Resource: Safe electric wiring
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240 volt plug has 3 outlets, but
box has 4 wires Resource: Safe electric wiring |
| Use only 600 volt wire. Lamp cord, extension cords are not rated 600 volt. Use copper wire only. Aluminum wire is fire risk and should be avoided or installed by professional. 30 amp breaker use 10 gauge / 120-240 volt 30 amp outlet can be installed on 30 amp breaker only/ use 10 gauge wire ... cannot be connected to 15-20-40 amp breaker.  Orange/ #10 gauge wire, with ground ... 30 amp capacity. Safe maximum: 30 x 80% = 24 amps. Buy: 10-2 gauge/ 30 amp 10-3/ 30 amp Southwire electric tools |
Yellow
12 gauge 20 amp 120 volt 20 amp outlet can be installed on 20 amp breaker, but not 15 amp breaker/ use 12 ga wire. ... cannot be connected to 30-40 amp breaker. 1  Yellow/ #12 gauge wire, with ground ... 20 amp capacity. Safe maximum 16 amps. Buy: 12-2 gauge/ 20 amp 12-3/ 20 amp NMB is house wiring UF is underground Rolls of stranded wire |
 Multimeters Voltage is tested across two separate wires. Ohms or resistance is tested across both ends of same wire. Amperage is tested along one or two points on same wire. Buy: Analog multimeter Multimeters at Amazon Klein multimeter Electric testers at Amazon Clampmeter for testing amp flow on line |
 Electrical tools must be insulated. Always best to disconnect power, but insulation failure, lack of proper grounding, grounded neutral, lack of GFCI, out-of-code wiring, generator operating without transfer switch, and other problems still pose a risk to anyone working on electric power ... even when breaker is off. Buy: Electrician tools kits KLEIN TOOLS Tools kits IRWIN tools KNIPEX Telephone cable knife Low Voltage Mounting Bracket for Telephone |
 Protect wiring from damage Use nipper instead of pliers or screwdriver for removing staples (and nails). Do not damage cable or wires inside cable. -Code says: Cable SHALL BE secured without damage to the outer covering. NEC sec. 336-15 Buy End cutting nippers at Amazon |
Double-pole 240 volt
breaker QP type 2" wide Plug-in breakers Buy double-pole: Choose from 15 to 125 amp |
 Kirk
asks:I have older house with a 240 volt 30 amp receptacle (outlet) for electric dryer. The wire coming into box for dryer plug has 4 wires. Two hot wires, a Neutral and a ground, but the new receptacle for dryer only has three slots. One each for the Hots ... but is the third screw for both Neutral and ground? I saw that the Neutral and Ground are connected in the Main Panel. Questions: What do I do with
the
bare Ground wire?
Can I combine the Neutral and Bare Ground to the same screw, since they’re like that in the Main Panel? Answer: Be careful here. The Neutral is NOT connected to a 240 volt 3-prong outlet. The Neutral should be capped off and not used.  If you have outlet or receptacle
with 3 prongs that you are installing
inside a box that has 240 volt with 4 wires (2 Hots, Neutral, ground),
then the Neutral is not used ... instead the Neutral is capped off with
twist on connector... makes
sure connector is
very tight ... covers all bare copper ... and cannot come loose.Result: the plug will have 2 hots and a ground. ... which is all that's needed for modern 240 volt appliances. The ground wire must be connected to green ground screw or screw marked G, but never connect Neutral and ground on same screw terminal. Look at markings on 3-prong receptacle and it should be marked X Y G. The X and Y terminals are usually black, dark brown, or brass colored and are for the two Hot wires. The G terminal is green, and is for the ground wire ... but do NOT connect the Neutral to any terminal. Resources: How to wire 240 volt outlets Why you need ground wire |
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 Terminology:(1) Receptacles and outlets are same thing, They are screwed into a box with a cover applied. They are wired to power line that comes from breaker box. They come in 15, 20, 30, 40, 50 amp sizes, offering a variety of configurations, including straight-blade and twist-lock, with 3-4-5 openings available for single and 3-phase applications. Every receptacle has an opening dedicated for grouned connection to whatever device is plugged into the receptacle. (2) Plug is the 'plug' at end of cord that you push into receptacle. They come in straight-blade and twist-lock. (3) Connector is the female end on an extension cord..They come in straight-blade and twist-lock. | |
