GENERAL WARNING: Never undertake a DIY electrical task or any other modification to you home if you're not qualified/certified to work on home electricity systems or when your home is insured. Always contact your insurance company and discuss your undertaking with the company. If you do not you will find out the hard way that the company will not cover you house or property if a disaster of some kind occurs. Ensure that you obtain the necessary permission and any certificates required. You have been warned!!
In a follow up to the article "Load shedding killed my Home Network Router? How to prevent this from happening to other equipment in future!" my son and I decided to prevent this from happening again. He is a fully qualified electrical engineer and has all the qualifications/certificates to work and certify any electrical low and high voltage undertaking. With 17 years service and currently a Senior Superintendent I was confident that he could easily come up with a project that will protect household equipment.
He decided to construct a 220v Time Delay Switching Unit that control the power feed at the electrical distribution board when power return after an Eskom load shedding period. This unit had to be robust/safe and must fully protect household electrical equipment. Therefor a small relay circuit would not perform the task we had in mind.
My son decided to use the following components for the project:
- 230v Avanti Multi Function Timer 11 Pin
- Timer Square 11 Pin Base
- 45 Amp Electrical Contactor
- 230v Green LED Pilot Light
- 230v Red LED Pilot Light
- 230v LED Compact Voltage Meter
- 220v LED Compact Amp Meter
- Cable House Wire 6.00mm Black
- Cable House Wire 6.00mm White
- Metal Din Rail for Circuit Breakers
- Major Tech Electrical Enclosure/Cabinet 350x300x130mm
- Circuit Breaker for additional protection even though the unit also runs through the Earth Leakage Circuit Breaker
I am not going to go into building detail as this might entice non qualified DIY enthusiasts to illegally construct and install such a build. See General Warning above.
Here is a bit of theory regarding the build:
A timer delay/relay
A timer delay switching unit has a timing element device that intentionally delays the switching ON/OFF of power flow immediately once the power is applied or removed from the contactor. A time delay has an inbuilt time delay function, so the contactor will not activate immediately once it is activated although it will wait for a fixed amount of time.
So this kind of “relay” is applicable where delays are required before the contactor activates like security systems, industrial automation and now power supply return after Eskom Load shedding.
A Contactor
A contactor is an electromechanical control device that used to make or break the connection between the load and power supply. The use of a contactor is similar to the relay. But the device used for higher current carrying application is known as a contactor and the device used for lower current applications is known as Relay.
A contactor has several contacts as per the application and load. Generally, these contacts are normally open (NO) contact. And hence the load is shut off when the coil of the contactor is de-energized. But the contactor can design for both normally open and normally close applications. The most common application of contactor is in the starter that used to turn ON and OFF the equipment like motor, transformer, etc.
A contactor is an electrically controlled switch used for switching a power circuit, similar to a relay except with higher current ratings.
Functions of the LED Pilot Lights
Red LED Light - Indication when all 220v power is OFF or ON during load shedding. OFF - No House Power. ON - Power available from the Grid.
Green LED Light - Indication that the contactor has switched and that house power is now available to use.
Functions of the LED Voltage and Amp Meters.
LED Volt Meter - Measures the voltage from the Grid
LED Amp Meter - Measures the amps drawn by equipment in the household.
Note: During load shedding all lights, meters etc is OFF. Once the power returns the Red LED Pilot light will be on as well as both the LED volt and amp meters. Green light will be OFF. The current voltage will be displayed but no amps as the contactor has not been energized as the Multi Function Timer is counting down for the period set. Once this period has expired the contactor will be energized and the Green LED light will be on. The Amp meter will also provide a measurement of the current amps drawn. Power will be available to use by the household. The delay will prevent over voltage/under voltage and power fluctuations etc. The period of time set for the timer is therefor important as to provide enough time for the power supply to "settle". Many times before the power comes on and goes off again after a few seconds. This might happen several times with high voltage fluctuations in the mix that can cause damage.
Function and operation of circuit breakers
By definition a circuit breaker is an electrical safety device, a switch that automatically interrupts the current of an overloaded electric circuit, ground faults, or short circuits. Circuit breakers "trip", shut off, current flow after protective relays detect a fault. Unlike fuses that were used previously, circuit breakers are not usually damaged so they can be reset as opposed to being replaced. Circuit breakers are used in residential and in industrial applications.
Future extensions to be installed for this unit
- Fitting audible alarm buzzers to indicate when the voltage or amps runs to high, Currently this is manually driven by observing the meters and then switch off the earth leakage breaker. This will reset the timer and it will count down again for the set period. We are currently looking at automating this function.
- Fitting a change over switch to switch between the generator and grid power supply.
Here is a useful link if you want to learn more about Time Delay Relay Basics: Relay Circuit and Applications
There you have it in a nutshell. I am quite confident that this unit provide protection in 95% of bad incidents. The other 5% is the risk factor while sleeping and not being able to monitor the return voltage after load shedding at night. I gladly take the 95% instead of having no protection at all. Thankfully the power supply in Mossel Bay is fairly stable but one never knows what could happen in the future.
I would like to thank my son for designing and building this unit. The only problem I have with the unit is that some of the younger generation cannot spell the word "Controller"! See spelling on cabinet. Yes and the necessary ECOC was obtained. Now onto the next project to alleviate the effects caused by load shedding. The next project has been lined up. More on this in a future posting.
Images: (Click on images for larger view.)
