Isolation, electrical

Equipment must be isolated from all electrical energy sources by opening and locking all main power supplies. If the main power supply cannot be locked out, a qualified electrician must physically disconnect the equipment from the power source. Lockouts of electrical equipment are to be made at the main power supply—the use of local switches may leave other portions of the equipment energized. Once the electrical lockout is complete, an attempt should be made to start the equipment locaUy to ensure it is properly isolated before the maintenance work starts (and then all switches should be returned to their off position and tagged Do Not Operate ). 

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Oxidation of Silicon. Silicon dioxide [7631-86-9] Si02, is a basic component of IC fabrication. Si02 layers are commonly used as selective masks against the implantation or diffusion of dopants into silicon. Si02 is also used to isolate one device from another. It is a component of MOS devices, and provides electrical isolation of multilevel metalliza tion stmctures (12). A comparison of Si and Si02 properties is shown in Table 1. 

Efforts are made in the construction of new, large tank farms to achieve electrical isolation of buried and cathodically protected fuel installations from all... 

The danger of corrosion is in general greater for pipelines in industrial installations than in long-distance pipelines because in most cases cell formation occurs with steel-reinforced concrete foundations (see Section 4.3). This danger of corrosion can be overcome by local cathodic protection in areas of distinct industrial installations. The method resembles that of local cathodic protection [1]. The protected area is not limited, i.e., the pipelines are not electrically isolated from continuing and branching pipelines. 

In enamelled tanks with protection electrodes of low current output, fittings [e.g., heating surfaces (cathodic components)] must be electrically isolated from the tank and the ground. Figure 20-2 shows such a bushing. Smaller cathodic components which take up only negligible protection current (e.g., temperature probes) do not need to be insulated. 

The action of different balancing resistors can be seen in Fig. 20-11. The enamelled water heater had an electrically isolated heating element of stainless steel with a 2.5 m surface area. With R = 600 Q, the tank can no longer be cathodically protected at / = 800 D, on the other hand, all is well [13]. The potential of the... 

Electrical isolation Heat radiation Cooling coils Recent incidents Vacuum relief valves Accidents at sea Fires Problem sources Emulsion breaking Chimney effects Interlock failure Choosing materials. 

For every piece of equipment in a substation, manual switches—called disconnect switches—are provided to enforce complete electrical isolation from equipment before any service is pertornied. Disconnect switches are placed in clearly visible locations so maintenance personnel can continuously confirm that the equipment is isolated. The disconnect switch cannot interrupt current, so it is opened only when the current has already been interrupted by an automatic switch such as a circuit breaker. 

To avoid galvanic problems, different materials of con-stmction may have to be electrically isolated or at least the electrical resistance between them increased to a level sufficient to reduce the corrosion current to an acceptable value. In some instances it is more practical to paint or otherwise coat the more cathodic of the two parts of the couple. The anodic material should not be coated, since even more rapid penetration would occur at any breaks in the coating. 

If changes have been made to the process (e.g. if incoming water quality cannot be maintained or other uncertainties arise concerning the corrosion behavior of the construction materials) it is possible to incorporate coupons or probes of the material into the plant and monitor their corrosion behavior. This approach may be used to assist in the materials selection process for a replacement plant. Small coupons (typically, 25 x 50 mm) of any material may be suspended in the process stream and removed at intervals for weight loss determination and visual inspection for localized corrosion. Electrical resistance probes comprise short strands for the appropriate material electrically isolated from the item of plant. An electrical connection from each end of the probe is fed out of the plant to a control box. The box senses the electrical resistance of the probe. The probe s resistance rises as its cross-sectional area is lost through corrosion. 

Ensure equipment has been electrically isolated and suitably locked out and tagged. 

Before carrying out any inspections or maintenance procedures on belt drives, make sure they are not in operation. Equipment operators should electrically isolate the drive system and lock-out and tag the machine that is to undergo maintenance. Once this precaution has been taken, the belts and pulleys can be removed from the machine for inspection, cleaning, and repair. 

Consider requirements for electrical isolation in order to restrict the spread of protective current. Alternatively assess extra current allowance for unrestricted spread. 

An integrated circuit (IC) is a monolithic assembly of electrically isolated circuit elements. What this means is that each circuit element is formed on top of, or beneath, other circuit elements to form a compact assembly. Each conductive layer is separated by a non-conducting layer, usually composed of an oxide such as silicon dioxide, Si02- The assembly includes... 

Note that lines of 0.13 p, i.e.- 0.13 microns, in width are being formed routinely in the manufacture of 1C dice today (Just 3 years ago, the number was 0.18 p. It is expected to go to 0.08 p by 2010). Once the basic circuit is formed, then subsequent steps on each individual die form both n- and p-layers, electrically isolated from each other by a dielectric such as Si02. Both resistors and condensers are routinely formed in place as well. Note that formation of some of the layers is accomplished by use of gases such as AsHs, BBr3, or PH3. 

Here, it is easy to see the various layers and steps necessary to form the IC. We have already emphasized the formation of the n- and p-wells 8uid the individual proeess steps needed for their formation. Note that an epitaxial layer is used in the above model. There are isolation barriers present which we have already discussed. However, once the polysilicon gate transistors are formed, then metal Interconnects must then be placed in proper position with proper electrical isolation. This is the function of the dielectric layers put into place as succeeding layers on the IC dice. Once this is done, then the wafer is tested. 

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