Vacuum interrupter pole assembly: the per-phase unit that does an arc chute's job in a medium-voltage vacuum circuit breaker
In a medium-voltage vacuum breaker there is no arc chute: each phase has a pole assembly — vacuum interrupter, insulated push-rod with contact-force spring, flexible connection and insulating support — set by stroke, wipe and a 1/8-inch erosion limit
A vacuum circuit breaker has no arc chute: it interrupts the current between two contacts inside a sealed vacuum interrupter, so what sits in each phase is a pole assembly: the interrupter, the insulated push-rod and spring that press its contacts together, the flexible connection that carries current to the moving contact, and the insulating support or epoxy body that holds it all. That assembly is what is bought, replaced and checked, and its behaviour is set by two short distances — the stroke that opens the contacts and the wipe that loads them.
Pole assemblies of medium-voltage vacuum circuit breakers, embedded (encapsulated) or assembled on insulating supports, including vacuum replacement breakers for air-magnetic switchgear: their parts, stroke, wipe, contact force, erosion limits and replacement as a unit. Arc chutes for air breakers are covered on the Arc chute page and replacement arc chutes for low-voltage air circuit breakers on their own page; the vacuum bottle itself — insulation levels, arc control and vacuum integrity — is covered on the Medium-voltage vacuum interrupter page; spring operating mechanisms are on the Spring operating mechanisms for circuit breakers page.
CNFX editorial research · Sources checked October 12, 2026 · 4 sources
From arc chute to pole: interrupter, push-rod with contact-force springs, flexible connection, insulating body
ABB's schematic of an embedded pole runs from the upper terminal through the vacuum interrupter and its stem to the lower terminal, with a flexible connection to the moving contact, an insulated push-rod carrying the contact-force springs, a fixing point and the connection to the drive. Embedding the interrupter is said to give high dielectric strength without further external measures and to protect it from moisture, dust and damage. [1] ABB's indoor and outdoor ranges span these ratings:
The older assembled form is described in GE's PowerVac ML-18 manual: molded interrupter supports, one per phase, carry the primary bars, interrupters, current transfer fingers and heat dissipation fins where used, and the mechanism moves the lower contact of each interrupter from open to a spring-loaded closed position. [2]
Eaton's DHP-VR shows the pole as the arc-chute replacement in practice: it is a direct roll-in replacement for DHP air-magnetic breakers, needing no change to the existing cells and keeping the cell switches, coding plates and interlocks. Its 5 kV poles use glass polyester primary insulation and the 7.5 and 15 kV designs cycloaliphatic epoxy; the 50DHP-VR250 at 4.16 kV nominal is listed at 1200 or 2000 A with 19 kV low-frequency and 60 kV impulse withstand. [3]
State whether the pole is embedded or assembled, the interrupter it carries, the breaker or switchgear it must fit (pole centres, terminal pattern, drive linkage), and whether it is a like-for-like spare or part of a vacuum retrofit.
02
Stroke, wipe and contact erosion: 0.54–0.60 in gap, 0.15–0.18 in wipe, replace at 1/8 in
Eaton defines the two: the mechanism gives the operating rod a fixed motion; the first part closes the contacts (stroke) and the rest further compresses the preloaded wipe spring (wipe). As contacts erode, stroke increases and wipe decreases. [3] GE describes wipe as the extra compression of a preloaded spring that applies force to the interrupter contacts and gives opening kick-off force. [2]
Ghorit's listing for its EP-12 embedded pole (12 kV, 630 or 1250 A, 25 or 31.5 kA) gives the metric picture: clearance between open contacts 9 ± 1 mm, rated contact pressure 3200 ± 200 N, contact limit erosion 3 mm, average opening speed 1.4 ± 0.2 m/s and closing speed 0.7 ± 0.2 m/s, contact bounce on closing under 3 ms and mechanical endurance of 10,000 operations. A footnote on the same listing says rated insulation values need external insulation such as SF6, oil or solid dielectric, so confirm whether the figures describe the pole or the bare interrupter. [4]
Editorial calculation: 1/8 in is 3.2 mm, close to Ghorit's 3 mm erosion limit; GE's 0.15–0.18 in wipe is 3.8–4.6 mm and its 0.54–0.60 in gap 13.7–15.2 mm, against 9 ± 1 mm for the 12 kV pole — gap and wipe are design values of each breaker, not interchangeable figures.
