for the machine. I ma heading out there this morning to check thing out.

get back to you later on what I find

 

[Riograndeelectric]

went out site today to see what problem was. seems like there Xerox net work laser copier, scanner, fax printer is creating havoc on the electrical circuit it is plugged into.

findings. are dedicated 20amp circuit the copier is on a MWBC and shares a neutral with 1 other circuit. wire length from panel to receptacle is 100 ft. building power source is 120/208 # pahse 400A amp service.
no flouresent light connected to either of the circuits.

I had my fluke 87 hooked into the Receptacle and ran the copier numerous times.

lowest voltage was 114V and highest was 123V. checking from H-N & H-G.

then went to panel and metered voltage at circuit breaker. finding was 120 V lowest and 127V highest.. amp ed out neutral conductors at panel with Copier running max was 21A highest 1.3 A lowest and avg 4.93 A
I un plugged copier and plugged in my Hilti Te55 Rotary hammer drill and metered voltage at Receptacle. 114.V lowest and 121V highest with Hilti running.


seems like the laser copier is sending out Harmonics on the line?
I am wondering if a power conditioner at the copier might help. I think the electrical problems lays within the copier.

 

[kwired]

Laser printers/copiers have heaters that melt the toner as it is applied to the paper, they cycle on and off sometimes quite frequently to maintain proper temperature to be able to operate when needed.

Put it on an individual circuit (not a MWBC) and then it will not cause voltage drop problems with other equipment on the same circuit or MWBC.

You did not mention what size conductor is this circuit or the max load. 100 feet is long enough that you may need to look at larger conductor for voltage drop issues.

If there is voltage drop the power conditioner will not fix that, it will still have the same load on the same undersized conductor ahead of the power conditioner, if the conditioner does fix voltage for the output it will cause even more drop on the input to get the job done.

 

[ptonsparky]

We had a customer with a particularly bad case of vd caused by the laser copier. No, can't blame it on the copier, the feeders to the panel were to dang small. Changed them and copier no longer was a problem.

 

[Riograndeelectric]

Laser printers/copiers have heaters that melt the toner as it is applied to the paper, they cycle on and off sometimes quite frequently to maintain proper temperature to be able to operate when needed.

Put it on an individual circuit (not a MWBC) and then it will not cause voltage drop problems with other equipment on the same circuit or MWBC.

You did not mention what size conductor is this circuit or the max load. 100 feet is long enough that you may need to look at larger conductor for voltage drop issues. conductors are #12 thhn in conduit form panel approx 70 ft then changes to 12-2 MC Cable on the last 30 ft

If there is voltage drop the power conditioner will not fix that, it will still have the same load on the same undersized conductor ahead of the power conditioner, if the conditioner does fix voltage for the output it will cause even more drop on the input to get the job done.

still not understanding why the amp reading on the neutral were so high even though the 2nd shared circuit was off.

 

[Riograndeelectric]

forgot to mention copier name plate rating is 16A

 

[George Stolz]

with Copier running max was 21A

forgot to mention copier name plate rating is 16A

I'd be on the phone with the tech support in a heartbeat to see why there is a 5A variance between nameplate and field readings, and to see what their minimum voltage allowance is. I'd swap the 12's with 10's in the EMT portion to ease the voltage drop as well.

 

[Riograndeelectric]

I'd be on the phone with the tech support in a heartbeat to see why there is a 5A variance between nameplate and field readings, and to see what their minimum voltage allowance is. I'd swap the 12's with 10's in the EMT portion to ease the voltage drop as well.

the 21A was a very short time I had my meter set on 100MS recording. the 21 amps was the highest recored and and 1.70 the lowest with the copier idling.
I plan on recommending the customer replace the #12 with #10 with dedicated #10 Neutra l& ground

any idea what was causing such high amp reading on the Neutral conductor. I recored amps at the highest peak and this was with the other shared circuit breaker turned off

 

[ptonsparky]

I'd be on the phone with the tech support in a heartbeat to see why there is a 5A variance between nameplate and field readings, and to see what their minimum voltage allowance is. I'd swap the 12's with 10's in the EMT portion to ease the voltage drop as well.

Had your meter calibrated lately? Doesn't matter if it is new. Only my 43B has been calibrated, certified or whatever. The others are just close enoughs.

 

[Smart $]

... any idea what was causing such high amp reading on the Neutral conductor. I recored amps at the highest peak and this was with the other shared circuit breaker turned off

With the other shared-neutral circuit turned off, your neutral current should be identical to the current on the in-use line conductor (same as if totally dedicated). You need two meters (or dual input, such as an o'scope) to monitor both line and neutral simultaneously.

These machines have motors too. The 21A could be motor(s) startup plus other non-motor current.

 

[kwired]

..
any idea what was causing such high amp reading on the Neutral conductor. I recored amps at the highest peak and this was with the other shared circuit breaker turned off

Either the hot conductor was carrying the same current (you never mentioned measuring that conductor) or you have another circuit tied to that neutral conductor someplace.

 

[growler]

any idea what was causing such high amp reading on the Neutral,this was with the other shared circuit breaker turned off

On a MWBC the neutral will normally carry the unbalanced load ( the difference between A and B. If you shut off circuit breaker B then the load ( neutral) will be whatever is current is on A.