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How to change 120 Volt subpanel to 240 Volt subpanel
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
HOOK UP Wires
White 14 gauge 15 amp
120 volt 15 amp outlet, AFCI, GFCI, timer, switch etc can be installed on 15 or 20 amp breaker. Never connect 15 gauge wire to 20-30-40 amp breaker.

White/ #14 gauge wire,  with ground ... 15 amp capacity. Safe maximum 12 amps.
Buy:
14-2 gauge/ 15 amp
14-3/ 15 amp

NMB is house wiring
UF is underground
50-60 amp breaker use 6 gauge /
240 volt 50 outlet can be installed on 50 amp breaker only
6-2 wire
Buy:
6-2 wire
Southwire electric tools
NMB is house wiring
UF is underground
40-50 amp breaker use 8 gauge /
240 volt 40 amp outlet can be installed on 40 or 50 amp breaker only
6-2 wire
Buy:
8-2 wire
Southwire electric tools
NMB is house wiring
UF is underground
     
Copper ground wire.
Every device, load, metal enclosure etc must be grounded. Ground wire must be continuous throughout installation, never switched on-off, never used as a Neutral wire.
Generally ... use same size as other wire in circuit
Buy:
12 gauge copper ground wire
Ground wire
Green ground wire
Ground pigtails
Ground rods/ ground clamps at Amazon
armored cable
Non metallic flexible cables must carry ground wire, but do not have hazard of short circuit causing injury from shock.

Armored steel cable can be used as a grounded connection, and will protect wires from damage. Metal can be energized from an insulation failure.

All conduit ...metal, plastic ... flexible and rigid ... must be attached to structure, and attached to enclosures, boxes.
Movement, damage and deterioration are major cause of electrical failure.
Buy:
Non-metallic flexible conduit
Power whip
Armored cable
Southwire armored cable cutter
Pull boxes
Southwire armored cable cutter
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
stranded wire
600 volt 12 ga Stranded wire ot THHN wire is good for conduit with multiple wires ... but stranded cannot be installed under screw terminals on outlets, switches, timers etc without risk ... of heat causing splayed strands ....that come loose ... and begin to arc. Connect stranded to short piece of solid copper wire, and attach solid to screw terminal. Do not solder residential or commercial wiring.

Project wire, extension cords, thermostat, bell and automotive wire are not rated for residential or commercial wiring. Only wire maked 600 volt can be used for permanent household wiring.
Buy:
Southwire 600 volt stranded wire
Rolls of stranded wire
HOOK UP Wires

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


Electrically insulated tools
When removing insulation from wire, do NOT score or put cuts on surface of copper wire. Doing so increases resistance and heat on wire and creates possible weak point.
Buy tools:
KLEIN TOOLS
Wire strippers at Amazon
Electric Wire Stripping Machine
Linesman pliers
Utility knife at Amazon
multimeter
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

GFCI circuit breaker
A GFCI circuit breaker will protect all boxes on circuit.

Circuit must be grounded. Ground wire must be continuous and connected to each piece of equipment.

White wire on circuit breaker must be connected to Neutral busbar inside the breaker panel.

Buy
GFCI circuit breakers
Push down
single-pole breaker
1" wide Push down breaker
Plug-in breaker
Buy single-pole:
Choose from 15 to 60 amp
Eaton CL series
Siemens 15-60 amp

Single-pole tandem breaker
Tandem breakers
Push down
double-pole breaker
2" wide Push down breaker
Plug-in breakers
Buy double-pole:
Choose from 15 to 125 amp
Choose from 15 amp to 200 amp
Eaton CL series circuit breaker
Siemens circuit breaker
Double pole GFCI

Indoor: Install between 2x4 studs or surface mount. Must be attached to structure, and grounded..
Keep enclosure door closed.
Buy Indoor 120-240 volt:
100 amp 6 space
125 amp 8-space
125 amp 20 space
125 amp 24 space
Main lugs/ subpanels

Outdoor:
Install above anticipated snowfall
... away from direct sun and exposure to physical damage.
Must be grounded.
Must be attached to structure.
Buy Outdoor/ from my affiliate links: 120-240 Volt
70 amp 2-space
60-100-200 amp 2-space
125 amp 8-space
Subpanels at Amazon

