IET logo
 
IET
Decrease font size
Increase font size
Topic Title: RLVS
Topic Summary: 411.3.2.5 & 411.8.3
Created On: 03 July 2013 03:33 PM
Status: Post and Reply
Linear : Threading : Single : Branch
Search Topic Search Topic
Topic Tools Topic Tools
View similar topics View similar topics
View topic in raw text format. Print this topic.
 03 July 2013 03:33 PM
User is offline View Users Profile Print this message


Avatar for Parsley.
Parsley

Posts: 993
Joined: 04 November 2004

I don't do much on construction sites but these two regs seem to conflict with each other 411.3.2.5 seems to state the disconnection time doesn't have to be met if the installation if relv is used and 411.8.3 seems to state that the Zs must comply with table 41.6.
Your thoughts are welcomed.

411.3.2.5 For a system with a nominal voltage U0 greater than 50 V a.c. or 120 V d.c., automatic disconnection in the time required by Regulation 411.3.2.2, 411.3.2.3 or 411.3.2.4, as appropriate, is not required if, in the event of a fault to a protective conductor or Earth, the output voltage of the source is reduced in not more than that time to 50 V a.c. or 120 V d.c. or less. In such a case consideration shall be given to disconnection as required for reasons other than electric shock.

411.8.3 Requirements for fault protection
Fault protection by automatic disconnection of supply shall be provided by means of an overcurrent protective device in each line conductor or by an RCD, and all exposed-conductive-parts of the reduced low voltage system shall be connected to Earth. The earth fault loop impedance at every point of utilisation, including socket-outlets, shall be such that the disconnection time does not exceed 5 s.
Where a circuit-breaker is used, the maximum value of earth fault loop impedance (Zs) shall be determined by the formula in Regulation 411.4.5. Alternatively, the values specified in Table 41.6 may be used instead of calculation for the nominal voltages (U0) and the types and ratings of overcurrent device listed therein.
Where a fuse is used, the maximum values of earth fault loop impedance (Zs) corresponding to a disconnection time of 5 s are stated in Table 41.6 for nominal voltages (U0) of 55 V and 63.5 V.
For types and rated currents of fuses other than those mentioned in Table 41.6, reference should be made to the appropriate British or Harmonized Standard to determine the value of Ia for compliance with Regulation 411.4.5, according to the appropriate value of the nominal voltage (U0).
Where fault protection is provided by an RCD, the product of the rated residual operating current (I/n) in amperes and the earth fault loop impedance in ohms shall not exceed 50."


Regards
 03 July 2013 03:59 PM
User is online View Users Profile Print this message



AJJewsbury

Posts: 11385
Joined: 13 August 2003

I'm not sure that 411.3.2.5 is particularly aimed at RLV systems (high impedance sources - maybe low power electronic inverters - came to my mind) - given that RLV can be 63.5V to earth and while the voltage at the point of the fault is likely to be half that (potential divided between c.p.c. and L conductors) - it's not obvious that the output of the souce of a RLV system will drop to <50V.

So assuming you can't prove that the transformer output will collapse below 50V on a L-PE fault, then you'll need to disconnect within 5s (not necessarily via table 41.6 if you pick RCDs). I suppose that's easier than table 41.1 which might otherwise demand 0.8s.

- Andy.
 03 July 2013 04:25 PM
User is offline View Users Profile Print this message


Avatar for Parsley.
Parsley

Posts: 993
Joined: 04 November 2004

I also wondered about the <50v requirement.

I seem to remember reading some GB and maybe OMS posts on this a few years ago, something about another standard and JPEL.

How do they get away with those long lengths of 110v lights on construction sites you see in the city, expensive 110v RCD's I guess, or are there a lot noncompliant temp installations out there

Regards

Edited: 03 July 2013 at 04:41 PM by Parsley
 03 July 2013 04:37 PM
User is offline View Users Profile Print this message



John Peckham

Posts: 7423
Joined: 23 April 2005

Parsley


I think that would be BS7375. and section 704 of the BGB.

-------------------------
John Peckham

http://www.astutetechnicalservices.co.uk/
 03 July 2013 04:54 PM
User is offline View Users Profile Print this message


Avatar for Parsley.
Parsley

Posts: 993
Joined: 04 November 2004

Thanks John, I am aware of 704 and GN7 section 4 haven't got a copy of BS7375

here's is Geoff post where he refers to JPEL http://www.theiet.org/forums/f...id=205&threadid=29712

I've also found one of OMS posts http://www.theiet.org/forums/f...&threadid=35617


[/L]

Looking at must 10KVA site tx they seem to be fitted with 16a or 32a type c MCB's so that means that cables are going to have a) pretty short in length or b) to be have larger csa's or c) use rcd's. I haven't seen 110v circuits with RCD's on my travels but I don't normally get involved in site temps.

Best regards

Edited: 03 July 2013 at 05:12 PM by Parsley
 06 July 2013 09:19 AM
User is offline View Users Profile Print this message


Avatar for MrOther.
MrOther

Posts: 531
Joined: 08 June 2010

Originally posted by: Parsley

Thanks John, I am aware of 704 and GN7 section 4 haven't got a copy of BS7375



here's is Geoff post where he refers to JPEL http://www.theiet.org/forums/f...&threadid=29712



I've also found one of OMS posts ">http://www.theiet.org/...s/f.....5617





[/L]



Looking at must 10KVA site tx they seem to be fitted with 16a or 32a type c MCB's so that means that cables are going to have a) pretty short in length or b) to be have larger csa's or c) use rcd's. I haven't seen 110v circuits with RCD's on my travels but I don't normally get involved in site temps.



Best regards


The hyperlink to OMS' post seems to be non-functional.
 07 July 2013 03:04 PM
User is online View Users Profile Print this message



AJJewsbury

Posts: 11385
Joined: 13 August 2003

The hyperlink to OMS' post seems to be non-functional.

It's just the forum software not keeping its formatting tags separate - try:
http://www.theiet.org/forums/f...id=205&threadid=35617

- Andy.
 09 July 2013 07:59 PM
User is offline View Users Profile Print this message


Avatar for MrOther.
MrOther

Posts: 531
Joined: 08 June 2010

Thanks Andy.
IET » Wiring and the regulations » RLVS

Topic Tools Topic Tools
Statistics

See Also:



FuseTalk Standard Edition v3.2 - © 1999-2014 FuseTalk Inc. All rights reserved.