IET logo
 
IET
Decrease font size
Increase font size
Topic Title: Quick Question- Disconnection Times-
Topic Summary:
Created On: 29 April 2013 05:13 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.
 29 April 2013 05:13 PM
User is offline View Users Profile Print this message



Sanft

Posts: 37
Joined: 22 August 2011

Afternoon All- I hope you are all well, I wonder if I could pick someones brain for some confirmation!

I'm having a hard time determining what to pass on Certification when inspecting test sheets in regards to disconnection times on MCB's.

On our Condition Reports/Installation Certificates- We have a field on the Schedule of Test Results relating to the disconnection times of circuits (As I'm sure many do that use specific software(s))- My question is:-

"Is the disconnection time listed on the Schedule of Test Results (The Field is Designated "Max Disconnection Time Permitted By BS7671") directly linked to the Size of the MCB (or if it is a distribution Circuit), as Regulation 411.3.2.2 states BASICALLY any Circuit >32A Or a Distribution Circuit will have a maximum disconnection time of 5 Seconds (And any less than that will be a maximum of 0.4 Seconds).

I ask because I am seeing Test Sheets come through that have say- 0.4 Seconds on a 40A Cooker Circuit, a 45A Shower Circuit etc. I'm just wondering if it would be wise to bring this to their attention that infact it should be 5 Seconds.

(I feel they will challange me on the Showers as it is special location, stating that 5 seconds is too dangerous etc. but the way I see things is that if it is RCD protected, this is not included within the Max Disconnection time as the RCD is simply Additional Protection to the Circuit) hence why we will always recommend RCD protection to Electric Showers within our industry-

Any advice on the situation would be very appreciated- I am about 90% sure it should be 5 seconds whatever the circumstance due to Regulation 411.3.2.2-

I am currently doing this on my Smart-Phone, but will check tomorrow morning for any friendly responoses-

Thank you Gents (And Ladies!),

King Regards,

Sanft
 29 April 2013 05:37 PM
User is offline View Users Profile Print this message



AJJewsbury

Posts: 11545
Joined: 13 August 2003

I think my reading of BS 7671 is the same as yours - final circuits rated >32A are permitted 5s disconnection times (on TN systems, 1s on TT). I guess the designer is free to choose a shorter time if it is thought desirable in the circumstances, but it's not a basic BS 7671 requirement. For bathrooms the 30mA RCD of course should give disconnection within 40ms for bathrooms etc anyway, so it's perhaps a bit of a mute point.
- Andy.
 29 April 2013 06:03 PM
User is offline View Users Profile Print this message


Avatar for OldSparky.
OldSparky

Posts: 592
Joined: 28 June 2011

asuming pre 17th edition installation, inspection on a domestic property i always put 0.4 s for the disconnection time.

i know previously it would have been 5s in some cases, as per a shower say, or cooker isolator with out socket outlet on.

i just put this in as it is the current max disconnection time, is it right to do so? i am not sure.
 29 April 2013 06:09 PM
User is offline View Users Profile Print this message


Avatar for OldSparky.
OldSparky

Posts: 592
Joined: 28 June 2011

asuming pre 17th edition installation, inspection on a domestic property i always put 0.4 s for the disconnection time.

i know previously it would have been 5s in some cases, as per a shower say, or cooker isolator with out socket outlet on.

i just put this in as it is the current max disconnection time, is it right to do so? i am not sure.
Statistics

See Also:



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