| What if your plug is 4 prong, but outlet is 3-prong Answer 2: If you have a new plug that is installed on end of a cord ... and the plug inserts into outlet or receptacle ... and the dryer or appliance cord has 4 wires ... Hot Hot Neutral ground ... which is uncommon today ... but can be found on some clothes-washing appliances where the washing machine plugs into dryer (whoever thought this up this idea should be fired) ... then assume the appliance requires a Neutral wire.  In
this case, the new plug must have 4 terminals X Y W G for attaching
the 4 wires. Buy: 4 prong plug 4-prong outlet Box cover for outlet Surface mount outlet The problem folks encounter with a 4-wire 240 volt single phase household appliance with a 4-prong plug, is modern household 240 volt wiring typically does not include a Neutral wire ... and the outlet or receptacle only has 3 prongs ... not the required 4 prongs. The solution requires a new 30 amp outlet with 4 prongs ... and adding a Neutral wire. Adding a Neutral can be accomplished 2 ways: (1) Change the 10-2
w ground cable coming from breaker box (main panel) to a 10-3 w ground
cable
Must
use electrically rated 600 volt wire as printed on cable sheathing.
Cannot use extension cord for permanent in-wall wiring.
(2) Bring a Neutral wire over from the a nearby 120 volt outlet. Best to use solid copper wire, and not stranded. Wires heat up when appliance is drawing amperage.  Continual
heating and cooling of 14-12-10-8 gauge wire under screw terminals
causes expansion and contraction that can cause stranded wire to splay
apart, come loose under terminal, start overheating, and eventually arc
and fail. Applies to switches, outlets and circuit breakers.Stranded wire can be joined with short piece of solid wire using twist on connector, and then the solid wire put under screw terminal.. To
bring Neutral from nearby outlet requires at least a 12-2 cable (on a
30 amp breaker) from the nearby 120 volt box. You can run a single wire
(not a 12-2 cable, but just a single wire) if and only if you install
inside conduit. | |
 Code
for 30 amp outlet:By code, a 30 amp outlet must be connected to 30 amp breaker. Cannot be connected to 15-20-40-50 etc amp breaker. Use minimum 10 ga wire .... suggest always use solid copper wiren and not stranded wire, and never aluminum wire. Can use larger 8 ga wire if wire fits screw terminals. Tighten screws very tight against wire. Resource: Color code for wire -Outlet must be installed inside electrically-rated rectangle box (deep box is easiest for heavy gauge wires ... metal or plastic). Box must match outlet. Box must have cover that matches the outlet. Buy: 30 amp outlet cover -Cannot use homemade box, round box, octagon box, square box, junction box, pull box, etc. -As an option, you can use all-in-one surface mount box with 30 amp outlet Buy 30 amp surface mount Wire or conduit must be clamped to box, and box attached to structure. Movement is a major cause of electrical failure, fire, short, hazard etc. | |
4-prong residential outlet: If the 240 volt residential outlet has 4 prongs
... then
the
markings will show X Y W G. With W for Neutral.By code, 240 volt outlets with 4 prongs must have 4 wires ... including 2 Hots, Neutral and ground. 3-phase 4 and 5 prong outlets 4 prongs 3-phase commercial outlet markings will show X Y Z G ... corresponding to 3 Hots and a ground ... and outlet must have 4 wires. 5 prong 3-phase outlet will be marked XYZWG ... and requires 3 Hot wires, a Neutral and ground. Resource: Difference single-phase and 3-phase Neutral and ground: It is against code to connect Neutral and ground wires to same screw ... it is against code to use a Neutral wire for ground, or against code to use ground for Neutral.  