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FAQs - Frequently Asked Questions -

On what principle does a thermostat work?
Bimetals are composed of two (Bi-) metals with different thermal expansion coefficients that are bonded together and rolled-out into a plate. The plate is punched-out in a disc or polygonal shape and formed into plate pieces. It switches the position to bend quickly at any specified temperature when heated and reverse (reset) at a temperature different from the said temperature when cooled. Utilizing this principle, the snap action of the bimetals is transferred to the switch by means of a ceramic rod called as "guide pin" to open/close the contact.

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How does a thermostat work?
Typical thermostat, N-type, is normally turned ON and will be turned OFF at any specified temperature with temperature-rise that causes the bimetals snap action, and will be turned ON with a snap action (reverse) when cooled. On contrary, R type is normally turned OFF, and will be turned ON at any specified temperature with temperature-rise, and will be turned OFF when cooled. However, some of N-type, of which OFF temperature setting is lower than ambient temperature, is normally turned OFF at ambient temperature and will be turned ON when cooled to any specified temperature (it is mainly used to control (ON → OFF) defrost heaters in ice makers and antifreeze heaters in cold-weather spec. equipment).

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What is like a manual reset type thermostat?
It has a structure "with Reset button" and "not allowing to be reset at ambient temperature once it has turned the switch OFF". it can be reset only by manually pressing Reset button. For example, if it is used for prevention of excessive temperature rise, it turns the switch OFF to stop the equipment, not allowing the equipment to be turned ON for restart, and it can be safely operated again by pressing Reset button to turn it ON after eliminating the causes of equipment's abnormal temperature-rise.
Click here to see Manual Reset Type Thermostats

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What is like a one shot type thermostat?
It has a structure not to be reset at ambient temperature once the thermostat has functioned (not to be reset in the normal atmosphere (temperature environment) as It is designed to be reset at -35°C or lower in accordance with the safety standards). This type is more reliable than thermal cut-off. In terms of test for response temperature, this type can be tested on a 100% basis as it can be reset when exposed to ultra low temperature (-150°C) and also is unlikely to be deteriorated by aging, while thermal cut-off can be tested only on a sampling basis and is likely to be deteriorated by aging. So, one shot type thermostats are more commonly used in substitution of thermal cut-off. Compared to general thermostat with the same basic design, one shot type can have electric ratings larger because of no need for endurance against repeated open/close actions.
Click here to see One shot type thermostats

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What is differential?
Differential is a difference in temperature between the point allowing the thermostat to first operate (to turn the switch OFF) and the point allowing the contact to return to its original state (to turn the switch ON), with a thermal energy produced and accumulated in this interval that causes snap action. The larger the differential, the stronger the force of bimetals snap action. Therefore, the differential may be a critical factor of productivity and lifetime (For instance, if it is specified to OFF at 150°C and ON at 135°C, the differential is 15 degs Celsius).

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In what applications are the thermostats used?
Thermostats are used in significantly various applications, such as

1: Heater temperature control (switching between ON ←→ OFF),
2: Prevention of excessive temperature rise (switching ON → OFF),
3: Anti-freezing to turn a heater ON when cooled (switching OFF → ON),
4: Substitution of thermal cut-off (switching ON → OFF),
5: Cooling temperature control by temperature detection to turn a cooling fan ON at any specified temperature and turn it OFF when cooled (switching between ON ←→ OFF).
Click here to see the Thermostat List by Application

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Please explain about the connected load with respect to the ratings.
The typically connected load is a resistive load free from inrush current when the power factor (cosØ) equals to 1. For a lamp load, an inrush current flows through by 10 to15 times higher at the power factor=1 and this may cause the contacts to be melted; for this reason the current must be lower than the general rating. For an inductive load, an inrush current flows through by 10 to 15 times higher, like a lamp load, and thus the current must be lower than the general rating. So, please consult us for any specific loads other than the resistive load. For equipment that uses the direct current, with the requirements substantially different from those for the alternate current, please refer to the Direct Current in the FAQs.

