Buyer's guide

How to choose a holiday detector

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This page is an unofficial buyer's guide. It is not affiliated with or endorsed by Amazon, AWS, API, or AMPP. It is not a review written for hire. Links below are placeholders. They are not live, and they are not product recommendations.

This page is for someone choosing an instrument that looks for holidays in a coating that is not conductive, on a substrate that is. A holiday is a path through the film: a pinhole, a skip, a crack, a place thin enough for the test to jump. The detector is not a thickness gauge and it is not a color judge.

There is no best detector on this page. There is a low-voltage wet sponge for the thinner films the maker allows, and a high-voltage spark tester for thicker films the maker allows you to spark. They are not interchangeable. The voltage, if you are in the high-voltage family, comes from the project specification or the coating maker. This page does not print a voltage table. Too high a voltage can burn a hole that was not there.

This page is not electrical training. High voltage, wet ground, and other people nearby are a safety problem. Read the maker's safety instructions before you buy a high-voltage unit for a crew, and again before anyone turns it on.

What you are trying to close

The probe is on the coating. The ground is on bare metal, on the same piece. An intact film that is not conductive holds the circuit open. A path through the film makes the instrument alarm. If the ground is on paint, or on rust, or on a piece that is not bonded to the one you are scanning, a quiet detector is not a good coating. It is an open circuit. When you shop, look at the ground clamp and the ground cable with the same attention you give the display. A bright screen with a cheap clamp is a bad instrument.

Two families

Low-voltage wet sponge. For thinner films. The maker of that model states a film-thickness limit. Stay inside it. A sponge tester will not inspect a thick lining, and turning the sensitivity knob will not change physics. The sponge has to be wet the way the maker says, sometimes with a wetting agent they name. A dry sponge is not a stricter test. It is no test.

High-voltage spark tester. For thicker films that are not conductive, and only when the coating maker and the specification allow spark testing. You want a unit where you can see the voltage you set, and where the manual tells you how they want that voltage chosen for a given film. A unit that locks you into a calculation you cannot explain is a poor fit for a report that has to say where the number came from. This page will not fill that blank in for you.

Electrodes are part of the purchase, not an accessory to forget. A flat brush, a spring for pipe, conductive rubber for some linings. Match the electrode to the shape you test. A flat brush on a small fitting misses the sides and calls them inspected. Buy the electrode for the geometry you actually have, including fittings, not only for the easy pipe.

Coatings that should not be sparked

Read the product data sheet before you choose a tester for that coating. Some films must not be spark tested. The maker will say so. A conductive lining can make a spark test meaningless or can be damaged by it. If the data sheet says not to spark it, a detector you already own is not a reason to spark it. Walk away and use the inspection the data sheet does allow.

A unit you can prove

Prefer a tester you can make alarm on purpose, on bare metal or on the check piece the maker provides, before you trust a silent scan. A detector you cannot prove is a detector you cannot defend. Mark holidays as they alarm. A mark with no repair is not an inspection. The repair method and the retest belong to the specification. The instrument only finds the path.

Speed of travel follows the maker. A faster unit is not a better unit if the electrode cannot cover the surface at that speed. Listen for an alarm you can hear in a noisy yard. A light with no sound, on a loud job, will be missed.

What to check before you pay

• Which family your films actually need, based on the maker's thickness limit for the tester and on the films you inspect. Do not guess across families.
• For high voltage: the voltage is visible, adjustable the way the manual describes, and you can say where the set point came from.
• Ground clamp, cable length, and whether the cable will reach the bare metal you really have, not the bare metal in a catalog photo.
• Electrodes for the shapes on your work.
• An alarm you can hear, and a way to confirm the unit alarms before the scan.
• Safety instructions you are willing to enforce with a crew. If you will not, do not buy the high-voltage unit.
• Case, spare electrode, and batteries or power, for the length of a real day.
• Any calibration certificate the project wants. Often a separate purchase. This page does not arrange one.

Mistakes that waste the purchase

Using a sponge on a lining that needs high voltage, or sparking a thin film the sponge was meant for, at a voltage that punches holes. A bad ground and a happy report. The wrong electrode for fittings. Sparking a coating the data sheet forbids. Writing "no holidays" with no voltage, no electrode, and no ground note.

What this page will not do

It will not print a voltage. It will not name a model as the one to own. It will not quote a price or claim that a given detector is sold on Amazon. Familiar maker names are examples of the category, not an endorsement.

Follow the project specification, the coating maker's data sheet, and the instrument maker's instructions, including the safety section.