Supplementary insulation

Quenching the vapour with cold air in the chamber may increase the rate of heat removal although excessive nucleation is likely and the product crystals will be very small. Condenser walls may be kept free of solid by using internal scrapers, brushes, and other devices, and all vapour lines in sublimation units should be of large diameter, be adequately insulated, and if necessary, be provided with supplementary heating to minimise blockage due to the buildup of sublimate. One of the main hazards of air-entrainment sublimation is the risk of explosion since many solids that are considered safe in their normal state can form explosive mixtures with air. All electrical equipment should therefore be flame-proof, and all parts of the plant should be efficiently earthed to avoid build-up of static electricity. 

What if we have an exposed conductor that is not connected to earth (such as for equipment with a two-wire ac cord), or if earthing is itself not an acceptable level of protection for that particular type of equipment as per safety regulations Then, besides the layer of basic insulation, we need another insulating layer (with identical dielectric withstand capability). This is called supplementary insulation. Together these two layers (basic + supplementary) are said to constitute double insulation. We could also use a single layer of insulation, with dielectric withstand properties equivalent to double insulation (i.e. 3000 V ac or 4242 V dc). That would then be called reinforced insulation. So for example, if the equipment is by design, meant only for a two-wire ac cord, we would need two layers of approved insulators (or... 

The focus is often on one outstanding aspect of material performance e.g. refractoriness, electrical or thermal insulation, chemical resistance or wear resistance - the other properties are, at best, supplementary (Table 4). Such materials are generally only achieved with synthetic raw materials in combination with appropriate process engineering, for which utmost cleanness is essential. 

There are five types of insulation. Basic, supplementary, and reinforced insulation are most often applied for safety purposes. 

Supplementary insulation. An independent insulation applied in addition to basic to ensure protection against electric shock in the event of a failure of the basic insulation (equals two levels). 

Double insulation. Insulation comprised of both basic and supplementary insulation (provides two levels). 

Where sleeving is used as supplementary insulation on internal wiring, it must be positively retained in position and is considered as such if it can be removed only by breaking or cutting or if it is clamped at both ends. 

Parts shall be adequately secured so that should any wire, washer, spring, screw, nut, or similar part fall out of position or come loose, it cannot reduce the distances over the reinforced or supplementary insulation levels specified in the standards. As mentioned, parts fixed in place by screws or nuts with self-locking washers or other means are not liable to come loose, and soldered wires are not considered adequately fixed unless they are held in place near the termination independently of the soldered connection. 

Supplementary protective bonding conductors in domestic premises will normally be of 4mm copper with PVC insulation to comply with lET Regulation 543.1.1 and must be connected between all exposed metalwork (e.g. between metal baths, bath and sink taps, shower fittings, metal waste pipes and radiators), as shown in Fig. 3.79. 

A further compHcation remains in the control of enzyme activities which to a large extent is dependent upon expression during the fermentation. One potential solution is to add supplementary enzymes to the cell-free extract. Such a precedent has already been set by a few reported cases where whole cells were mixed with the isolated enzyme for ex vivo cofactor recycle. E>espite these problems, there is no doubt that as genetic engineering for expression of the desired enzyme is improved, more systems wiU be tested in the cell-free environment [26]. At the very least it is clear that cell-free extracts, combined with network topology analysis can provide an excellent basis for effective analysis and targeting of the network so as to insulate the desired pathway from undesired enzymatic reactions [27]. 

Portable apparatus may be of Class I construction, in which case the metalwork is earthed by a protective conductor which is a separate core in the flexible supply cable, or it may be of Class II construction, having no protective conductor terminal as its metalwork is not earthed. The essential safety feature of Class II apparatus is that the basic insulation is supplemented by additional insulation to provide a further safety barrier and danger arises only if both insulating layers fail. There are two types all insulated where the supplementary insulation is a plastic case, and double insulated where there is a metal case but live parts are separated from it by two layers of insulation. It is not advisable to use enclosed ventilated Class II apparatus in wet environments, because moisture may penetrate and provide a conductive film between the touchable surfaces and internal live conductors. 

Provisional supplementary classification of dense and insulating refractory castables 1972 1978... 

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