I need to produce a diagram of a typical wiring system for a small factory showing the arrangment from the incomeing service cable to a 3-phase motor, with seperate distribution to lighting and other single- phase circuits. can any one help me please neal

A one phase 3 wire system has a center tap. Two hots and a neutral. Typical 120/240 volts.
A three phase 4 wire system has Three hots in a Y or Delta. The Y system has three hots and the neutral comes from the center of the Y, this is the neutral and grounded conductor, 120 volts from hot to ground and 208 volts hot to hot. In a 3 phase system the voltage is not doubled hot to hot as in a single phase system because the hots are 120 degrees phased from each other and the square root of 3 is the factor, multiply the 120 volts by 1.73 to get 208 volts hot to hot. Multiply 208 by the reciprocal of 1.73 and get 120 volts. Your exact application is not given so it is not known. A delta system is a triangle and the angle of each triangle is a hot wire, one angle would be grounded or the center tap of one of the sides of the triangle. Y is the configuration of the windings of the alternator or transformer and Delta is the configuration as a triangle of the windings of the alternator or transformer where the power supply is.

With a three phase home service, you can only connect two hots from your single phase generator, and the neutral. One of the house's hot does not get connected and any three phase loads in the house should be switched off and kept from energyzing or a circuit breaker or fuse serving that 3 phase load may trip.
Only one power supply can be connected at a time. The power company power must not be connected at all while using an alternate power supply unless your power supply has means to synchronize the alternating cycle.

It is adviced that the loads be kept within 10% of their rated voltage, especially motors.

Reversing rotation of 3 phase motors:
CAUTION: Before attempting any repair of electrical equipment verify the power is disconnected to the device.
CAUTION: Three phase motors could potentially be controlled by frequency control systems. It is recommended a trained electrician perform repairs to any electrical system. In particular, consult a trained electrician if the system includes a frequency control system.

Most 3 phase motors can reverse rotation simply by swapping any 2 of the 3 phase wires. A typical 3 phase wiring circuit will include a safety ground wire (usually green) and 3 phase wires, often designated A/B/C, or 1/2/3, or color coded to distinguish each. By swapping the terminal connection of any 2 of the three phase wires, for example, 1 & 2 or 2 & 3 or 1 & 3, but leaving the third phase wire unchanged will reverse the rotation of most motors.

I'm not sure what you mean about 4 wires coming into your trailer.
4 wires is typical of 3-phase service, but typical trailer usually has single-phase residential service.
Copy following link to see main breaker box and component parts for single-phase residential wiring.
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

What kind of diagram are you looking for? Large business and warehouses have 3 Phase. I've not heard of a house. but let me know. Typically 110 comes out of one breaker and one neutral wire (and saftey ground is 3rd) 220 comes out of two hot leads and one neutral wire (single phase). 3 phase comes out of 3 hot leads and one neutral but is still 220 volt.

8145-20 240Volt Paragon timer is not 3-phase.
Clock motor is 240V.
You need a transformer to convert 3-phase to single phase 240V to operate timer.
Then timer outputs can control 3-phase power using 3-phase contactors
Contactor below is 3 phase with 240V coil
http://www.grainger.com/Grainger/DAYTON-Contactor-2UTP7?Pid=search

Defrost timer wiring diagrams show below:
http://waterheatertimer.org/Paragon-timers-and-manuals.html#defrost

Assuming that the motor has 9 leads and the wire numbers are still on the wires, for 240 volt 3 phase connections:

Connect T1, T6, and T7 together with L1 (A phase)

Connect T2, T4, and T8 together with L2 (B phase)

Connect T3, T5, and T9 together with L3 (C phase)

If you're not sure which of the incoming wires from the supply are L1, L2, and L3, just pick one. If the rotation is wrong just swap any 2 (TWO) phase wires.

Are you asking how to draw it like CAD or what to include in the diagram. I would hate to ask why you have to produce this diagram. This type of diagram is always furnished with the complete electrical drawings of a facility when built. To produce an ACCURATE diagram is not so simple. Normally you would also include the wires sizes, conduit sizes, and panels and sub panels as well as main trainsformer size. If this diagram is to be used to say calculate available fault currents for an arc flash study, it should only be done by an experienced individual, such as an electrical engineer. Are you getting paid enough for this responsibility?

does it have capacitors on the motor (humped covers on top) If not then it may ot be a single phase. also on the motor name plate or on the inside cover of the connector box it should have wiring diaphragm that will tell you how to wire the motor, single phase motor will show 2 line connections and a three phase will show 3 line connections,,, line connections are represented by L-1 L-2 L-3 these mean incoming power.

Your question is a bit unclear, but I assume you are asking how to wire the pressure switch in a piston compressor.

See the diagram, below.

You should have a wire from the L1 (first incoming main voltage) terminal to the pressure switch, and from the other pressure switch terminal back to the starter coil. You will also have a wire from L2 (second main voltage terminal) to the overload, and from the other overload terminal to the other side of the coil. In this arrangement, the motor starter coil must be rated at the SAME VOLTAGE as your incoming power.

This diagram works the same for single phase machines (they just don't have the third wire coming from the supply through the starter and overload to the motor.

If your machine has other safety controls (like a low oil switch), It can be wired in series with either the pressure switch or the overload.

Your question is a bit unclear, but I assume you are asking how to wire the pressure switch in a piston compressor.

See the diagram, below.

You should have a wire from the L1 (first incoming main voltage) terminal to the pressure switch, and from the other pressure switch terminal back to the starter coil. You will also have a wire from L2 (second main voltage terminal) to the overload, and from the other overload terminal to the other side of the coil. In this arrangement, the motor starter coil must be rated at the SAME VOLTAGE as your incoming power.

This diagram works the same for single phase machines (they just don't have the third wire coming from the supply through the starter and overload to the motor.

If your machine has other safety controls (like a low oil switch), It can be wired in series with either the pressure switch or the overload.