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Please explain about lifetime.
Contacts will be getting fatigue due to arc generated by the contact's open/close actions at the rated current applied. The higher the applied voltage/current, the faster the contact wearing-out. The fatigue contacts will have higher contact load and some of them will be turned OFF; in the worst case there might be a risk where the contacts are melted and not allowed to be turned OFF (the endurance is dependent on the current applied). Otherwise, in terms of the nature of the bimetals, the larger the differential, the larger the snap-action force, resulting in the bimetal less frequently operating with the bimetals cracked due to stress by repeated operations. If the bimetals cracked, the response temperature of the bimetals may be changed. In the worst case, the contact would fail to function (the endurance is dependent on the differential). For instance, our CS-7 thermostat (Differential 15Diff, 125V AC, 15A, and power factor = 1), the endurance is 100,000 cycles.

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What are the precautions for the environment to use thermostats?
Please do not use the products in the following conditions that may cause to affect the properties (Please, contact us for the products needed to be used in such conditions).
(1) Usage in the atmosphere polluted by corrosive gas (hydrogen sulfide etc.) may cause to affect the contacts with contact failure.
(2) Usage in the environment with ammonia gas produced may cause the product to fail to fully perform the properties due to stress corrosion cracking caused by brass material which is used in the contact fittings and some terminals. For instance, ammonia gas was actually generated from a novolac type phenolics resin casing.
(3) Usage in or long term exposure to highly humid environment may cause to deteriorate the insulation resistance, notably resin casing type that may be fail to perform its normal performance due to expansion caused by moisture permeated into the casing.
(4) Application with silicone rubber and grease may cause to damage the contact function of the contact due to low molecular siloxane gas produced.

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Why the thermostat doesn't work at the expected temperature?
The heat conduction and the thermal resistance between the heat source and the bimetals causes each temperature not to always correspond due to a time lag. The thermostat self-heats by the current passing through it, with the temperature of the thermostat getting higher than the actual ambient temperature, and does not actually function at the expected temperature. Such a factor must be adequately taken into account in defining the operating temperature. For this purpose, we offer a sample of bimetals with a thermocouple to measure the thermostat temperature. We recommend you to test this sample on the actual equipment.

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What safety standards are applicable to thermostats?
As the standards to protect human life and property, safety standards are established in every country for the security of the domestic people, including UL (North America), CSA (Canada), VDE (Germany), and JET (Japan). WAKO thermostats have been approved by various safety standards dependent on the model. Please contact us for the details.

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How to install a thermostat?
If you have no holder to install a thermostat, you could select a thermostat with flange or bracket to hold it using screws. For flanges and brackets, several options are available. You can select the most suitable type. In some case, we can offer special type customized to meet your needs. For installation with the thermal sensitive surface contacted, the thermostat should be installed on a sufficiently flat surface. Any bad installation may cause the thermostat to malfunction with the cap top surface being deformed.

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To what extent of direct current can be used?
For DC, different from AC, the circuit has no zero crossing points and, in nature, the arc discharge tends to last longer every open/close action of the contact, with damage to the contact larger. This tendency of arc discharge lasting longer is more apparent with higher voltage and current; in the worst case the circuit may be disabled to be shut down with a constant arc discharge. The electric power to enable the contact to open and close is about 1/20 to 1/30 of AC (at 30V or less), however, it may be further limited by the type of load. So, please contact us for specific details that meet your requirements.
For instance, a thermostat with ratings 125V AC/15A,
AC power enabling to open/close: 125×15=1875W,
DC power enabling to open/close: 1/20 of AC; 1875÷20=94W,.
Current at 24V DC applied: 94÷24=4A.

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Do you distribute your products to individuals?
We are sorry but, direct distribution to individuals is not available. Our products are distributed only via our distribution agents. For the details, please see the page "About Sales".

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How can I order your products?
Our agency will send you a form to fill your required specifications. Please complete it and send it back to the agency. For the details, please see the page "About Sales".

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In what range of operating pressure can you manufacture pressure switches?
We can manufacture them in the range of the operating pressure between 0.05MP and 12MPa. However, the products are subject to some limitations including media and actual operatiing pressure. For the details, please contact us.

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What type of pressure media can be used in the pressure switch?
Polyimide film or rubber is used for a diaphragm of our pressure switches. So, any media that will not cause to deteriorate the diaphragm can be used. The typical media not to be used in are highly permeable gas such as hydrogen and helium (causing to increase the permeation leakage), highly strong acidic and highly alkaline chemicals (causing to chemically deteriorate the diaphragm). However, the materials of diaphragm and sealing are dependent on the media. Please be sure to contact us in advance for the availability of any media to be used.

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