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#199217 - 02/16/11 05:50 PM Secondary Transformer Calculation
Up2code Offline
Member

Registered: 05/15/07
Posts: 55
Loc: 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 06:59 PM Re: Secondary Transformer Calculation [Re: Up2code]
Trumpy Offline

Member

Registered: 07/05/02
Posts: 8540
Loc: SI,New Zealand
What is this guy getting from the PoCo at the moment, mate?
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Let's face it, these days if you're not young, you're old - Red Green grin

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#199223 - 02/16/11 07:04 PM Re: Secondary Transformer Calculation [Re: Up2code]
Up2code Offline
Member

Registered: 05/15/07
Posts: 55
Loc: Missouri
120/240V Single Phase. But POCO is willing to bring 480/277V to his facility if needed.

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#199225 - 02/16/11 07:40 PM Re: Secondary Transformer Calculation [Re: Up2code]
HotLine1 Offline

Member

Registered: 04/03/02
Posts: 6805
Loc: 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!
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#199245 - 02/17/11 09:01 AM Re: Secondary Transformer Calculation [Re: Up2code]
Up2code Offline
Member

Registered: 05/15/07
Posts: 55
Loc: 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!

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

Member

Registered: 04/03/02
Posts: 6805
Loc: 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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