When we talk about electrical protection, the two elements that naturally come to mind are the divisional circuit breaker and the differential switch. But it also happens that we talk about a differential circuit breaker (a “diff circuit breaker” or an “electrical differential”) and this term is often misused.
I have therefore decided to give you all the information that will allow you to:
Understand what a differential circuit breaker in electricity is.
Why and when to use it in the electrical panel.
How to choose it.
How to connect and secure an electrical differential circuit breaker.
What is a differential circuit breaker:
Reminder on the protections of the electrical installation:
Before I go directly to the ground leakage circuit breaker, I will recall two notions of protection that are fundamental in the electrical installation:
Protection of property (devices connected to electrical outlets).
The protection of natural entities.
Protection of property:
It is provided by the magneto-thermal circuit breaker (we also speak of divisional circuit breaker, fuse holder, circuit breaker but also “electrical lead”).
Whatever its name, this equipment is dedicated to protecting the material goods in the house.. This includes lighting, elements connected to the sockets, household appliances (oven, hob, washing machine…).
The circuit-breaker therefore monitors two phenomena, namely electrical short-circuit and electrical current overload.
The protection of people:
This is the most important protection at the GLVS level (which means General Low Voltage Switchboard).
It protects people from the risk of electrical current leakage (which can cause significant damage when it passes through the human body). I explain this information in my guide “Electricity: Understanding Before You Start”.
This protection is provided by the differential switch (also called Inter Diff, or ID) which measures the permanent current difference between the phase and the neutral.
Coupled to the grounding circuit, the differential switch is essential to ensure the safety of people with regard to electricity.
Role and definition of the differential circuit breaker:
The differential circuit breaker therefore combines the two functions of protecting material assets and protecting natural entities.
It performs the role of the differential switch combined with that of the divisional circuit breaker:
Differential Circuit Breaker = Divisional Circuit Breaker + Differential Switch
You will have understood that:
The magneto-thermal system will protect against overloads and short circuits (property protection).
The differential system against current leakage (protection of people).
The difference between an electric differential circuit breaker and a differential switch:
As I explained above, the difference between the differential switch and the differential circuit breaker is that the latter has an additional feature.
Why do I want to emphasize this difference?
To be careful with the use of technical terms:
Because in many cases and in many videos, the term ground leakage circuit breaker is used incorrectly.
Take for example Leroy Merlin’s video titled “How to install an electrical panel” (visible here):
At the beginning of the explanation, in the hardware part, it says, and I quote “a 30mA differential circuit breaker per row” – at exactly 40 seconds:
The use of the term 30mA differential circuit breaker is not appropriate.
It is a differential switch that must be installed ahead of the divisional circuit-breakers, at the beginning of the electrical box row.
A significant price difference:
This is one of the apparent differences between an “inter diff” and a differential circuit breaker: the price.
Let’s take the case for two Legrand references:
The 30mA 32A AC type ground leakage circuit breaker, reference 4 107 08 (here in the Legrand online catalogue), is displayed at a catalogue price of 248.4 euros including VAT.
The differential switch 40A 30mA type AC reference 4 116 11 coupled to a 32A divisional circuit-breaker to obtain the same function are at the catalogue price of 135.12 euros including VAT.
A 30mA ground fault circuit breaker costs about 1.5 to 2 times more than its equivalent ground fault circuit breaker + differential circuit breaker.
This is another criterion that differentiates these two elements of the electrical box!
Why use it instead of a differential switch:
If the price is so high, why use an electric differential circuit breaker?
Mainly used in the commercial sector:
GFCIs are rarely used in domestic electrical installations, but rather in the commercial and industrial sectors.
Here is the reason:
In offices, the circuits are grouped according to a logic similar to the one you may know for your house.
But there is an additional constraint on the domestic worker: productivity.
A faulty electrical circuit must not disturb all or part of the electrical installation.
How can this be possible?
Let’s take an example.
Fault on an industrial electrical cabinet:
A factory electrical box consists of several rows.
