nuetral to ground voltage
nuetral to ground voltage
(OP)
Not sure if this is the right forum but here goes. We have some new circuits ran of a 20 kva UPS system in our office. One of the circuits feeds 4 network data switches. they have burned up 3 data switches in the last 5 months ever since these circuits were put in. We noticed that there is 2.5 volts between the nuetral and ground on this circuit. any thoughts if this could be taking them out or what could cause this voltage to occurr. We measured in the panelboard where they originate and the voltage is zero. Some of the other circuits they ran that are close to the ups( within 50') are around 1.5 volts. theone that the 2.5 volts is on is about 200' away from UPS. Any thoughts. Someone said that this may be normal and harmonics could be playing a role. I don't want to spend a huge amount of time on this if this could be normal and it wouldn't affect the switches.





RE: nuetral to ground voltage
Check to see what is going on with your load and see where the neutral to earth rise is coming from, is it UPS derived or is your load causing it ? Maybe your load is already galvanically isolated from the supply and there is no earth reference and you are floating, If so I cant see where you are buring out your kit, maybe there is some pull through from your kit to other equipment that it fed from a seperate source, giving circulation currents and such.
Be careful about grounding your neutral after the UPS, some UPS units hate this....
rugged
RE: nuetral to ground voltage
Make sure this is measured properly with the oscilloscope if the scope is AC powered, to avoid yet more ground loop noise e.g. standard trick is to make a differential measurement using a two channel scope with inputs added and inverted.. Do NOT connect the scope probe ground leads to anything..
It's possible you may have peak voltage spikes higher than 2.5volts RMS. The waveform may give you a clue as to the source of the noise.
And as posted above, don't add any connections between neutral and ground in an attempt to fix the problem. There should be only one bond between neutral and ground and that's at the XO point.
We just fixed a problem at a customer account where there was an additional connection.. and neutral current was flowing on conduit all over the place and green wire grounds.. i.e. any available parallel path from improper ground/neutal connection back to the UPS.
RE: nuetral to ground voltage
If the voltage is zero between N and G at the source, its all that matters. N should be grounded only at one place that is at the source or the first disconncet after the transformer.
If there is a current (I) in the neutral, and you measure the voltage between N and G near the load end of a relatively long circuit you will and should see a voltage drop equal to I*R, where R is resistance of the neutral conductor. Draw a diagram and do your math, you should reach your own conclusion.
RE: nuetral to ground voltage
----------------------------------
One day my ship will come in.
But with my luck, I'll be at the airport!
RE: nuetral to ground voltage