General Applications

The facility side of power engineering: keeping lightning and surges off equipment, lighting a space, describing and billing a load, and grounding a system. It carries 8–12 of 80 questions across five subtopics: lightning protection, surge protection, illumination, energy management and demand calculations, and grounding. It draws on the Handbook and on the NEC (NFPA 70-2020).

What the problems look like

Short calculations and code lookups, often from a site plan, load profile or one-line. Recurring shapes — lightning: strike frequency against tolerable frequency, a rolling-sphere reach, a protective-angle check; surge: a traveling wave at a line-to-cable junction, arrester discharge current, protective margin against BIL, SPD type and rating; lighting: a luminaire or floodlight count, illuminance at a point, a cavity ratio, NEC lighting loads; demand: a factor from a 24-hour profile, an interval or ratchet bill, an energy saving, NEC demand factors; grounding: grid resistance, touch voltage, ground potential rise, and Article 250 conductor sizing.

By exam day you should be able to —

• compare N_D = N_G·A_D·C_D, with A_D = LW + 6H(L + W) + 9πH², against N_c = 1.5 × 10⁻³/C;
• set a rolling sphere from d_s = 10·I_p^0.65 (m, kA) and find its reach at grade, r = √(2Rh − h²);
• split a traveling wave: v_t = [2Z₂/(Z₁ + Z₂)]·v_i and v_r = [(Z₂ − Z₁)/(Z₂ + Z₁)]·v_i;
• run the lumen method, MMI = N·(lamps/luminaire)·(initial lumens/lamp)·LLF·CU/area with LLF = LLD·LDD, and the point method, E = (I/D′²)·cos θ;
• tell the demand ratios apart: demand factor = maximum demand/connected load, load factor = average/peak, diversity factor = ΣD_i,max/D_g, utilization factor = maximum demand/rated capacity;
• compute grid resistance R_g = (ρ/4)·√(π/A) + ρ/L (upper limit, grid shallower than 0.25 m), touch voltage E_touch,70 = (1000 + 1.5·C_s·ρ_s)·0.157/√t_s, and GPR = I_G·R_g;
• size the three Article 250 conductors, each from its own table.

Where people lose points

• Demand ratios: check the denominator — connected load, peak, or rating. A diversity factor is at least 1 and divides; a demand factor is at most 1 and multiplies. Losses follow the square of the load, so average loss uses the loss factor.
• Interval demand: billed demand is an average over the whole interval. A shed acts only on the minutes that remain.
• Lumen method: carry both CU and LLF, each once. "Maintained" means end of the maintenance cycle. Count luminaires, not lamps. Floodlights use beam lumens and CBU.
• Point method: the inverse square takes the slant distance; θ is measured from the normal to the receiving surface, so cos θ = D/D′ for a horizontal plane. Use the height above the lit point.
• Lightning: take (L + W) as printed — the 6 already covers four sides. Before using a protective angle, convert to feet and check the 50 ft limit, then the band from vertical: 63° up to 25 ft, 45° to 50 ft. For a sphere, keep the h² term and size it on the smallest stroke current.
• Surge: an arrester clamps only its own terminals. Add the lead voltage L·di/dt; an open cable end doubles the wave. Arrester current at a line end is (2v_i − v_discharge)/Z₀. Compare BIL only with the lightning-impulse protective level; the margin is BIL/protective level − 1.
• Article 242: SPDs serve 1000 V and below, surge arresters above. Compare an SPD's short-circuit current rating directly with the available fault current.
• Article 250: Tables 250.66 and 250.102(C)(1) both enter on the largest ungrounded conductor, summing parallel sets; Table 250.122 enters on the overcurrent device rating. Apply 250.66(A) only for rod, pipe or plate electrodes, and 250.122(B) by circular-mil ratio, excluding ampacity corrections. Touch voltage carries 1.5 where step carries 6.

Have these at your fingertips

The relations above, cold. Most sit in the Handbook under Lightning Protection, Protection Zone Determination, the lighting Calculations section, Demand Calculations, Energy Management, Step Voltage (where C_s is printed), Touch Voltage, Substation Grounding Resistance and Schwarz's Formula. The rolling-sphere reach, GPR and the surge relations are not printed. Load calculations are NEC Article 220, surge devices Article 242 and grounding Article 250. The exam opens one chapter of a standard at a time, and all three sit in NEC Chapter 2.

Going deeper

• Grounding and ground resistance testing on the PE Power exam — grid, rod and Article 250 sizing on one site
• The PE Power handbook and code books — working one chapter at a time
• Symmetrical components and unbalanced faults on the PE Power exam — the zero-sequence path behind ground-fault current
• Measurement and Instrumentation — soil resistivity and electrode tests

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