Design and safety standards of electronic thermostats

Design and safety standards

of electronic thermostats

°STELPRO electronic thermostats are designed to meet the highest safety standards. Each unit is certified by agencies such as CSA and UL. Their seals of approval are widely recognized and accepted by the relevant authorities, safety inspectors and experts, code enforcers as well as major manufacturers, distributors and retailers.

The standards applicable to electronic thermostats make it possible to guarantee their safety fully during use, even in the event of a wrong product selection, incorrect installation or eventual failure.

Impact resistance

All our housings are designed to withstand major impacts without exposing the user to possible electrical shocks. During testing, we drop a sphere two inches in diameter that weighs more than one pound from a height of 51 inches onto the device’s housing.

Flame and high-temperature resistance

The materials used in the design of electronic boards and housings meet the UL94-5VA standard, which is the most stringent in terms of flame resistance. Even in the event of extreme electronic circuit failure, the housing must be able to contain flame propagation and ensure the protection of the users by not exposing any live component.

Electrical anomaly resistance

Transient phenomena: Electronic circuits are designed and tested to resist power surges, momentary interruptions, undervoltages and other transient network phenomena caused by lightning, power outages or any other event that affects power supply quality.

Electrical overloads: During testing, thermostat power circuits are overloaded with current representing more than 150% of their rated capacity. They must also withstand short-circuit tests that simulate a bad connection.

Electronic component failure

Electronic circuits are designed to remain safe even in the event certain critical components fail. During testing, failures are deliberately provoked to check the devices’ tolerance. Devices must remain safe at all times.


At °STELPRO, we perform rigorous tests on every product we design to ensure they meet the safety standards of the countries where they are sold. For controls, we use the UL60730 or CSA C22.2 No.24 standards. A list of tests performed is outlined in Table 1.

We also perform tests that go beyond what safety standards require, ensuring better quality and longer life for our products.

Our thermostats are subjected to a battery of intensive environmental tests under high-temperature and -humidity conditions, among other things. They must remain fully functional and safe.

  • Moisture bath: 15 days in a 86° F/95% relative humidity environment. The product must remain functional during and after the test.
  • Temperature and humidity cycles: 15 days of three-hour cycles alternating between 109° F/60% relative humidity and 122° F/95% relative humidity. The product must remain functional during and after the test.
  • Temperature cycles: Seven days of cycles between -22° F and 140° F. The product must remain functional after the test.
  • Extreme temperatures: Testing the product to the limits prescribed for operation and storage.


List of tests performed on our products (based on the UL60730 standard).

Clause Description Comments
UL60730-1, 11 Construction Requirements – Materials

See Annex D and/or UL746C for Requirement of Polymeric enclosures.

Must be 5VA rated: This is the highest (most flame retardant) UL94 rating.

UL60730-1, 14 Heating – Electrical Test parameters

Not a voltage sensitive circuit therefore loaded to most unfavorable current which is 1.06 times the rated current.

Voltage may not be lower than 10% of rated voltage.

We verify that at a maximum control temperature (30°C) the electrical components and materials remain inside their specified operating limits.

UL60730-2_09, 17 Endurance – Overload + Endurance Tests

Two samples required designated shall be subjected to 50 ON/OFF cycles of operation at a rate of 6/minute at the following value:

  • Table 15 (17.2.2) – 1.5 times rated current

SAMPLE 1 and SAMPLE 2 shall be subjected to 6000 cycles at a rate of one per minute (3sec ON, 3sec OFF) at 110% of both the rated current and voltage.

SAMPLE 2 shall be subjected to an additional 30000 cycles at rated voltage and current.

UL60730-1, 18
UL746C-section 22
+ section 56
Resistance to impact

No live part shall become accessible;

Dielectric test required after impact to verify if a risk of electric shock is possible.

56.3 – Ball impact test

  • Any surface exposed in normal mounting position shall be tested with;
  • A steel sphere of 2 inches in diameter weighing 0.535kg from a height of 51 inches producing a 6.8 Joules impact.

56.4 – Samples shall be cooled to a temperature of 0°C for 3 hours prior to testing (test done on sample still cold)

UL60730-1, 21 Resistance to Heat, Fire and Tracking – General All non-metallic parts shall be resistant to heat, fire and tracking. UL746C is used as the reference standard for compliance in the US. 5VA material shall be used to encapsulate live parts. V-0 or other flame resistant material can be used on parts that do not contain live parts;
UL60730-1, H.26.5 EMC Requirements - Voltage Dips/interruptions/Variations

Control shall tolerate voltage dips and interruptions in the power supply network:

Voltage Dips: 30%, 0.5s – 60% , 0.5s

Voltage Interruptions: 100%, 1 cycle of supply waveform every 0.5s and 60s

10 seconds between each dip or interruption

Control shall tolerate short term supply variations

  • 40% of Rated voltage
  • 0% of Rated voltage
  • Decrease voltage in 2 seconds, stay at reduced voltage for 1 second, then increase voltage in 2 seconds
  • 10 second intervals between each voltage test cycle;

Execute voltage variations three times;

UL60730-1, H.26.8 EMC Requirements – Surge Immunity Test For AC Mains:
  • Test Level 3 for Line to Line = 1 kV (2 ohms source impedance)
  • Test Level 3 for Line to Earth = 2 kV (12 ohms source impedance)
For signal input lines longer than 10 meters:
  • Test Level 3 for Line to Line = 1 kV (2 ohms source impedance)
  • Test Level 3 for Line to Earth = 2 kV (12 ohms source impedance)
2 impulses at positive polarity at the following phase angles:
  • 45, 90, 270
2 impulses at negative polarity at the following phase angles:
  • 90, 225, 270
UL60730-1, H27 Abnormal Operation – Faults Testing

Control shall be wrapped in cheesecloth

Temperatures shall not exceed 1.5 times the values of clause 14 for reinforced insulation except in the case of thermoplastic material.

Shall comply with clause 8 and 13.2

Types of components tested;

  • Fixed Resistors: Open (All types), Short (All types except, thin/thick film and wire-wound.
  • Capacitors:Open (all types), Short (All except, X1 and Y types, Metallized film)
  • Inductors: Open (all types), Short (All except Wire-wound)
  • Diodes: Short and Open (All types)
  • Semiconductor type: Short and Open (All types)
  • Optocouplers: Short and Open
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