Heat Dissipation in sealed electrical enclosures

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

 

LV Switchgear Functions & Selection

DOWNLOAD :

http://www.schneider-electric.com.au/documents/electrical-distribution/en/local/electrical-installation-guide/EIG-H-LV-switchgear.pdf

 

Low Voltage Motor Control Center Installation Manual

DOWNLOAD :

 

http://www05.abb.com/global/scot/scot209.nsf/veritydisplay/008793e38b573ad8c12579cf00081a22/$file/2TDA090000P0001_REVB.pdf

 

Handbook of Electrical Installation Practice

DOWNLOAD :

http://www.beknowledge.com/wp-content/uploads/2011/01/c4ca4Electrical_Installation_Practice__Stokes.pdf

 

Terms AC1 and AC3

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.

Three-phase Distribution Boards And Socket Circuits (Trade of Electrician Standards Based Apprenticeship)

DOWNLOAD :

http://www.ecollege.ie/site/liu/electrical_notes/LL232.pdf

 

Cross Reference (Approximate) NEMA, UL, CSA, vs. IEC Enclosure Type

 

(Cannot be used to convert IEC Classifications to NEMA Type numbers)

International Standard Agencies

Understanding Type 2 Coordinated Protection in Motor Branch Circuits

The new IEC (International Electrotechnical Commission) standard, publication

947 “Low Voltage Switchgear and Control, Part 4-1: Contactors and Motor Starters,”

has been recognized by UL (Underwriters Laboratories) and is becoming

widely accepted by designers and users of motor control in the U.S. This standard

addresses coordination between the branch circuit protective device and the motor

starter. It also provides a method to measure performance of these devices if a short

circuit occurs. This standard defines two levels of component protection in the

event of a short circuit: Type 1 and Type 2 coordination.

 

This Product Data Bulletin describes:

 

_ How to conformto the new standard using motor controls built to meet

NEMA and IEC standards

_ Related benefits associated with Type 2 coordination

The IEC standard for motor starters and contactors, 947-4-1, defines two levels of

protection/coordination for the motor starter (contactor and overload relay) under

short circuit conditions. Each level of protection is achieved by using a specific

combination of motor starter and short circuit protective device.

_ Type 1 Coordination

Under short circuit conditions, the contactor or starter shall cause no danger

to persons or installation and may not be suitable for further service

without repair and replacement of parts.

_ Type 2 Coordination

Under short circuit conditions, the contactor or starter shall cause no danger

to persons or installation and shall be suitable for further use. The risk

of contact welding is recognized, in which case the manufacturer shall indicate

the measures to be taken in regards to equipment maintenance.

Faults in electrical systems are most likely to be of a low level, which are handled

well by motor controllers built to meet Type 1 coordination standards. After the

fault is cleared, the only action necessary is to reset the circuit breaker or replace

the fuses. In situations where available fault currents are high and any period of

maintenance downtime is crucial, a higher degree of coordinated protection may

be desirable.

Many industries are dependent upon the continuous operation of a critical manufacturing

process. In these conditions, it is especially important to understand that

Type 1 protection may not prevent damage to the motor starter components. In order

to ensure that high level fault or short circuit does not interrupt a critical process,

it may be prudent to consider implementation of Type 2 coordination in the

selection and application of low voltage motor controllers.

Type 2 coordination, which has no equivalent U.S. standard, does not permit damage

to the starter beyond light contactwelding, easily separated by a screwdriver or several

coil operations. Type 2 coordination does not allowreplacement of parts (except fus-

es) and requires that all parts remain in service. Beyond providing basic electrical and

fire protection, it also minimizes lost production, reduced productivity and unscheduled

disruptions resulting fromdowntime needed to replace or repair a starter.

 

SQUARE D Product Data Bulletin

Why Are Copper Bus Bars Plated?

Even though copper is the most popular choice for use in bus bars, and used very often in other electrical applications because it is more resistant to rust and corrosion than other metals, this doesn’t mean that it won’t oxidize over time.

 

When metals oxidize, the resistance in the conductive metal will increase, requiring more power to be used to carry current along the surface. When the copper oxidizes beyond a certain point, the metal can begin to flake and fall apart.

 

Many metals are plated in order to help them retain their positive qualities and attributes. When it comes to copper bus bars, plating is an important factor in longevity as well as maintaining the integrity of the conductive surface. When copper bus bars are not plated, over time the surface will oxidize. When that occurs, then more power is required to push electricity along the surface because the oxidized surface simply doesn’t conduct as well as a smooth, plated surface.

