480 vs. 208-volt service

[hbendillo]

I had a construction manager for a client get all bent out of shape because I suggested a 208-volt service for a couple of buildings for a project on which I was working. We were only in the schematic design phase for the project but based on what I knew, we did not need a 480-volt service for the buildings. One building was a hospice (elderly care) facility of about 18,000 square feet and the other an admininstration building of about 22,000 square feet (two story). I still haven't been able to talk to the construction manager but apparently he thinks practically all commercial buildings require a 480-volt service. He also may have been involved in similar projects for which the engineers showed a 480-volt service.

In my opinion too many engineers fall in love with having 480-volt services designed for buildings on projects with which they are involved. A big reason is flexibility I think. They want to be ready for all possible loads and the voltages required. But they are having the owners pay a premium for the flexibility unnecessarily I think. What are your cut off points for 480-volt vs. 208-volt services?

 

[BJC]

Depending on where these are at ( Having a little electric heat may vary the load a little) your looking at 600 and 800 amp services. That's an easy 208/120 installation. The only loads that you might even consider to be 480 would be the elevators and air conditioning. Both of those are available in 208/120. You'll want to specify reduced voltage starting you'll never see a blip.
The lighting load for the office building is going to less than a 100 amps and you can't use 277 lighting in the residence bldg.
The 480 volt service will require step-down transformers to run receptacles, lighting, etc.
I usually start such projects with a reference from one of the Means books that show 8va/ SqFt for an office building and 9-10Va/ SqFt for a retirement home/ extended care facilliy. They are a good ball park figure and never wind up far from there.

 

[EEJaime]

While BJC is pretty much right on, there are sometimes added factors which might influence your decision. Are both buildings on one service? Is there to be a Central heating/cooling plant? Are future additions to the site anticipated? If there are large concentrated loads, then it sometimes makes sense to feed these at a higher utilization voltage, but that is to be decided on a case by case basis.

 

[dpc]

You also have to consider how far you will be running the 208V feeders. 480 V will look better if you have long distances to deal with.

 

[alehman]

And offset the length of the feeders with the higher cost of 480 equipment, transformers and transformer losses.

 

[stevenal]

Check the utility rate schedule as well. I've heard of folks converting to 480 for efficiency, only to find that pf penalties start kicking in at that voltage.

 

[cavype]

Remind your PM that most buildings in NYC have a 208 volt service. Based on the sizes you mentioned I think a 208 volt service would be appropriate unless they have large data center rooms and high computer usage.

The serving utility company may have criteria as to the service voltage requirements based on load.

 

[powerhusker]

Also consider fault currents. Any time you get up to 300 kva transformers and larger, the fault currents on 208 V systems get crazy high.

 

[JJHorak]

Is light flicker during an HVAC system start or elevator operation a bigger issue at 208V?

I think arc flash analysis is a simpler process at 120/208, whenever Ifault is below 10kA anyway.

 

[centurion7]

Comparative cost point between the two type of systems is around 50,000 square feet for buildings such as this. For the square footages your refering too, 208 is the way to go. The additional costs of transformers and perhaps additonal space required electrcially cannot be justified for a mear 20,000 square foot +/- facility. B th buildings will more than likely incorporate air conditioning but the elderly care facility will most likely have a lot of split systems. Is there a central chiller plant?. Max Connected load for buildings of this type will hover around 15va/sq. ft. aka 330 KVA max. Demand will settle in around 125-150 KVA but code doesn't allow us to diversify so you'll need to settle for 300 KVA +/-. And 15 VA/sq. ft. is pushing the high side. Bottom line, for buildings of this size, there is nothing gained by going 480V, but additional square footage to accomodate the transformers.

 

[advidana]

If your client has a lot of building all on 480 volts, He may have standardize his supply and construction methods for panels, motors, HVAC and light fixtures. But if you want to lose a client keep insising on the 208 volt systems.

 

[itsmoked]

advidana; Has some sage advice there..

Your should do your due diligence explaining why 208V might be preferred including the 'transformer garden' aspects then do as the customer/customer's agent wants.

Keith Cress
Flamin Systems, Inc.-

http://www.flaminsystems.com