The effect of growth on electrical equipment reliability and safety

Growth is something that every company, regardless of industry sector, has as a stated goal. Increased revenue, greater market presence, and the prestige of leading an industry are appealing to most organizations, so the incentives for growth are strong.

However, as most industrial facilities struggle to maximize production and increase efficiencies, the addition of electrical equipment can actually work to their detriment. This kind of growth – increased loads on existing electrical apparatus, and the addition of new apparatus to existing electrical infrastructure – can have deleterious effects on many aspects of equipment reliability.

This article explores how the growth of equipment, when not properly tracked and managed, can negatively impact overall equipment health, personnel safety, and ultimately, the bottom line of a facility. This impact can be in the form of power quality issues, increased ambient temperature in equipment rooms, and on the work/rest cycle of maintenance and reliability team members.

Turning up the heat

There is a physical condition known as thoracic outlet syndrome that affects mainly the upper limbs of a person's body and that can result from physical over-training. Symptoms include inflammation in the shoulders and arms as well as both pain and numbness. In athletes, it's commonly understood to be the result of too much of a good thing, and can be remedied by a more controlled approach to a person's workout goals.

This condition is a good metaphor for almost any other type of otherwise positive growth, including industrial facilities where the goals can include meeting more aggressive production schedules, increasing throughput, and increasing productivity in the same space, all of which can lead to less than optimum equipment conditions. If the conditions are recognized and corrected in a timely fashion, long-term damage can be avoided. However, when equipment conditions are ignored and growth is not managed safely and effectively, the negative outcomes can be quite serious, and even life threatening.

Let’s look at electrical load first. The National Electric Code (NEC) gives guidance on what typically is referred to as the “80% Rule”. This rule states that for continuous duty, which is defined in NEC Article 100 as maximum current for longer than three hours, a circuit fed from a single source should not exceed 80% of the capacity of the circuit. So, for a 20 amp circuit, 16 amps of continuous duty should not be exceeded. Having spent the greater part of our adult lives performing various types of electrical predictive maintenance (PdM) services, we can say that this rule is broken as often as it is followed. What may not be as readily apparent is the detriment of such conditions.

Perhaps you’ve heard of the joule effect? Heat generated in a circuit or conductor is a product of the resistance of the circuit and the current through the circuit. The amount of heat energy generated goes up as current (i.e., load) increases, and it increases at the square of the current. This phenomenon often is expressed as the equation P=I2R, with P being Power (in the form of heat). What is often not understood by otherwise conscientious electrical professionals is the fact that electrical resistance is a product of temperature. So, as we increase the load on a circuit, we increase the amount of heat generated in the circuit. That heating causes an increase in electrical resistance in electrical components subjected to the increase in ambient temperature where the circuit in question, or the larger electrical system component, is located.

Most electrical apparatus are rated according to an expected ambient air temperature in the environment where the apparatus is installed. When an electrical space is occupied by numerous electrical apparatus, heat is already being generated under normal loading conditions. What then is the impact when we add load, because of growth? New equipment needs to be fed from somewhere, right? We have an electrical room right there, and there’s space in the panels, so problem solved. Actually no, we may have just caused a problem rather than found a solution.

It’s like the old joke about not being out of money because you’ve still got checks in your checkbook. Just because there are open circuit breaker slots in a panel does not mean that capacity is available to accommodate the added equipment. Once we start to over-duty circuits, more heat is generated. NEC Table 310.15(B)(16) gives allowable ampacities of insulated conductors, and includes temperature withstand ratings for the various types of commonly used insulation. The caveat here, and it is mentioned in the table, is that these figures are based on an ambient temperature of 30ºC (86ºF).

Just for the sake of clarity, let’s define “ambient temperature”. Merriam-Webster defines ambient temperature as “interface temperature between a surface and the fluid medium surrounding that surface”. To be technically accurate, “ambient temperature” is not always synonymous with “room temperature” unless, of course, the electrical apparatus is in the open air of the room. Usually, electrical apparatus is inside of an enclosure, and there is typically a difference in temperature between the room where that enclosure is found and the temperature inside of the enclosure. The temperature inside of the enclosure should be considered the ambient temperature for any electrical components internal to that enclosure.

