# Electrician asked why a neutral required on a 480/480 UPS?



## just the cowboy (Sep 4, 2013)

Welcome

Good information. Most VFD's don't like anything but a solidly grounded system, or they blow MOVs unless they are disconnected because they reference to ground.
How about on UPS's
1. Ungrounded systems
2. Corner grounded systems.

Cowboy


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## JCAUPS1 (May 19, 2020)

*Senior Field Engineer C10 RME*

Hello, On UPS systems--Depending on what type IE Transformerless-Modular -Input transformer-Ungrounded? Have not encountered that situation fortunately - A modern UPS (Transformerless) The AC Capacitors are referenced to ground (UPS Chassis) on each input phase-The DC buss is also referenced to UPS Chassis ground. UPS systems I have worked on do not utilize a corner Delta ground (Corner Ground) & would cause a phase shift to the output of the UPS inverter.

Good question man.

Take Care


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## VELOCI3 (Aug 15, 2019)

View attachment UPS SNAPSHOT.pdf


Nice little job from a couple years ago. Neutrals and all. 

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## JCAUPS1 (May 19, 2020)

Nice


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## brian john (Mar 11, 2007)

JCAUPS1 said:


> 480/480 UPS systems require a Neutral? Yes when utility power is not present the UPS inverter phaser uses the neutral as a reference.
> 
> Without the Neutral -- as a reference when constructing
> its output phasor in the absence of a bypass source.
> ...


The UPS Nameplate states what is required installing a 4-wire feed to a UPS with no termination point for a neutral is a waste of copper.


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## JCAUPS1 (May 19, 2020)

The Neutral is connected on the Output Load side of a 480/480 UPS not the Input feed--Also depends if there is a input transformer versus transformerless UPS, Yes that would be a waste of copper running a input neutral with no termination point.


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## VELOCI3 (Aug 15, 2019)

Just finished today wiring up this 208V Vertiv UPS. No room in the MBC to shape and hi press everything. Rectifier has 600 amp input and bypass is 500 amp. 


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## VELOCI3 (Aug 15, 2019)

UPS end of a smart row


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## brian john (Mar 11, 2007)

JCAUPS1 said:


> The Neutral is connected on the Output Load side of a 480/480 UPS not the Input feed--Also depends if there is a input transformer versus transformerless UPS, Yes that would be a waste of copper running a input neutral with no termination point.


Then the UPS is NOT 480-480 it is 480-480/277


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## VELOCI3 (Aug 15, 2019)

Look at the single line I added above. The UPS is 480 3W in and 480 3W out. No neutral in the UPS. 


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## JCAUPS1 (May 19, 2020)

Sorry it's 480/480--Just repaired for AMR Modesto--in this case it was a eaton 9390 & the UPS was installed without the Output Neutral soon as the input breaker opened & the UPS went to battery "Boom" ! blew the control power supplies up (1 power supply for each mode of operation) Bypass,Online & Battery mode.


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## JCAUPS1 (May 19, 2020)

The code in your state requires flex into a UPS? In California it's just for Transformers.


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## VELOCI3 (Aug 15, 2019)

JCAUPS1 said:


> The code in your state requires flex into a UPS? In California it's just for Transformers.



Flex is factory mine is THHN (uppermost wires)


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## brian john (Mar 11, 2007)

JCAUPS1 said:


> Sorry it's 480/480--Just repaired for AMR Modesto--in this case it was a eaton 9390 & the UPS was installed without the Output Neutral soon as the input breaker opened & the UPS went to battery "Boom" ! blew the control power supplies up (1 power supply for each mode of operation) Bypass,Online & Battery mode.


If it is 480-480/277, the Output Transformer is what derives the neutral you ground the neutral. BUT the neutral is not run to the output transformer from the source that would be an NEC violation as you would be grounding the neutral downstream from the main neutral ground bond.

If the Bypass is 4-wire with a neutral then you do not ground the output neutral as it is grounded from the source neutral but as I stated this is a 480-480/277 UPS.



> Without the Neutral -- as a reference when constructing
> its output phasor in the absence of a bypass source.
> *If the neutral is floating, the centerpoint of the phasor can “drift,*” which can damage the UPS or


Right here you state THE NEUTRAL IS FLOATING when means there is a neutral on the output, hence 480/277. If there is no neutral ground bond the phase voltages vary (float) in reference to ground depending on the load on each phase.


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## JCAUPS1 (May 19, 2020)

Ok-This is a Eaton 9390-The Neutral lug E12 on the output-We have some sharp cookies in this forum--The Neutral/Ground is bonded at the output side-A neutral bond is made. The OEM installed a NRK-Neutral Reference Kit-Which appears to be a small 3 phase transformer connected between the Neutral lug & ground & 3 control wires connected to the rectifier input section. So when input VAC disappears The inverter phaser has the neutral reference from the rectifier.Sorry for the confusion.


