neutral to ground voltage

Reply

  #1  
Old 06-28-12, 07:21 AM
Member
Thread Starter
Join Date: May 2010
Location: USA
Posts: 21
neutral to ground voltage

When my 1 KW microwave is running at full power, there's a 1.1 V difference between neutral and ground at the outlet it's plugged into.
I have some voltage-sensitive equipment - an increase of 1 V causes a noticeable difference.
Could this 1.1 V difference be eliminated?
thanks
Laura
 
Sponsored Links
  #2  
Old 06-28-12, 04:37 PM
chandler's Avatar
Banned. Rule And/Or Policy Violation
Join Date: Dec 2005
Location: USA
Posts: 39,968
How are you measuring this, Laura? Measure with an analog meter. What type kitchen equipment do you have that is sensitive to 121 volts or 119 volts? The difference in voltage could be attributed to the wiring, the way the grounding conductor and the neutral are attached in the breaker panel. Have you looked in the panel to make sure all the grounding and neutral screws are tight?
 
  #3  
Old 06-28-12, 05:13 PM
CasualJoe's Avatar
Member
Join Date: Jan 2010
Location: USA
Posts: 9,307
there's a 1.1 V difference between neutral and ground at the outlet it's plugged into
Are you reading across the neutral and ground? Or are you reading across the hot conductor and neutral and across the hot conductor and ground?
 
  #4  
Old 06-28-12, 07:26 PM
Member
Thread Starter
Join Date: May 2010
Location: USA
Posts: 21
I measured voltage between the neutral and the ground. It's a digital meter, but I'm sure it's not just random noise. When the microwave is off it shows 0 volts between neutral and ground. Yes, my electrician tightened screws in the breaker panel.
Could I measure resistance at the panel?
I measured the voltage at the end of 25' and 75' extension cords I have, and there was no voltage drop from the outlet they were plugged into.
I have a voltage-sensitive motor.
 
  #5  
Old 06-28-12, 07:34 PM
Tolyn Ironhand's Avatar
Group Moderator
Join Date: Nov 2007
Location: Twin Cities, MN
Posts: 12,099
The voltage you are reading could very likely be phantom voltage or just plain inductance.

I measured the voltage at the end of 25' and 75' extension cords I have, and there was no voltage drop from the outlet they were plugged into.
You measured no voltage drop because you did not have a load on it. The voltage drop formula is:
VD=2xLxRxI/1000
L= length of the run
R = resistance of the wire
I = Load current

Get a extension cord with multiple places to plug into. Connect your meter on one outlet and connect a good sized load (toaster, hairdryer) to the other. Turn it on and watch the voltage drop. Also, the voltage in your home will vary from day to day, and even time of day, depending on the load in your neighborhood.

If your motor is that sensitive, I suggest getting a voltage regulator. Just Google "voltage regulator"
 

Last edited by Tolyn Ironhand; 06-28-12 at 08:08 PM.
  #6  
Old 06-28-12, 08:30 PM
Member
Join Date: Jun 2012
Location: USA
Posts: 999
That voltage difference is normal as your microwave is a large load (66% of maximum on a standard 15A circuit). Is the motor on the same circuit or a different one? Depending on what you need you could get a high end UPS that handles brown-outs. In the commercial world they use buck-boost transformers for things like tanning beds that are sensitive. Otherwise you still could see a drop when your neighbor runs their air conditioner with electric oven and dryer. Utility voltage varies by time of day and season.

Plug your numbers in and this will tell you what percentage drop to expect. That is also what the neutral will read above ground (might be half that as I don't know if they factored in the return).
Voltage Drop Calculator - for single and 3 phase ac systems and dc systems
 
  #7  
Old 07-03-12, 11:48 AM
Member
Join Date: Mar 2010
Location: USA
Posts: 2,946
This one volt voltage difference won't affect the microwave oven.

Could you plug other equipment that is voltage sensitive into a different branch circuit?

Ground problems (ground loop problems) with electronic equipment can also be fixed by running a separate ground wire, exposed, among the varous pieces of equipment with connection to the internal grounding via a screw that penetrates to a metal chassis or a collar that fits snugly over one of the input/output jack shells. The far end of this wire may be connected to a known ground such as the screw holding the cover plate on a receptacle that is properly grounded.

The voltage difference described here shows the importance of connecting the ground wire system (equipment grounding conductors) to the neutrals only at the panel, where the fat ground wire (grounding electrode conductor) from a ground rod is also connected. When current flows properly on the neutral conductor, the voltage relative to ground out where the load is will float. We do not want the voltage at the far end of any ground wire to float relative to the ground potential at the panel, which floating would happen if ground and neutral were interconnected in many different places.
 
  #8  
Old 07-04-12, 07:00 AM
Member
Thread Starter
Join Date: May 2010
Location: USA
Posts: 21
I gather it's not something to worry about, but I wonder if something can be done about it so my motor can run more evenly.
Yes, I could get a voltage regulator, but it would have to output voltage accurate within about +/- 1% to be good enough. I found a voltage regulator that does that, but it cost $2700 and is probably overkill, does anyone know of something cheaper?
If I could get a voltage regulator that only needs to step down, to a voltage you specify, that would work pretty well. The input voltage to the motor, after being lowered by the rheostat, is about 104 V.
The utility co. voltage is pretty good, it's usually 120-124 volts.
Laura
 

Last edited by goldym; 07-04-12 at 07:17 AM.
Reply

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Thread Tools
Search this Thread
Display Modes
'