module 8 / application of health & safety and electrical principles

Ways of taking precautions for risks.

If you take just a moment to think about what you are doing, or are about to do, you will find that you can avoid most potentially dangerous situations. Another of the most effective ways to reduce the risk of accidents is to try to remove the cause, such as storing conduit horizontally and locked away. Reporting potentially hazardous situations to your supervisor will be affective.

What are the important things to ask when looking for hazards for a risk assessment?

• What are the actual and/or potential hazards?

• Are these hazards significant?

• Are the hazards covered by satisfactory precautions so that the risk is small or should new or revised precautions and/or procedures be put in place?

What is a hazard and a risk?

• A hazard can be defined as: anything that can cause harm (e.g. working from ladders or scaffolding, substances such as asbestos, chemicals, electricity, etc).

• A risk can be defined as: the chance, high or low, that somebody will be harmed by the hazard.

Step 1 of carrying out a risk assessment.

step 1 is looking for hazards.

Take a walk around the workplace. Look at what could reasonably be expected to cause harm. such as faulty electrical connections, damaged cables, materials that are ejected from machines, pressure systems. Also check with your employees, as they may have noticed things that are not immediately apparent to you.

Step 2 of carrying out a risk assessment.

Step 2 is decide who might be harmed and how.

Apprentices and trainees, young workers, new and expectant mothers etc., who may all be at particular risk. Visitors, contractors, cleaners, maintenance workers, etc., who may not be in the workplace all the time. All of these and more could be harmed.

Step 3 of carrying out a risk assessment.

Step 3 is evaluate the risk.

Evaluate the risks and try to decide if the precautions that may already be in place are adequate or if more should be done. Assess how likely it is that each hazard could cause harm. This evaluation and assessment will determine whether or not more needs to be done to reduce the risk. However, you must accept that even after all reasonable precautions have been taken, some risk usually remains.

Step 4 of carrying out a risk assessment.

Step 4 is to record your findings.

If you have 5 or more people in employment you must record any significant findings in your assessment, this means writing down the hazards and conclusions. You must also tell your co workers of this as well as keep the sheet in a safe place as it can protect you from a civil liability.

What you must record is: A proper check was made, you asked who may be affected, all the obvious significant hazards were dealt with, taking into account the number of people who could be involved and the remaining risk is low and the precautions taken are reasonable.

Step 5 of carrying out a risk assessment.

Step 5 is to review your assessment.

Sooner or later the existing situation will change. You will bring in different substances or procedures, or new machines that could lead to new hazards. If there are any significant changes, these should be added to the risk assessment to take account of the new hazard. However, if a new job introduces significant hazards of its own, you will want to consider each of these in their own right.

What causes most slip, trips and falls in the work place.

Most slips, trips and falls come from either lifting and handling, or working at heights. More than a quarter of all work related accidents are connected to manual handling.

Most causes can be due to:

• Fluids spilt on the floor

• Polythene sheeting that may be left lying around

• Projecting scaffolding poles and other objects

• The plastic strapping from around bricks or other packaging

• Trailing cables (one of the most common causes of trips)

Checks before lifting loads.

Before you lift any load you should always make the following checks:

Assess the weight, size and shape of the load.

Has it got sharp edges?

Is there somewhere you can put it down, either en route or when you get there?

Is the route free of obstructions?

Will the load fit through the doors and are the doors open?

What is a time sheet?

Timesheets are very important to you and your company. These are the permanent record of the work done on a site and include details of:

• Each job

• Expenses

• Overtime

• Travelling time

The information on the time sheet allows the company to track its costs and to make up your wages. If you work on several sites over the course of a week, you may need to fill in a separate timesheet for each job.

What is the purpose of a job sheet?

Some electrical contracting companies issue job sheets to their electricians. These job sheets provide detailed information about a job to be done. Job sheets frequently require the customer to sign them to indicate that the work has been done. Usually they will include:

• A clear description of the work to be carried out

• Any special instructions or special conditions (e.g. pick up special tools or materials)

• The customer’s name and address

What is the purpose of a variation order (VO)?

The purpose of the VO is to record the agreement of the client for any extra work to be done, as well as any change that this will make to the cost and completion date of the project. A variation order is issued when the work done is different, or varies, from the original work agreed in the contact and listed in the job sheet. This is done so the terms of the previous contract aren’t broken.

What is the purpose of a day worksheet?

Work that is done outside the original scope of the contract, perhaps as a result of a variation order initiated by the architect for example, is known as day work. Day work sheets are usually quoted at a higher price and need to be signed of by the client.

It is important that the installation team who are on site record any extra time, plant and materials that may be used when doing day work. Once work is completed, completed day work sheets need to be taken to a office receipt.

What is the purpose of a purchase order?

Before a supplier will send out any materials or equipment, they will require a written purchase order. The purchase order should include details of the material, quantity required, and may (sometimes) specify a particular manufacturer.

The purchase order may also specify a delivery date and address. Purchase orders may be created from phone calls, emails websites etc,. A conformation code will be sent to the client right after.

What is the point of a delivery note?

