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86 ⏐⏐⏐ RESISTANCE<br />

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FIG. 3.39<br />

Electric baseboard: (a) 2-ft section; (b) interior; (c) heating element;<br />

(d) nichrome coil.<br />

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the fins to remove any possibility of conduction between the current<br />

passing through the bare heating element and the outer fin structure.<br />

Ceramic materials are used because they are excellent conductors of<br />

heat and because they have a high retentivity for heat so the surrounding<br />

area will remain heated for a period of time even after the current<br />

has been turned off. As shown in Fig. 3.39(d), the heating wire that runs<br />

through the metal jacket is normally a nichrome composite (because<br />

pure nichrome is quite brittle) wound in the shape of a coil to compensate<br />

for expansion and contraction with heating and also to permit a<br />

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