When do I use a 100 kVA transformer?

Use 100 kVA when your calculated load (with safety margin) is at or below that rating.

Should transformer sizing include future expansion?

A safety factor such as 1.25 is commonly applied to avoid immediate overload and allow growth.

Use this page as a quick reference for common transformer sizes, then calculate your specific load.

Transformer kVA is based on load current and voltage. For three-phase systems, sizing uses 1.732 x V x I / 1000. For single-phase, use V x I / 1000.

Add a safety margin for startup and future growth, then choose the next standard kVA size.

Can I use an exact match kVA transformer?

It is usually better to size to the next standard rating to avoid overload under real operating conditions.

Do I need to check primary current too?

Yes. Primary current affects breaker and feeder sizing on the supply side.