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#199217 - 02/16/11 09:50 PM Secondary Transformer Calculation  
Up2code  Offline
Member
Joined: May 2007
Posts: 55
Missouri
Hello All! Hope all of you have been hanging in there. Wife & I finally got internet back out here in the sticks! WooHoo! I have been asked to bid changing a Single Phase 400 Amp, 120/240V Single Phase Service over to a new Three Phase, 277/480V service, primarily for the customers new 460V pressure washers. An isolated single-phase transformer will be required for his new 120V plugs, lights, etc. Anyone know where I could find information/calculation on sizing the new KVA transformer that I will be needing? Thanks!


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#199222 - 02/16/11 10:59 PM Re: Secondary Transformer Calculation [Re: Up2code]  
Trumpy  Offline


Member
Joined: Jul 2002
Posts: 8,211
SI,New Zealand
What is this guy getting from the PoCo at the moment, mate?


Let's face it, these days if you're not young, you're old - Red Green grin

#199223 - 02/16/11 11:04 PM Re: Secondary Transformer Calculation [Re: Up2code]  
Up2code  Offline
Member
Joined: May 2007
Posts: 55
Missouri
120/240V Single Phase. But POCO is willing to bring 480/277V to his facility if needed.


#199225 - 02/16/11 11:40 PM Re: Secondary Transformer Calculation [Re: Up2code]  
HotLine1  Offline


Member
Joined: Apr 2002
Posts: 6,811
Brick, NJ USA
Our POCOs here require a load calculation of some detail ('ESI') for service installs/upgrades. That results in them providing a service.

Usual or common here for a comm/lite ind is 200 to 400 amp 277/480, 4 wire from a pole mounted set of pots.

Inside is a 277/480 mcb panel at either 200 or 400 amps. From there. dependent on the 120/208 volt loads, a 75 KVA xfr is set 100 amp primary, 200 amp secondary into a 42 circuit space panel.

Without any load info from you, we can only provide 'spec' info.

PS: The secondary (common here) is 120/208 volt, 3 phase, 4 wire...careful if you need 120/240 volt!



John

#199245 - 02/17/11 01:01 PM Re: Secondary Transformer Calculation [Re: Up2code]  
Up2code  Offline
Member
Joined: May 2007
Posts: 55
Missouri
I thought about going with 120/208V 3 phase secondary, which would serve his plugs, lights, compressor just fine. But there are currently 2-100 Amp 120/240V, single phase disconnects, which serve 2 permanent office trailers, which have to be powered back up. So single phase secondary is a must now. Yes, POCO is requesting a Load Sheet from me before they will hook up the new 480/277/400A service. Which the size of my secondary xfr is all I'm lacking. On top of that, customer has informed me he "might" add on in 4-5 years if business is good. Thanks for info all!


#199251 - 02/17/11 04:12 PM Re: Secondary Transformer Calculation [Re: Up2code]  
HotLine1  Offline


Member
Joined: Apr 2002
Posts: 6,811
Brick, NJ USA
Up:
"2-100 Amp 120/240V, single phase disconnects, which serve 2 permanent office trailers, which have to be powered back up. So single phase secondary is a must now."

IMHO, there should be no effect on the trailers, as long as there is no 240 volt specific equipment within them.

Most (not all) HVAC that I have come upon is happy with 208 to 240 volts.

Either way...75 KVA would be my way to go.



John


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