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## JCAUPS1 (May 19, 2020)

This is a transformerless UPS-No output transformer.


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## JCAUPS1 (May 19, 2020)

A direct Neutral to ground bond was considered but there was 6 amps on the building ground grid which tripped the Main breaker to the building with a ground fault--So Eaton has resolved this issue with the newer 9395 UPS.


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## cuba_pete (Dec 8, 2011)

JCAUPS1 said:


> A direct Neutral to ground bond was considered but there was 6 amps on the building ground grid which tripped the Main breaker to the building with a ground fault--So Eaton has resolved this issue with the newer 9395 UPS.


Our APC Symmetra has a similar design. We don't have the ground currents, but planning ahead prevents problems down the road just in case.


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## brian john (Mar 11, 2007)

JCAUPS1 said:


> A direct Neutral to ground bond was considered but there was 6 amps on the building ground grid which tripped the Main breaker to the building with a ground fault--So Eaton has resolved this issue with the newer 9395 UPS.


Ground currents on the building ground will not pass through the UPS, some ground current would travel through the neutral ground bond at the UPS. That there are 6 amps is nothing in the whole scheme of things. If 6 amps is tripping the ground fault you have ground fault issues bad relay or grounds on your neutral downstream of the neutral ground bond. Not sure where you are at but I could fix both issues.

Why GFPE switches/CBs trip.

1. Human intervention, a worker accidentally or intentionally grounds a branch circuit conductor.
2. Defective Ground Fault Relay or CT.
3. Grounds downstream of the Neutral to Ground Bond
4. A Ground Fault.

For a main the lowest setting is (IN MY EXPERIENCE) no lower than 60 amps, but the average is 100 amps or higher.


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## JCAUPS1 (May 19, 2020)

Yes the trip unit's settings were set fully counter clock wise-Set fully clock wise--Old Eaton Magnum series--Yes I understand ground currents do not pass through the UPS--The neutral was tried bonded to ground is when the Main Tripped-This is a transformerless UPS--It is a older building--This UPS replaced a APC Silcon--The load harmonics are filtered Through LC circuits that filter the 7th 14TH harmonics--The load is high in harmonics due to the ton of single phase power supplies (Servers) Thanks Brian for your excellent input!


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## brian john (Mar 11, 2007)

JCAUPS1 said:


> Yes the trip unit's settings were set fully counter clock wise-Set fully clock wise--Old Eaton Magnum series--Yes I understand ground currents do not pass through the UPS--The neutral was tried bonded to ground is when the Main Tripped-This is a transformerless UPS--It is a older building--This UPS replaced a APC Silcon--The load harmonics are filtered Through LC circuits that filter the 7th 14TH harmonics--The load is high in harmonics due to the ton of single phase power supplies (Servers) Thanks Brian for your excellent input!


Single-phase 480 or single phase 277?

If this is a data center they use 480/277 for loads or for distribution to PDUs or Wye delta transformers?

Single-phase loads typically do not result in 7th and 14th harmonics. TYPICALLY Single-phase loads result in triplen harmonics in the odd order 3rd, 9th, 15th, 21st...........

Or are the 480 VAC loads to drives, rectifiers? which usually have high 5th - 7th, 11th - 13th .........

Just trying to figure out what is going on.


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## JCAUPS1 (May 19, 2020)

PDUs --Yeah don't quote me on the harmonic's =The UPS LC circuits consist of 3 -Inductor/Capacitor sets with different size inductors- I think it's for the server harmonics the UPS is designed for the 5th/7th & 14th--Then you have the customer plug in a couple of HVAC's so that messes with the UPS fighting to sustain 60Hz with thier motorized loads going on & off & PF shifting--Also the loads are about 200 Ft away from the UPS. The site uses Emergency Lighting systems as well which are 277 input with Ferroresonant transformers designed for fluorescent lights but the site is using LED's so that changed the power Factor from capacitive to inductive--Their fed off Utility now-They were on UPS but soon as they switched to digital ballast the UPS kept tripping to bypass...


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## brian john (Mar 11, 2007)

This site sounds like a mess designed or put together by people that have no clue about how to work in/with data centers.


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## JCAUPS1 (May 19, 2020)

Yes Sir- Buildings are designed for 20 Year Infrastructure--The Old UPS used a 480 transformer--Then they retro-fitted a transformerless UPS they bought used & was not installed by the OEM. Power distribution is from 1985. Computers are much faster now & draw less current & this facility was built before Type K transformers were made. It is what it is. I appreciate talking to you Brian


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## JCAUPS1 (May 19, 2020)

My first name is John....So cool name man!


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