In USA.

Source: 208v, 60 hz, 2-wire (2 phases from 3 phase "Y" supply). Load: 240v, 20A.

I presumed that sizing a buck-boost transformer is simple KVA math (source
volts * load amps). But...

This PDF document:

on the last page says: - - - "An example of an everyday application is always a good way to explain the intent of the ³Code.² Example: A 1 kVA transformer Catalog No. T111683 has a primary of 120 x 240V and a secondary of 12 x 24V. It is to be connected as an autotransformer at the time of installation to raise 208V to 230V single phase.

When this 1 kVA unit is connected as an autotransformer for this voltage combination, its kVA rating is increased to 9.58 kVA (may also be expressed as 9,580 VA). This is the rating to be used for determining the full load input amps and the sizing of the overcurrent protect device (fuse or breaker) on the input.

Full Load Input Amps 9,580 Volt Amps / 208 Volts = 46 Amps" - - - I'm puzzled by the 10x increase of KVA rating. When and how is this true?

What size B-B transformer do I need?

Thanks.

Source: 208v, 60 hz, 2-wire (2 phases from 3 phase "Y" supply). Load: 240v, 20A.

I presumed that sizing a buck-boost transformer is simple KVA math (source

This PDF document:

*<http://www.acmepowerdist.com/pdf/Page_104-109.pdf*on the last page says: - - - "An example of an everyday application is always a good way to explain the intent of the ³Code.² Example: A 1 kVA transformer Catalog No. T111683 has a primary of 120 x 240V and a secondary of 12 x 24V. It is to be connected as an autotransformer at the time of installation to raise 208V to 230V single phase.

When this 1 kVA unit is connected as an autotransformer for this voltage combination, its kVA rating is increased to 9.58 kVA (may also be expressed as 9,580 VA). This is the rating to be used for determining the full load input amps and the sizing of the overcurrent protect device (fuse or breaker) on the input.

Full Load Input Amps 9,580 Volt Amps / 208 Volts = 46 Amps" - - - I'm puzzled by the 10x increase of KVA rating. When and how is this true?

What size B-B transformer do I need?

Thanks.