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Join Date: Apr 2012
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RCCB for DC Networks

04/27/2012 11:50 AM

As per IEC 61008, Class B RCCBs are for DC Networks,what is the operating principle for them?

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#1

Re: RCCB for DC Networks

04/27/2012 4:23 PM

They trip when too much current passes through them.

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#2

Re: RCCB for DC Networks

04/28/2012 1:13 AM

Type B

Ensures tripping for residual AC currents, pulsating DC currents and smooth DC currents, whether suddenly applied or slowly rising.

Type AC RCDs will only provide protection against full wave AC fault currents, but fires can be caused by pulsating DC fault currents, and such fault currents can only be detected by Type A or Type B RCDs.

By definition, AC current comprises of positive and negative half cycles with respect to a zero reference point, and an AC fault current can start to flow to earth at any point during either half cycle. An AC Type RCD will only trip in response to either the positive or negative half cycles of the AC earth fault current, whereas an A Type RCD will respond to both half cycles. As the AC Type RCD is blind to either the positive or negative half cycles of an AC fault current, the fault current could flow for up to 10mS before the RCD will see the fault current. This 10mS will be added to the response time of the device.

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#3
In reply to #2

Re: RCCB for DC Networks

05/03/2012 12:12 PM

Hello,

In fact RCCB type B are dedicated to be connected to AC network, in which it is possible that there is pure d.c. residual current. For example, if you have a 3-phase motor speed drive, you have to use type B RCD upstream to protect against electric shocks. Why ? In case of fault dowstream the bridge rectifier, a pure d.c. residual current will flow in your body. In this case type B RCD will detect such a fault and type in 40 ms.

Type B RCCB comply to an international standard IEC 62423, and in addition, they also comply to IEC 61008-1, because type B RCD, as said above detects a.c. residual current, pulsating d.c. residual currents, high frequency residual currents and pure d.c. residual currents.

It is also important to remind that such devices are intended to be connected to ac netweor only.

To my knowledge, there is no standard for RCCB for d.c. network.

Jean-François REY

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