Relays vs PLCs

Only the simplest powered electrical systems and equipment require just an on-off switch.

In reality, most processes need a control system to manage commands and/or direct or regulate the behaviour of other devices or systems.

Originally, these control systems would have been designed using Relay Logic which is a large array of hard-wired controls utilising sensors, switches, timers, relays & contactors.  Relay Logic has many applications, including Compressor Control systems, Lighting Controls, Machine Safety Circuits and much more.

With the development of microprocessors in the 1960s, Programmable Logic Controllers (PLCs) were created.  PLCs use programming language, referred to as ladder logic, to create the relay logic and as such offer many advantages over traditional relays.


The main advantages of PLCs over relays are:

  • Reliability. PLC Systems with their solid-state components tend to last longer than the moving parts of electromechanical relays
  • Troubleshooting. PLCs are generally easier to identify problems as there are less wires in a PLC. In a physical relay each device needs a minimum of four wires to operate whereas a relay output sends out one wire to the output device.
  • Easy expandability. If you want to add functionality to a PLC you can just add it to the programme and set up the constraints, where a relay system needs the new physical component added and the necessary wiring to make it work.
  • Smaller size. The space required for a PLC system vs the cabinet needed for a relay logic circuitry is much smaller.

While PLCs offer many advantages, relays do still have a place within a control system. They provide a simple and efficient tool that requires no advanced programming for proper commissioning. Relays can be particularly useful:

  • where there are only a few IO points per control system.
  • where the application require little troubleshooting of wired logic.
  • to reduce alarms & response tasks from Safety PLCs.
  • where there are interposing voltage relays.

If you would like advice on the best control system for your application, get in touch with the EAS team today on 07 834 0505 so we can work together to find the best solution for you.


vsdsVariable Speed Drives (VSD) control motor speed in response to varying process demands in your plant. The motor speed adjustment can be based on feedback from the process; for example flow rate, temperature or pressure so that process control can be improved.

Due to the ‘magic’ of affinity laws, small decreases in the speed of pumps and fans or the pressure of pumps can lead to large decreases in energy use meaning the use of VSDs can provide significant energy savings. For example:

  • Using a VSD to reduce the speed of a motor reduces energy consumption by around 50%
  • Using a VSD to reduce the pressure of a pump by 20%, reduces the energy consumption by around 28%

Other benefits of using VSDs include:

  • Reduced stress on system components
  • Accurate system control of parameters such as flow, pressure  and temperature
  • Improved workplace safety through reduced heat and noise levels

Variable Speed Drives are a vital component of your plant and as such they require regular preventative maintenance checks to ensure your plant is operating at peak performance.
Key checks include:

  • Visual check:
    These are done to ensure the drive is clean and the cooling fan and cooling system are all in good condition. Dust on VSD hardware can cause a lack of airflow, diminishing performance. Dust also absorbs moisture which can contribute to failure.Connections should also be checked as heat cycles and mechanical vibration can lead to sub-standard connection and cause erratic operation resulting in damage to machinery.
  • Settings:
    Parameter settings should be checked and recoded so that if there is a failure, the drive can be easily replaced. EAS utilise Drive Software to enable us to upload the correct settings straight back into your drive to get it up and running as quickly as possible.
  • Stocktake of spare parts:
    By performing a stock take of the spare parts available we can ensure that any breakdowns can be handled quickly and efficiently. It also gives the opportunity to identify drives where spare parts are no longer available so that a planned upgrade of the drive can be scheduled where it will be least disruptive to production.

Why are preventative maintenance checks so important?
Preventative maintenance checks reduce the risk of your manufacturing equipment failing, resulting
in costly unplanned downtime. With regular preventative maintenance checks of your variable speed drives and other key equipment you can:

  • Reduce the chance of unplanned downtime
  • Gain more control over budgeting and scheduling for equipment replacements and upgrades
  • Increase the life of your critical machinery

If you need assistance checking your Variable Speed Drives or other plant and equipment are in top condition – get in touch with the EAS team today on 834 0505.

Can your staff and customers exit your building safely in an emergency?

Eexit-smmergency Lighting is designed to ensure that if there is a power failure, there will be enough lighting to allow people to exit your building safely.

The Australian and NZ Standard AS2293 outlines the level of light (lux) required to ensure people can exit safely from the building.  Different levels of lighting may be required on exit routes depending on factors such as changes in floor levels or in areas where there are dangerous machines or hazardous processes operating.

It is vital that emergency lighting systems kick in as soon as they are required, particularly in areas where there may be dangerous machinery or hazardous processes operating or where a significant number of people (greater than 250) will be using the escape route. AS2293 outlines the level and timeframe of lighting that must be available. It also requires that there be sufficient back-up power to allow emergency lighting levels to be maintained until evacuation of all staff can be completed or full power restored.

EAS can provide you with a complete solution for all your emergency lighting needs. From design, installation, and commissioning to the installation of both temporary and permanent standby generators, back up Uninterruptible Power Supplies (UPS) systems in various sizes. We can provide an emergency lighting solution that will fit your needs whether it is for a small office building or a large industrial plant.