Imagine that on one of these rows, there is a differential switch at the head of the line. This ID protects the socket circuits of the administrative part of the factory (offices with computers) and the machine circuits of the production part.
If on one of the machines there is an insulation fault (current leakage to the ground), the differential switch at the head of the line will trip. It will then deprive the entire row of power supply.
The administrative part will therefore be deprived of power because of a single failed machine.
To overcome this type of power failure, in many facilities, critical electrical circuits are protected independently by differential circuit breakers.
Thus, if a circuit is triggered because of a problem, there will be no operating loss for the entire facility. Only the faulty electrical circuit will be disconnected.
In the following picture, we see that each of the circuits is individually protected by differential circuit breakers.
If an element is faulty (a computer for example), it is only its circuit that will be affected and not a set of power cables.
In the following picture, all electrical circuits are independent of each other and protected by electrical differential circuit breakers.
This electrical connection is always made in order to ensure the continuity of service of the installation. Here, we are talking about electrical circuits for plugging in computers.
To simplify electrical wiring:
The use of a differential circuit breaker can also simplify electrical wiring.
In fact, when installing an appliance that requires the addition of a circuit-breaker in the electrical panel (such as a heat pump, air conditioner, specialized electrical outlet, etc.), it is necessary to work on an entire row of the electrical panel.
In many cases, the electrical switch in this row was cut off at the end of the last divisional circuit breaker. This means that the old switch(es) must be removed and a new electrical switch for the new circuit breaker must be installed.
An additional problem is that you have to find a horizontal electric switch that is compatible with the brand.
And it can be problematic when the electrician who made the electrical box used a little-known brand of electrical equipment.
This is when the use of a differential circuit breaker can simplify electrical wiring:
The ground leakage circuit breaker is connected to the power supply terminal block of the electrical box (as explained in the next chapter). There is therefore no modification to be made on the row in question.
How to select one: size, type, differential threshold, brand:
Differential circuit breaker rating:
The size of the differential circuit breaker is chosen according to the electrical circuit supplied:
10A or 16A for a lighting circuit.
16A or 20A for an electrical plug circuit.
20A for a dedicated circuit with a maximum power of 4600W.
32A for a dedicated circuit with a maximum power of 7360W.
40A for a dedicated circuit with a maximum power of 9200W.
It is the same principle as when sizing the electrical panel where the divisional circuit-breakers are chosen according to the circuit supplied.
Type of electric differential circuit breaker (A, AC, HI):
The type of the differential circuit breaker is the same as the type of the differential switch:
Type AC: It is used to protect common electrical circuits such as lighting, household electrical outlets, some specialized electrical outlets (other than those protected by type A).
Type A: It is used for the protection of specialized circuits. These are household appliances with electronics on board (washing machine, hob) that produce components that disturb AC-type inter-differentials.
Type HI / HPI / SI: It is used for devices that are sensitive to untimely power outages: freezer, alarm, computer.
Differential protection threshold: 30mA or 300mA?
The differential threshold is the current threshold above which the differential circuit breaker will trip. In practice, this threshold is the maximum threshold, the ground leakage circuit breaker will trip first.
In residences, this threshold is 30mA (Obligation with respect to the NFC 15-100 standard).
In the industrial and commercial sectors, in certain specific cases, this differential threshold is increased to 300mA.
Monobloc or with adaptable differential block:
There are two types of ground leakage circuit breakers, monoblocks and adaptable blocks.
Both models are modular, i.e. they are mounted on the DIN rails of the electrical box.
The one-piece electric differential circuit breaker:
The monobloc ground leakage circuit breaker model is similar to a differential switch (except that it performs an additional function).
It generally takes up space for 2 to 4 modules in the electrical box, depending on the size.
The adaptable differential block:
This type of equipment exists so as to make it possible to transform a simple existing circuit-breaker into a differential circuit-breaker. It is also reserved for circuit-breakers of a fairly large size or three-phase (3 phases) or four-pole (3 phases + neutral) diff circuit-breakers.
