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There is also a bonus lecture that I am working on at the moment which will be added to the course as soon as it is done. Then it will be on to creating the next one:)
This a very interesting problem that has been sent to me by one of our readers, so let’s take a look at what is happening here. Bear in mind, I do not have the exact details of the installation, so I will try and picture the installation from what is happening.
To start off with, consider how the single phase motor will work. When we apply power to it, the starting winding will ‘kick-start’ the motor in the desired direction after which the running winding maintains the motor in the ‘run mode’.
Now let us consider the likely installation:
The pump has to pump water up to the next point which is higher than the position of the pump. In other words, it has what we call a vertical lift
(sorry all, tried getting a picture of the layout in here but seems I have an issue uploading at the moment)
So if you started the motor, it will start in the right direction and pump water to the outlet. So far there is no problem. When you have no need for it to run any longer, you stop it and it waits for the next start. Everything here is normal. There is no motor or pump fault as it works exactly as intended.
Now, you need this to run again after 5 or 10 minutes. You proceed to start it and, once again, it works as it should. Now the situation may change. After you have stopped it, you try to start it again within a very short time and there we have it, the motor runs in the wrong direction and spins off the impeller.
Why did this happen?
Very interesting problem. The issue here is not an electrical one but rather mechanical. What is happening is that the water in the pipe is running back to the pump when you stopped it, thus spinning the pump backwards. When this is happening and you start the motor, you may not have sufficient torque to stop this and the force of the water maintains the direction in which it was spinning. Once your running winding takes over, it does not care which direction this motor is running in. It simply maintains whichever direction you have started with.
The solution? Get the mechanical boys to put a non-return valve close to the pump. This will prevent the water running back and reversing your motor direction.
Hope this solves your problem and keep them coming. Not always easy to solve and I may not be able to get them all, but surely within our readers circle we will be able to answer all questions?
Welcome to another post from Sparkyhelp.
Today we will look at one of the most common faults you may be called to on a domestic or commercial installation. The RCD (earth leakage device) keeps on tripping.
This is a fairly common thing to happen, yet can keep you searching for hours, especially if it is an intermittent fault. The first thing is to find out when it tripped, in other words, did they turn anything on and that was when it tripped? You will find that in a lot of cases, the occupant plugged something into a socket outlet and when it tripped the RCD, they unplugged it and now the RCD won’t latch again when trying to turn it back on. They pay no attention to what they tried turning on as obviously that was not what caused it and they don’t tell you about it.
First, let us assume that is what happened. Turn off all the circuit breakers associated with the RCD. Now reset the RCD and once that is on, turn on the circuit breakers one at a time. It is always good to wait a few seconds before turning the next one on. Everything stays on? Great, job done. It trips when you turn on one of the circuit breakers? Move to the next step.
If one circuit trips the RCD, repeat the procedure to reset the RCD but leave the faulty circuit turned off. If it is not clear what is supplied from this circuit breaker, move through the installation and determine which outlets have no power. Once you know that, you can proceed to unplug all devices on that circuit and then restore power to the circuit. The next step is to find the faulty device. Do this by testing each device, not by turning them back on!
Now let us say that the RCD will not reset at all even when all the Circuit Breakers have been turned off. This is a little more complicated and what I generally do in this case is to isolate my main switch, test to make sure it is isolated and then remove the connections from the load side of the RCD. In other words, it has nothing connected to it apart from the supply. Once I have done that I will CLOSE the board first and then turn the main switch back on. Now I will reset the RCD and if it stays on, I will once again isolate the main switch, open the board and move to the next sequence of testing.
Where you come across an intermittent fault, it is not that easy to find and you will be relying on the readings you get when testing the insulation resistance. Look for the circuit that has the worst reading and start looking at that. Be warned, this could turn into a very long process to find the culprit!
Here is what you NEVER do: disconnect the earth wire from the equipment that causes it to trip. You will come across the old fridge or washing machine that works, but does trip the RCD every so often. This is telling you there is a fault. Do not disconnect the earth from it and use it. You are risking causing someone serious injury if not worse.
As Electricians, it is always a difficult question to answer. Should I specialise in a specific niche or not?
The answer is not an easy one. You need to establish where you want to be working and as we all know, this seems to change pending a number of things like economic situation, company stability etc. Our field is a very diverse one and in some countries you need a specific license to operate in some sectors of our trade whilst in others you do not.
So how do you decide? The honest answer is that you need to understand what you are passionate about. If you love fault-finding on industrial installations, make that your speciality but do not ignore the rest of the fields. Make sure you still stay up to date on wiring regulations, new technology etc. The reason for this is that you may find yourself having to make a change to your career at some stage and you do not want to be in a position where your skills are not up to date.
