<P> Beyond the basic profiles or contours (smoothwall, corrugated, or ribbed), innerduct is also available in an increasing variety of multiduct designs . Multiduct may be either a composite unit consisting of up to four or six individual innerducts that are held together by some mechanical means, or a single extruded product having multiple channels through which to pull several cables . In either case, the multiduct is coilable, and can be pulled into existing conduit in a manner similar to that of conventional innerduct . </P> <P> Conduit is of relevance to both firestopping, where they become penetrants, and fireproofing, where circuit integrity measures can be applied on the outside to keep the internal cables operational during an accidental fire . The British standard BS 476 also considers internal fires, whereby the fireproofing must protect the surroundings from cable fires . Any external treatments must consider the effect upon ampacity derating due to internal heat buildup . </P>

Emt is about thinner in wall thickness than rmc and is known in the field as