I need a wiring diagram for connection of a 3-wire plug to my home panel - Square D, 240V, 200amp service panel.

Hello, I really need the make/model number to help you accurately but with the info you've described, I can tell you what to check first. 1st, some oven operating know-how--they operate on 240v AC. That means there are *2 hot wires, each with 120v*, a "neutral" wire, and a ground wire. To power up the control panel, the makers usually just run a wire up from one of the incoming AC supply wires, known as L1 and L2. Importance: it is possible to have the control panel work perfectly, lights and all, and have the problem you're describing--quite possibly THE OTHER 120v supply wire has become disconnected, either at the back of the oven where the terminal block is located, or at the 240v outlet on the wall. Also, the heavy cord with the plug on the end might have corroded/broken/burned up, so check it, too. Also, check that 240v is *getting* to the 240v outlet--this will tell you if the problem is at the panel box or at the oven-end of things. An old outlet might hold one blade of the plug tightly and the other will be too loose to make a good connection. BE CAREFUL WHEN CHECKING ELECTRICALLY HOT CONNECTIONS--240V WILL KILL YOU, DEAD. Make your movements deliberate, be focused, take your time. If you are hesitant about any of this, call for service! I hope I helped you!

First of all most home thermostats operate on 24volts. If you want to have one that directly turns the 240 volt power on and off you need to get a special 240V line voltage thermostat. How many wires come out of your heater? Most 240v circuits have three wires. A white wire for the common and two black or black red wires that are +120 volts and negative 120 volts. That's why a 240 volt plug has 3 prongs instead of two. If you look at the wiring diagram that comes with the thermostat it should give you an idea of how to hook the wires up. In your particular case though, I think I would try making friends with an electrician.

you must understand this : your electric oven must be indicate if it is a single phase( use 3 wires for 230 2 hot wires + 1 Neutral see the diagram like dryer? you must sure about this. Normally any appliance for home are single phase NOT 3 phase.

2) If you electric oven, say 3 PHASES( use 4 WIRES, 3 hot wires+1 Neutral wires) this for industrial application +comercial NOT for home

However if you system is 3 phase you must need to install 3phase transformer.

200 amp is 3/0 copper wire up to 100 feet.
Use size 250 wire up to 150 feet.
Use size 350 wire up to 200 feet.
Be sure to put wire in conduit.
http://waterheatertimer.org/images/Wire-size-and-amp-chart-700.jpg
http://waterheatertimer.org/How-to-install-a-subpanel.html
http://waterheatertimer.org/See-inside-main-breaker-box.html

If you need further help, I’m available over the phone at https://www.6ya.com/expert/gene_9f0ef4df2f9897e7

WH40 is 240Volt timer.
WH40 will not work with 120V circuit.

See WH40 wiring illustration at following link:
http://waterheatertimer.org/How-to-wire-EH40-hot-water-heater-timer.html

There are two hot wires in 240V circuit because every circuit requires two wires to complete the circuit.
Hot wires from breaker connect to terminal 1 and 3.
Notice that small white wires are also connected to terminals 1 and 3.
Small white wires power clock motor located on back of mechanism, so this says power from breaker box must arrive on terminals 1 and 3. This insures that clock motor runs continuously.
If clock motor only runs when manual override switch is clicked ON, then your Hot and Load wires are reversed.

Bare ground wire connects to green ground screw.
Wires going to Load (water heater) connect to terminals 2 and 4.

FYI: Terminal A is not used unless circuit also has a Neutral wire,
See basic water heater circuit Diagram #2:
http://waterheatertimer.org/240-v-water-heater-circuit.html

Terminal A is also used if you want to convert WH40 to 120V timer by replacing 240V clock with 120V clock.
How to convert Intermatic 240V timer to 120V timer
http://www.fixya.com/support/t7353947-intermatic_timer_wg

A) 5 terminal ET70115C.
Voltage selector set to 240.

B) BUT you say you have 120Volts from breaker >>> confusing, so I'm proceeding on basis that you meant to say 240V from breaker.
Add a comment at any time.

C) Review timer:
5-terminal ET70115 timer has NO and NC terminals
NC is normally closed >> this terminal has power when timer is OFF
NO is normally open >> this terminals has power when timer turns ON
For water heater, you want NO terminal 4 so water heater turns ON when timer turns ON

D) Wire for 240Volt water heater

Two hot wires from breaker connect to terminals 1 and 2. This powers timer clock.
Jumper wire connects between terminal 2 to terminal 3. This sends power to the switch circuit.
Wires to water heater connect to terminals 1 and 4

E) 5-terminal timer turns off 1 hot wire to 240V water heater.
Turning off 1 hot wire will stop 240V circuit from working; Water heater thermostats also turn off one hot wire.
240V water heater has black and red wire.
Wire from terminal 4 should connect to Black wire on water heater.

Diagram shows two wires on terminal 1
Two wires on terminal 2
One jumper wire on terminal 3
One wire on terminal 4
Zero wires on terminal 5

I'm not sure what happened on here, but your problem with a motor is listed under the heading for a 200amp main breaker. What kind of a motor are you talking about? Gas, electric? what brand what model?

If you have wired many 110, then you will have no problem. The only difference is that both legs carry power. You will still connect one side to L1 (or Line) and the other side to, what we will now refer to as L2 (or if this was 110 we'd say neutral). Sometimes there is a third wire, this is the ground wire, which goes back to ground at the box. Hope this helps.

you get 120V from any phase (black OR red) to neutral
you get 240V from phase to phase (between black and red) and in this scenario you don't need the white wire.
So for you, connect the black to 1 pole of the breaker and the red to the other pole, connect the green wire to the ground strip and you are done.
A white wire is NEVER connected to a circuit breaker anyway, it is a grounded wire, it would be like connecting a green wire to a black wire, bad idea.
the National electrical code specifies red and black wire color for 240VAC circuits.
As Ask Hank mentionned, nothing wrong with 10/3 wire.

no, not to code plus the expense would not justify , you can purchase the 200 amp panel with the main already installed cheaper than purchasing the 200 amp breaker in most cases and still meet the code check on a panel package called a home owners kit ge makes one square d , makes one either good quality , you get the 200 amp panel, several breakers such as 20 amp 50 amp 30 amp by far the best route for you