L1 - Manual Starters Flashcards
What are the three common types of manual motor starters?
1- Toggle switch: Max 1HP @ 230V-
a snap-action toggle switch can be used.
Available in single or double pole versions, they have horsepower-rated contacts so they can interrupt motor current and typically have over-load protection built into them.
Ideal For- Light duty like table saws and drill presses
2- Push button starter: Max 5HP @ 230V-
similar to snap-action but have
separate on-off pushbuttons.
Ideal For- Medium duty applications
3- Drum switch: Max 3HP @ 240V or 1.5HP @ 120V-
Rotary-action selector switch that can control speed and change direction of a single-phase motor. Installed between the power switch and motor,
rotating the knob can speed up the motor, slow it down or even change it’s direction.
List three significant ratings found on manual motor starters.
Common Ratings - There are three significant electrical ratings for manual starters.
The motor ratings referenced below can be taken from the motor nameplate.
1- Voltage: Starter voltage rating must meet or exceed motor rating
2- Ampacity: The ampacity capacity of the thermal overload component
must be in-line with the motor nameplate amps (Full load amps / FLA)
* This is a term for the maximum current carrying capacity, in amps, of a particular device. The current carrying capacity is normally associated with electrical cable and is determined as the maximum amount of current a cable can withstand before it heats beyond the maximum operating temperature.*
3- Horsepower: Starter HP rating must meet or exceed motor rating at operating voltage
1hp = 746 Watts
* Horsepower(hp)= Voltage x Amperage x % EFF x power factor x 1.73/746*
What are the different maximum ratings for a drum switch?
3hp@240V
1,5hp@120V
Briefly explain the two major difference between a single phase toggle switch starter and a single pole light switch.
- Hp rated contacts
- Overload protection
- Able to interrupt locked rotor current
List two types of overload relays
OVERLOAD RELAYS: Overload relays protect the motor, motor branch circuit, and motor branch circuit components from excessive heat from the overload condition.
Overload relays are part of the motor starter (assembly of contactor plus overload relay). They protect the motor by monitoring the current flowing in the circuit.
* Manual motor starters use thermal (heat sensitive) types of overload protection*
1 - Bimetallic:
Two thin pieces of dissimilar metals are attached together.
Because they have different coefficients of thermal expansion, they grow and shrink at different rates, causing the strip to bend as it heats up. This bent piece of metal
can then be used to either close a normally open contact (which then shuts off the motor) or press a button that will trip the motor.
2 - Melting alloy (AKA solder pot):
A ratchet wheel attached to one of the contacts is stuck motionless in a pot of solder.
If the solder gets hot enough from
over-current, it will melt and the ratchet wheel will be able to turn free, which then pulls the contacts up.
(sounds janky A-F - still used in lots of NEMA systems) * NEMA connectors are power plugs and sockets used for AC mains electricity in North America and other countries that use the standards set by the US National Electrical Manufacturers Association. NEMA wiring devices are made in current ratings from 15 to 60 amperes (A), with voltage ratings from 125 to 600 volts (V).*
What is the difference between low-voltage protection and low voltage release?
- LVP: Will not restart when power returns after a power outage
LVR: Will restart when power returns after a power outage.
Also:
Low-Voltage Release (LVR) or Undervoltage Release (UVR)
- is ideal in certain applications, such as pumps, fans, blowers, Dangerous equipment such as saws and machinery do not want unexpected
start-up.
These applications require Low-voltage protection (LVP) or Under
Voltage Protection (UVP).
This stops the equipment from automatically restarting after loss of voltage. Manual starters DO NOT provide this.
Which manual AC motor starter does not provide overload protection?
Drum switch
*** Max 3HP @ 240V or 1.5HP @ 120V-
Rotary-action selector switch that can control speed and change direction of a single-phase motor.
Installed between the power switch and motor, rotating the knob can speed up the motor, slow it down or even change it’s direction.***
Are horsepower rating for a manual starter the same at all voltages? Why?
No. Because the motor amps would be higher at lower voltages.
What two things determine the heater selection for a manual starter?
Motor FLA - Heater selection table
What type of rating do the contacts of a manual motor starter have? Why?
Horsepower. Because they can handle in rush and locked rotor current.
Why does a manual starter for a 240V motor have two power contacts?
To open both ungrounded conductor to the motor:
What problem can occur if after a period of time a starter is constantly being reset?
Overloads will wear out. You will start having nuisance trips.
Why do motor starters have overload relays? What can happen if they are not used?
- To protect the motor against continuous high current.
- motor can be damaged - burn out
Manual motors starters have ‘low voltage release’. What does thus term mean? What application would it be useful for?
Motor will stop with a power loss-restart when power returns-pumps, fans, blowers
When sizing a starter for a certain horsepower, what else has to be taken into account?
Voltage and ampacity
