Electric Work: Installing a 550lb transformer above a drop ceiling.

Commercial and Industrial Wiring and Raceway Chart (continued)

Conductor size based on 75C Terminal rating [110.(C)(1)].

Ampacity based on four 90C current-carrying conductors

Table 310.15(B)(3)(a) and

Table 310.(B)(16).

Maximum continuous nonlinear load in an ambient temperature of 30C limited to 80 percent of

the overcurrent device rating or

the conductor ampacity,

which ever is less

[210.19(A), 240.6(A), 215.2(A)(1)].

To ensure ease of installation, raceways are sized to

six THHN conductors in PVC conduit [Annex C. 10].

Copper equipment grounding conductor is sized in accordance with Table 250.122.

Maximum continuous load is limited to 80 percent of 75C

conductor ampacity because the conductor ampacity is lower than

the overcurrent protection device rating.