IEC 60755 establishes the types of earth leakage protection, defining them according to the type of leak that they measure and protect against.
The leak basically depends on the type of charge that it comes from. Therefore, taking the most basic example, a purely resistive charge (the classic Edison incandescent light bulb, for example), provided it is powered by a source using alternating current, will leak to earth with a perfectly sinusoidal differential current.
But load types have developed exponentially since Edison's time. Especially in relation to the use of loads for power electronics, which have become widespread in recent years. Type B earth leakage protection is the only protection that safeguards people and loads against leakage of alternating current (AC), direct current (DC) or mixed current (AC/DC).
Types of earth leakage protection
The IEC 60755, IEC61008-1, IEC 62423 and IEC-60947-2-M standards establish the following types of earth leakage protection:
This protects against alternating sinusoidal currents, applied both suddenly as well as smoothly and progressively.
Although it’s prohibited in some countries in the European Union, in Spain its use is mainly extended to the domestic level, where more basic loads predominate.
This one deals with the same cases as the AC type and also includes:
- Protection for direct pulsating currents
- Protection for direct pulsating currents superimposed on a continuous earth leakage current of up to 6 mA
These are applied with or without angle control, regardless of polarity, that may appear both suddenly as well as smoothly and progressively.
It’s the commonest protection type in industrial settings and, in some parts of Europe, it’s also compulsory for domestic use.
This covers the scenarios included in type A (remembering that type AC has already been mentioned) and it also provides:
- Protection for composite earth leakage alternating currents (including wave composition with frequencies of 1 kHz), appearing both suddenly as well as smoothly and progressively, intended for circuits powered between phase and neutral or phase and the grounded middle conductor.
- Protection for alternating earth leakage currents superimposed on a smoothed direct current (mixed current).
These types of earth leakage are the least commonly used; they are mostly used in special single-phase applications.
It deals with the scenarios for type F (that is, type AC + type A) and also provides:
- Protection for sinusoidal differential currents up to 1000 Hz
- Protection for alternating earth leakage currents superimposed on smoothed direct currents up to 0.4 times the nominal sensitivity of the protection device or up to 10 mA (whichever is higher)
- Protection for smoothed continuous earth leakage currents.
- Protection for pure continuous earth leakage currents that may arise from correcting electrical circuits (for example, 3 or 6 pulse bridge connections) that are applied with or without angle control, regardless of polarity, that appear both suddenly as well as smoothly and progressively.
This is the most complete type of protection. It guarantees the measurement and protection against loads of alternating current, pulsating current or pure direct current.
Typical loads and applications that need to use type B differential protection
The way charges have developed over the 21st century presents a response as described in the cases referred to in the description of the leakage types protected by type B earth leakage protection. The most typical applications and loads are as follows:
Industry: Variable speed drives, used in countless different processes, such as conveyor belts, air conditioning, pumps, cranes, elevators of any kind, etc. In short, any process that requires a variable speed movement to carry out its function. What motor does not incorporate a drive nowadays?
Offices: UPSs for data protection centres
EV charging: EV charging points. Photovoltaics
Equipment with power electronics, Inverters, Harmonic filtering (active filter), etc.
When should I protect my loads with Type B protection? Legal framework and requirements for earth leakage protection TYPE B
In Spain the Low Voltage electrotechnical regulation (REBT 2002) establishes in ITC-BT-24 (Spanish) the obligation to protect the installation against direct and indirect contacts for installations with type TT earth connection plans (all the mass of the electrical equipment and the neutral of the transformer on the same earth).
However, except for ITC-BT-52 (Official State Bulletin No. 316), which is specifically for EV recharging points and where it is established that the protection will be type B or type A with a supplementary protection for continuous currents of values greater than 6 mA, the regulation does not establish any advice or criteria for selecting the type of earth leakage in our facility.
So, how do I choose for other cases?
We’ve already shown that the type of earth leakage dictates the type of loads it protects from, based on its response. It makes sense, therefore, to bear in mind that each load will use a type of earth leakage protection based on the type of earth leakage it can present.
IEC 60755 standard sets out the general requirements for residual current devices. It establishes the different types of leakage in relation to the different types of charges.