In fact, if in a GBT there is already protection for the electrical circuit and you want to switch this circuit to independent differential protection, it is possible to use a differential system that can be adapted to the circuit.
This block is composed of a lower row of teeth to which the existing circuit-breaker is connected. This row is connected to a differential block.
The starting electrical connection is made below this differential block. It is most often connected directly to a four-pole distributor.
The use of such a device with an existing circuit-breaker requires checking the compatibility between the adaptable differential block and the circuit-breaker already present in the electrical box.
Concerning brands, I am used to working with Legrand, Schneider Electric and Hager that I present here.
But I also use the Gewiss brand equipment, which in its differential range offers circuit-breakers of reduced width (in module).
Since industrial electrical cabinets are very often well charged, this space saving is not insignificant.
Connect the differential circuit breaker:
One-piece differential circuit breaker:
Previously, I discussed how to connect a differential circuit breaker in the electrical box, let’s take a closer look:
How to connect it:
The “one-piece” ground leakage circuit breaker is connected as a divisional circuit breaker. The power supply comes from above and the outlet to the electrical circuit from below.
Or plug into the electrical panel?
The electrical ground leakage circuit breaker is not positioned at the head of the line, unlike the “inter diff”, which is positioned in front of all the circuits/divisional circuit breakers it protects.
Generally at the end of the row (after the remote switches, timers or the day/night switch) it is directly connected to the power supply terminals.
Adaptable differential block:
The connection of the adaptable block is done with an additional step:
The circuit-breaker is connected to the differential block to form the differential circuit breaker (this is the additional step).
The power supply comes from the power supply terminals to the top of the circuit breaker.
The start to the electrical assembly is from the bottom of the differential block.
What equipment should be used to connect a differential circuit breaker?
Once again, just like the differential switches and connections in the electrical panel, it is necessary to use:
H07VK electrical wire in the right wire section. This flexible cable makes it easier for electrical wires to circulate inside the GLVS.
End caps with insulating flanges. These insulated electrical connectors allow a protected and reliable electrical connection over time (as long as they are installed with a crimping tool).
Example of an electrical diagram with differential circuit breaker:
Here is an example of wiring a 30mA ground leakage circuit breaker on a single row inside the electrical box:
The phase/neutral power supply terminals are connected before the inter diff on one side (left) and before the ground leakage circuit breaker on the other side (right).
In this type of electrical installation, if a fault appears in the circuit protected by the ground leakage circuit breaker, it is only the latter that will trip.
All divisional circuit breakers protected by the 40A 30mA AC type differential switch at the top of the electrical panel row will continue to receive the power supply.
They will not be disturbed by the malfunction that has occurred on the power line protected by the 30mA ground leakage circuit breaker.
Can a differential circuit breaker be cascaded under a 30mA differential switch?
There is no point in doing that.
If there is a fault on the circuit powered by the electrical ground leakage circuit breaker, the ground leakage switch may trip before.
The benefit of using a differential circuit breaker will therefore be lost.
Are there any different D-curve circuit breakers for use with air conditioning motors?
There is indeed this type of D-curve differential circuit breaker. This one allows to temporarily accept an overload that corresponds to the start of the air conditioning motor.
What is the direction of connection of the ground leakage switches?
Unless otherwise specified in the manufacturer’s instructions, the connection can be made independently from the top or bottom of the modular component.
Where to buy ground leakage switches?
It is a rather specific material, which can be found quite easily among specialists in the online sector.
Here are some links sorted by brands at Domomat:
Schneider Electric 30mA ground leakage circuit breakers.
The components in the Hager brand with a four-pole model.
But you can also find “diff circuit breakers” in DIY stores. For example, you can find all the references of the 30mA ground leakage circuit breaker available here at Castorama (which you can book online and retrieve in store).
I also advise you to have a look here at the online seller Domomat, which specializes in the selling of electrical equipment.