Let us look at the other side of what you will be expected to do in the ever changing environment we work in. Start with the domestic installations. 15 years ago this would have involved light and power with no technology involved at all. If you look at some of the installations today, you are going to come across a so called ‘smart home’ with state of the art technology. All of a sudden you are expected to know how to not only install this equipment, but also to maintain and fault-find them.
If you had not stayed current with your skills, you will end up not having the faintest idea on where to start. This is why we say to make sure you keep yourself up to speed with what is happening in our trade. You are going to need varied skills to stay afloat in today’s installations.
You may do a service call to a commercial site and find a very old piece of equipment fitted with a 3 phase forward/reverse started hooked onto the back of a thumbwheel with micro switches to trigger the delay and change of direction. If you do not understand how these circuits work, be prepared for a long struggle to get the machine back into operation.
Now go back to the original question of specialising. If you look at how the previously segregated fields are now starting to overlap on installations, specialising could leave you out in the cold. Personally, I love industrial installations and most of all, fault-finding on machinery. It is a challenge to walk up to a machine that you know nothing about, find the fault and get it back into production but, do not limit your skill to that only! Make sure you still get exposure to other installations.
If you are stuck on this question, I hope this has given you some perspective on it. So until next time, remember that the bitter taste of poor quality by far outlasts the sweetness of a cheap price. Do not cut prices to get the work and then put yourself in a position where you take shortcuts to avoid losing money!
Stay Safe out there!
Hi everyone. Happy to be able to get back to our blog again and we will be kicking off with a very interesting topic:
Installing an Earth Leakage or RCD to an existing control circuit. You have been tasked to install this device to the incoming side of the control circuit. There are a number of control circuits leading from this board and currently each has its own circuit breaker. There is a master PLC that allows for starting and monitoring the equipment. Looking at the existing circuit, it represents something like the below:
You have been tasked to install this device to the incoming side of the control circuit. There are a number of control circuits leading from this board and currently each has its own circuit breaker. There is a master PLC that allows for starting and monitoring the equipment. Looking at the existing circuit, it represents something like the below:
The PLC has a number of inputs which are from different circuits, but has only a common neutral to the input card which comes from the main neutral bar. Your instructions are to install it as per the next sketch:
The question here is: Will this work?
Simple answer; No!
You will be creating an imbalance between the active and neutral by using a neutral to the PLC Input card that is not from the device you installed.
The problem you have here is that there are other circuits on the same card so you will not be able to move the PLC Neutral to the Earth Leakage as you need to install one for every control circuit and you will end up in a very confusing mess.
Your solution here is to install your device to the supply side of all the circuits. In other words we are going for ‘blanket protection’ here. This will give you the protection you want but could lead to longer downtime on a fault as you will lose all the circuits under a fault condition which means you will spend a bit more time establishing which circuit has the fault on it.
There we go, a nice and easy one to get back into the swing of things. Remember to stay tuned for some exciting training sessions we will be hosting soon. To all of the members, I will be sending you a free PDF version of a small book on Time Management as a gift soon.
Till next time, same saying: Stay Safe and make sure the work you do is of the highest possible standard!
Hi Everyone,
After a long absence, we can now finally release some great news!
SparkyHelp will be offering live online training sessions on a number of electrical and fault finding topics. We will be doing this in collaboration with PCE Training who offers a number of corporate training courses, Project Management as their flagship, but also including time management, motivation in the workplace, personal productivity, etiquette excellence to name a few.
We really do appreciate all your support over the years and would like to now hear from you if you have specific training requirements. Please go to the PCE Training website and use the contact form to make your request and suggestions.
Prepare yourself for training that will take you to the next level in your career!
By Now you have most likely played with the Alpha Controllers a little. (remember, the software can be downloaded free from the Mitsubishi site). What we will do this time is to show you how to create your own user function. This is a very helpful tool as you can create your own functions and register them for use in future programs as well. Could save you a lot of timeJ
Once you have the software open, you simply click on the icon for: User Function. Now point to the program area and left click again. This will bring up a dialog box where you can type in the comment and also select the number of inputs and outputs you want this to have. For the example I have used, I selected one input and two outputs. This will then open a new program area showing the input(s) and output(s) you selected. Now you simply create the program you want inside this block.
Have a look at the example below to see what it would look like.
The program bit in the example is just something I put together to show you how the user function works. This waits for an input to turn on, in this case I worked with an input that will be on for a very short time then turn off again, at which point we will set our S/R relay on and count the first count on the timer. This will also turn on the first output to show us the signal was seen. After a delay of 5 seconds this output will turn off and wait for the next input signal. We will repeat this 5 times at which point the counter will activate output 2 showing us we have reached 5 counts. Once this happens, the second delay timer will time out the 3 seconds which it was set for, and clear the counter to start the cycle again.
As I said, this was just some random thoughts.
Now, once you have written the program you want, you simply close this by clicking on the white X as shown below.
