hot and neutral reversed when inverting

[Michaelg_apc]

This was originally posted on APC forums on 5/26/2009

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I have a ES 350 that never did work very well. I just discovered that when it is inverting the hot and neutral lines are reversed. Is there a fix for this?

[Michaelg_apc]

This was originally posted on APC forums on 5/26/2009

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I will have to assume that my unit is not working. On battery I read about 30-40 VAC from either hot or neutral to ground. With about 85 VAC between them.

[BillP]

This reply was originally posted by Angela on APC forums on 5/26/2009

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how do you know this is happening? is this while the UPS is online or on battery?

when this UPS is on battery, you will see around the following voltages, which is normal:

H-G: ~115v
H-N: ~50-60v
N-G: ~50-60v

This is due to a [floating neutral|http://emea-en.apc.com/cgi-bin/emea_en.cfg/php/enduser/std_adp.php?p_faqid=2946] since the UPS isolates itself from the wall outlet.

While online, you should see more normal voltages such as:

H-G: ~120v (or whatever your wall outlet voltage is)
H-N: ~120v (or whatever your wall outlet voltage is)
N-G: 0v

just want to make sure the voltage you are seeing is due to the notes above but if not, let me know.

[BillP · Accepted solution]

This reply was originally posted by Angela on APC forums on 5/26/2009

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are you using a true RMS meter? what is the voltmeter model?

a non true RMS meter will read anywhere from 80-90v on battery because the UPS outputs a step approximated sinewave. with a non true RMS voltmeter, it will have problems taking samples from the step in the sinewave and give you an inaccurate reading.