Load centers with main breaker
120-240 Volt with breakers.
Install between 2x4 studs, flush with finished surface.
Must be attached to structure and grounded.
Buy main load center:
200 amp INDOOR 30 space HOM
125 amp outdoor 12 space
Intermatic T30000R5
Outdoor subpanels with space for breakers, timer, switches, outlets, GFCI, low voltage transformer etc/ 120-240 Volt.
Flush mount, widths vary.
Must be attached to structure and grounded.
Resources:
60-125 amp with & without timers
With freeze protection panels for pools
How to wire control centers
3-phase subpanel
3-phase subpanel
W and w/o main breaker

Not for residential installation
Commercial 3-phase panels are made for 3-pole, 2-pole and 1-pole breakers.
Rated for any service up to 600 volt.
Buy:
Siemens 3 phase load centers
24 space 125 amp
24 space 125 amp
3-pole breakers

Resources:
3-phase Wiring
Difference between single-phase and 3-phase
single-pole breaker
QP-type
1" wide Push down breaker
Plug-in breakers

Breakers can get warm, but should never be hot.
If breaker is installed on damaged busbar, it will arc and overheat, causing breaker to trip and eventually melt the busbar.
Do not install a breaker that is rated for fewer (less) amps than Load.
Look at rating plate on each Load that is on the circuit, divide total wattage on circuit by voltage to find amps.

Buy single-pole:
Siemens 15-60 amp

Single-pole tandem breaker
Tandem breakers

Buy QO breaker
20 amp Square D
double-pole breaker
QP type
2" wide Push down breaker
Plug-in breakers
Fits subpanels above
Fits residential/ commercial panels
Attach screws very tight against solid copper wire.
Do not use stranded wire. Attach short jumper of solid wire to stranded wire and then put solid under screw terminals.
Match breaker amp rating with wire size.
Note: each side of a double 20 amp breaker is 20 amp.

Buy double-pole:
Siemens 15-125 amp
Square D 30 amp breaker

Double pole GFCI
breaker base
Breaker base/ repair existing subpanel ... or building a control box
60 amp 4 breaker
125 amp 8 breaker
Buy:
124TP2608A 4 breaker spaces
124T2530A 8 breaker spaces
Din rail mounted circuit breakers
Din rail fuseholders

How to install 1" wide push-down breaker
Push-down breaker
Attach wire to breaker first. Make sure no insulation is under the screw plate. Solid copper wire only. Never use stranded wire. Do not attach more than one wire under screw terminal. Match wire and breaker size.
Notch on breaker sits against rail or cleat
Rotate breaker down to busbar
Push breaker down over vertical busbar
Buy single-pole:
Siemens 15-60 amp

Buy double-pole:
Siemens 15-60 amp

Resources:
How to replace circuit breaker
Match breaker and wire size

Household NM-B Wires are color-coded so inspectors/ electricians can easily identify which wire is used during construction
Use only 600 volt electric cable
Never use extension cord for permanent in-wall wiring.
Do not use aluminum wire, unless breaker, subpanels and all devices are rated for AL. Best to avoid altogether. Do not splice aluminum and copper together. Aluminum is a fire hazard.

Match wire size and breaker amp rating
If your home was wired by professional electrician who pulled permits, then circuit breaker and wire size will match. If manufactured home or travel trailer has not been altered by homeowner then breaker and wire size will match.

If breaker is oversized for wire... fire danger
Breaker can let too much amperage onto the wire. Wire will overheat and can cause fire.
Call electrician if you suspect wiring is not correct,

Buy:
Southwire Romex® wire at Amazon

Resource:
Match breaker and wire size
Main lug wiring Absolute electrocution danger..
Main breaker terminals are still Hot when main breaker is turned off.
... unless meter is pulled
How to pull meter

If you are not familiar with safe electric practice, best not attempt conversion.
120 Volt subpanelLarger image
Check wiring and circuit for 120 volt panel
Step 1)
Basic 120 Volt subpanel can supply power for 120 volt single pole breakers but not 240 volt double pole.

Step 2) Inside the main circuit breaker box, identify single pole breaker supplying power to 120V subpanel. Note the amperage of breaker and wire size. Example illustration shows 30 amp 120 volt single pole breaker.

Step 3) Important:
Identify if other 120Volt outlets and switches are on same circuit ... does the 30 amp single breaker inside main panel supply power to anything other than the subpanel?
Turn breaker OFF, and check which outlets and switches are on that breaker. It is against code if 20 amp switches, outlets etc are connected to 30 amp breaker. A 30 amp breaker can only be used for 30 amp outlets, switches, and other 30 amp loads like the subpanel, water heater etc.
This means that single-pole breakers inside subpanel must be 20 amp, if they serve 20 amp outlets, switches etc

Step 4) The change-over to 240Volt will NOT work if other 120 volt outlets and switches are on same breaker ... why? Because the circuit is going to be changed from 120 to 240 volt ... and those other 120 volt outlets and switches will be energized with wrong voltage.