Having said that, the addition of electrical equipment to an existing electrical architecture will drive up both the device ambient temperature and the overall room temperature. This thermal impact must be considered not only for how it affects equipment, but also how it affects personnel. We’ll explore that further in a moment.

Where are you growing?

Another potential impact of electrical growth is on space. The added equipment has to go somewhere, and as mentioned earlier, just because there is available space doesn’t mean that equipment should necessarily be installed there. NEC Article 110.26 discusses the spacing requirements for electrical equipment. Many folks are aware of the 36 inch rule for clearance in front of electrical enclosures. How many places have you been where the yellow and black striped tape is on the floor indicating that particular boundary? And why do these boundaries exist?

Simply put – in fact, as stated in the first paragraph of Article 110.26 – “to permit ready and safe operation and maintenance of such equipment”. Further in this article are some very specific guidelines for the width, height, and depth of the “working space”. One such rule regarding working space width states that the working space must permit “at least 90 degree opening of equipment doors or hinged panels”. When we begin to overcrowd electrical spaces, we may restrict movement of covers, encroach on working spaces, and begin to negatively impact the egress from the working area, which is another consideration of equipment spacing discussed in Article 110.26.

Keeping your people safe

Hopefully the cumulative effect of electrical growth is becoming clearer. The thermal impact: more current means more heat. The spacing impact: more equipment means less working space. There can be a negative impact on personnel from each of these sets of conditions as well. While some of those impacts might be easy to recognize, some might not be.

Thermal impact is the most obvious of these: fatigue levels increase in high-temperature, high-humidity environments. This is further exacerbated in qualified electrical personnel due to the application of arc flash rated Personal Protective Equipment (PPE). The purpose of arc flash rated PPE is to protect personnel from the potential of burn injury in the event of the release of energy from an arcing fault in electrical apparatus. The level of PPE is driven by the amount of potential energy present at each point along the electrical distribution path. In some instances, the PPE required for maintenance tasks can be cumbersome. Level 3 PPE requires a flash suit hood, 25 calories per centimeter2 full body coverage, gloves, and leather shoes, so imagine how much more heat stress an employee adorned in this level of PPE would be subjected to in a very short period of time.

OSHA gives guidelines for the work/rest interval for PPE application in high-temperature, high-humidity areas. For ambient temperatures over 90ºF, the work rest cycle is 20 minutes of work, followed by 20 minutes of rest. While this guideline exists, in a high-tempo maintenance environment, we’d be willing to bet that this interval is often not followed. The result is increased risk of heat-related injury to the employee. This can be multiplied in an environment where additional equipment and the associated increase in area ambient is overloading any conditioned space measures.

Less obvious is the danger to overall electrical safety by overcrowding electrical rooms and production areas with added equipment over time. There is a provision in the Institute of Electrical and Electronics Engineers (IEEE) Standard 1584, Guide for Performing Arc Flash Hazard Calculations, that allows the over-current protective device clearing time to be limited at two seconds for the purposes of incident energy calculations. This "Two-Second Rule", as it is known, is often applied for electrical apparatus with a higher than two-second clearing time when it can be reasonably expected that a qualified electrical person could egress the area of the arcing fault in two seconds or less. This guideline is widely applied when using only the clearing time causes incident energy calculations to be restrictively high.

Imagine an instance wherein a maintenance electrician is interfacing with a device where, unknown to him, the two-second rule has been applied, and then in the event of an arcing fault, he is subjected to higher energy exposure than he is protected against because egress from the area of the fault is inhibited by equipment overcrowding. In such a case, the qualified electrical person would be applying PPE in accordance with the label, when that PPE level was arrived at with an expectation that the apparatus in question would continue to have adequate working space to allow egress.