480 4 Wire, how common?

Status
Not open for further replies.
W

waltppiva

Member
Pardon my basic question but I've learned of some UPS units that require an input neutral on the 480 volt models. Initially I thought this was odd because all 480 volt systems I've ever seen are Delta 3 wire with no neutral. When trying to get more info on the 480 with neutral issue I was told that it is very common (90% of applications)that 480 volt systems are actually wye (grounded wye) but they just don't pull a neutral from the service panel. I was told many people think 480 3 wire is Delta when it is most commonly a Wye without a neutral pulled. Is this correct? Do most 480 volt systems have a neutral available and are actually Wye?

Thanks for your input.
Walt
 
That depends if the system is solidly grounded or high resistance grounded.
In a solidly grounded system, the neutral can be run with the ungrounded conductors to the panel. Phase to Neutral loads (277 V) can be served by this system.

In a high resistance grounded system, a resistor is connected from the Neutral point of the transformer to the Earth and to the bonding system. In this case, the system does not have a "Neutral" and so a Neutral wire may not be run with the circuit conductors to the panel. Only Phase to Phase loads may be served by this system.

So, many of the 480 Volts systems come from a Wye secondary. Those that are solidly grounded often have Neutrals. Those that are high resistance grounded do not.
 
Most 480V 3-phase sytems I've worked with are 480/277 Wye.

Wye.gif
 
Walt,
In the case that Bob mentioned, 277 Volts is being used for lighting. This tells you that the Transformer is solidly grounded.

I have had to specify 480V/480V transformers on a number of occasions because a facility needed 277 Volts and all that they had were 480 Volt high resistance grounded systems. So you connect the 480V Delta primary of the transformer to the existing 480V system. You solidly ground the Wye secondary of the same 480 Volt transformer and you have 277 Volts available for phase to neutral loads.
 
eric stromberg said:
I have had to specify 480V/480V transformers on a number of occasions because a facility needed 277 Volts and all that they had were 480 Volt high resistance grounded systems.
Click to expand...
I've never seen one of those, but my gut tells me that's a high-dollar transformer. Sounds like extra special order.
 
mdshunk said:
I've never seen one of those, but my gut tells me that's a high-dollar transformer. Sounds like extra special order.
Click to expand...

You raise a good question. These were industrial facilities and the cost wasn't really an issue. But now you've got me curious. I'll look into it.
 
Eric you spec's 480 to 480 for lighting wouldn't the transformer be 480 to 480/277?

I have installed several of these to boost voltage in areas with 465/268 and were suffering from end of the line voltage drop, they were receiving 441/255 at no peak and 432/249 during peak summer time usage. The UPS was 480 and voltage adjustments had been made out the wazoo (no generator). This site dumped several times due to depleted battery. We installed the 480 Delta to 480/277 Wye and adjusted the taps to supply 492/284 at no load (when voltage should be 465/268). Over-voltage above the 492/265 was not an issue as this site rarely if ever saw the expected 465/268.


The cost of the transformer was about 25% above a standard dry type delta/Wye 480-208/120.
 
Thanks

Thanks

Thanks everyone for your input. I think you answered my question. Most 480 services do have a neutral available to pull from, it must just be specified as such for the UPS installation.

Thanks again for your expertise!
Walt
 
Eric you spec's 480 to 480 for lighting wouldn't the transformer be 480 to 480/277?

That would have been clearer. It was inferred by the description that it was a delta primary and wye secondary.
 
Status
Not open for further replies.
Top