IET
Decrease font size
Increase font size
Topic Title: Sub mains from 3 phase board
Topic Summary:
Created On: 20 March 2019 11:08 am
Status: Read Only
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.
 20 March 2019 11:08 am
User is offline View Users Profile Print this message



Ketla17

Posts: 4
Joined: 08 September 2018

I'm installing a 3 phase board main switch not rcd. taking single phase sub mains to various offices / mess rooms. In the 3 phase board should I fit rcbos or am I ok with standard breakers and then rcds in the offices /mess rooms. Hope this makes sense.


Thanks
 20 March 2019 11:34 am
User is offline View Users Profile Print this message



daveparry1

Posts: 8020
Joined: 04 July 2007

Depends upon cable type & installation method as to whether rcd is needed at the supply end.
 20 March 2019 11:58 am
User is offline View Users Profile Print this message



Ketla17

Posts: 4
Joined: 08 September 2018

All cables to be SWA parts buried in the ground parts on tray
 20 March 2019 12:44 pm
User is offline View Users Profile Print this message



Zoomup

Posts: 6117
Joined: 20 February 2014

Your new S.W.A. distribution circuits (sub-mains) will be o.k. without R.C.D.s at the origin if the local subboards have R.C.D.s to protect final circuits, and if A.D.S. of the distribution circuits is o.k. This arrangement will reduce the likelihood of nuisance tripping of an R.C.D. knocking out a whole final subboard, which would be the case if R.C.D.s are positioned at the distribution circuit's origin.

Z.
 20 March 2019 12:46 pm
User is offline View Users Profile Print this message



broadgage

Posts: 3170
Joined: 07 August 2007

RCD protection is not generally needed for SWA unless a high earth loop impedance requires this.

If you decide to fit an optional RCD to the three phase board, then this almost certainly needs to be a less sensitive and time delayed type, in order to discriminate with the presumed 30ma quick acting types installed downstream.

Although not part of your enquiry, be aware that standard MCBs in the three phase board may not discriminate with MCBs in the downstream local distribution boards, in the event of short circuit.
If sensibly sized they should discriminate for overloads.
Statistics

New here?

  • To participate in discussions, please log in and introduce yourself.

See Also:



FuseTalk Standard Edition v3.2 - © 1999-2021 FuseTalk Inc. All rights reserved.

 
..