GE notes that its very low-gradient wipe springs let considerable loss of wipe be tolerated without affecting performance, which is why it allows wipe to fall to 0.075 in before adjustment. [2]
Check
GE PowerVac ML-18
Eaton DHP-VR
Contact gap (open)
0.54–0.60 in; more at the centre pole than the outer poles [2]
Ask the supplier for stroke, wipe, contact force and erosion limit for the exact pole and breaker, and how each is checked in service.
03
Replacing a pole: a complete factory-set assembly, then gap, wipe and vacuum checks
GE supplies ML-18 interrupters only as complete assemblies — the vacuum interrupter mounted in its support with the primary studs and disconnect fingers — and warns not to remove or reinsert the interrupter in the support because special factory tools are needed. After fitting, the contact gap is checked against 0.54–0.60 in, the erosion indicator arm is re-aligned (the only time it may be moved), and the vacuum interrupter integrity test is run. [2]
Eaton's DHP-VR takes the same view more strictly: there is no provision for adjusting wipe and stroke in service, and a pole unit with inadequate wipe is replaced. [3] ABB lists the factory checks on each embedded pole: dimensional conformity, voltage drop across the pole, a mechanical function test, contact spring force and visual inspection. [1]
Editorial note: for a spare pole, ask for the same factory records — voltage drop (or resistance) across the pole, contact spring force and a dimensional report — with the interrupter serial number, so the in-service wipe and erosion readings have a baseline.
04
What to send for a vacuum breaker pole assembly
Paste it into your enquiry below or into an email to a maker, then replace every bracket.
Breaker: [make, type, rated voltage, current, breaking current; or switchgear for a vacuum retrofit]
Pole: [embedded or assembled; insulation material; pole centres and terminals]
Interrupter: [type, contact gap, contact force, erosion limit]
Mechanics: [stroke, wipe, opening / closing speed, bounce]
Insulation: [lightning impulse and power-frequency withstand; altitude]
Records: [voltage drop across pole, spring force, dimensional report, serial numbers]
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Compiled and source-reviewed by the CNFX editorial team.
Each manufacturer above links to the page on that company's own website where the product is listed, with the date we checked it. How we source and review
· Page last updated 13 October 2026
Buyer questions
Does a vacuum circuit breaker have an arc chute?
No. The arc is interrupted inside the sealed vacuum interrupter; each phase has a pole assembly with interrupter, push-rod with contact-force springs, flexible connection and insulating body. [1][2]
What is contact wipe?
The extra compression of the preloaded wipe spring after the contacts touch; it loads the contacts and helps them open. Wipe falls as contacts erode. [3][2]
When must the interrupter or pole be replaced?
GE and Eaton both set 1/8 in of contact erosion as the limit; Eaton also replaces the pole unit if wipe is inadequate. [2][3]
Can the interrupter be swapped inside its support?
GE warns against it: ML-18 interrupters come as complete assemblies and need factory tools to remove or reinsert. [2]
Sources and what still needs a direct check
Sources checked 2026-10-12. Pole construction, ratings and factory checks come from ABB's embedded poles presentation; assembled-pole construction, wipe, gap, erosion and replacement from GE's PowerVac ML-18 instruction book GEK-86132G; stroke and wipe definitions, the air-magnetic replacement and no-field-adjustment rule from Eaton's DHP-VR instruction book I.B. 6513C80G; metric mechanical data from Ghorit's EP-12 listing.
