12. Live Testing Flashcards
12.1 - What is considered HV?
Anything above 1000Vac and 1500Vdc
12.2 - On a typical Three-Phase system, what voltage would you expect to measure between Phase-Phase?
400V
12.3 - On a typical Three-Phase system, what voltage would you expect to measure between Phase-Earth?
230V
12.4 - On a typical 110V transformer used for portable power tools, what voltage would you expect to measure between Live and Neutral?
110V
12.5 - On a typical 110V transformer used for portable power tools, what voltage would you expect to measure between Live and Earth?
55V, due to the being center tapped to earth.
12.6 - Are the contacts of an E-stop button normally opened or normally closed and why?
E-stops are normally closed contacts. This allows the circuit to operate in normal conditions, however, in an emergency and the button is pressed, the circuit will open.
12.7 - If multiple E-stops are to be connected in a single loop, how would they usually be connected? In Series or Parallel?
Connected in Series. This will mean that triggering any of the one E-stops will break the circuit and de-energise it.
12.8 - What are the visual differences between a motor wired in Delta compared to a motor wired in Star?
- In a Delta connection, the motor windings will be connected end-to-end. This forms a closed loop.
In the terminal box phases will be connected… U1-W2, V1-U2, W1-V2. - In a Star connection, one end of each of the three windings are connected together at a common point. This is the Neutral point.
In the terminal box phases W2, U2, V2 will be connected together.
12.9 - How would you check to see if a motor is starting to seize or if it is being overloaded in some way?
- The motor could feel hot to touch - Overheating.
- Excessive vibration.
- Noise - Grinding/squealing.
- Tripped circuit breaker or if the circuit breaker has not tripped, a clamp meter can be used to determine if it drawing the correct load.
- Measure voltage - If a motor does not receive the correct voltage is will draw a higher current.
12.10 - Name some different types of controller modules i.e. CAN/PLC inputs.
- CAN Modules
- PLC Modules
- Data Acquisition Modules
- Fieldbus Modules
- I/O Expansion Modules
Digital Signals (24V - ON/OFF) for example, PLC outputs and inputs.
Analogue Signals (4-20mA) for example, PT100 Temperature Sensor.
12.11 - Describe the function of an RCD and what it is designed to protect against in a circuit?
An RCD is a safety device that is designed to protect against shock and fires.
The RCD will monitor outgoing and incoming current, which should be equal under normal circumstances. If an imbalance is detected between outgoing and incoming currents, it will trip the circuit within milliseconds.
12.12 - Describe the Test for dead procedure.
Using an approved and calibrated voltage tester and associated proving unit…
Prove the voltage tester with the unit…
Test for absence of voltage at point stated in AWP…
Prove the voltage tester with the unit.
12.13 - What is your understanding of GS38 (Electrical test equipment for use on low voltage electrical systems)?
- Equipment used on circuits not exceeding 1000Vac.
- Test leads and device must be insulated and have finger guards.
- Must have spring loaded tip with a max length of 4mm.
- Must have fused leads not exceeding 500mA.
- Must display CAT markings.
- Regularly inspected.
12.14 - What is the function of a Live/Line Conductor, Neutral and Earth?
- Live conductor carries current to the load (device, appliance etc.). It is typically at a high potential to earth.
- Neutral conductor returns the current from the load and back to source (generator, transformer etc.).
- Earth (Ground) conductor provides a safety path for current to flow back to ground in the event of a fault (e.g., a short circuit). (Diverts stray currents).
12.15 - What PPE would you consider for Live Testing?
- Arc flash/flame resistant clothing (With correct calorific rating)
- Gloves
- Safety glasses/Visor
- Safety boots
- Rubber mat
- Rated hood/balaclava