Step 5) If the breaker serves more than the subpanel, then a dedicated wire must be installed for the subpanel.
Move wires inside subpanel 240 Volt subpanel
Step 6)
Move wires inside the subpanel to start the conversion to 240 volt.
Add black tape to White wire that will be carrying voltage. This is a convention to notify that the white wire is not a Neutral.

Step 7) The new 240 volt subpanel will not have a Neutral wire. Why? because the white wire is going to be converted from a Neutral to a Hot.
No Neutral means No 120 volt inside the new 240 volt subpanel, and means that a 120 or 240 volt GFCI breaker cannot be installed inside the subpanel.
However a new 240 volt breaker is going to be added inside the main breaker panel, and that breaker can be a GFCI.
Resource: How to wire GFCI breaker
Buy:
240 volt GFCI breaker
GFCI circuit breakers

Step 8) Tighten wires very tight using allen wrench or screwdriver as required. Use screwdriver that matches width of slot on screws so wires are thoroughly tightened.
240 Volt subpanel
Larger image
Change wiring inside main breaker box for 240 volt
Step 9) If the new subpanel is going to be strictly 240 volt without 120 volt, then all that's needed is to move the white wire and add a double breaker.

Step 10) Install 240V breaker.
The changeover requires a new double breaker installed close to where the old single-pole was located.
By code, the 240V breaker must be a single connected breaker, and not two independent 120V breakers, unless those breakers are connected by a bar. Why? Because a 240 volt breaker must trip both legs off during an insulation failure or overamperage event. If one leg trips, and other leg doesn't, it causes serious safety risk.

Not enough space?
Step 11) Make space for new double breaker.
If the main breaker box or panel has no extra spaces for new breakers, then double up two lightly-used 120 volt onto a tandem breaker. The tandem uses 1 space for 2 circuits.
Buy: Tandem breakers

Step 12) Remove old single breaker and install double pole breaker. New breaker must have same amp rating as single breaker ... and is required by code to have properly sized wire to match breaker ... and that breaker and wire match expected load.
Resource
: Breaker, wire, motor charts
Note if the the breaker is 30 amps, then both sides of breaker are 30 amp.

Step 14) Move black wire from the old single-pole breaker to new 240V breaker.
Move white Neutral to new 240V breaker.
Add black tape to any white wire that carries voltage ... this is a convention to notify when white is not used as a Neutral.

Step 15) Review: 240V Subpanel will NOT work for 120Volt breakers since ground wire cannot be used as Neutral. It is against code, and dangerous to use ground wire as Neutral. (Or use Neutral as a ground)
120 Volt is NOT available in the subpanel using this diagram.

Step 16) Safety: Wires cannot run over the top of breakers or busbars in either main panel or subpanel.
If wires are too short, then add a length of wire and join with twist on wire connector.
Wires can be over top of other wires, but not at the point where wires connect to busbars or breaker.
Push all wires to sides of box.
120 volt and 240 volt subpanelLarger image
Do you want both 120 volt and 240 volt inside subpanel?
If both 120 and 240 volt breakers are needed inside subpanel, then a new cable with red, black, white and ground wires is required.

The new cable would have 3 wires plus ground wire running between subpanel and main breaker box.

This diagram on left has 10-3 wire from main breaker box to subpanel ... and carries 2 Hots, Neutral and ground wires for both 120 and 240 volt breakers inside subpanel.

NOTE: Code requires Ground and Neutral wires to be connected to separate busbars inside both main panel and subpanel.

Buy:
Southwire 600 volt cable
Ground bar with attachment screws
Ground bars at Amazon
GFCI in breaker box
Larger image
Add 240 volt GFCI breaker inside main breaker box
Outdoor circuits are always safer with GFCI protection, and GFCI installation might be required to meet local codes.
Caution, only 1 GFCI per circuit.

