Electrical Troubleshooting Flashcards
What is the sequence of operation?
Indicates the progression of operation for all devices on the elementary diagram.
What is CR on an electrical diagram?
Control relay
According to the NEC when should fuses be used?
Fuses should be installed on an ungrounded conductor and never installed in a grounded conductor.
What is the meaning of a limit switch symbol with a downward pointing arrow next to it?
The same device appears on a lower line on the schematic.
Which diagram shows the arrangement of components on a control panel?
A control panel layout
Which diagram shows the actual location and routing of circuits?
They are shown on a wiring diagram
What is shown on a lighting diagram?
Location of lights, lighting panels, and receptacles, and telephone wiring.
Which diagram shows the power distribution wiring from input to transformer to output?
A riser diagram.
What is not shown on a lighting diagram?
HVAC vents and ducts
What is shown on a power installation drawing?
It only shows the power outlets.
What is the most important step in troubleshooting?
To change one componant at a time.
What kind of protection does a combination motor starter offer?
It offers overload and short circuit protection.
Circuit breaker and thermal disconnect
What type protection does a start-stop device provide?
It only provides undervoltage release. The coil drops out when voltage becomes too weak to hold in the coil. When power is restored it automatically pulls back in. Not good for heavy machinery.
What should you check if a motor stops for no reason?
First check the thermal overload relays
What are the main causes of a magnetic coil burning up or short circuiting?
Overvoltage
Excessive current
Too frequent operation
If you measure no voltage when the main contacts of the controller are closed the problem probably lies in the…..
Controller ( contacts not making up)
Basic steps to follow upon a trouble call are?
Talk with the operator, ask about conditions and availability
press start, reset overload relay
troubleshoot from there
Current ratings on contacts of control relays are usually 10A pilot duty. what types of loads to they have?
other relay coils, other contactors, or pilot lights
When using an electronic time delay relay, both the time delay assembly and the relay coil are in series with……….
the line and the initiating contact
Most reversing starters with low voltage remote pushbuttons are………
electrically interconnected
mechanically interlocked
What is wired into the control circuit of a reversing motor for overtravel protection?
limit switches
Operating a heavily loaded motor at reduced voltage can cause it to have high , causing overload tripping.
Slip
A three phase induction motor can be reversed by?
Switching any two leads
Two speed starters for squirrel cage motors are achieved by ………
changing the number of magnetic poles in the stator
Deterioration of a selenium rectifier is can be indicated by ………
a reduction in output voltage
an increase in input current
sluggish operation of relays
How should a good diode test with a resistance test?
Should be low ohms in one direction (free flowing under 20 ohms )
Very high in the other direction (blocking k ohms )
Regular leakage of air in a pneamatic system is usually ……….
small enough to be ignored.
What initiates the operation of an air piloted valve?
A surge of air. valve position maintained by pressure
In regards to control logic a latched electrical relay is an example of a ……..
bistable device
If a motor runs with an open circuit, the speed and the winding temp .
speed decreases
temp increases
What does oil accumulation around brushes and slip rings/commutator rings do?
mica insulation deteriorates causing arching
increased brush wear
forms a grinding surface
What does mixing grades of brushes together due to the riding surface?
Creates uneven pressure and load distribution among the brushes.
What determines the kind of lubricant you should use for a bearing?
operating temp
What should be done before working on things that have been soaked with water?
Disconnect all power
pull all fuses
lock out disconnects and circuit breakers
A pole phase group in a polyphase stator may become shorted. Usually indicated by high temp. in the faulted coil group.
T
When testing a 3 phase delta connected winding with a compass for a short what should you see when you break one conn. and apply dc to winding if everything is connected properly?
the compass will indicate alternating north and south poles around the stator frame. A Y connected test will result in a random deflection of the compass
What are the 4 main causes of mechanical vibration?
Too much clearance at the bearings
bent shaft
imbalanced rotor
misaligned couplings
What are the common reasons a split phase motor makes excessive noise while operating?
loose rotor bars
worn bearings
worn centrifugal switch
*NOT too little end play
Planned preventative lighting includes……
group relamping
periodic fixture and bulb cleaning
troubleshooting
What should be the first step in troubleshooting lighting?
Assure its seated properly and making good contact
How long does NEMA recommend for overnight lamp seasoning?
12 hr full output before dimming
All HID lamps require a startup and restrike before achieving full brightness
T
What is a “log”
a detailed description of all input commands, logic responses, outputs, and a machine motions
All elementary diagrams must have all lines numbered consecutively.
T
One of the best ways to learn about new equipment is to troubleshoot it before, during and after installation
T
Before releasing new equip. after install be sure to check fuses and overloads for proper size, remove any leftover shipping material, actuate moving parts
T
As a means of identifying the motor, attach a permanent metal tag with he company’s inventory number stamped on it .
T