While the design and install of emergency lighting systems is a key part of ensuring your building complies with the NZ building code, it is also vital that these systems are regularly maintained to ensure that they operate when they are needed, and your building warrant of fitness is valid. EAS can assist you with routine testing and repair services, ensuring that all aspects of the Emergency Lighting system are operating as intended. During these routine checks, the team will inspect and record all aspects of the system, such as verifying the physical condition and illumination of each light, maintaining the BWOF documentation & ensuring all lighting is in the required place.

If you need help with the installation or maintenance of your emergency lighting system, get in touch with he EAS team today on 07 834 0505.

Instrumentation & Calibration

Instrumentation is the term used to describe all the different devices (or instruments) that are indicating, measuring, and recording physical quantities within your plant to ensure that your production processes are operating effectively.

Some types of measures commonly monitored include:


Flow meters are used to measure the flow in a process pipe. This can be product, water or chemicals used to sanitize the plant. They are used to record trends in product movement; how much water a plant uses or chemical usage for Clean in Place (CIP).

EAS has recently installed flow meters for clients to measure site water usage to identify opportunities for water saving initiatives. We have also used vortex flow meters on demin water lines where there is low conductivity.



Temperature is one of the most important measures in production processes. Temperature monitoring can be used for anything from room temperature for controlling air supply to monitoring fluids in process pipes and many more. There is a diverse range of temperature measurement devices depending on the process or part of the plant being monitored.

Just some of the ways we have assisted clients with temperature gauges include:

  • monitoring chiller rooms to control the temperature in the room and of the product
  • measuring flue temperatures on gas boilers
  • tracking the temperature of hot glue lines on packaging machines
  • monitoring chilled water supply and return lines to process plants and for measuring the load on chillers.
  • In motor control centres to control ventilation

pH measures how acidic or basic a solution is. In food manufacturing changes in pH levels can affect the taste, freshness and shelf life of products. pH is one of the most common chemical measures as it is used in waterworks, sewage treatment plants and the production of food/beverages and health products.

EAS has recently installed pH sensors to provide pH protection on irrigation lines to prevent pasture loss and in stormwater lines to identify any spills before they get into our waterways.



There are many more types of instrumentation that EAS can provide to assist with your plant monitoring including pressure, conductivity, chlorine and turbidity.

It is also essential that any instrumentation is regularly calibrated to ensure you are getting accurate measures.  Calibration compares the measures provided by the device being tested and the standard. Regular calibration of your instruments allows you to be confident they are accurately measuring inputs and outputs to ensure your facility is operating at peak performance.

The EAS team have a wealth of experience in installing and calibrating equipment for your plant or process. We have also recently employed Blair Pussell, a qualified industrial and control technician who has a wealth or knowledge and experience to assist you with your plant instrumentation.

If you would like advice or assistance on ensuring you have the equipment in place to monitor the performance and productivity of your plan, get in touch with the EAS team today on 07 834 0505.



Growing Economy


Forgive and Forget


In between jobs


On cloud nine

June 2021 Riddle Answer

The third room is the safest because the lions would have died of starvation.

Equipotential bonding – and why on earth you need it.

Equipotential bonding and earthing are essential parts of electrical safety. Both play an important part in preventing electrical shocks in your plant.

Electrical equipment requires earthing to ensure that if a fault occurs that the voltage has a safe path to travel where the surge in current will trip a breaker, cutting power to the equipment, making it safe to touch.

For example, if your fridge had a loose wire, that wire is live and if someone touched it, they would get an electric shock. The chances of touching the loose wire may seem slim, however if the fridge is not earthed and that wire touches the frame or body of the fridge, this would then cause the whole fridge to become ‘live’ meaning that if you walked up to the fridge and touched it you would be shocked or electrocuted.

The principal of earthing is to take that live current away, allowing it to travel down the electrical installation earthing path, where the surge in current trips a breaker supplying power to the fridge. This cuts all power to the fridge and makes it safe to touch.


In addition to earthing electrical equipment further safety measures need to be taken to protect workers from the risk of electrical shock from other conductive equipment in your plant.

This is done by equipotential bonding. Equipotential bonding connects all accessible metalwork whether associated with the electrical installation (known as exposed metalwork) or not (extraneous metalwork) to the electrical service earth.

Within your building there will be many services that use metal connections including water pipes, gas piping, HVAC ducting and even the metal structure of the building itself.  These can all provide a risk of current flowing through paths not designed to carry a path and create the risk of electrical shock for your workers.

Examples of what may require equipotential bonding as part of your electrical installation:

  • Metal water service pipes
  • Metal gas installation pipes
  • Other metal services pipes and ducting
  • Metal central heating and air conditioning systems
  • Exposed metal structures or parts of the building
  • Lightning protection systems.

How does Equipotential bonding work?:
Equipotential bonding aims to limit the magnitude of touch voltages. Without equipotential bonding the risk is that the voltage flows between the ‘live’ electrical equipment and other conductive equipment in your plant – essentially making all metal parts in your plant ‘live’.  If someone was to touch two of these things at the same time, they would create a circuit.  Because of the difference in energy between the ‘live’ item and the other conductive equipment in your plant, energy would flow from the high potential point to the lower potential point as fast as possible via the connection (your worker). This could be fatal if the voltage is high enough.  Equipotential translates to equal potential, so by bonding all the conductive parts it allows the potential (voltage) to be the same, reducing the risk.