Illustration shows overview of main breaker panel and 2-pole 240Volt GFCI.
Adding a GFCI inside main breaker panel will protect subpanel and every circuit connected to subpanel.
The GFCI 240Volt breaker has white wire that connects to neutral busbar.
Buy:
240 volt GFCI breaker
GFCI circuit breakers

Install subpanel for Tankless electric
Larger image
More subpanel wiring
buck boost transformer



Pull 120 volt from 240 volt ... Siemens industrial transformers Typical household use would be to step 240 volt down to 120 volt.
Inexpensive .... reliable ... requires enclosure
5.1 x 5.6 x 3.6 inches ; 3 pounds
Different models have input for 120 with 24 volt AC output, input for 240 with 120 volt output ... or input 480 volt with 240 volt output.
Outputs are AC.
Buy:
Siemens industrial transformers

Choose enclosure that is large enough
Bud industries hinged box 6x8x4
Metal outdoor Enclosure/ with 1/2-3/4" knockouts
Polycarbonate enclosures drill for knockouts
Thomas and Betts 6x6x4 plastic with cover at Amazon
Bud industries 11x7x5 box no knockouts
Tapered drill bit 1/4"-1-3/8 holes
tapered drill bit
Example Nema 3R indoor outdoor enclosures
2T511GA enclosureAltelix enclosure

Resources:
Siemens control transformers
Siemens transformers
Siemens MT0050AExample wiring diagram for transformer
If the input voltage is 220-230-240 volt, then connect one wire to terminals H1 and H3, connect other wire to H2 and H4.

If input voltage is 440-460-480 volt (480 for Americas), then connect one wire to H1 and other wire to H4, then jumper a wire between H2 and H3.
Larger image of transformer
Buy:
Siemens MT0050 industrial transformer

Note: 60 Hz Hot to Hot 240 volt is for power grid in Americas, 50 Hz Hot to Neutral 230 for Europe, and 50 Hz Hot to Neutral 220 for Australia etc.

When ordering: "If the dual voltage is separated by an “X” (120 x 240), the transformer can be connected only for 120 volts or 240 volts.
But, if it is separated by a “slash” (120/240), an additional Neutral connection is possible since the mid-point becomes available for 240/120 3-wire operation."
Resource pdf pg 4
Read more about transformers
Encapsulated step down Transformers/ Typical household use would be to step 240 volt down to 120 volt.
Convert 240Volt to 120Volt without neutral wire from breaker box

Convert 480Volt to 240Volt
Type 3R outdoor enclosure

 Wiring:
480Volt input connects to H1 H4, and then H2 and H3 are connected together
240Volt output connects to X1 X4, and then X2 and X3 are connected together

240Volt input connects to H1 H4, and then H3 connects to H1, and H2 connects to H4
120Volt output connects to X1 X4, and then X3 connects to X2
Buy:
500 watt 240-120 volt step down
1000 watt 240-120 volt step down
1000 watt step down
2000 watt 240 volt to 120 volt step down
Encapsulated transformers
Acme step down - 120/240 primary/ 120 240 secondary

Resources:
Acme ransformer wiring
Dry transformer installation
Match wire and breaker size
How to wire a subpanel
Read about household single-phase electricity
Read about 3-phase
How to wire 3-phase timers


linesman pliers

front cutting pliers
Utility knife
Electric tools:
Buy:
Linesman pliers

Buy:
Wire strippers at Amazon

Buy:
Crescent-brand end cutting nipper at Amazon
End cutting nippers at Amazon

Buy:
Utility knife at Amazon
Electricity leaves power plant Resource: Electricity:
The grid is defined by three parts: transmission, distribution and end user. The following links show how it works
Power plant to end user power pole
Power pole to residential breaker box
Power pole to commercial breaker box

How to wire residential electric
How to wire commercial 3-phase

Why you need ground wire
How to wire 3-phase timer
3-phase water heater

Contactors/ relays
Type 1 and type 2 surge protection surge protection
Programmable timers

Woods timers
surge protection
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Electronic parts

Industrial supplies

Tools and home improvement

Home and garden

Hayward pool
Pentair pool

Southwire electric
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Tools

DEWALT
Black and Decker
Stanley
SKIL
Makita
Porter-Cable
Bosch

Irwin Hand tools
Klein hand tools
Fluke electrical testing
Dremel hobby tools

Campbell Hausfeld air powered
Tekton automotive

Powerbuilt automotive
Saws and saw blades
box timers Resource:
Compare box timers
DPDT timers
Intermatic
Control water heater w/ Z-wave
Intermatic control centers Resource:
Intermatic control centers: and parts
Digital control centers and parts
Tork control centers and parts
Subpanels
All control centers and parts
Enclosures
programmable timer Resource:
Programmable timers
Countdown timers
Off delay timers
On delay timers
Timer modules
Din rail
Twin & one-shot
Woods
Intermatic
Tork
Low voltage power packs Recirculation systems
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