outlet grounding in a commerial building

[Mark Patterson]

I would like to fine out what is the amount of volts from the neutral to the eq. grounding port in a reguler 110 comerial duplex out can be. I just some repairment from the zerox company tell me that it wshould never be over .5 volts or if it is it can take out the control boards on there copy and fax machines. Can you guy tell me if over .5 volts is too much and is there somekind o APC of something that I can control the grond voltage going to these untis..

 

[don_resqcapt19]

When you measure the voltage between the neutral and the grounding conductor, you are really measuring the voltage drop on the neutral conductor. If your design permits a 2% drop on a 120 volt circuit and if you assume that half of the drop is on the ungrounded conductor and the other half on the grounded conductor you would have 1.2 volts between the neutral and the grounding conductor.
Equipment that fails with a small difference in voltage between the neutral and the grounding conductor is poorly designed equipment.

 

[hurk27]

I have got a few calls like this, and I told the tech to tell the manufacture to stop referencing the EGC as a signal path, because there is no way I can maintain a .6% voltage drop without using superconductors, and they haven't quite developed these conductors yet for building wiring use just yet:roll:

 

[broadgage]

Although the NEC does not place a limit on voltage drop, 3% is often regarded as good practice or a design guide.
3% of 120 volts is of course 3.6 volts, which would be about 1.8 volts between the neutral and the EGC.
Twice this voltage might well be present briefly if the branch circuit serves loads with a high starting current.

As others post, if equipment can be damaged by more than 0.5 volts between neutral and EGC then it is poorly designed.