The recommended alternativeis to make effective use of the self-cooling
capabilitiesof a cabinet by meansof creating an internal air circulation and
achieve temperaturereductionthroughthe cabinet surface. If this doesnot
provide sufficient cooling, thenadditional coolingcould be providedby fixing
an air to watertypeheatexchangeto the cabinet.
15.5.9 Fieldboxes
Fieldboxesare frequentlylocated in hygienicproduction areas,and in such
circumstancesthe requirements statedbelowshould be strictly followed.Where
practicable and material availability allows, as a general principle it is
recommended for hygienic installationsthat the installer should standardise on
304 stainlesssteelfieldboxes.However, plasticmaybe acceptableprovidedits
exterior has a smooth finishthat can be cleanedeasily.A fieldbox should havea
minimum indexof protection of IP 55 allowingdustto be removedfromthe
enclosure'sexterior by watercleaning.
Special attention shouldbe givento the construction of doorsof fieldboxes.
In general,thereshould be a waterseal (PVC strip)between the doorand the
fieldbox. The capillary actionshouldbe reducedby providinga folded lip along
the top insideedgeof the door.For metal enclosures, the doorshould be
provided with a stud-welded earth terminal. Internal to the body of the
enclosure,fourstud-weldedgearplatefixingsand a furtherstudweldfor the
earthterminal should be provided.In orderto preventcondensate dripping from
the box into the product, field boxesshouldnot be placedin or abovethe contact
area. Furthermore, field boxesshouldbe located suchthateasyaccess for
maintenance and cleaningis practicable.
Boxes mounted on the wallor on a frameshouldbe:
∑ sealedto the wallor framewitha foodstandard siliconsealantso that soil
trapsare not created at the rear of the fieldbox,or
∑ stood-offthe wallor frameby a minimum distanceof 25 mm to enablethe
spacebetween the frameand box to be cleanedproperly.
RemoteI/O blocksand/orvalve islandsshouldbe installedin cabinetsor field
boxes.Thisis because the surfaces of valveislandsand remoteI/O blocksare
not easyto clean.
On/offvalvesand control valvesfrequentlyrequireone or more instrument
air connections,the air beingsupplied throughinstrumentair tubes. In principle,
the installation requirementsfor theseair tubesare similarin natureas thosefor
electricalor control cabling. Valvesshould be procured suchthat onlya single
instrumentair connection is requiredand other air distribution is integralto the
valve (Fig. 15.6).
15.5. 10 Lighting
Commonly,flush-mounted luminairescomplete with integral controlgearare
installed in the ceilingsof hygienicproduction areasfor generaland emergency
256 Handbookof hygiene controlin the foodindustry