Start With the Breaker, Not the Instrument

Most breaker analyzer quotes get built backwards. Somebody picks a model, then finds out in the field that it will not cover the breaker in front of them, or that they paid for channels and diagnostics nobody uses.

The order that works is the other way around. Count what you have to test, decide which measurements you need in the same box, and let that pick the instrument.

This guide walks the four questions that decide the configuration. It is written for utility and NETA test crews working medium and high voltage breakers, and it assumes no prior familiarity with any one manufacturer’s model numbers.

Question 1: How many timing channels?

Timing channels are the single biggest driver of both capability and price, and the number you need is set by breaker construction, not by voltage class.

Count the interrupters (breaks) per phase, then multiply by three.

Pre-insertion resistors do not change the count. Where a breaker has PIRs, they are timed through the same channels and the same connections as the main contacts. No extra channels needed.

Buy for the largest breaker in the fleet, not the average one. The channel count is set at the factory and cannot be added later.

Question 2: Do you need contact resistance in the same instrument?

Contact resistance and timing are two different tests, and plenty of crews carry two boxes: an analyzer for timing and a separate micro-ohmmeter for resistance.

Putting the micro-ohmmeter inside the analyzer is worth it when:

• You are testing at height or in a cramped enclosure where a second instrument means a second trip up
• You want dynamic resistance measurement, which needs the current source and the timing system talking to each other
• You are doing Both Sides Grounded testing on dead tank breakers, which depends on the built-in current source

Plenty of crews build it in simply because one instrument is easier to manage than two, and that is a fair reason on its own. If you already own a micro-ohmmeter you are happy with and access is not a problem, carrying two instruments works too.

If you do build it in, the current rating is a real decision, not a spec-sheet number. Higher current gives better resolution on very low resistance joints and is what most utility acceptance specs are written around. Lower current covers routine medium voltage maintenance testing at a lower cost. Match it to the acceptance criteria you actually test against, and check whether your spec names a required test current before you choose.

Question 3: Do you need Both Sides Grounded testing?

Conventional timing and contact resistance measurement requires removing the safety ground from one side of the breaker. It is the least popular step in the procedure, it consumes outage time, and it puts the crew on an ungrounded conductor.

Both Sides Grounded (BSG) testing removes that step. The grounds stay connected for the whole test.

This is the question most likely to be answered wrong at quote time, because BSG is not one option. It depends on the breaker type, and the requirements differ:

Two practical consequences:

BSG is a factory-built option on the analyzer. It is not a cable set or an accessory you add later out of a catalog. If there is any chance a BSG requirement appears in the next few years, specify a platform that can carry it.

Not every analyzer platform supports every BSG type. GIS in particular requires a specific pairing. Confirm the platform before the requirement lands, not after.

We published a full breakdown of the GIS method, with the manufacturer’s application note: Both Sides Grounded method for GIS.

Question 4: Which diagnostics beyond timing?

Timing tells you whether the breaker operated within spec on the day you tested it. The diagnostics below tell you whether it is degrading, which is what condition-based maintenance programs are actually built on.

Coil current signature analysis. A coil current trace shows armature motion, latch release, and mechanism binding as distinct features. Changes in that signature appear well before timing drifts out of tolerance. Underused in US practice relative to its value, and it comes with the standard accessory set, so there is no extra decision to make here.

Motion and travel. Transducer inputs give contact wipe, over-travel, rebound, damping time, and average velocity. If your maintenance standard specifies travel curves, this is not optional.

Transducers are not one size. Rotary and linear transducers suit different breaker mechanisms, and mounting kits make the difference between a quick hookup and an improvised one. If you are replacing an older analyzer, ask whether the new one can use your existing transducers through adapters. Some manufacturers support this, and keeping transducers you already own can save a significant part of the cost.

Vibration fingerprint. Records the mechanical signature of an operation and compares it against a baseline. Non-invasive, and useful on breakers where opening the mechanism is the expensive part.

First Trip. Tests the breaker on its first operation after a long idle period, without a maintenance operation first. This is where sluggish mechanisms actually show up, because the first trip after months of sitting is the one that reveals the problem. Any breaker that sits closed for long periods is a candidate.