Materials delivered directly to a site will arrive with a delivery note. The delivery note should contain the following information:

• A list of the type, quantity and description of any materials that are being delivered in this particular load

• The name of the supplier

• The time period allowed for claims for damage

• Who the materials are being sent to

When materials arrive on site you should make sure you try to do the following:

• Check each item against the delivery note.

• Check for obvious signs of damage.

• Ensure that they are unloaded and stored correctly.

What is the purpose of a site report?

Site reports contain details of work progress, defects, problems and delays and most companies require regular reports about the progress on site. Sometimes additional reports on particular problems or incidents will be made and such reports may enable the company to:

• Provide evidence when they make claims for progress payment

• Spot problems that keep being repeated and take action to eliminate them

• Take prompt action to avoid any difficulties that may be building up

Site report memo is usually short and brief, normally about a single issue such as materials not being delivered on time or a particular safety issue.

How transferring measurements in a diagram are used.

Scale drawings are used for planning and preparing an installation. Scaled drawings use fixed ratios, for example 1:150. This would mean that every 100 mm on the drawing is 150 times bigger in reality. Scaled drawings can therefore be used to plan detailed installations in advance.

How to take recording in-site measurements for materials for a job.

When you arrive on a site to take measurements it is always best to carefully record them in a notebook, and keep this safe. If you measure incorrectly of forget the measurement It could mean that you order too much or too little material. That is why its best to write down the measurements and to keep it safe.

If you are required to carry out measurements on site, there are a number of tools that you can use to help, such as long measuring tapes and laser distance measurers.

How to prepare a materials list for a new project.

If you are working for a large contractor you would probably be able to order the materials needed from a central store. If not, then you could order them directly from a local wholesaler. In either case, the process of working out what you need is exactly the same.

The first thing to do is to get a copy of the layout drawing. As it would be a scaled down drawing it is possible to take measurements from the diagram and work out the actual dimensions of the building, so that you can prepare a materials list for the job.

Step 1: Count up all the major pieces of equipment needed

Step 2: Decide the best runs of conduit and trunking

Step 3: Calculate lengths of trunking, conduit and cable required

Step 4: Include accessories, fixings, etc.

Step 5: Consider special access equipment like a ladder.

4 Key tips to presenting the right image.

• knowledge, being able to answer all types of questions and to convey your answers in great description will show who ever you are talking to that you are very experienced and knowledgeable. This can give a good lasting impression on who ever you are talking too.

• Confidence, Being confident enables who you are talking to, to be insured and trusting in you as they will feel that they have gave their project into the right hands. This will make the progress go a lot more smoothly.

• Appearance, Looking business like will set the conversation in a good way as the clients first impression on you will be enticing to do business even if they don’t mean to judge you.

• Attitude, being kind and well mannered will be appreciated by the client as talking to you about he installation because it will reassure them and they will trust you know what you are talking about.

How does an AC generator work?

AC generators are normally produced by magnetism. As the magnet begins to rotate around the loop, starts to pass through the lines of flux (magnetic field). This is when we start to introduce electromotive force (emf).

Maximum induced emf will occur when the magnets travel 90 degrees and the loop will have cut through the maximum lines of flux. As we keep on rotating the number will gradually reduce to zero as the loop lies between the lines of flux.

The magnets have now completed a positive half cycle. If we repeat the cycle the emf will be induced into a negative half cycle. If we were to put this cycle onto a diagram it would be called a sine wave.

What is known as the voltage measurement from positive to negative peak?

Its known as the peak to peak value.

What are hertz and what is the equation for this?

When one cycle of emf is generated with one complete revolution of the loop over a period of one second, then we would express this as a frequency of 1 Hz. The frequency of the waveform is equal to speed of the loop’s rotation.

Frequency (f) = Number of revolutions (n) x Number of pole pairs (p)

If this is applied to the simple AC generator we looked at earlier, and the loop is rotated at 50 revolutions per second, then:

Frequency = 50 x 1 (there is 1 x pole pair) = 50 Hz

What does periodic time mean for a wave form and what is the equation for this?

Periodic time or period means he amount of time it takes to complete one cycle of a wave from.

Therefore, if 50 cycles are produced in one second, one cycle must be produced in a fiftieth of one second. This relationship is expressed using the following equation:

Periodic time(T)= 1/frequency = 1/f

Formula for heat produced in a DC current.

You know that when current flows into a resistor, heat is produced. When direct current is flowing in a resistor, the amount of electrical power converted into heat is expressed by the formula:

P = i2 x R or P = V x I

What is a emf?

EMF (Electromotive Force) represents the voltage induced in the generator's coil as it rotates through a magnetic field. This voltage is what drives the electrical current to flow in the generator's circuit. Essentially, EMF is the "push" that moves electrons through the circuit.

How is the root mean square (RMS) or the effective value of a waveform (voltage and current) is calculated?

In DC circuits, RMS is calculated by simply multiplying the voltage and the current. Where as, AC circuits are a little difficult as the voltage never stays the same.

Divide a AC half cycle into as many times as you can and square each value you have. (the more you can divide the values, the more accurate the RMS will be). Then add all the values together and divide that figure by the total values you recorded.

Finally, find the square root of the final value. This value is what is known as the RMS value.

