As modern-day people, we are largely dependent on electricity for a great deal of things daily – from prepping meals and using electronic devices for chatting, shopping, and doing payments to using power tools. This is true for residential as much as commercial purposes, and modern-day lifestyles sure take their toll on electrical circuits.
Electrical damage is something that would be a given if not for the job of switches and circuit breakers. But even so, it’s still possible to get some higher contact resistance which happens when there is some resistance to the flow of the current. This can be the result of the contact between breakers, switches, or even relays, connectors, contactors, and other devices used for switching.
The Need for a Ductor Tester
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To prevent this, and consequently avoid more serious issues with power outages, or worse – fires, it’s useful to conduct periodic maintenance with contact resistance tests serving as the basic preventative measure. It’s of utmost importance, especially for those connectors that carry a higher amount of current.
Also known by the name of ductor tests, these are carried out with a reliable ductor tester that measures the electrical resistance between the connections responsible for reducing the electrical current flow. This could be between connectors, busbar sections, cables, joints, and terminations, among others.
The reasons for this can vary. Sometimes it may be due to the loose connection between these parts, other times there may be joint tension, or even contact corrosion or contamination. A test can determine if there’s a problem and allow you to prevent a more serious issue by solving it properly and promptly.
How Does It Work?
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Also called Ohmmeter, the specialised ductor tester which can be found in several types, such as the micro, mega, and milli-ohmmeters, is designed to measure current resistance in micro or milli ohm levels by checking whether the connections are properly made and operational.
It’s useful for detecting tension on bolted joints, contaminated contacts, corroded contacts, loose connections as well as eroded surfaces. Depending on the specifics of the case, or suspicion of issue, there are two of the most common contact resistance checks: the visual and the ductor ohm meter test for contact resistance measurement. The first, as the name implies, relies on visual inspection of the circuit breaker contacts for any signs of damage.
The second relies on checking the fixed current, specifically the four-wire (Kelvin) DC voltage drop, through the contacts with the help of the special tester, i.e. instrument. For proper reading, two current connections are required for the current flow injection that can show results of 100A, 200A, or even higher pressure, plus two leads for the voltage drop that’s measured separately.
Connect the voltage cables as close as you can to the connection you’re checking, and make sure it’s within the circuit by the connected leads. The micro-ohmmeter can eliminate EMF thermal effects besides measuring the resistance contact. The reading can then be added to one of the voltage drops.
Two Types to Choose From
When you decide to carry out the resistance testing, there are these two types of instruments you can check this with:
Series Type Ohmmeter
This specific type has four unique resistors, the R1, R2, RX and RM respectively, each of which has its role. The first one is in charge of limiting the current flow, the second one is the zero adjusters, the third one is known as unknown, and the fourth is the internal resistor. The ohmmeter also consists of internal battery voltage – E, plus two output terminals A and B.
Shunt Type Ohmmeter
In this type of ohmmeter that’s suitable for small current resistance values, there are the RM, R2 and E batteries as the main parts, while the RX is in charge of the connection to the A and B output terminals. The readings can be either zero (when A and B are closed), or infinite (when A and B are open).
Things to Keep in Mind
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What’s important to note here is that the test with the instrument depends on certain factors. Among these are the type of the connector, whether or not it’s welded or bolted, or maybe even soldered or clamped, followed by the metal surface area, the contact pressure, and the exact maximum contact resistance of the manufacturer.
The minimum resistance isn’t of importance, however, remember the maximum can vary from one manufacturer to another, so you ought to check properly to know what you’re getting into before the actual testing. Moreover, in case the reading is low resistance, it’s necessary to re-do the test of the contacts with a higher current.
This is crucial considering the higher current helps you avoid connection issues as well as oxidation typical for the terminals. For those who want to check the Hot-joint and Bus-Bar systems, it’s recommended to join the result of the contact resistance with thermal imaging. If this isn’t the first test, it’s advisable to also keep an eye on the previous test results. Another word of advice is to choose a ductor tester that allows you to save up the data of your tests so you can keep track of future comparisons.
One that allows you to save the data on a PC or USB for future analysis is also handy. Carry out the testing consistently with every periodic check-up, make sure you provide the same conditions, and use the same leads to know which connection, joint, or device could turn into a potential problem.