Coil diagnostics come as standard. Motion transducers and vibration sensors do not, so be honest about whether the crew will actually use them. Hardware that never gets connected is a line item, not a capability.

Working it through

Answer the four questions in order and the configuration falls out:

1.  Largest breaker in the fleet, breaks per phase, times three
2.  Contact resistance in the box or a separate instrument, and at what test current
3.  BSG required, and for which breaker types
4.  Which diagnostics the crew will genuinely use

We have put this on a one-page worksheet you can take into a planning meeting or attach to a requisition:

[FORM GOES HERE. Copy the form block from /pq-checklist. Button text: Download the Breaker Analyzer Selection Worksheet]

Do you need the SAT II as well?

The CAT250 handles timing, static and dynamic contact resistance (SRM and DRM), and coil control on six outputs, three open and three close. What it does not give you is an adjustable supply for the breaker’s coils and spring-charging motor. The DV Power SAT II series coil analyzer fills that gap.

Coupled together, the CAT250 and SAT II work as one test system, run from DV-Win software. The SAT II supplies the coils and the motor. That lets you test a breaker when the substation battery is not connected or available, and run undervoltage condition tests at voltages you set.

With both units hooked up, you can run the full sequence without changing connections: timing; contact resistance, static and dynamic; undervoltage condition test, also called minimum trip voltage; coil resistance; motor test, covering spring-charging time, current and voltage; and motion measurement with a transducer fitted.

One hookup, one test record, no reconnecting leads between tests.

CAT250 and SAT II wired to the breaker’s coils and spring-charging motor. Diagram courtesy of DV Power.

SAT40A II at a glance: motor output up to 40 A AC/DC, 10 V to 300 V DC or 10 V to 250 V AC. Four coil outputs, 15 A max each, DC and AC. Output ripple below 0.5%. Weight 11 kg (24.3 lb).

When the SAT II earns its place: you test breakers during outages when station DC is isolated; your test plan calls for minimum trip voltage checks; you want motor current and charging time on the same record as timing and contact resistance.

When you can skip it: the CAT250 offers minimum trip voltage as a built-in option. If station battery is always available to you and minimum trip voltage is the only extra test you need, that option may cover it.

Not sure which setup fits your test program? Send us your breaker list and we will quote the CAT250 both ways, with and without the SAT II.

Frequently asked questions

How many timing channels does a circuit breaker analyzer need?

Count the interrupters, or breaks, per phase on the largest breaker in the fleet and multiply by three. One break per phase needs 3 channels, two breaks need 6, four breaks need 12. Channel count is set at the factory and cannot be added later.

Do pre-insertion resistors need extra timing channels?

No. Where a breaker has pre-insertion resistors, they are timed through the same channels and the same connections as the main contacts. They do not change the channel count you need.

What is Both Sides Grounded testing?

Both Sides Grounded testing measures breaker timing and contact resistance with the safety grounds on both sides left connected, instead of removing one to take the measurement. It shortens preparation, shortens the outage window and keeps the crew behind a ground for the whole test.

Do I need a micro-ohmmeter built into the analyzer?

Not always. Building it in is worth it when you test at height or in cramped enclosures, when you need dynamic resistance measurement, or when you plan Both Sides Grounded testing on dead tank breakers, which depends on the built-in current source. Many crews also build it in simply to carry one instrument instead of two.

Where ProgUSA fits

We have supplied electrical test equipment to utilities, NETA firms, and industrial users since 2005, with demonstrations, training, and U.S.-based calibration.

On breaker test specifically, we carry the DV Power CAT range, which spans handheld timers through the CAT250 and CAT500 platforms, and we will tell you when a smaller configuration covers what you need. If you want to work through a fleet and a spec with somebody who has done it before, that is a phone call, not a sales process.

DV Power also makes adapters for Doble and Vanguard transducers, so crews switching platforms can keep the transducers they already own. Linear and rotary transducers and optional mounting kits are available for different breaker designs.

Contact: 407 332 8678 | info@progusa.net

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