Field guide
Arc Flash Labels for Motor Control Centers (MCCs)
Is a label required?
Yes. MCCs are worked energized constantly — bucket insertion and removal, starter troubleshooting, megger and voltage testing — and NFPA 70E §130.5(H) plus NEC 2026 §110.16 both land on exactly that kind of equipment. An MCC lineup without labels is one of the most common findings in a new facility walkthrough, and one of the most corrected.
What the label shows for this equipment
The MCC label shows the standard set: nominal voltage, incident energy at the working distance, arc-flash boundary, PPE level, assessment date, available fault current with its as-of date (motor contribution included — see below), and a study or label ID. Large lineups label per section or per work zone when values differ; bucket-level work is usually governed by the main bus calculation, but the label should say which calculation it represents. Configuration is often HCB — horizontal bus in a box — which is the configuration our engine computes highest at typical inputs.
NFPA 70E table-method rows for this class
| Equipment class row | Max fault current | Max clearing time | PPE category |
|---|---|---|---|
| 600 V class motor control centers | 65 kA | 0.03 s (2 cycles) | 2 |
| 600 V class motor control centers | 42 kA | 0.33 s | 4 |
Rows come from NFPA 70E-2018 Table 130.7(C)(15)(a), cells cross-verified against multiple independent reproductions. If your fault current or clearing time exceeds the row, the table does not apply — an IEEE 1584-2018 calculation is the path, which is what the calculator runs.
Notes specific to this equipment
Two MCC-specific notes. First, motor contribution: running induction motors feed a fault for its first few cycles, so the available fault current at an MCC is the utility-plus-transformer figure plus the motor contribution — the calculator's fault-current assistant applies it. Second, the two table rows above bracket the reality of MCC work: with fast clearing you sit in Category 2; let clearing stretch toward a third of a second and the same lineup is Category 4. The upstream device feeding the MCC — not the bucket breakers — usually sets the clearing time for bus work, so that device is the one to document.
What to collect before you calculate
Per lineup: the upstream protective device and its settings (this is the clearing-time source for bus work), available fault current at the MCC including motor contribution (motor horsepower totals from the bucket schedule), bus orientation for the configuration choice, and section layout for per-section labeling. The MCC bucket schedule and the upstream breaker's trip-unit face are the two documents that answer most of it.
Other equipment guides
Get the label numbers for your equipment in the free arc flash calculator — panel specs in, a reviewable record and label preview out. The master field list lives at arc flash label requirements; sizes and stock at the arc flash label template page.
Direct answers
Frequently asked questions
What PPE category does the NFPA 70E table assign to MCCs?
Two rows: Category 2 for 600 V class motor control centers at up to 65 kA and 0.03 seconds clearing, and Category 4 at up to 42 kA and 0.33 seconds. The row that fits depends on the actual fault current and clearing time — both must hold.
Do motors raise the available fault current at an MCC?
Yes. Running induction motors feed current back into a fault for the first few cycles, so a complete fault-current figure at an MCC adds motor contribution on top of the utility-and-transformer value. The calculator's fault-current assistant includes this adjustment.
Is an MCC always HCB configuration?
Frequently but not always — MCCs commonly use horizontal bus construction (HCB), but the configuration is decided at the specific work point. Bucket-level work can differ from main-bus work; check the section construction rather than applying a lineup-wide rule.
Source trail
Sources
Standards references identify the applicable document or section where possible. Standards text may require licensed access. Report a factual issue through the process on our corrections page.