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Frequently Asked Questions (FAQs)

Still have questions? Check out these lists of frequently asked questions below and see if maybe what you are searching for is in here!



Q: What is the dimple on a thermal protector?

A. On a miniature thermal protector there is a dimple formed during the calibration process.  The most sensitive side is opposite the dimple.


Q: Is there an explosion proof thermostat?

A. Our NWP series is produced in accordance to the IEC/IEN standard 60079-15.


Download General Catalog

1/2" Disc Thermostats

Q: What is the standard differential (hysteresis or ΔT) of the 1/2" Disc Thermostat?

A. 30°F (17°C)


Q: Are tighter or wider differentials available?

A: Yes, 15°F to 100°F (8°C-56°C)


Q: What is the tolerance on opening and reset?

A: Tolerances are as follows:


50°F to 249°F (10 to 120°C)   250°F to 320°F (121°C to 160°C)
OA Open +/- 5.4°F (3°C)   OA Open +/- 7.2°F (4°C)
  Close +/- 10.8°F (6°C)     Close +/- 10.8°F (6°C)
CA Open +/- 10.8°F (6°C)   CA Open +/- 10.8°F (6°C)
  Close +/- 7.2°F (4°C)     Close +/- 7.2°F (4°C)


Q: Are 1/2” Discs available in a one shot (one shot meaning that it actuates once and cannot be reset)?



Q: Can the thermostat withstand vibration?

A: Yes, standard test is 2mm amplitude with a vibration frequency of 1,000 C.P.M. (Cycles per minute) applied in the x, y, and z direction for duration of 20 minutes.


Q: Can the thermostats withstand DC voltages?

A: Yes, tested by manufacturing only the following ratings apply:

12 VDC 10 Amps   30,000+ cycles
24 VDC 7.5 Amps   30,000+ cycles
48 VDC 4.5 Amps   30,000+ cycles


Q: Are the OA and CA thermostats submersible?

A: No, however Selco has the ability to over mold thermostats so that they are moisture resistant.


Q: How do I know if I need gold contacts?

A: If your amperage is .250 Amps (250 mA) or less. Gold contacts prevent premature failure due to oxidation of the contacts at low amperage levels. Oxidation forms an insulation layer on the contact and low current does not arc enough to burn off the oxidation.


Q: At what rate of temperature rise will these devices remain accurate?

A: Devices are tested at 1.8°F (1 °C) per Minute but can see a rate of temperature rise as fast as 10°F and remain accurate.


Q: Will the thermostat fail open or closed?

A: There is a 90 % probability that the thermostat will fail open.


Q: Why does the thermostat rattle?

A: In its normal state of NC or NO, the transfer pin moves back and forth. Once the thermostat trips, the pin will push up against the contact arm and stop the rattle.


Download 1/2" Disc Thermostats FAQ

Bulb and Capillary Thermostats

Q: What Capillary length is available?

A: Standard is 36 inches (915 mm).

Customs can range from:

  • In Copper - 18 inches to 8 feet (457 mm to 2438mm)
  • In Stainless Steel - 18 inches to 4.6 feet (457 mm to 1420mm)



Q: How many inches of capillary should I immerse in the media?

A: Recommended is 2 inches (50 mm).

If less than or more than 2 inches may vary from actual calibrated set point. Manufacturing calibrates at 2 inches immersed.


Q: What type of media is used in testing bulb and capillary thermostats?

A: 90°C (194°F) and lower the media is water.
91°C to 400°C (196°F to 752°F)
the media is a salt bath.


Q: What is the rate of temperature rise while testing bulb and capillaries?

A: 1°C to 1.5°C (2°F to 3°F) per Minute


Q: At what rate of heat increase is the bulb and capillary most accurate?

A: 4°C (7°F) per minute.
The faster rate of temperature rise the less accurate the thermostat will be (another term for this would be Thermal Delay or Thermal Lag).


Q: What is the differential (also referred to hysteresis) available on bulb and capillaries?

