Cut Sheet

14
Technical Data TD01701001E
Effective March 2017
UL low-voltage busway
Pow-R-Way III
EATON www.eaton.com
Physical data (continued)
Table 18. Ampere ratings needed to be at or below 1000 amperes/sq in density
UL 857 ampere rating
Bar size
Copper Aluminum
Standard
density
1000 A/sq in
density
Adjusted
rating
Standard
density
1000 A/sq in
density
Adjusted
ratingCu Al
225 225 1.62 556 556 None 556 556 None
400 400 1.62 988 988 None 988 988 None
600 600 1.62 1481 873 1200 — — —
800 — 1.62 1975 985 1350 1481 873 800
1000 — 2.25 1778 941 1600 — — —
1200 800 2.75 1745 873 2000 1164 985 1000
1350 1000 3.25 1662 982 2000 1231 941 1200
1600 1200 4.25 1506 800 2500 1129 873 1350
2000 1350 5.50 1455 1000 2500 982 864 1600
— 1600 6.25 — — — 1024 800 2000
2500 2000 8.00 1250 909 4000 1000 1000 None
3200 — 2.00 x 4.25 1506 800 5000 — — —
4000 2500 2.00 x 5.50 1455 1000 5000 909 909 None
— 3200 2.00 x 6.25 — — — 1024 800 4000
5000 4000 2.00 x 8.00 1250 N/A N/A 1000 1000 None
Application note
The above table is meant to help the user and specifier select the
higher busway ratings to meet the performance specification of
a current density value no higher than 1000 A per sq inch. The
current density values of our standard busway offerings based upon
temperature rise are listed in the 4th and 7th columns of the table.
These ratings are UL Listed and labeled, and safe to apply. However,
certain jurisdictions or applications require a better margin of safety,
and choose to use a 1000 A/sq inch density standard.
When the lower than standard densities are required, such as
1000 A/sq inch, then the only option is to oversize the busway
from the standard bar sizes and ampacity ratings. Oversizing
provides more bus bar material in cross-sectional area, and
results in lower current densities and lower temperature rises
for a given value of load current.
By example, take the case of 1600 A copper busway. The standard
product uses a bar size of 0.25 x 4.25 inches (1.0625 sq inch in area)
and which results in 1506 A sq inch density (calculated by
1600 A/1.0625 sq inch = 1506 A/sq inches), as listed in the table. If
a project or application using bus runs expected to carry 1600 A of
load current stipulated that the current densities experienced by the
busway should be no greater than 1000 A/sq inch, then oversizing to
busway bars used in the standard 2500 A rating using 0.25 x 8.00 inch
bars (2.0 sq inch area) yields a current density of 1600 A/2.0 sq inches.
800 A/sq inches for the 1600 A of load current.
Why not just oversize to 2000 A busway? The 2000 A bar size is
0.25 x 5.50 inches or 1.375 sq inches. Computing the new density
yields 1600 A/1.375 sq inch = 1164 A/sq inch, which is higher than
the desired value of no greater density than 1000 A/sq inch.
Therefore, the table provides a quick method of determining the
ampacity of busway required to meet current density values no
greater than 1000 A/sq inch for given values of load current. The
most important columns of data are the 1st, 7th, and 10th.
Eaton warrants that the Pow-R-Way III product will perform as
intended regardless of the method of selection, either temperature
rise only or current density. Eaton encourages specifiers who use
current density as the criteria for busway selection to select and
specify the busway ratings recommended in the above table under
the Adjusted Rating column, and to not rely upon the contractors or
bidders to resolve the matter in the later stages of a project. If sizing
busway is strictly based upon current density, do not specify or
use the standard ampacity values based upon the UL and NEMA
temperature rise standard on Contract Drawings.