Dividing the square root by 2 is the equivalent to roughly 1.414 or multiplying by 0.707

Vrms = V peak x 0.707

Irms = I peak x 0.707

How to use the heating affect method for an AC circuit.

If a DC alternator heats up a resistor in a circuit to 100 degrees, then a AC alternator will only heat it up to 70.7 degrees. This is expresses using the formula:

Heating affect of 1A maximum AC = 70.7 = 0.707

Heating affect of 1A maximum DC = 100 = 0.707

Imax = Irms x 1.414 is the equation to find out how much heat is produced from a resistor in an AC circuit.

Why does a DC alternator produce more heat than a AC alternator?

Because DC stays at a peak voltage the entire time, where as the AC alternator peaks for a very short amount of time.

Why do generators use electromagnets instead of permanent magnets?

They use electromagnets because by changing the direction of current flow the poles of the electromagnet can be reversed. And by adjusting the amount of current flowing through the wire, the strength of the electromagnet can be controlled.

How can a DC motor be reversed?

By reversing the direction of the current through the armature. This is normally achieved by reversing the armature connections only and is the easiest way. Reversing the direction of the current through the field, thereby changing the field polarity.

How is a DC series motor constructed and what is it best suited for?

The series motor is also called a universal motor because it can be used in both DC and AC situations. It has the field coil wired in series with the armature which gives it a high starting torque (rotational force) and also means it has a variable speed characteristic. This type of motor is good at starting heavy loads, but the speed will increase as the load is decreased.

How is a shunt motor constructed and what is it best suited for?

The shunt motor has the armature and field circuits wired in parallel, and this produces constant field strength and motor speed, although the speed can still vary with load changes.

How is a compound motor constructed and what is it best suited for?

The compound motor combines the characteristics of both the series and the shunt motors. This means that it has high starting torque and reasonably good speed torque characteristics. However, because it is complex to control, this particular arrangement is usually only used on large bi-directional motors.

Why did AC generators become the main choice?

• Transformers make it easy to adjust AC to a higher or lower voltage very efficiently. This is useful, because transmitting at high voltage reduces current and power loss and allows the use of smaller cable sizes, lowering costs.

• Good AC motors (and generators) are easier and cheaper to build and maintain than good DC motors.

How does a relay work?

A relay is an electromechanical switch that uses an electromagnet to create a magnetic field to open or close one or many sets of contacts.

• Control a high-current circuit with a low-current signal, as in all the lights in a theatre auditorium or of a leisure centre being controlled from a single 5 amp switch in the foyer or reception.

• Control a high-voltage circuit with a low-voltage signal, as in some types of modem.

• Control a mains-powered device from an extra low-voltage switch.

What are the things to consider when choosing the correct relay?

Contact arrangement - The contact geometry indicates how many poles there are, and how they open and close.

Coil voltage – this indicates how much voltage (e.g. 230 V, 24 V ) and what kind (AC or DC) must be applied to energise the coil. Always make sure that the coil voltage matches the supply being fed into it.

Contact ratings – this indicates how heavy a load the relay can run

How a Low pressure mercury lamp is constructed and how it produces visible light?

Its basically a glass tube having a filament at each end, with the tube filled with low pressure mercury vapour and a mix of additional gases such as krypton or argon. The inside of the glass tube has a phosphor coating and at each end there is a sealed set of oxide-coated electrodes, known as cathodes. In use, an ark forms causing the ionisation of the mercury gasses emitting ultra violet light.

This in turn excites the tubes phosphor coating and converts it into visible light. A choke or a transformer is used to give a quick initial charge of voltage to activate the lamp but then decreases to maintain the light.

What is colour appearance for a lamp?

This is the actual look of the lamp. The two ends of the scale are described as warm and cold. These extremes are related to temperatures: the higher the temperature, the cooler the lamp.

This is important for the overall effect, and generally warm lamps are used to give a relaxed atmosphere, while cold lamps are used wherever efficiency and business-like attitudes are a priority.

What is colour rendering for a lamp?

This describes a lamp’s ability to show colours as they truly are. This can be important depending on the building usage, such as a art gallery or a museum. The rendering of colour can also affect people’s attitude to work etc.

What is lamp efficacy?

This refers to the lumen output for a given wattage. For fluorescent lamps this varies from between 40 and 90 lumens per watt.

What should site members do for visitors when they visit a site that don’t have facilities?

• Brief the visitor on site safety

• Check the reason for the visit

• Check the validity of the visitor

• Establish whom they wish to see

• If a request is made that is beyond your authority, contact an authorised person

• Issue an identification badge if necessary

• Issue them with a hard hat and high visibility jacket if necessary

• Log their arrival time and departure time

• Receive visitors in a manner that fosters goodwill

General guidelines fore safe working practising and storing

• Check that the plugs and cables of hand-held power tools are in good condition.

• Replace frayed cables and broken plugs.

• Electrically powered tools must be PAT certified in accordance with your employer’s procedures and HSE guidance.

• Ensure handles are properly fitted and secure, and free from splinters.

• Keep cutting tools, saws, chisels, drill bits, etc. sharp and in good condition.