Electrical Guidelines

Service considerations for temperature increases over ambient temperature in electrical panel boxes, switches, wiring, motors etc.

Celsius            Fahrenheit

High voltage

>50                  >100                Danger           Immediate repair required

>30-50           >90-100         Critical           Repair as soon as possible

>20-30             >70-90             Warning         Schedule repair

<20                    <70                  Alert               Monitor

 

Low Voltage

>30                  >90                    Danger           Immediate repair required

>20-30           >70-90             Critical           Repair as soon as possible

>10-20           >50-70             Warning         Schedule Repair

>5-10              >40-50             Alert               Monitor

 

These problems may be caused by

Circuit overload

Electrical circuit overloads happen when more amperage is put across an electrical wire or circuit than it was designed to handle. For instance, a #14 wire can safely carry 15 amps and should be protected by a 15-amp breaker. If it happens to get connected to a 20-amp breaker instead, the breaker will allow 20 amps of current to flow through a wire that can only handle 15 amps. The wire and breaker may start to heat up and could cause start an electrical fire.

Ampacity of the circuit can be calculated by dividing the amount of wattage by the voltage. Let’s say you have a 1,000-watt hair dryer that runs on 120 volts. Divide that out and you’ll get 10 amps of current draw. On a 20-amp circuit, that’s half of the circuit used already.

Now, think about having a meal at your house. You plug in a couple of crock pots that each draw 1,000 watts of power and you can see how the circuit is at maximum capacity. The problem is, that likely there are other things plugged in also and undoubtedly the circuit will trip. In this case, the only way to solve the problem is to plug one of the devices into another outlet on a different circuit.

Circuit overloads can also be caused by loose or corroded wires and connections. This could be a breaker connection, a splice in a box, especially if the connection has been exposed to moisture, it could be a wire is not making good contact under a wire nut splice, only because the wire were not lined up evenly when installed, or it may be a loose connection on a part of a light fixture. Of course, the list goes on and on. The point is, if the breaker trips or the fuse blows, there is a problem. It may be a short or just a circuit overload.

 Corroded / Loose terminals

Badly corroded buss, breakers and connections will eventually overheat from the arcing (commonly seen as flickering lights) and is a potential fire hazard..

Oxidized or corroded wires will increase the resistance of conductors and create the potential for arcing causing overheated components.

Corrosion can result in circuit breakers failing to trip, make connections less reliable, and make the equipment unsafe to touch.  The sound of arcing (a cracking or popping sound) indicates a problem.

External heat sources

If there are external heat sources that raise temperature in an electrical cabinet above ambient room temperature a secondary air ventilation system for the cabinet should be considered

Grounded

The word GROUNDED means connected to the earth.  The grounded wire does not normally carry current and is used to connect all exposed electrical devices to the grounding electrode (rod) or grounding electrode system.

When all surfaces are connected together and to earth, the voltage between them and earth even when a fault occurs remains near zero.  This minimizes the shock potential and is a requirement for any electrical system.  In a system with the proper protection devices, the possibility of someone receiving an electrical shock when touching a faulty appliance and a ground outside the electrical system such as a water piper or sink will be non existent.

In North American there may be some leakage through appliances between the black wire (live current) and the white wire (grounding).  The capacitive leakage current is caused by the fact that the wiring, transformers and interference filters all have some capacitance between the ground and live wire. The amount of current is limited to be quite low (limited to be between 0.6 mA to 10 mA depending on equipment type) so it does not cause dangers and big problems.

The ground wire circuit should have the capacity to carry whatever stay current that may be seeking ground.  It the ground wire does not have the capacity to safely carry the load it will melt resulting in no ground for the circuit, a very dangerous situation.

Phase Imbalance                   (Voltage variation between ground and current circuits)

Electrical equipment; especially motors and their controllers; will not operate reliably on unbalanced voltages in a 3-phase system. The difference between the highest and the lowest voltages of the power sources should not exceed 4% of the lowest voltage. Imbalances may cause overheating of components; especially motors.  Intermittent shutdown of motor controllers is a possibility. Motors operated on unbalanced voltages will overheat, many overload relays can’t sense the overheating. In addition, many solid-state motor controllers and inverters include components that are especially sensitive to voltage imbalances.

Phase imbalance occurs when single-phase equipment with various current ratings are connected to one of the source phases of a three-phase source. When three-phase equipment is connected to the same power system, problems may result.

Phase imbalance can result in high or excessive third order harmonics, nuisance tripping of circuit breakers and destructive over-heating leading to failure of other components in the distribution system.

Emissivity of the material must be considered.  (see Factors affecting Thermal Infrared Images)

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