building standards call for 480/277

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wyreman

wyreman

Senior Member
Location
SF CA USA
Occupation
electrical contractor
We have a big building project here and I was on the Building Standards subcommittee. We required 480v distribution for lighting panels and hvac. For some reason, this large project, with many engineers, has this brand new $42M building [if I understand my supervisor correctly] running only 208v. I don't know the size of the main. 1600A is typical here. There is a big argument [aside from being over budget, etc. etc.] that there was no need to enforce the 480v guideline, now that it is done, because there is no "great efficiencies" to be gained by running the equipment on 120/208v instead of 277/480v. It is agreed that there are one time cost savings in being able to use smaller feeder wire to build it in, but the Electrical Engineers say with authority [from what I hear] there are no important cost savings in the operation.

So they are the authorities and they are probably right.
Just seems counterintuitive to me. :cool:
I guess when they size the wire right there are no ongoing benefits...
I mean we have plenty of buildings that are run at 110/208 but I thought there was some other reason that 277 was mo' better during operation besides the installation cost.
 
I know that it gets crazy expensive to buy HVAC equipment over 50 tons that is setup for 208. Extra special order. They make all that big stuff for 480 only, and if you want 208, you can wait up to a year on it. I've got a customer still waiting from FEB on a 200 ton McQuay chiller setup for 208.
 
They are just finishing up drilling the geothermal field which is why I had to disable the 4160v in my earlier question
:wink: required Short Circuit Current Rating of main disconnect
that got no replies...
 
A thorough economic analysis would need to be performed. With the limited information it is not possible to determine the best option. Things that would certainly need to be considered is KVA or MVA expected load and what impact that has on size of service(s). As KVA goes up so does short circuit current, therefore ratings may be an issue as well. But on the other side, at 480V you will need a bunch of small step-down transformers to go from 480-208Y/120V, and additional 480V distribution and separate 208Y/120V panels. This may be offset by the the smaller conductors to distribute the 480V with less losses. But again, all those small transformers add additional losses. As Marc stated, mechanical equipment is often the driving factor. All things equal, the Owner will want cheapest first cost (engineers worst enemy) with a quick return on investment. Longterm maintenance is usually not a factor, because in many cases the original Owner/Developer will sell after he gets his money and profit back. Maintenance becomes someone else's headache.

Politically, if it isn't wrong (technically or safety) to do it one way or the other, then suck it up and just do what the Owner wants, then he's happy, you get paid, and maybe he calls you next time.
 
"...in many cases the original Owner/Developer will sell after he gets his money and profit back. Maintenance becomes someone else's headache... ...just do what the Owner wants, then he's happy..."​

I mostly maintain little electrical systems for the government. ;) I am kind of looking out for us owners...
 
[/QUOTE] I mostly maintain little electrical systems for the government. ;) I am kind of looking out for us owners...[/QUOTE]

Wouldn't that be an oxymoron?

If you make your living maintaining them for the government, then you probably want the cheapest most maintenance intensive install possible, that way you have more work.:grin: :grin:
 
For comparison -
Assume 1000 kVA Transformer (?? why not )
1. A 1000 kVA, 208 Volt transformer is MUCH bigger than a 480 Volt.
2. FLA @ 208 = 2776 Amps. FLA @ 480 = 1203 Amps. 3000 Amp 208 V switchgear is MUCH more expensive than 1600 Amp 480V.
3. Short Circuit Current (assume 6%Z) 20050 Amps @480, 46267 Amps @ 208.
3a. Due to (3), you'll spend more on higher-rated branch circuit panelboards than you ever will on dry-type transformers.

We have a 208 volt, 1000kVA building - nothing but trouble & heartaches.

db
 
In the building Owner's best interest you may want to pay close attention to volage drop. 208V just doesn't carry any kind of significant load very far without voltage drop problems. The conductors may get even larger.

The only efficiency difference I can see would be no transformer losses for the receptacle loads if they had the whole building at 208Y/120V. It just seems like a waste of money for a large building not to operate at 480V. The added ampacity needed for 208V quickly raises the costs of materials for panels, circuit breakers, disconnects, conductors.
 
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