Combining neutral with ground Ground and neutral

1 combining neutral ground

1.1 fixed appliances on three-wire circuits
1.2 portable appliances
1.3 technical equipment

combining neutral ground

stray voltages created in grounding (earthing) conductors currents flowing in supply utility neutral conductors can troublesome. example, special measures may required in barns used milking dairy cattle. small voltages, not perceptible humans, may cause low milk yield, or mastitis (inflammation of udder). so-called tingle voltage filters may required in electrical distribution system milking parlour.

connecting neutral equipment case provides protection against faults, may produce dangerous voltage on case if neutral connection broken.

combined neutral , ground conductors commonly used in electricity supply companies wiring , fixed wiring in buildings , specialist applications there little alternative, such railways , trams. since normal circuit currents in neutral conductor can lead objectionable or dangerous differences between local earth potential , neutral, , protect against neutral breakages, special precautions such frequent rodding down earth (multiple ground rod connections), use of cables combined neutral , earth surrounds phase conductor(s), , thicker normal equipotential bonding must considered ensure system safe.

fixed appliances on three-wire circuits

in north america, cases of kitchen stoves (ranges, ovens), cook tops, clothes dryers , other listed appliances grounded through neutral wires measure conserve copper copper cables during world war ii. practice removed nec in 1996 edition, existing installations (called old work ) may still allow cases of such listed appliances connected neutral conductor grounding.

this practice arose three-wire system used supply both 120 volt , 240 volt loads. because these listed appliances have components use either 120, or both 120 , 240 volts, there current on neutral wire. differs protective grounding wire, carries current under fault conditions. using neutral conductor grounding equipment enclosure considered safe since devices permanently wired supply , neutral unlikely broken without breaking both supply conductors. also, unbalanced current due lamps , small motors in appliances small compared rating of conductors , therefore unlikely cause large voltage drop in neutral conductor.

portable appliances

in north american , european practice, small portable equipment connected cord set permitted under conditions have merely 2 conductors in attachment plug. polarized plug can used maintain identity of neutral conductor appliance neutral never used chassis/case ground. small cords lamps, etc., have 1 or more molded ridges or embedded strings identify neutral conductor, or may identified colour. portable appliances never use neutral conductor case grounding, , feature double-insulated construction.

in places design of plug , socket cannot ensure system neutral conductor connected particular terminals of device ( unpolarized plugs), portable appliances must designed on assumption either pole of each circuit may reach full positive voltage respect other.

technical equipment

in north american practice, equipment connected cord set must have 3 wires, if supplied exclusively 240 volts, or must have 4 wires (including neutral , ground), if supplied 120/240 volts.

there special provisions in nec so-called technical equipment, professional grade audio , video equipment supplied so-called balanced 120 volt circuits. center tap of transformer connected ground, , equipment supplied 2 line wires each 60 volts ground (and 120 volts between line conductors). center tap not distributed equipment , no neutral conductor used. these cases use grounding conductor separated safety grounding conductor purposes of noise , hum reduction.

another specialized distribution system formerly specified in patient care areas of hospitals. isolated power system furnished, special isolation transformer, intention of minimizing leakage current pass through equipment directly connected patient (for example, electrocardiograph monitoring heart). neutral of circuit not connected ground. leakage current due distributed capacitance of wiring , capacitance of supply transformer. such distribution systems monitored permanently installed instruments give alarm when high leakage current detected.