Time delayed rcd’s and fault protection | on ElectriciansForums

Discuss Time delayed rcd’s and fault protection in the UK Electrical Forum area at ElectriciansForums.net

dlt27

-
Joined
Jul 4, 2011
Messages
196
Reaction score
30
Have been to a farm today that has a 100mA time delayed RCD main switch covering a DB that has MCB’s on majority of circuits ( less than 32A) and 30mA RCBO’s on sockets, lighting etc.
What I was thinking was does this comply with regs as circuits less than 32A should disconnect in less than 0.2s so because time delayed rcd fitted the circuits just on MCB’s don’t comply.
I thought to comply the RCD must trip within 200mS and before voltage rises above 50v.
Am I correct or am I being daft ( not for the first time )?
 
Is it a tt system,if it is then mcbs may not comply,regarding the install of the cabling.
i would be incline to change mcbs to rcb’os on the mcbs.
The time delay would disconnect in 250 ms,I believe.
 
Last edited:
It is a TT system. Am I right in thinking if I I change time delayed to a normal 100mA then will be ok because it will trip within 0.2s, but if leave as time delayed I would have to fit RCBO’s to everything..
[automerge]1575618235[/automerge]
705.411.1 says just about values of RCD’s, but nothing about time delayed. Thanks
 
What I was thinking was does this comply with regs as circuits less than 32A should disconnect in less than 0.2s so because time delayed rcd fitted the circuits just on MCB’s don’t comply.
Hi - check out BBB Appendix 3 Table 3A for maximum disconnection times. If I’ve understood correctly, you need 200ms and looking at the table some S types will do that.
 
It is a TT system. Am I right in thinking if I I change time delayed to a normal 100mA then will be ok because it will trip within 0.2s, but if leave as time delayed I would have to fit RCBO’s to everything..
[automerge]1575618235[/automerge]
705.411.1 says just about values of RCD’s, but nothing about time delayed. Thanks
If you change the RCD to a non time delayed type, you will find the RCBOs will not achieve selectivity with the RCD, and will cause nuisance tripping of the whole DB.
Bear in mind also that the disconnection time of 0.2 seconds relates to prospective residual fault currents significantly higher than the rated residual operating current of the RCD. Therefore, in line with Wilko's reference to table 3a of appendix 3, it is likely that in the event of a fault to earth, the 0.2 seconds disconnection time will be met.
 

Reply to Time delayed rcd’s and fault protection in the UK Electrical Forum area at ElectriciansForums.net

News and Offers from Sponsors

  • Article
Join us at electronica 2024 in Munich! Since 1964, electronica has been the premier event for technology enthusiasts and industry professionals...
    • Like
Replies
0
Views
714
  • Sticky
  • Article
Good to know thanks, one can never have enough places to source parts from!
Replies
4
Views
1K
  • Article
OFFICIAL SPONSORS These Official Forum Sponsors May Provide Discounts to Regular Forum Members - If you would like to sponsor us then...
Replies
0
Views
3K

Similar threads

  • Question
Yes Table 3A that was in Appendix 3 of the 17th edition of BS7671 and in BS 7671:2018 (Blue Book) up to the release of BS7671:2018 +A2:2022 (Brown...
Replies
11
Views
838
  • Question
much more information required. Is the supply to the first building a DNO supply or a sub main cable from another building ? if it is a sub main...
Replies
5
Views
1K

OFFICIAL SPONSORS

Electrical Goods - Electrical Tools - Brand Names Electrician Courses Green Electrical Goods PCB Way Electrical Goods - Electrical Tools - Brand Names Pushfit Wire Connectors Electric Underfloor Heating Electrician Courses
These Official Forum Sponsors May Provide Discounts to Regular Forum Members - If you would like to sponsor us then CLICK HERE and post a thread with who you are, and we'll send you some stats etc

YOUR Unread Posts

This website was designed, optimised and is hosted by untold.media Operating under the name Untold Media since 2001.
Back
Top