Wednesday, March 12, 2014

Low Voltage Circuit Breakers

  March 12, 2014 Blogger   No comments

Based on IEC 60947-2 (LV switchgear and controlgear - Part 2: Circuit breakers):

 

In (Rated current)

 

The rated continuous / uninterrupted current that the circuit breaker can carry.

 

Icm (Rated short-circuit making current)

 

The short-circuit current that the circuit breaker can withstand as it is closing where the act of closing initiates the fault.

 

Icu (Rated ultimate short-circuit current)

 

The maximum symmetrical short-circuit current the circuit breaker can interrupt.

 

Ics (Rated service short-circuit current)

 

The breaking capacity such that the circuit breaker is tested to carry its current continuously. The test sequence verifies that the breaker can be returned to service. Ics is the maximum current the breaker can interrupt multiple times and be returned to service without being damaged and is expressed as a % of Icu.

 

Icw (Rated short time withstand current)

 

This is the steady state symmetrical fault current the breaker has to be able to carry for a duration of 0.05s to 3s without exceeding its thermal integrity.

Tuesday, March 11, 2014

Enclosure Powder coating RAL codes & chart

  March 11, 2014 Blogger   No comments

RAL is a colour matching system used in Europe. In colloquial speech RAL refers to the RAL Classic system, mainly used for varnish and powder coating but nowadays there are reference panels for plastics as well. Approved RAL products are provided with a hologram as of early 2013 to make unauthorised versions difficult to produce. Imitations may show different hue and colour when observed under various light sources.

 

 

Tuesday, March 4, 2014

Determining Temperature Rise

  March 04, 2014 Blogger   No comments

The temperature rise inside a sealed cabinet without forced ventilation can be approximated as follows.

First calculate the surface area of the enclosure and, from the expected heat load and the surface area, determine the heat input power in

watts/ft.2

 

Then the expected temperature rise can be read from the Sealed Enclosure Temperature Rise graph. Find where the input power

intersects the line for the enclosure material and read the approximate expected temperature rise at the left.

example:

What is the temperature rise that can be expected from a 48 x 36 x 16 in. painted steel enclosure with 300 W of heat dissipated within it?

solution:

Surface Area = 2[(48 x 36) + (48 x 16) + (36 x 16)] ÷ 144 = 42 ft.2

Input Power = 300 ÷ 42= 7.1 W/ft.2

From the Sealed Enclosure Temperature Rise graph:

Temperature Rise = approximately 30 F (16.7

Heat Dissipation in sealed electrical enclosures

  March 04, 2014 Blogger   No comments

heaT DissipaTion in sealeD elecTrical enclosures

The accumulation of heat in an enclosure is potentially damaging to electrical and electronic devices. Overheating can shorten the life

expectancy of costly electrical components or lead to catastrophic failure.

enclosure maTerials

The following discussion applies to gasketed and unventilated enclosures. Higher temperature rises can be expected with unfinished

aluminum and unfinished stainless steel enclosures due to their material's less efficient radiant heat transfer. Non-metallic enclosures

have similar heat transfer characteristics to painted metallic enclosures, so the graph can be used directly despite the difference in

material.

enclosure surface area

The physical size of the enclosure is the primary factor in determining its ability to dissipate heat. The larger the surface area of the

enclosure, the lower the temperature rise due to the heat generated within it.

To determine the surface area of an enclosure in square feet, use the following equation:

Surface Area = 2[(A x B) + (A x C) + (B x C)] ÷ 144

where the enclosure size is A x B x C in inches.

This equation includes all six surfaces of the enclosure. If any surface is not available for transferring heat (for example, an enclosure

surface mounted against a wall), that surface's area should be subtracted. Note: Enclosure volume cannot be used in place of surface area.

enclosure heaT inpuT

For any temperature rise calculation, the heat generated within the enclosure must be known. This information can be obtained from the

supplier of the components mounted in the enclosure.

enclosure TemperaTure rise (ΔT)

research has shown for every 18 f (10 c) rise above normal room

temperature 72 - 75 f (22 - 24 c), the reliability of electronic

components is cut in half.

The temperature rise illustrated by the curves in the Sealed

Enclosure Temperature Rise graph is the temperature difference

between the air inside a non-ventilated and non-cooled enclosure

and the ambient air outside the enclosure. This value is described

in the graph as a function of input power in watts per square

foot. In order to predict the temperature inside the enclosure,

the temperature rise indicated in the graph must be added to the

ambient temperature where the enclosure is located

 

Thursday, February 27, 2014

Tuesday, February 25, 2014

Terms AC1 and AC3

  February 25, 2014 Blogger   No comments

AC-1 - This category applies to all AC loads where the power factor is more than 0.95. These are primarily non-inductive or slightly inductive loads, such as heating. Breaking the arc remains easy with minimal arcing and contact wear.

 

AC-3 - This category applies to squirrel cage motors with breaking during normal running of the motor.

On closing, the contactor makes the inrush current, which is about 5 to 7 times the rated full load current of the motor.

On opening, the contactor breaks the rated full load current of the motor.

Monday, February 24, 2014

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