Neutral / earth fault

[vbyrne]

Could some one give me a simple explanation why a trip will not blow on a Pme system and on others and is this dangerous

 

[AA410]

Good question do you mean an R C D ?

 

[ChrisElectrical88]

:-/ I have no idea what the question is here!

 

[telectrix]

had this yesterday on a TN-S. both RCDs failed to trip on test button and with MFT. found the cable responsible and dissed it, both RCDs now tripping fine. further investigation next week as 1. the cable is short and disappears behind meter board. 2. no idea what the cable feeds as nothing seems to have stopped working.

 

[GLENNSPARK]

had this yesterday on a TN-S. both RCDs failed to trip on test button and with MFT. found the cable responsible and dissed it, both RCDs now tripping fine. further investigation next week as 1. the cable is short and disappears behind meter board. 2. no idea what the cable feeds as nothing seems to have stopped working.

it`l be for a bypass...

 

[telectrix]

it`l be for a bypass...

nope. it goes into the wall and upstairs. it's a 7/029 T/E. possibly for immersion that's been removed. will find out next week.

 

[GLENNSPARK]

nope. it goes into the wall and upstairs. it's a 7/029 T/E. possibly for immersion that's been removed. will find out next week.

likely....

 

[vbyrne]

Could some one give me a simple explanation why a trip will not blow on a Pme system and on others and is this dangerous

Sorry lads what I meant to say was way does a RCD not blow when I have a dead short between neutral and earth on a pme system

 

[Plonker 3]

I would say because the RCD is faulty.

 

[Marvo]

RCD will only trip if there's current flowing down to earth. If there's no load on the RCD it won't trip. Other option is that it's faulty, if you ramp test it you'll know for sure.

 

[Hawkmoon]

Are you asking why an RCD won't trip when you have Earth-Neutral link at incomer (as per PME/TNCS)?

If so this is because the RCD only monitors the circuit it is protecting (on the load side of the unit)

There is plenty of literature etc around explaining in detail how RCDs work - if you are in training it's worth a look.

If I misunderstood your question then ignore!

 

[UKMeterman]

Hi he is right it is possiable due to the lack of load to cause and IR drop for an RCD not to trip with an NE short on a lightly loaded circuit. Try page 42 http://www.google.co.uk/url?sa=t&rc...q8sRmLDuIT05Wlw&bvm=bv.57155469,d.bGQ&cad=rja

 

[i=p/u]

It's like why dies it keep tripping when applying a load... But you have got the grey as the earth instead of neutral......, I know