3 Phase and Computer Power Distribution Units

[Dave Brenchley]

Good Day Folks !
Need an opinion ..
I am a computer hardware educator with enough electrical experiance to keep me out of trouble, I've cracked a number of panels to tap mains for stage lighting and beleive I have a firm grasp of the basics ..

My reason for this query ... at times we engage other specialists for our education materials. One such item I am currently reviewing is on power and power distribution within a computer rack.
In this paticular course the writer states the most common 3 phase power in the US is Delta .. and International Wye

This has not been my experiance .. 90% of the panels I've opened are Wye 208/120 480/277 ..

where as this paticular computer manufacturer's PDU's listed for US are stated as 208 Delta.

Am I mistaken in assuming;
1. if the equipment will operate 208 single phase that a "delta" PDU can be attached to a wye main , and the neutral not used in the line cord (3P + G) ? Hence his comment about US usage is with regard to PDU's and not the mains
or
am I mistaken in my thought High Tension is primarily Delta and the majority of distro is Wye in the US?

Any input is appreciated .. would like some feedback from the real professionals before I go back at this author ..

THANKS !!!
Dave

 

[infinity]

I think that they mean that they're Delta/Wye. 480 volt Delta input 208Y/120 volt output. I know of no system that is 208 volts Delta.

 

[Dave Brenchley]

THANKS Rob .. 480^ input 208Y output utilizes a transformer (I believe) .. these PDU's just "break out" the lines to recepts.
Your unaware of a 208^ mains ? I've seen reference to a 230^ is this in use in the US?

I'm thinking (perhaps) incorrectly these PDU's are being tagged delta for 2 possible reasons.
1. The neutral is not used
2. The load appears delta

If one were to put a ratio of ^ panels they've encountered vs Y, regardless of voltage, what percetage of panels would be wye in the US.

Forgive me, I'm just a stickler for accuracy in our education, and a statement such as being made, if not accurate make us look foolish, and misinforms the students ..

 

[iwire]

If one were to put a ratio of ^ panels they've encountered vs Y, regardless of voltage, what percetage of panels would be wye in the US.

Very tough question and will be diffrerent depending on who you ask, what they do and where they live in the US.

If you ask a guy that works industrial jobs they will see a lot of delta sources.

On the other hand a guy like me that does large retail, offices etc all I see is wye.

Now I have worked with a lot of PDUs and often they are as Rob mentioned 480 delta input and 208Y/120 output.

Perhaps they have a 208 delta output for use in computer rooms that run the servers at 208 but that sure seems odd because at some point someone is going to add equipment that requires a 120 volt supply.

 

[Jraef]

...
In this paticular course the writer states the most common 3 phase power in the US is Delta .. and International Wye

Hogwash.

In my experience, the only time a utility supplies Delta power ONLY to an end user any more is when the vast majority of loads are motors, and any lighting / outlet power will be coming off of the user's internal transformer. For the most part, all utilities are now trying to standardize on Wye supplies. Not everyone uses it of course, but if you look at the service entrance it has a neutral landing from the utility even if nothing is connected to it.

I see this kind of statement a lot, most often when the author is not from here. The problem is, there ARE SOME Delta service drops in this country, so if you are an equipment mfr. you have to be careful about selecting components that are only rated for use in Wye systems (they are a little less expensive). This confounds foreign equipment mfrs, because they can't use the exact same design all over the world, they have to accommodate us. It leads to some foreign engineers mistakenly believing that Delta supplies are predominant.

208V here is ALWAYS 208Y120. There is a SMALL AMOUNT of 240/120V Delta "Red Leg" systems, where one set of the 240V Delta windings are center tapped for 120V to Neutral but that is the exception rather than the rule. Generally, those types of services are not going to be in places where there are server racks that need 3 phase power. it can happen, it just means you have to check.