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Identifying DC Fault Currents as A Protection Objective

by Nathan Zachary
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Smart Homes and Vehicles, Photovoltaics and Power Factor Correction are the new buzzwords. That, when put into practice, make it more difficult to assess risks in modern electricity installations. A qualified electrician working on such an installation requires extensive specialized knowledge. We offer specialized services and products at APC ups price in Pakistan.  

Including detailed knowledge of standards and in-depth knowledge of possible protection. And monitoring equipment. The potential DC fault currents in such systems are the focus of this article.

Effects Of DC Fault Currents Greater Than 6 ma

For DC fault currents greater than 6 mA, saturation effects in the current transformer RCD ( Residual Current Device ) can cause a negative change in both response time and response value when using a Type, An RCD.

At worst, this type of RCD either fails to activate in the event of high DC fault current or goes “blind”. So, it can no longer guarantee the protection function provided by the device.

To prevent this from happening, it can use a Type B RCD or it must detect the potential DC fault current by some other means to allow the circuit to trip. A mix of type A and does not allow type B RCDs on the same circuit. And this must be taken into account in new installations or when expanding existing ones.

Below is a graph illustrating the definition of 6 mA DC fault current:

Regulatory Requirements for Devices and Installations

According, the following is applicable for devices:

Pluggable electrical equipment with a nominal input ≥ 4 kVA must design in such a way that the DC component superimposed on the protective conductor current does not exceed 6 mA.

For pluggable electrical equipment with a nominal input ≥ 4 kVA and permanently connected equipment , regardless of its nominal input, must include information on protective measures in the operating manual.

For protective conductor DC currents greater than 6 mA, shall select suitable protective devices, such as a Type B Residual Current Device (RCD).

Consequences Of This Regulation on Devices

For device manufacturers, this means that it must detect DC fault currents greater than 6 mA and switched off , for example, with an integrated Bender solution or may only use the device in conjunction with an upstream B-type RCD.

Consequences Of This Regulation in Current Building Installations

In many building installations, additional protective measures for protection against electric shock included in the form of a protective RCD (type A) along with the basic protection with overcurrent protective equipment.

For this reason, in recent years numerous standards and develops specifications that take this fact into account and that demand the corresponding requirements on electrical equipment (loads, sources or storage) or electrical installations to maintain the required protection objectives.

The result is that the responsibility does not only fall on the manufacturers of plug-in photovoltaic plants; charging stations for electric cars; energy efficient LED lighting; or energy-optimized units with frequency converters, but also on designers, builders, and operators of electrical systems.

Cost Effective Solutions to DC Fault Currents

Here is a summary of practical information about the problem and possible cost-effective solutions.

Electric Currents and Their Effects on The Body

For an AC voltage with a frequency of 15. A 100 Hz, can perceive the current from 0.5 mA. and up to 10 mA, humans may experience involuntary muscle spasms and difficulty breathing. “Letting go” or “releasing” is difficult because of the spasms.

At approximately 50 mA, the threshold for ventricular fibrillation exceed. Which in turn can be fatal. Of course, the duration of the current flow is an important factor; see the following figure.

It is precisely on the basis of these times that the overcurrent protection devices and residual current devices (RCD) limits, not the amperage. The type of residual current protection device expects to use will depend on the type of fault current.

Selection of residual current protection devices: RCD type B or the type sensitive to all currents

In addition to the fault currents detected by a type A RCD, a type B RCD can also detect fault current shapes that may occur in the following faulty circuits.

Residual current protection devices sensitive to all types of current (AC/DC) have a frequency range of 0 to 2000 Hz and intends for single-phase and multi-phase AC systems. They are not suitable for use on pure DC networks.

Risk Assessment Assistance

At Electric we offer Bender universal protection devices, sensitive to current, for industrial applications. For pure residual current measurements, single channel, and multi-channel products such as the have been the right choice in monitoring equipment for many years.

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