Figure 1. This terminal block for a dual-control electric blanket has four positive temperature coefficient (PTC) wires leading from it — two on either side.


Figure 2. PTC wire, center, is minute compared to the pencil at top and #14 AWG copper conductor at bottom; however, the two double strands of helically wound wire are distinctive and unlike anything else in a fire environment.


Figure 3. Both conductors for PTC wire are actually two, fine metallic conductors wound side by side (microscopic view).

To learn more about electric blanket fires, order Fire Findings, Vol. 8, No. 4

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