A: Closest is 2°C (3°F to 4°F) on lower temperatures and 9°C (16°F) on high temperatures.
Widest – Varies on temperature setting

  • On 4-40°C (40-104°F) Max. Diff. Is 4-5°C (7-9°F)
  • On 30-90°C (85-195°F) Max. Diff. Is 9-12°C (16-21°F)
  • On 50-300°C (120-572°F) Max. Diff. Is 25-30°C (45-54°F)



Q: Is the Stainless Steel used on the Stainless Steel Bulb and Capillary 304?

A: Yes, it is 304 stainless steel.


Q: Does the bulb and capillary lose accuracy with longer capillary lengths?

A: No


Q: What is the CAP-MR series rated to?

A: The CAP MR series thermostat is M1 rated, not M2 which is trip free. Consult Selco for other options.


Download Bulb and Capillary Thermostats FAQ

Control Knobs

Q: Should I use a collet knob, push-on knob, or a set screw knob on my application?

A: The type of shaft you are using and your application will determine which type of knob is best for you

Collet knobs are only recommended for a smooth, round shaft (no splines and no flat on the shaft). Collets are a good choice when a secure fit is important. A tool must be used to install or remove collet knobs.

A push-on knob can only be used on a splined shaft or a D shaft. A push-on knob is a good choice when cost savings is an important factor. Push-on knobs are held on by an interference fit, which means that they can be installed and removed relatively easily.

A set screw knob is recommended for either a round shaft or a D shaft. A set screw knob is a good choice when you are using a D shaft, and you want a secure fit. Set screws are not recommended for splined shafts. A tool must be used to install or remove set screw knobs.


Q: What materials are Selco knobs made of?

A: Nylon - The majority of the collet knobs and push-on knobs are made of nylon 6, with a matte finish. This material is stable in the temperature range of –20 degrees C to +70 degrees C.

Thermoplastic Elastomer – The Soft Touch knobs have bodies that are made of thermoplastic elastomer,which has a soft, textured velvet touch. The pointers on the soft touch knobs are made of a hard polypropylene.

ABS - Many of the set screw knobs are made of ABS.

Aluminum - The remaining set screw knobs are made of aluminum.

Thermoplastic - Some of the appliance knobs are made of thermoplastic and withstand temperatures up to +70° C.

Thermosetting - The remaining appliance knobs are made of thermosetting material and withstand temperatures up to +220°C.


Q: What is your minimum order for knobs?

A: Selco has a $50.00 minimum order. In addition to the $50.00 minimum, certain knobs will have a minimum order quantity. While Selco does stock many different varieties of knobs, we are not able to stock every variety. The knobs that we do not stock usually have a minimum of either 500 or 1,000 pieces.


Q: What is your lead-time for knobs?

A: Many knobs can be shipped immediately from stock. Other knobs are made to order. For knobs that are made to order, the lead time can be anywhere from 3 weeks to 8 weeks. Please call Selco to get an accurate lead time for the specific part number that interests you.


Download Control Knobs FAQ


Q: What is the minimum order quantity (MOQ) for your electronic controls?

A: Our custom electronic controls require a minimum production run of 500-1000 pieces, which can be scheduled to ship to you in up to 4 shipping lots. Contact your Selco representative for more details.


Q: Can I get a sample of an electronic control so I can test it out?

A: Yes! Please contact Selco and we will go over your application, annual usage quantity and pricing. We’re happy to send samples out to potential customers that meet sample criteria.


Q: I like the (Selco Control), but it needs to do (minor change). Can you do that?

A: Of Course! Please contact Selco and we can work with you to customize the unit so it fits your application’s needs. We can revise software, change LED/display colors, and more! Depending on the amount of Engineering time needed to complete your request, customizations may require Engineering fees. A minimum order commitment may apply


Q: I want to work with Selco to design a custom control, but it will need to get agency approvals like UL or CSA. How do we do that?

A: Selco is very familiar with UL and other agencies. We can work with you to get the agency approvals needed. Contact Selco for more details.


Q: I need to repair my equipment, and the control needed is from Selco Products. How do I buy a replacement part?

A: Please contact the original equipment manufacturer to purchase a repair unit


Download Electronics FAQ