Minutes of Meeting Volume 17 (Paperback)

This historic book may have numerous typos and missing text. Purchasers can usually download a free scanned copy of the original book (without typos) from the publisher. Not indexed. Not illustrated. 1902 edition. Excerpt: ...pressure. Present practice, which is giving excellent results, is to allow for 5,000 to 25,000 volts working pressure a minimum thickness of rubber insulation of.030," and of paper of.040," for each 1,000 volts working pressure. The distributisn of the insulation in multiple conductor cables deserves consideration. If two or more similarly insulated cores are laid. or stranded together, the thickness of the insulation between conductors is double that between each conductor and the earth (usually the lead sheath of the cable). If a system were to be permanently free from grounds, or if the circuit was of such a nature that the pressure between conductors was under all conditions greater than between each conductor and the earth, as in a three-wire net-work with neutral conductor grounded, this arrangement would be proper. In most systems. however, accidental grounds do occur on one leg of the circuit. bringing the full potential to bear for the time being between all the other wires of the system and the earth. Further, this is apt to happen during the burning-out of a transformer, cable, or possibly a generator, at which time the potential is very apt to exceed the normal when the short circuit is broken. It is better, therefore, to use the so-called split type of insulation with multiple conductor cables--that is, to put one-half of the total thickness of the insulation required on each conductor and the other half of the insulation on in the form of a jacket surrounding the cores after they have bieen stranded together. This gives the same thickness of insulation between each copper core and the earth as exists between conductors and also reduces the total diameter and cost of the cable. The idea is an old one and the...