Calculating the Dielectric Strength

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Calculating test voltage

One of the most common questions our technical support department are asked is: “What test voltage should I use to test my coating?”

It depends on a whole host of different factors from the thickness of the material to less obvious considerations like the weather!   

It is clear that you must determine the correct test voltage needed for your particular application as this will decide which type of machine you need. You will find the formulae and an online tool for calculating the test voltage on this page. 

Don’t fall into the trap of thinking the formula below will solve all your problems in calculating the test voltage. You must also consider a number of other factors (see: You should also read this) before you have an accurate idea of the required test voltage.   

You should also read:  

  1. Calculating the Dielectric Strength
  2. DC holiday detectors expertise

The level of test voltage used depends on the type of fault you are trying to find and the electrical properties of the coating material. As a general rule the NACE standard SP-02-74 has been found to work well in most cases. This is shown below: 

Test Voltage formula using thousands of an inch: 

How to test voltage explained


Test Voltage formula using microns: 

How to test voltage explained

Test voltage formula using microns 

To help you work out the test voltage using the above formulae we can provide you with a sliding Test Voltage Calculator with our products. 

Online Test Voltage Calculator 

Instead or resorting to your calculator or our sliding test voltage calculator use our online utility now. 

  1. Choose the units you are working in 
  2. Enter the coating thickness 
  3. Press Calculate.   

The recommended test voltage as defined by NACE SP-02-74 is displayed. 

Test Voltage Calculator

The recommended Test Voltage as defined by NACE SP-02-74 is displayed.

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