RCD Installation to an Existing Circuit

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:

 

RCD 1

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:

RCD 2

 

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!

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