Bonding is usually achieved with a large earth wire in good secure contact with the exposed extraneous conductive part(s) which is connected directly back to the main switchboards main earth bar and via this to the earth electrode. Equipotential bonding of earthed equipment ensures workers in an equipotential zone are protected because there is a nearly identical level of electrical potential between all points of the body.

Equipotential bonding also has a secondary goal of mitigating noise in the electrical network. Operation problems that can occur without effective equipotential bonding and grounding include:

  • Communication failures
  • Drifts or deviations/measuring errors
  • Abnormal heating on the powering stages (inverters, converters etc) and motorization.
  • Burning of electronic components without apparent motive even on reliable equipment
  • Intermittences

EAS has the skills and experience to deliver high quality electrical solutions you can trust. If you’d like to find out more about ensuring the safety of your staff and equipment, get in touch with the EAS team today on 07 834 0505.

May 2021 – Riddle Answer

He was cleaning the windows on the inside of the building!

What’s happening with copper prices and how does this affect your electrical work

Copper with its corrosive resistance, electrical conductivity and superior heat transfer make it one of the most important metals in use today.

When it comes to the electrical industry, nearly all electrical wires and cables today use copper. This means that the increasing demand and pricing is having a significant impact on cable pricing.

What is driving these increases?
The demand for copper is increasing dramatically as worldwide economies ramp up with the roll out of vaccines. The increasing push by governments for sustainable energy generation is also contributing to demand with copper being the key metal in generation, transmission, storage and consumption of electricity.

As demand has continued to grow, unfortunately supply has not kept pace with the worldwide pandemic effecting production. International Copper Study Groups in Peru, the world’s second largest producer of copper, reported a 12.5% plunge in output in 2020. With demand increasing and supply constrained, copper prices are reaching highs not seen in many years.



Is this a short-term problem?
While the roll out of vaccines across the world should assist with increasing the supply of copper, the worldwide demand for copper is forecast to continue to grow. Some analysts are predicting that growth will be as much as 50% over the next ten years as the world moves to low carbon options.  For example, the production of a petrol/diesel car uses 16kg of copper compared to an electric or hybrid car which requires 60kg.


What does this mean for you?
EAS quotes your jobs based on the current pricing for cable. While we have traditionally guaranteed this pricing for a period of 30 days, the constantly increasing copper prices and demand for stock means that we cannot always guarantee pricing for this length of time. If we are aware of an impending price increase, your quote validity may reduce, which gives you the opportunity to get your orders in before prices increase again.

In addition to the pressure on copper pricing, International shipping availability is also stretched which has resulted in approximately 20% less capacity and as much as a 50% increase in rates, further adding to unpredictability with sourcing materials.

We highly recommend if you have projects where a significant amount of cable will be required you confirm these as soon as possible so that we can lock in supply and pricing.

If you have any questions, don’t hesitate to get in touch with the team on 07 834 0505.

Injection Testing for Circuit Breakers

Circuit breakers can go long periods of time without activation. If they fail when activated, this can have catastrophic consequences for your staff and plant if an arc flash were to occur; and will certainly cause extensive damage to your electrical systems. Primary & Secondary injection testing should be included as part of your Preventative Maintenance plan to ensure the reliability and safety of your power circuit breakers.

Primary Injection Testing
Primary current injection is usually the preferred test method because it includes the current sensors, wiring and the current conduction path in the circuit breaker as part of the test. However, it will not always detect sensor wiring and polarity problems.

Primary injection tests work by injecting a calculated amount of low voltage (Typically 5 to 10 Volts) with high current through the breaker and measuring how long it takes for the breaker to trip. The calculated amount of current is different for each type of function you want to test. Based on the time-current curve for the breaker, each testing current value will have a required time response for determining acceptability.

Common primary injection tests include:

  • Power Transformers (Through Faults)
  • Relay Testing
  • Bus-work, Switchgear and HV Breakers
  • Low voltage breakers
  • Switchgear Testing
  • Heat runs
  • Stability tests
  • Loose Connections
  • Core Identification

Secondary Injection Testing:
Secondary Injection Tests are always completed before the Primary Injection Tests. It is done to minimize the risks during the initial testing to the Low Voltage side of equipment under test. This check verifies the correct operation of the protection controls that are downstream from the inputs to the protection relays.

Some trip units allow for just testing of the electronic trip functions of the breakers, this form of testing is much more readily accessible and easier to complete. Secondary trip testing differs from Primary in that the high currents are not applied through the line and load contacts of the breaker. This generally involves disconnecting the trip from its standard operating circuitry and connecting it to a specialist test that can inject, measure and record the actual operation characteristics of the breaker under test.

If you need help incorporating primary and secondary injection testing as part of your preventative maintenance programme get in touch with EAS, your specialist industrial electrical team today on 07 834 0505.