Journeyman Electrician: Cabling and Conduits

Electrical Cable

The following are common cable assemblies:

Types of Conduit
Metallic conduit is designated with the following letters:

Conduits

Nonmetallic varieties include:

Conduit in concrete is considered to be in a wet location. 
Conduit or raceways encased in concrete should be a minimum of 1” deep to prevent cracking of the concrete.  There is a minimum cover requirement for buried conductors and conduit.  Cover is defined as the shortest distance between the top of a buried conductor and the finished grade.

Volt Receptacles and Plugs
Older homes may have ungrounded receptacles, and lamps and other small current devices sometimes use ungrounded plugs.  They may be unpolarized with both prongs being the same size, or polarized with the wider pin being neutral. These appear as shown:


Modern low power (15 amps) receptacles contain a grounding pin and are configured as:

Higher power (20 amps) plugs have a horizontal pin for the neutral, and 20 amp receptacles are configured to accept either 15 or 20 amp plugs.  It is acceptable to wire a 15 amp receptacle into a 20 amp circuit, because any device that requires the higher current would have the horizontal neutral pin that wouldn’t fit the lower current receptacle. 

The configuration of the 20 amp devices is:
30 Amp receptacles are sometimes used for even higher current 125 volt devices such as air conditioners.

Corona Effect
A corona occurs when there is a high potential difference between two transmission wires causing the discharge of electricity due to ionization of air from the high voltage.  It is characterized by a glowing region of air and a hissing sound.  Several thousand volts may be required to produce this effect and a very small current results because the ionized air has a relatively high resistance.  Coronas occur most commonly at sharp points on the conductive surfaces that tend to magnify the electric field strength and where the air gap between the conductors is small.

Rigid Metal Conduit
The reason for installing wires in a conduit is to protect them from damage.  Rigid metal conduit resembles water pipe and can be threaded or unthreaded.  Pipe and conduit threads are tapered unlike machine screw threads that are straight.  Unthreaded conduit required fittings for connections to other pieces.
Lock nuts are used on threaded conduits when they are connected to junction or outlet boxes.  Rigid conduit attached to an outlet box should have a locknut on the outside and a bushing on the inside.
Installed conduits should not have low points between successive outlets because this would allow water to collect there if it entered the conduit.
Wires are pulled through the finished conduit connections with a device called a fish tape.  The usual lubricant used on the wires is powdered soapstone.  Condulet fittings are special devices that are used instead of bends in conduit.  They have small plates on the side that when removed make pulling the wires easier.  A box with a blank cover can also be used to facilitate pulling the conductors, and this is called a coupling box.

Pipe and Conduit Fittings For threaded conduit: nipples are male to male fittings.  A close nipple is a short nipple that has threads over its entire length.  L’s make right angle turns.  Sleeves are female to female connectors.  Bushings and locknuts are used for connecting to boxes and other devices. Various connectors and adapters are used for unthreaded conduit.  The threadless conduit pieces are slid into them and secured either with set screws or compression fittings.  The fittings include couplings to connect two lengths of conduit together and threaded adapters with locknuts for installation into boxes.