Safety and cor­ro­sion in elec­tri­cal pan­els

DEMM Engineering & Manufacturing - - ELECTRICAL TECHNOLOGY -

In ser­vice in­spec­tion of elec­tri­cal pan­els is a re­quire­ment of nu­mer­ous elec­tri­cal stan­dards in­clud­ing AS/NZS 3000 Elec­tri­cal In­stal­la­tions and AS/NZS 3019 Pe­ri­odic Ver­i­fi­ca­tion. Part of the in­spec­tion process should in­clude an as­sess­ment of any rust or cor­ro­sion present within the panel. Rust and cor­ro­sion can oc­cur on both steel, cop­per and sil­ver com­po­nents used within the elec­tri­cal panel and if left unchecked can give rise to se­ri­ous prob­lems.

A study un­der­taken in the USA of some 1,052 elec­tri­cal pan­els found 12 per­cent of them had se­vere cor­ro­sion is­sues, to the level that the cor­ro­sion needed im­me­di­ate re­me­di­a­tion un­der the re­port­ing rules present. Light cor­ro­sion was present in some 40 per­cent of all pan­els in­spected.

Cause and ef­fect of cor­ro­sion

Causes of cor­ro­sion in elec­tri­cal pan­els can in­clude the pres­ence of mois­ture from the at­mos­phere, poor in­stal­la­tion prac­tices al­low­ing wa­ter to en­ter the panel or the pres­ence of cor­ro­sive gases such as hy­dro­gen sul­phide.

The ef­fect of cor­ro­sion in elec­tri­cal pan­els in­cludes: • Gen­eral un­safe op­er­at­ing con­di­tions

re­sult­ing in earth leak­age; • Elec­tri­cal mal­func­tion (in­ter­mit­tent)

through to com­plete elec­tri­cal cir­cuit fail­ure; • Over­heat­ing; • Fire.

From a safety per­spec­tive any of the above is of con­cern, rang­ing from mi­nor through to sig­nif­i­cant is­sues which can ul­ti­mately af­fect the well-be­ing of both peo­ple and equip­ment/ build­ings.

Light cor­ro­sion such as sur­face rust on the panel en­clo­sure will gen­er­ally not re­sult in elec­tri­cal fail­ure but is an in­di­ca­tion that all is not well in­side the elec­tri­cal panel and that re­me­dial ac­tion should be im­ple­mented. Se­vere cor­ro­sion will man­i­fest it­self with rust ev­i­dent on any steel com­po­nents used in­side the panel such as steel screws used in ter­mi­nal con­nec­tors. Cor­ro­sion on ser­vice en­trance wiring, fuse blocks or cir­cuit break­ers and bus­bars/con­nec­tors is a sure sign of ma­jor is­sues ahead.

Cor­ro­sion due to the en­vi­ron­ment

a. Mois­ture and wa­ter ingress. Wa­ter and mois­ture in­side an elec­tri­cal panel are the ma­jor causes of cor­ro­sion seen. This can oc­cur through: • Im­prop­erly sealed ser­vice en­try con­duits or the seal has de­te­ri­o­rated and per­ished over time; • Con­den­sa­tion in­side the elec­tri­cal panel due to changes in tem­per­a­ture or hu­mid­ity lev­els; • Sur­face wa­ter leak­ing in to the elec­tri­cal panel, gen­er­ally from be­hind the panel, due to poor in­stal­la­tion prac­tices or the fail­ure of ca­ble glands. b. Cor­ro­sive gases Gases such as hy­dro­gen sul­phide, chlo­rine, hy­drochlo­ric acid and sul­phuric acid will cause cor­ro­sion of the elec­tri­cal panel. The higher the level of cor­ro­sive gases present the more rapid the rate of cor­ro­sion with some pan­els go­ing out of ser­vice af­ter as lit­tle as three months. Th­ese gases are present in some in­dus­trial op­er­a­tions such as pa­per mills and waste wa­ter treat­ment plants but also oc­cur in na­ture such as in geother­mally ac­tive ar­eas.

Rec­om­men­da­tions

Haz­ardous and un­safe con­di­tions may be present in elec­tri­cal pan­els due to rust and cor­ro­sion. As the cor­ro­sion re­sis­tance of the parts used in­side an elec­tri­cal panel are gen­er­ally note known it is bet­ter to pre­vent cor­ro­sion from oc­cur­ring through var­i­ous abate­ment mea­sures.

Re­sis­tance against cor­ro­sion can be im­proved by prop­erly seal­ing elec­tri­cal pan­els against wa­ter and mois­ture ingress, pro­vid­ing dry con­di­tions in­side an elec­tri­cal panel by the use of heaters or a des­ic­cant and pro­tect­ing against cor­ro­sive gases by the use of pos­i­tive air pres­sure, air scrub­bers or neu­tralis­ers.

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