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This page provides a guide-line for Voltage and Temperature derating. A short description is provided as required. How-to derate components;

Connector Voltage Derating:

Derate connector voltage to 25% of rated operating voltage
.... Operating voltage = Connector rating / 0.25
Derate connector operational temperature by 50^oC
.... Connector rating = operating temperature + 50^oC
Current is normally specified as some number of pins carrying some specific amount of current, at some defined temperature. Increase the current carried over any particular pin and the number of pins carrying current most decrease. Decreasing the amount of current over the defined pins may allow more pins to carry current. Refer to this page for a manufacturers listing for Connectors

Cable/Wire Derating:

Refer to this page for a manufacturers listing of Wire and Cable. Cable manufacturers will provide different numbers based on the insulation used for the wire. The table below lists copper wire with a Teflon [TFE] insulation. Teflon insulation has a higher operation temperature range then other insulators, for example PVC. The table below is based on data derived from MIL-STD-975, using 70^oC as the operating temperature. To derate based on number of wires in a bundle:
I_BW = I_SW x (29 - #_wire) / 28 @ [1 to 15 Bundled wires]
I_BW = I_SW x (0.5) @ [more then 15 Bundled wires]
I_SW = Single wire
I_BW = Bundled wires
To derate by temperature use; derate by 80% at 150⁰C, 70% at 135⁰C, or 50% at 105⁰C {Per MIL-STD-975}
To derate for Commercial wire use the table below;

Ampacity Tables for many conditions (Commercial Wiring):
IEEE Standard 835, IEEE Standard Power Cable Ampacity Tables
IEEE Standard 848, Procedure for the Determination of the Ampacity De-rating of Fire Protected Cables
ICEA P-54-440, NEMA Pub. No. WC 51 - Ampacities of Cables in Open-Top Trays
Use the National Electrical Code [NEC] system for premises wiring, and not the Military data on this page.

Voltage Drop per Foot:
V = I x L x (R/1000) x 1.004 x (T-20)
V = Voltage Drop, I = Current, R = Resistance per 1000 foot
L = Length of wire in feet, T = Estimated wire Temperature under load ^oC
Refer to the AWG Table for Resistance per length

{Component Derating Guidelines}

Potentiometer Derating:

A list of Potentiometer manufacturers
This page shows the derating curve for an Adjustable WireWound resistor

{Component Derating Guidelines}

Resistor Derating Example:

Power ratings are normally specified at +25^oC and must be reduced as the resistors temperature increases. A derating chart is often used, with derating starting at 70^oC. Since parameters are application dependent, power de-rating curves or charts should be considered general rather than absolute, and only used as a guideline. The safest designs use the largest physical size operating at conservative temperatures and power ratings.

Derating Resistor Networks, Derating Thermistors. A list of Potentiometer manufacturers

{Component Derate Guideline}

Fuse Derating:

Fuses are specified to interrupt within a maximum of 5 seconds when driven at 200% of their rated current for nominal ratings up to and including 10 amperes. A fuse with a nominal rating of 15 amperes is specified to interrupt within a maximum of 10 seconds when driven at 200% of its rated current. The power supply shall be capable of delivering appropriate levels of current to achieve short fusing times. There is an additional derating of 0.2%/°C for an increase in the temperature of fuse body.
A manufacturers listing for Fuses

{Component Derating Guidelines}

Switch Derating:

A manufacturers listing of Switches

{Component Derating Guidelines}

Inductor Derating:

Inductors are also derated by reducing the maximum operating temperature based on the insulation class and reducing the operating voltage. A manufacturers listing of Inductors

{Component Derating Guidelines}

EMI Filter Derating:

Derate to 50% of rated voltage and 50% of rated current, using a maximum temperature of 85⁰C
A manufacturers listing of EMI/RFI Components

{Component Derating Guidelines}

Diode Derating:

A manufacturers listing of Diodes

{Back to Component Derating Guidelines}

Power Supply Derating Guidelines:

Operating Temperature range is normally 0 to 50^oC, derate 20% for each additional 10^oC increase above 50^oC.
Operating Temperature range; 0^oC to +70^oC. Full power to +50^oC then derate 2.5%/^oC to +70^oC. Or, derate linearly from 100% load @ 50^oC to 75% @ 60, derated at 10% per ^oC to a Maximum of +65^oC
Forced air cooling [20CFM nominal]: a power supply may require a forced air flow to operate at its rated maximum temperature rating. Derate 20% with out cooling
Open Frame supplies: may require an additional 15% power de-rating when covered by a frame.
About: The power supply specification should detail its operation, use the above as a rule of thumb. Normal operational temperature range is defined as ambient _[Maximum]
A list of Power Supply manufacturers.

{Back to Component Derating Guidelines}

Ambient temperature: The temperature of air or other media in a designated area, particularly the area surrounding equipment.

Engineering Key words: Component Derating, Derate, American Wire Gage, AWG, Ampacity, Fusing, Wire Sizing, Insulation, Rated Temp, Temperature, Guide, Guideline, Example, Class.

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