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Topic Title: Quick Question
Topic Summary: CPD's
Created On: 24 January 2014 07:42 AM
Status: Read Only
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 24 January 2014 07:42 AM
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Posts: 22
Joined: 25 July 2008

Hi Guys

I'm not 100% and require clarification that would a Circuit Protection Device operate from current flowing the opposite way?

This question is specifically aimed at LV ACB's and HV RMU's with fused switches, TLF's or IDMT relays.

Would appreciate a detailed answer on this if anybody can help?

Kind Regards
 24 January 2014 12:26 PM
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Posts: 128
Joined: 06 February 2013

You need to care, your list is a mixture of devices that would break the fault current and devices that would detect it. Just because a device can detect a reverse current doesn't mean that the fault breaker is rated to break it. At a high level see the following but if you're going to design something you need to look into it fully first. AC and DC will be different for some devices e.g. ACB my comments relate to AC.

LV ACB will probably detect reverse fault current but you need to check with mnfr as to this and whether it would be rated to break reverse fault.
HV fuse will detect and break both ways.
TLFs will detect both ways, breaking depends on the device that interrupts the fault current. Older OCBs will generally break both ways but you need to check.
IDMT will normally detect both ways but some have directional element that stops this and these will only detect fault current in the forward direction. Breaking faults depends on the device interrupting the current.
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