ICC E3 common mistakes
ICC E3 · Understand the traps and how to avoid them.
Applying the general 125% continuous-load multiplier to every load in a feeder or service calculation instead of only to the loads the code actually designates as continuous.
Candidates memorize 'continuous loads get 125%' as a blanket rule and then apply it to noncontinuous loads, lighting in dwelling units, or the largest motor, inflating the total and selecting an oversized conductor or service.
What to do instead
Before multiplying, classify each load as continuous or noncontinuous using the code definition, then apply 125% only to continuous loads and to the specific items the calculation method calls out (such as the largest motor). Write the classification next to each line of the calculation so the multiplier is defensible.
Treating the dwelling-unit general lighting and receptacle load as a simple VA-per-square-foot product without applying the permitted demand factors in the correct sequence.
The table-based demand factors are easy to look up but easy to mis-sequence; candidates multiply by a demand factor before summing, or apply a demand factor to a portion of the load that is not eligible for it.
What to do instead
Lay the calculation out in strict order: total general lighting VA from area, add small-appliance and laundry branch circuits, add other loads, then apply the demand factors to the correct subtotal only. Recompute the total a second time by a different route (per-phase or per-line) to catch sequencing errors.
Sizing an overcurrent device from the calculated load without checking it against the conductor's ampacity after adjustment and correction factors are applied.
Candidates size the conductor for the load, then independently pick a breaker 'close to' the load, forgetting that ambient temperature correction and conductor bundling adjustment can lower the conductor ampacity below the device rating.
What to do instead
Always run the sequence: calculate load, select conductor, apply adjustment and correction factors to get adjusted ampacity, then select the overcurrent device that protects that adjusted ampacity (using the permitted next-standard-size rule only where the code allows it). Show the adjusted ampacity number explicitly.
Confusing the grounding electrode conductor, equipment grounding conductor, and main bonding jumper and assigning the wrong sizing table to each.
All three are 'grounding' conductors, so candidates grab whichever table they remember first; the sizing bases differ (service conductor size versus equipment grounding conductor size versus the service disconnect rating).
What to do instead
Build a one-page comparison for yourself: what each conductor connects, what it is sized from, and which table governs. On every question, first name the conductor's function in words, then choose the table.
Assuming a standard 15 A or 20 A general-purpose branch circuit may serve any receptacle load, including fixed appliances and specific equipment that the code requires to have an individual branch circuit.
Candidates reason from everyday practice rather than from the code's list of loads that require dedicated circuits, so they approve a design that violates the individual-circuit requirement.
What to do instead
Memorize the short list of loads that require individual branch circuits (specific appliances, motor-driven equipment, certain heating and cooking equipment) and check every fixed appliance on the plan against that list before approving a shared circuit.
Missing that a plan set lacks the required fault-current or available short-circuit information, and approving the overcurrent devices without it.
Candidates focus on wire sizing and device ratings and treat short-circuit current as an engineering detail outside the plan review scope, so they never ask for the value that justifies the interrupting rating.
What to do instead
Add a fixed checklist item to every review: available fault current at the service and at each panel, plus the interrupting rating of every device. If the number is absent, the review is incomplete regardless of how good the rest of the plan is.
Reviewing special occupancies (hazardous locations, health care, assembly, motor fuel dispensing) using the general Chapter 1-4 rules and skipping the occupancy-specific articles.
The general rules feel sufficient and the special-occupancy articles are long, so candidates skim them and miss classification, wiring-method, and location restrictions that override the general rules.
What to do instead
For any special occupancy, start from the occupancy article and its classification scheme (class/division or zone, or location category), then layer the general rules on top. Note in the review which specific article drove each requirement.
Approving a feeder or service design without verifying that the neutral or grounded conductor is sized for the actual unbalanced load rather than simply matching the ungrounded conductors.
Candidates default to 'same size as the phase conductors' and do not consider that the neutral may be reduced for certain loads, or conversely must be full-sized or larger for harmonic-rich loads.
What to do instead
For every feeder, state the basis for the neutral size: maximum unbalanced load, permitted reduction, or a prohibition on reduction. If the plan does not show the basis, mark it as an information request.
Failing to distinguish which code edition and local amendments govern the plan under review, and citing requirements from a different edition.
Candidates study from mixed sources or from memory of a prior edition, and the administrative provisions that fix the applicable edition are treated as boilerplate.
What to do instead
Make the first step of every review an explicit check of the adopted edition, effective date, and any local amendments, and record it at the top of the review notes. Cite section numbers from that edition only.
Treating the plan review as a pass/fail judgment on the drawings alone, without documenting deficiencies as specific, code-cited comments that the designer can act on.
Candidates want to demonstrate knowledge by writing long explanations, or they write vague comments like 'not per code', which fails the administrative requirement for a clear, actionable review record.
What to do instead
Use a fixed comment format: location on the plan, the requirement with section citation, what is deficient, and what would resolve it. Keep each comment to those four elements and avoid narrative.