Nobody understands the way loads respond better than the manufacturer itself.
Therefore, when we select a type of earth leakage protection, we must consult the load manuals containing instructions on how to manage its correct protection. Otherwise, in the event of an equipment malfunction, or worse, in the event of an electrical incident due to human error, by not following the manufacturer's instructions, the responsibility for misuse will obviously rest with the end user.
The most reputable manufacturers of drives, UPSs, electric vehicle recharging units, active filters, etc. specify in the section on installation recommendations or warnings the correct load protection and for avoiding untimely trips, the earth leakage protection to be installed must be TYPE B.
Manual example of a 6-pulse drive manufacturer:
Compatibility with RCCBs.
If you are installing an earth leakage protection device (RCD), the frequency converter will function without unwanted tripping and will provide adequate protection whenever a type B earth leakage device is used
We have seen that in order to select the type of earth leakage protection we need, we must look at the load response. However, when we install earth leakage devices in series, upstream of the charge, what selection criteria should we use?
This is what is known as vertical selectivity. The correct selection of the characteristics of the earth leakage devices in series, from the beginning of the charge, through the set of charges (sub-frames) and reaching the protection of the mains panels, should not only take into account the type of charge, but also we must consider other aspects that will indicate the correct coordination of the protection system.
These 3 conditions must always be met in vertical selectivity:
- Ammeter: The sensitivity of an earth leakage must be at least 3 times the sensitivity of the earth leakage device installed downstream.
- Chronometric: The time response of an earth leakage device must be at least twice the maximum time of the earth leakage device installed downstream.
- Type: The earth leakage must be of the same type or higher than the earth leakage device installed downstream
Thus, for vertical coordination of types of earth leakage device, the following table may be helpful:
Therefore, whenever we protect a load with type B protection, all the protection that is in series upstream (subframes, general earth leakage protection) must also be type B
CIRCUTOR Solutions for Type B Earth Leakage Protection
Given the growing requirement of users to cover protections of this type of charge, CIRCUTOR has a wide range of type B earth leakage protection solutions.
IDB-4: 4-pole type B RCCB for three-phase and single-phase installations up to 63 A. Sensitivity of 30 or 300 mA (direct earth leakage device), instantaneous trip time.
WGB-35-TB: Earth leakage relay with transformer included (MRCD), for loads up to 125 A. Sensitivities of 30 or 300 mA, instantaneous or selective trip time.
RGU-10B: Earth leakage relay associated with transformers of the WGC-TB (MRCD) range, up to 180 mm internal diameter, allowing protection of charges of up to 800 A. Sensitivity from 100 mA, programmable trip time.
RGU-100B: Earth leakage relay associated with transformers of the WGB (MRCD) range, up to 110 mm internal diameter, allowing protection of loads of up to 400 A. Sensitivity from 30 mA, instantaneous and programmable trip time.
CBS-400B: Earth leakage relay associated with transformers of the WGB (MRCD) range, up to 110 mm internal diameter, allowing protection of loads of up to 400 A. Sensitivity from 30 mA. With 4 channels for the protection of 4 totally independent circuits. Instantaneous and programmable trip time.
In addition to the protection systems mentioned above, CIRCUTOR also has a novel and innovative type B earth leakage protection system with automatic reconnection:
RECB: 4-pole type B RCCB with automatic reclosing for three-phase and single-phase installations up to 63 A. Sensitivity of 30 or 300 mA (direct differential device). Instantaneous trip time.
We have seen how the different types of earth leakage devices (AC, A, F and B) are defined, according to international framework regulations, and according to the type of leakage they protect against. In other words: the type of earth leakage device is intrinsically linked to the operation and technology of the load to be protected.
It is therefore essential, for the correct selection of the type of earth leakage device, to know what response it has and how the load to be protected works. Manufacturers of the loads, in their manuals and advice, will indicate the approach to take and how to make the selection.
It is equally important to respect all vertical selectivity conditions for the correct coordination of our protection upstream of the charge and at the head of the installation, also respecting the type of earth leakage device.
With these basic guidelines, we will not only ensure maximum continuity of service to preserve the protection of the charges and assets of our facility, but we will also guarantee the safety of individuals.
Product Manager Circutor