Electrical fault-finding,
made clearer.
A practical diagnostic and learning hub for electricians, apprentices and trade learners — fault logic, test steps, expected readings, circuit diagrams and the principles behind them. On the tools, even offline.
Can't name it? Use the guided finder — pick the gear and what it's doing.
185+ worked faults · isolate and prove dead first · learning aid, not a substitute for licensed judgement.
Contactor has voltage at the coil but won't pull in
You measure the rated control voltage (e.g. 24V) across the coil terminals, but the contactor refuses to energise — no clunk, no pull-in, contacts stay open.
Most likely first
- 1Open or burnt-out coil
- 2Measuring a 'phantom' or floating voltage
- 3Wrong coil voltage rating fitted
First test
Re-measure coil voltage right at the coil terminals while a colleague (or the logic) calls the contactor in.
Expect: Rated coil voltage present and roughly steady at the moment of call-in.
What this is
A trade-focused tool for diagnosing electrical faults and learning how the gear actually works — domestic, commercial and industrial.
Who it's for
Sparkies chasing a fault on site, apprentices building the method, and anyone learning how control gear behaves.
How it helps
Turns a vague symptom into ranked causes and an ordered set of tests — with the readings to expect — not part-swapping and hoping.
What it covers
Starters, control circuits, RCDs, contactors, VSDs, PLC basics, three-phase, testing and safe isolation.
The honest bit
A learning and support tool — it doesn't replace licensed judgement, the standards, manuals or your safe work procedures.
Everything in one place
Jump straight to the part of the site you need.
Fault Finder
Pick the gear and symptom, get ranked causes and a test plan.
OpenElectrical principles
How the gear works — devices and theory in plain English.
OpenDOL & motor starters
Direct-on-line, star-delta and soft-start, with diagrams.
OpenForward / reverse
Reversing control, phase swap and the interlock logic.
OpenStar-delta starting
Reduced-voltage starting, the timer changeover and delta links.
OpenVSD basics
How a drive makes variable speed, and its common faults.
OpenPLC basics
Inputs, outputs and the scan — control logic explained.
OpenRCD / RCBO guide
Safety switches, types, and why they trip.
OpenContactors & relays
Coils, auxiliaries and seal-in circuits.
OpenMotor faults
Won't start, hums, trips the overload, runs hot.
OpenTesting & safety
Safe isolation, E-stops, interlocks and protection.
OpenCalculators
Cable size, max demand and voltage drop. Coming soon.
How fault-finding works here
The same method you'd use on the tools, structured step by step.
01Pick the gear
Choose the equipment or circuit you're on — or just search the symptom.
02Match the symptom
Say what it's doing in plain terms; the finder narrows it down.
03Isolate & test safely
Work the ordered test steps with the readings you should expect.
04Check likely causes
Ranked most-likely-first, with what each result points to.
05Learn the principle
Understand the why behind the fault, so the next one's faster.
Browse by category
Jump straight to the kind of gear you're working on.
Contactors & relays
Coils, contacts, chatter, and switching faults.
Motors & overloads
Won't start, tripping overloads, and running faults.
Forward / reverse circuits
Direction control, interlocks, and reversing logic.
Limit switches & sensors
Proximity, photo-eyes, and position switching.
VSDs
Drive faults, start commands, and trip codes.
PLC inputs / outputs
Inputs not reading, outputs on but device dead.
Popular learning paths
Popular fault guides
Real symptoms, worked through the way you'd actually do it.
Contactor has voltage at the coil but won't pull in
You measure the rated control voltage (e.g. 24V) across the coil terminals, but the contactor refuses to energise — no clunk, no pull-in, contacts stay open.
Contactor chattering or buzzing instead of holding in
The contactor rapidly clicks/buzzes, pulls in and drops out repeatedly, or hums loudly without seating cleanly. Often comes with arcing noise and heat.
Contactor contacts welded closed — load won't switch off
The contactor won't drop out when the coil is de-energised. The load stays powered even with the control circuit off, because the main contacts have welded together.
Work safe — every time
Isolate and prove dead before you touch anything — and prove your tester on a known live source before and after. Use approved, in-date test equipment and rated PPE. Follow your site procedures, and verify everything against the current standards and the manufacturer's manual. Apprentices: live testing under direct supervision only.
This site is a learning and support tool — it can't see your installation and doesn't replace a licensed person's judgement. If you're past your competence or authorisation, stop and hand it on.
Important — read before using
Sparkie Sidekick provides general, practical troubleshooting guidance to support qualified decision-making. It is written in our own words and is not a substitute for formal training, electrical standards, regulations, or manufacturer documentation. Typical readings are illustrative only and vary with equipment, ratings, and conditions.
You are responsible for working safely and legally. Always follow your local electrical regulations and wiring rules, your site's safe work procedures, and lockout / tagout (isolation) requirements, and consult the manufacturer's documentation for the specific equipment. Treat circuits as live and prove dead before working.
Electrical work should only be carried out by a licensed or otherwise qualified and authorised person. Apprentices and trainees must only work on or test live circuits under proper supervision and with the required authorisation. This app is aimed at an Australian audience but is kept general; verify everything against the rules and standards that apply where you work.
Sparkie Sidekick is provided “as is”, without warranty of any kind. To the extent permitted by law, we accept no liability for any loss, injury, or damage arising from use of, or reliance on, this information. Use of this app is at your own risk.