# IS vs IEC Transformer Tolerances

**URL:** <https://forumautomation.com/t/is-vs-iec-transformer-tolerances/14456>\
**Category:** Electrical\
**Tags:** transformer\
**Created:** [September 30, 2026, 3:26am UTC](https://forumautomation.com/t/is-vs-iec-transformer-tolerances/14456 "2026-09-30T03:26:54Z")\
**Posts on this page:** 1\
**Page:** 1

<div class="post-metadata">

**Author:** ![Rabert](https://forumautomation.com/user_avatar/forumautomation.com/rabert/32/6784_2.png) [@Rabert](https://forumautomation.com/u/Rabert)\
**Post date:** [September 30, 2026, 3:26am UTC](https://forumautomation.com/t/is-vs-iec-transformer-tolerances/14456/1 "2026-09-30T03:26:55Z")

</div>

## IS vs IEC Transformer Tolerances

When evaluating a transformer, guaranteed values and specified tolerances are important during technical and commercial review.

 ![1](https://cdn.forumautomation.com/original/2X/f/f1b5e4c4dea59e9e71d662ede1a4683577f46da3.jpeg)

## Total Losses

**[IS 2026](https://forumelectrical.com/top-12-iec-standards-in-electrical-engineering/)** and IEC 60076 both allow a tolerance of plus 10 percent.

## Individual Loss Component

IS 2026 and IEC 60076 both allow plus 15 percent, subject to the applicable total loss limit.

## Impedance at Principal Tap

For impedance of 10 percent or higher, both standards specify plus or minus 7 point 5 percent.

For impedance below 10 percent, both standards specify plus or minus 10 percent.

## No Load Current

Both IS 2026 and IEC 60076 allow a plus 30 percent tolerance.

For many basic transformer tolerances, IS and IEC requirements are closely aligned.

However, purchasers can specify tighter contractual tolerances than the standard requirements.

When reviewing a transformer specification, check the guaranteed values, tolerances, test methods, and acceptance criteria.

The standard provides the technical framework, while the purchase specification defines the specific contractual requirements.