8557 Mercruiser SCREW, KIT, AIR HORN/THROTTLE BODY

Thermostat (bimetal)
One type of thermal protection is the bimetallic thermostat. The bimetal thermostat contains normally closed silver contacts that open when the contacts reach the temperature of operation. Thermostats can be connected in series or independently.Thermistors
There are two types of thermistors as follows:
Positive Temperature Coefficient (PTC)
Negative Temperature Coefficient (NTC)Thermistors are heat detectors that are made of semiconductor compounds that vary in resistance as the temperature changes. of operation. Thermistors can be connected in series or independently.Note: Thermostats and thermistors must be connected to a control. The control must be able to stop operation of the generator or creates some type of notification for the operator that a problem exists.Thermistor - Resistive Temperature Device (RTD)
An RTD is a calibrated resistance element. RTD operation is based on the principle that the electrical resistance of a metallic conductor varies linearly with temperature changes. The terminals of the detector must be connected to a control panel which includes a temperature gauge.Note: The RTD type thermistor allows monitoring of the absolute temperature. The information provided by the RTD is used to provide a temperature reading. The RTD is also used as an input for parameters that are set for alarm and shut down events according to preset temperatures.
Illustration 1 g03775207
The following formula is used to convert the value of the resistance to a temperature measurement for a PT 100 thermistor.
Illustration 2 g03776184
Ω = resistance measured on the PT-100The protective devices, when requested, are shown in the wiring diagram specific to each generator.Temperature Limits for the Windings
The temperature of the winding must be kept below the temperature limit rating of the thermal class of the insulation on the winding. The total temperature is determined by the following:
Illustration 3 g03795231
Refer to Illustration 3 for the total temperature calculation.Note: The ambient temperature is typically considered up to 40° C (104° F).Above 40° C (104° F), the working conditions are considered special. Table 1 shows the numerical values and composition of the permitted temperature of the hottest point of the winding.
Table 1
Insulation Class     F     H    
Ambient temperature    
40° C (104° F)    
40° C (104° F)    
T = temperature rise (resistance method)    
105° C (221° F)    
125° C (257° F)    
Difference between the hottest point and the average temperature    
10° C (50° F)    
15° C (59° F)    
Total: Temperature of the hottest point    
155° C (311° F)    
180° C (356° F)    Note: If the generator is exposed to winding temperatures above the values listed in Table 1, the service life of the insulation and service life of the generator is reduced substantially. A high operating temperature can cause the generator to melt insulation and short the windings causing a fire.Thermal Protection for the Bearings
Temperature sensors are available for installation on the bearings. The sensors are to protect the bearings from damage due to overheating.Alarm and Shut Down
The temperature parameters for unit alarm and shutdown must be set as low as possible. The temperatures can be determined based on the results of tests or by the operating temperature of the generator. The temperature for initiating an "Alarm" should be set as follows:
10° C (50° F) above the operating temperature of the generator
While at full load
Consider the highest ambient temperature where the unit is installedThe temperature that will cause a shutdown must be set to a lower temperature than the temperatures listed in Table 2 and Table 3.
Table 2
Stator Winding (1)    
Class of Insulation     Maximum temperature of protection setting    
Alarm Shut down    
F    
140° C (284° F)    
155° C (311° F)    
H    
155° C (311° F)    
180° C (356° F)    
( 1 ) Maximum temperature of stator - continuous dutyNote: The temperature for generators that are used in emergency standby systems can be allowed up to 25° C (77° F) above the temperature for continuous operation. The allowance in temperature per the standard NEMA MG 1 and MG-22:40-1- 22.84. Generators that are installed in higher temperature conditions reduce the service life of the generator.
Table 3
BEARINGS    
Maximum Temperature Setting    
Alarm     Shut down    
110° C (230° F)    
120° C (248° F)    Space Heater
Some generators are equipped with a heater to prevent condensation of water that can occur due to long periods without operation. The heater must be programmed to turn on after the shutdown of the generator and turn off before the unit is placed into operation. The required power for the space heater is shown on the identification plate that is located on the generator.Note: If the space heater remains energized while the machine is in operation, generator windi