This will close this area and place your user function into the main program as can be seen below.
Now you just draw in your input and output lines and your program is done. See how this allows you to have a very simple main program? All you see are the functions and not a mass of lines and blocks to try and decipher. To see what is inside a User Function, you simply double click on and it will open up so you can have a look at the programming inside.
Have a bit of a play with this and create your own User Functions that can then be “dropped” into your programs in future. It will save a lot of time.
Till next time, hope you find this useful and remember, Safety First!
Time for us to take a look at another circuit. This time we will look at a very basic Plugging Control Circuit. What does the name mean? It is merely a circuit where we prevent rapid changing of direction of the motor. In other words, we want to prevent the operator from going in one direction and immediately switch to the other direction before the motor has come to a stop.
If you have a look at the circuit below you will notice a few things. The first is that there is no retaining contact to keep the circuit energised in either the Forward or Reverse direction. This means you must hold the start button down to keep the motor running. As soon as you let the start button go, the motor will stop.
The next items you will notice are the two Timers. We have a timer that will be energised as soon as the Forward or Reverse buttons are pushed. Whilst holding the button down the timer will time out the pre-set time and only then will the contactor be energised. As soon as you let the button go and push the next one, the second timer will start it’s time and there will be a delay once again before the contactor is energised.
Please remember this circuit is a very basic example of how it can be done. Please ensure that you test and ensure the safety of operation for any circuit you design before implementing it into a machine.
Have a think about where you would be able to use this type of control and why it would be useful in that application. Till next time, remember Safety First and Production Second. Never take risks in order to maintain production!
Plugging Control
When we look at a star/delta starter, there are some basic rules to follow. I know we have had a look at this type of starter before, but thought it might be worth doing it again to assist with fault finding tips. The first schematic shows how NOT to wire the circuit. You will notice it relies on just the timer to switch between the star and delta contactors. This means it relies on the normally closed contact to be fully open before closing the normally open contact. This is commonly referred to as split second timing and is not good practice. There may be an instance when the two contacts are both in the closed position for a split second. That will lead to both the star and delta contactors being energised which leads to a not so good result. Take a look at the circuit and see if you agree.
Now let’s take the same circuit and make a few changes to it. These changes will add electrical interlocking between star and delta which eliminates the issue discussed above. You will notice I also added a normally open of the main contactor here which is something I prefer to have in the circuit.
Hope you find this useful and please always remember that the tips and posts on this blog are only intended as guidelines. Please ensure any installation you do meets all your local Legislative Standards at all times.
And for those who have not done so, remember to collect your copy of the Manual for Electricians Volume one which you can find at: www.lulu.com/spotlight/SparkyHelp
Till next time, always put safety first. Think before you do and always ask yourself “what if” when you prepare your job safety analysis. Hope you all have a great week
Hi All
It has been a while since the last newsletter, but we are back on track and with the New Year well underway, I thought we could start with a simple, but very useful, application to monitor a circuit. Most of you would have come across a piece of equipment failure where you wish you could have been notified when it started right?
Let’s use the following example:
You are called to a Freezer and the defrost elements have failed. Problem is this was only noticed when the entire evaporator has turned into a solid block of ice. The only way for you to replace/repair the elements is to get rid of the ice. Just that costs you half a day alone plus you have the client anxious as he needs the freezer running. So, how could this have been avoided? We will use a very simple circuit to do this for us.
Assume the elements are 3 phase. First, test the elements with your continuity tester to make sure they are all working. We will then install 3 current sensing relays, one on each phase going to the elements. With power on, you adjust the relay until the normally open contact closes. Simply put, this means that the current being drawn by the element is the same as the setpoint on your current sensing relay. This means that when you have one element fail, the current draw is lower and the relay will not switch. Make sense?
This now provides us with a contact that will “make” when we draw current and we will use this contact to provide us with the alarm signal. We mentioned the Mitsubishi Alpha Controllers previously and this is what we will use here again. The elements are switched by a contactor. We will use a normally open from this contactor to provide us with and input to tell us that we are now in defrost mode. With this input on, we also need the 3 signals from the current sensing relays to be on. If any one of them is not, we go to alarm state.
You can make it easier here for yourself to use each one of these inputs as a different line for the alarm. That way you can see which phase the faulty element is on. For the alarm there are many options. You could use an output to turn on an audible alarm which would work well provided there is someone on site. The other alternative is to send this output to a dialler or GSM modem to provide the alarm to the person on call. The options are yours. Decide which will work best for you and modify the circuit to suit.
Have a look at the circuit below and see if it makes sense to you. Note I have not labelled the inputs or output. Work out what they are. If this does not make sense to you, let me know and I will post a circuit “walk through” to explain.
By the way, if you have not had a chance to, check out my book on www.lulu.com/spotlight/SparkyHelp
Till next time, stay safe and take pride in your work!
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