 

Plating, using tin or silver acts as a coating over the surface of the copper, helps to protect the copper from oxidizing. While this will not completely prevent oxidizing over a long period of time, it will dramatically reduce the effects of such oxidization. The reason why tin and silver is commonly used in the plating technique for copper is that both metals are considered soft metals, easier to work with when plating, and more importantly they don’t offer a great deal of resistance to electrical conductivity.

 

Which is better? Tin or Silver?

 

Throughout the industry there are different thoughts about which metal is better for plating copper, tin or silver. 10 microns of tin will outperform 1 micron of silver. With the price of silver climbing, tin becomes more economical, even though ten times the amount of tin will be required to do the same job.

 

When using silver to plate copper bus bars, a minimum of 3 microns should be used, and preferable 6 microns. On top of that, an anti-tarnish would need to be applied as well to protect the finish. In most fixed bus bar applications, tin is recommended. Silver should be used for moving bus bar parts in which arcing may be a concern.

 

For both tin and silver plating, anti-tarnish is important to keep the surface clean and conductive. When working with copper bus bars, plating is essential not only for longevity, but also integrity and safety.

 

Copyright :

http://blog.prv-engineering.co.uk/2012/05/why-are-copper-bus-bars-plated/

 

CE marking

 

The CE marking indicates a product’s compliance with EU legislation and so enables the free movement of products within the European market. By affixing the CE marking to a product, a manufacturer declares, on his sole responsibility, that the product meets all the legal requirements for the CE marking, which means that the product can be sold throughout the European Economic Area (EEA, the 28 Member States of the EU and European Free Trade Association (EFTA) countries Iceland, Norway, Liechtenstein). This also applies to products made in other countries which are sold in the EEA.

 

However, not all products must bear the CE marking, only product categories mentioned in specific EU directives on the CE marking.

 

CE marking does not indicate that a product was made in the EEA, but merely states that the product has been assessed before being placed on the market and thus satisfies the applicable legislative requirements (e.g. a harmonized level of safety) enabling it to be sold there. It means that the manufacturer has:

 

verified that the product complies with all relevant essential requirements (e.g. health and safety or environmental requirements) laid down in the applicable directive(s) and

if stipulated in the directive(s), had it examined by an independent conformity assessment body.

It is the manufacturer’s responsibility to carry out the conformity assessment, to set up the technical file, to issue the declaration of conformity and to affix the CE marking to a product. Distributors must check that the product bears the CE marking and that the requisite supporting documentation is in order. If the product is being imported from outside the EEA, the importer has to verify that the manufacturer has undertaken the necessary steps and that the documentation is available upon request.

 

Copyright CE-Marking

IEC 60364 Electrical Installations for Buildings

IEC 60364 Electrical Installations for Buildings is the International Electro technical Commission's international standard on electrical installations of buildings. This standard is an attempt to harmonize national wiring standards in an IEC standard. The latest versions of many European wiring regulations (e.g., BS 7671 in the UK) follow the section structure of IEC 60364 very closely, but contain additional language to cater for historic national practice and to simplify field use and determination of compliance by electrical tradesmen and inspectors. National codes and site guides are meant to attain the common objectives of IEC 60364, and provide rules in a form that allows for guidance of persons installing and inspecting electrical systems.

The standard has several parts:

 

Part 1: Fundamental principles, assessment of general characteristics, definitions

Part 4: Protection for safety

Section 41: Protection against electric shock

Section 42: Protection against thermal effects

Section 43: Protection against overcurrent

Section 44: Protection against voltage disturbances and electromagnetic disturbances

Part 5: Selection and erection of electrical equipment

Section 51: Common rules

Section 52: Wiring systems

Section 53: Isolation, switching and control

Section 54: Earthing arrangements, protective conductors and protective bonding conductors

Section 55: Other equipment

Section 56: Safety services

Part 6: Verification

Part 7: Requirements for special installations or locations

Section 701: Electrical installations in bathrooms

Section 702: Swimming pools and other basins

Section 703: Rooms and cabins containing sauna heaters

Section 704: Construction and demolition site installations

Section 705: Electrical installations of agricultural and horticultural premises

Section 706: Restrictive conductive locations

Section 708: Electrical installations in caravan parks and caravans

Section 709: Marinas and pleasure craft

Section 710: Medical locations

Section 712: Solar photovoltaic (PV) power supply systems

Section 713: Furniture

Section 714: External lighting

Section 715: Extra-low-voltage lighting installations

Section 717: Mobile or transportable units

Section 740: Temporary electrical installations for structures, amusement devices and booths at fairgrounds, amusement parks and circuses

 

Wikipedia