Forensic Engineers and Consultants

Archive: Electrical and Control Systems

Danger Lurking in the Hot Tub

Several dangers involving the use of a hot tub (spa) may readily come to mind, such as the risk of shock or electrocution, or the risk of drowning for unsupervised young children.  Not so readily apparent is the effect of overheating the human body, or “hyperthermia”.

Some individuals are more susceptible to the effects of hyperthermia, including the elderly, young children, and those in poor health.  The effects of hyperthermia, or overheating of the human body, cause direct responses such as headache, nausea, heat exhaustion, increased cardiac output, lethargy, confusion, heat stroke and unconsciousness.  The onset of hyperthermia is defined as being at 99.5° F; if the body temperature reaches 104° F, a life-threatening medical emergency exists.  Read More

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Figure 1: A typical Ground Fault Circuit Interrupter (GFCI) Receptacle.

Testing…testing… Is this thing on?

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Many people just take for granted that something is just going to work, and in many cases assume that it will work forever.  One such device that does not get enough attention is the Ground Fault Circuit Interrupter (GFCI).   Simply put, a GFCI is a protective device that compares the current flowing on the hot and neutral wires of the circuit and will “trip” to disconnect power to the circuit if a small imbalance of current is detected.  The imbalance of current is an indication of a dangerous alternate path for the current to flow from a damaged line cord or a fault inside an appliance and constitutes a shock hazard to a person. Read More

Ground rod installed in the earth with clamp.

Grounding versus Bonding – Understanding the Difference in Building Electrical Systems

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While a teenager might be very familiar with being “grounded”, there is confusion over the meaning of the word in the electrical sense. In building electrical systems, “grounding” and “bonding” are two terms that are often misunderstood. Improper application of the concepts of grounding and bonding may create lethal shock and fire hazards. “Earthing” is a term which comes from the European International Electrotechnical Committee (IEC). Earthing is synonymous with grounding but often thought to have a different meaning. Read More

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Flood Damage to Electrical Equipment

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As a result of the recent weather, those of us in South Carolina have gained a renewed appreciation of the damage that can result from flooding. Even a few inches of flood water can result in property damage and a loss of services in addition to the immediate risk of physical harm. Read More

Figure 2: A view of a typical PLC.  The blue and red wiring to the right terminate at the PLC’s input / output wiring connections. The processor is to the left at the keyed switch.  This PLC has capacity to communicate over an Ethernet data link.

Forensic Examination of Losses that Include Programmable Logic Controllers (PLC’s)

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Many modern machines and processes are controlled by Programmable Logic Controllers (PLC’s).  PLC’s are essentially computers that have the ability, properly connected and programmed, to interface with the outside world and control the actions of a machine like a robot or conveyor.  The PLC has a processor for processing the user programmed logic, and also has input / output (I/O) wiring provisions for both analog (e.g. temperatures and pressure transducers) and digital (e.g. limit switches and indicator lights) devices.  Read More

Gas valves from a process furnace that experienced an explosion. The final gas safety shut off valve has its wiring cover partially open. This can be an indication that someone was directly powering the valve and bypassing the control system safety logic. Open wiring covers on controls should be fully investigated.

Stay in Control: Manipulation of Electrical Controls Can Lead to Fires and Explosions

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We have a saying at Warren, “When we go to work on a new case, usually someone else has had a very bad day.” If you are a plant manager at a factory, you know it’s a bad day when you hear the fire alarm or a loud explosion emanating from the back of the plant. Read More

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