Why? - (a) The ground wire must be separate and provide a direct, low-resistance path for short circuit to reach the ground rod driven into soil outside home or building. This allows unrestricted flow of excess current (or overcurrent from short circuit or insulation failure) to be absorbed by earth. The ground is first line of defense against injury and damage ... assisting the circuit breaker (overcurrent protection) absorb excess power and minimize damage or melting of wires and devices ... and help protect against personal injury. (b) Neutral wire performs a different function from the ground wire, even though both Neutral and ground busbars are bonded (connected) together inside the main panel. The Neutral carries voltage when 120 volt loads are operating. While the ground carries voltage only when there is an insulation failure or short circuit. Across the entire grid, the Neutral is bonded to a ground rod at every pole, transformer, substation, etc all the way back to the power plant. The Neutral runs continuously back to the generator coils, completing the circuit for all single-phase loads, while the array of ground rods (and substation circuit breakers) help prevent overvoltages and short circuits from damaging the grid. Resources See inside main breaker box. Electricity from power plant to household (c) The Neutral must be a continuous throughout a home or business, and cannot be switched on-off. A Neutral is never switched. This ensures proper operation of 120 volt appliances, devices etc. (d) If Neutral is used as ground wire, or ground used as Neutral, or both are connected together ... and there is a short circuit ... the overamperage can enter the device that is connected to Neutral wire ... and cause damage or personal hazard. (e) A grounded Neutral is a noted hazard that is against the electric code, and can be hard to detect until there is a short circuit or while doing electric maintenance. The electrician, or homeowner would naturally assume ground wire is not energized ... except a grounded Neutral is carrying hazardous power that shows up on the ground wire and can cause unexpected injury, burns, etc, even if breaker is off. Turning off main breaker will solve the risk, but not correct the problem of a grounded Neutral.  Neutral and ground inside
breaker box:Fig 8-4 Larger image Kirk observed that the Neutral and ground are connected together on same busbar inside his breaker box or main panel. Older main breaker panels often have a single busbar for both Neutral and ground wires ... these panels are still in use from 30 years ago, and allowed if approved by local code ... but are not best practice. Modern panels have separate busbars for Neutral and ground ... and each busbar is located on opposite sides of the panel ... and bonded (connected) by metal bar. All grounds must be connected to ground busbar, and Neutrals connected to Neutral busbar. Separate busbars means less resistance on the ground wire for runaway current (caused by a short) to reach earth. Less resistance means faster and unobstructed route to earth ... to protect breaker, and wires, and equipment ... allow faster response time for GFCI, and better protection against nearby lightning strike. The Neutral wires are connected to Neutral busbar .... Note the big Neutral wire coming in from power company transformer is only connected to the Neutral busbar ... while the ground busbar is connected to a copper wire that travels to the ground rod ... driven to depth needed to reach reliable earth connection. Note about
illustration Fig 8-4:
Illustration shows Neutral and Ground on same side of breaker box ... for convenience ... to give enough space for adding wires and words. |
 Larger image Single-phase 240 volt outlet is marked X-Y-W-G or X-Y-G X and Y are Hot, W Neutral, G ground 120V and 240V need two wires to complete circuit, plus ground wire for safety. 120V requires 1 hot and 1 neutral. 240V requires 2 hots. Neutral is not needed for 240volt electric circuit, but is sometimes included on electrical device. NOTE: you cannot put all 9 of these devices on same breaker since some are 30 amp and some are 50 amp. Illustration only shows how to connect wires to XYWG terminals. Resources: See inside main box Figure volts amps watts Select correct wire and breaker Electrical formulas Commercial 3-phase outlet is marked X-Y-Z-G or X-Y-Z-W-G Resource: How to wire 3-phase |
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