Do I have to change the Test Voltage when I change the material type?
No, if you are only doing a standard test using the NACE calculated test voltage. Yes, if the Dielectric Strengths are different and you are trying to find Air Bubbles, Thin Areas etc.
Do I have to change the Test Voltage when the substrate is concrete as opposed to steel?
No, the concrete only connects the Test Voltage to one side of the material, it is not being tested. If the concrete is dry the sensitivity of the Holiday Detector may need to be increased to compensate.
How small a hole can I find using a Holiday Detector?
If air can pass through the hole the Holiday Detector can find it.
When I re-test a membrane applied to concrete I find other faults that did not show up on the first test, why is this?
These are thin areas where the Test Voltage was equal to the Dielectric Strength of the material. The first test was enough to weaken the material in the thin area but not enough to make a fault. The second test was enough to break down the material.
Can I test coatings that are damp because of dew etc?
No, dampness makes the surface conductive and any test with a Holiday Detector becomes ineffective. All surfaces must be clean and dry.
I test the insides of tanks and every time I touch the metal case of the Holiday Detector I receive a shock, why is this?
This is because you are working in close proximity to the high voltage which is charging you up. In your case this is more noticeable because you are standing on an insulator, which is stopping this charge leaking to earth, also the surface has been charged to the test voltage. All that can be done is to wear insulating gloves and avoid touching earthed metal. It is more noticeable in dry conditions.
When testing a surface and moving the electrode, sometimes the alarm sounds for no apparent reason, as no fault can be found – why?
As the electrode moves over the surface it charges it to the test voltage, taking current from the Holiday Detector which activates its alarm. The charge current is proportional to the area of the electrode on the surface, also if the surface is damp this will have the effect of increasing the area needing to be charged. The answer is to adjust the sensitivity of the Holiday Detector but if this is not possible make sure that the surface is clean and dry. The only other option is to reduce the area of the test electrode.
