EA-STT 2000 B 4,5 Isolation Variac - Voltage Tester Screwdriver Illuminates  - Page 1
Forum section: electronics / beginners

author: 2X
author_rank: Frequent Contributor
timestamp: March 19, 2025, 08:41:39 pm
content: Hello,I have bought the EA-STT 2000 B 4,5 Isolation Variac/Transformer, but when I place the voltage tester screwdriver one the transformers output it illuminates. This happens maybe because of the stray capacitance between primary and secondary windings and consequently there is a high impedance conection between them?If the above are true, why it is called it isolation transformer?I tried the same thing also on a fixed(not variable) isolation transformer 1:1 and the same thing again with the tester screwdriver. If I connect an oscilloscope probe on the secondary winding (Primary 230VAC to Secondary 230VAC) I will trigger the RCD or I will blow the oscillospope or No and why?EA-STT 2000B-4.5 - Transformer 0..260V / 4.5:https://elektroautomatik.com/shop/en/products/industrial-power-supplies/ac-sources/power-supplies-variable-and-isolating-transformer-ac-dc/232/transformer-0..260v/4.5Datasheet:https://elektroautomatik.com/shop/media/pdf/79/f6/66/datasheet_ea4000-stt2000.pdf

author: johansen
author_rank: Super Contributor
timestamp: March 20, 2025, 02:00:35 am
content: some isolation transformers have a grounded 1 turn metal foil between the coils, which greatly reduces the coupled capacitance. you will still have a symetrical 60 or 120vac relative to ground on both the outputs, unless the transformer was designed to have the coil wound in a way to maximize coupling to ground on one end of the coil, and minimize it on the other.

author: bdunham7
author_rank: Super Contributor
timestamp: March 20, 2025, 04:02:28 am
content: Could you share the details of the voltage tester screwdriver? Is this a two-lead device where you ground one end and probe with the other or is it a non-contact voltage detector device?

author: 2X
author_rank: Frequent Contributor
timestamp: March 20, 2025, 08:07:21 pm
content: The screwdriver tester is the below.https://www.sas.com.gr/en/product/unbreakable-main-tester-vde-150-250-volt/I tried also with the same screwdriver tester on a laboratory where have an isolation transformer with 1:1 ratio (Primary 230VAC/50Hz to Secondary 230VAC/50Hz) and the screwdriver lights. Do you know if somebody touch only one of the terminals from the secondary winding wil not trigger the RCD?Also, I find out that also someone else have noticed this at an isolation transformer:Isolation Transformer Lights-Up Tester Screwdriverhttps://electronics.stackexchange.com/questions/593557/isolation-transformer-lights-up-tester-screwdriver

author: bdunham7
author_rank: Super Contributor
timestamp: March 20, 2025, 08:20:53 pm
content: It only takes a small current--a few hundred µA to light that neon bulb and you are serving as the second electrode. So that could be leakage from the primary to secondary or from the secondary to ground. It's probably normal, but you'd have to test with some load (a 10K resistor will work) to be sure. Does it light up when you probe either terminal or just one?

author: Fenstergucker
author_rank: Regular Contributor
timestamp: March 21, 2025, 05:16:01 am
content: I have an 'EA STT-2000 B-3A' and a test screwdriver also lights up on one phase. But you can connect this phase to neutral or ground and no current flows.Peter