Question 1

Why does a transformer need a future growth margin when a generator calculator doesn't emphasize one?

Accepted Answer

Transformers are fixed infrastructure that's costly and disruptive to replace once installed, while generators are comparatively easier to supplement or upsize later, so building in growth headroom matters more for a long-lived, hard-to-replace asset like a transformer.

Question 2

What future growth margin should I use?

Accepted Answer

20% is a common planning default for moderate expected growth, buildings anticipating significant future expansion (more floors, added equipment, EV charging infrastructure) should use a higher margin, 30% or more, to avoid a premature capacity shortfall.

Question 3

How is transformer sizing different from generator sizing?

Accepted Answer

Both use the same diversity and power factor logic to convert connected load into kVA, but transformer sizing adds a future growth margin on top since transformers serve a building for decades, while a generator's sizing calculation typically doesn't need that same long-horizon buffer.

Question 4

Should I round up to the next standard transformer size?

Accepted Answer

Yes, transformers come in standard manufactured sizes (like 100, 160, 250, 315 kVA and so on), round your calculated requirement up to the nearest standard size available from your supplier rather than ordering a custom, non-standard rating.

Transformer Capacity Calculator

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