# 33 kV VCB (Vacuum Circuit Breaker) Megger / Insulation Resistance Test

**URL:** <https://forumautomation.com/t/33-kv-vcb-vacuum-circuit-breaker-megger-insulation-resistance-test/14132>\
**Category:** Electrical\
**Tags:** test\
**Created:** [May 29, 2026, 6:08am UTC](https://forumautomation.com/t/33-kv-vcb-vacuum-circuit-breaker-megger-insulation-resistance-test/14132 "2026-05-29T06:08:04Z")\
**Posts on this page:** 1\
**Page:** 1

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**Author:** ![Rabert](https://forumautomation.com/user_avatar/forumautomation.com/rabert/32/6784_2.png) [@Rabert](https://forumautomation.com/u/Rabert)\
**Post date:** [May 29, 2026, 6:08am UTC](https://forumautomation.com/t/33-kv-vcb-vacuum-circuit-breaker-megger-insulation-resistance-test/14132/1 "2026-05-29T06:08:04Z")

</div>

## 33 kV VCB (Vacuum Circuit Breaker) Megger / Insulation Resistance Test

The **[Megger (IR) test](https://forumelectrical.com/high-voltage-hv-motor-megger-test-procedure/)** of a 33 kV VCB checks the insulation health of the vacuum interrupters, bushings and control circuits before commissioning or after maintenance.

 ![1](https://cdn.forumautomation.com/original/2X/0/0ea1ae7053b44ae7b772881af7df788c78d917e6.jpeg)

## Test Equipment

- 5 kV or 10 kV Megger (recommended for 33 kV)
- Proper earthing cable
- Test record sheet

## Safety Precautions

**[VCB (Vacuum Circuit Breaker)](https://forumelectrical.com/what-is-vacuum-circuit-breaker-vcb-explain-its-working-principle/)** must be OFF, racked-out AND isolated.

All control supplies removed.

Ensure proper grounding.

After each test, discharge the breaker.

## IR Test Points for 33 kV VCB

## 1). Phase to Phase (Contacts OPEN)

**Purpose**

Check insulation between phases.

**Connection**

- Megger Line (L) → R phase
- Megger Earth (E) → Y phase
- B phase left free

**Repeat**

R–B, Y–B

**Condition**

Contacts OPEN

**Test Voltage**

- 5 kV (minimum)
- 10 kV (preferred, if allowed by manufacturer)

## 2). Phase to Earth (Contacts OPEN)

**Purpose**

Check insulation of interrupter to ground.

**Connection**

- Megger Line (L) → One phase (R)
- Megger Earth (E) → VCB body / earth
- Repeat for Y & B

**Test Voltage**

5–10 kV

## 33 kV VCB Testing with Circuit Breaker Analyzer

(ON / OFF Condition Verification)

**Purpose of CBA Test**

- Confirm contact position (OPEN / CLOSED).
- Measure closing time, opening time.
- Check contact travel and synchronization.
- Verify mechanical & electrical health.