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Building Design and Construction Handbook - Merritt - Ventech!

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Horsepower<br />

15.38<br />

TABLE 15.3 Protection of Three-Phase 208-V Motors <strong>and</strong> Circuits<br />

Size <strong>and</strong> class<br />

of motor<br />

Ampere<br />

rating Class<br />

Branch circuit<br />

protection*<br />

Maximum<br />

size fuse<br />

permitted<br />

by the<br />

code<br />

Timedelaycartridge<br />

or lowpeak<br />

fuse<br />

that can<br />

be used<br />

Ordinary<br />

service<br />

Motor-running protection†<br />

Size of time-delay-cartridge<br />

or low-peak fuse<br />

Heavy<br />

service<br />

Maximum size<br />

40�C<br />

motor<br />

All other<br />

motors<br />

1 ⁄2 2.1 Any 15 5 2 1 ⁄4 2 1 ⁄2 2 8 ⁄10 2 1 ⁄2<br />

3 ⁄4 3 Any 15 8 3 2 ⁄10 3 1 ⁄2 4 3 1 ⁄2<br />

Size of fused switch<br />

or fuse holder<br />

Maximum<br />

size<br />

switch<br />

that can<br />

be used<br />

Size that<br />

can be<br />

used with<br />

time-delaycartridge<br />

or lowpeak<br />

fuses<br />

Minimum<br />

size of<br />

starter:<br />

NEMA<br />

size<br />

Minimum<br />

size <strong>and</strong><br />

type of<br />

wire:<br />

AWG<br />

or<br />

MCM<br />

1 3.7 Any 15 8 4 4 1 ⁄2 5 4 1 ⁄2 30 30 00 14 R 1 ⁄2<br />

1 1 ⁄2 5.3 Any 15 10 5 6 ⁄10 6 1 ⁄4 7 6 1 ⁄4<br />

2 6.9 1 25 12 7 8 9 8<br />

2 20 12 7 8 9 8 30 30 0 14 R 1 ⁄2<br />

3–4 15 12 7 8 9 8<br />

Minimum<br />

size of<br />

conduit:<br />

diameter,<br />

in<br />

3 9.5 1 30 15 10 12 12 12<br />

2 25 15 10 12 12 12<br />

3 20 15 10 12 12 12 30 30 0 14 R 1<br />

⁄2<br />

4 15 15 10 12 12 12<br />

5 15.9 1 50 25 171 ⁄2 20 20 20 60 30<br />

2 40 25 171 ⁄2 20 20 20 60 30<br />

3 35 25 171 ⁄2 20 20 20 60 30 1 12 R 1<br />

⁄2<br />

4 25 25 171 ⁄2 20 20 20 30 30<br />

71 ⁄2 23.3 1 80 35 25 30 30 30 100 60<br />

2 60 35 25 30 30 30 60 60<br />

3 50 35 25 30 30 30 60 60 1 10 R 3<br />

⁄4<br />

4 40 53 25 30 30 30 60 60

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