DIY Forum

 

Ultimate HandymanUltimate Handyman on Pinterest

 

DIY Forum/Home improvement advice forum

 

 

A-Z CONTENTS | DISCLAIMER | DIY VIDEO | HOME | SAFETY FIRST | FORUM RULES

It is currently Tue Oct 16, 2018 5:41 pm
Visit Hilti


Time zone: Europe/London [ DST ]




 

 


Post new topic Reply to topic  [ 3 posts ] 
Author Message
 Post subject: dISCONNECTION TIMES
PostPosted: Mon Jul 16, 2018 12:00 pm 
Offline
Newly registered Member

Joined: Sat Jun 09, 2018 4:08 pm
Posts: 38
Has thanked: 11 times
Been thanked: 0 times
Hopefully you can assist.
Never really got to grips with these, all that sticks in my head is .4 or 5 seconds, if anything greater, then you are likely to get a nasty shock.
Many homes these days have MCBs, can I assume that a MCB is a BS EN 60898?

Can I assume (in most circumstances), if a home has the above, then page 58 of the regs (Table 41.3) is the table to use to find the ZS value ensuring the above trips within time / or less of course.

What is the difference a distribution and a final circuit?

Gong back to my first note, a MCB tripping within .4 sec (I get this, as extremely quick) However, 5 seconds seems a long time to wait!

On the noted page 58 / Table 41.3, it highlights .4secs and 5 seconds - why?

Keen to read all your return Reponses

Apologies to be wet around the ears!

Your answers will certainly help.

Thanks


Share on FacebookShare on TwitterShare on DiggShare on DeliciousShare on Google+
Top
 Profile  
Reply with quote  
 Post subject: Re: dISCONNECTION TIMES
PostPosted: Mon Jul 16, 2018 6:32 pm 
Offline
Approved Electrician

Joined: Sun Apr 24, 2011 7:01 pm
Posts: 2696
Location: South Yorkshire
Has thanked: 166 times
Been thanked: 581 times
A distribution circuit is one that powers another CU or a distribution board.
A final circuit powers lights, sockets, cookers etc.

The maximum earth loop to trip a MCB (ie a device to BS 60898 for modern MCBs, older models had different BS numbers and different maximum earth loops) is actually the same value for 0.4 and 5 seconds disconnection times. So as long as the maximum earth loop given in table 41.3 is met then the MCB will always trip in 0.4 seconds if there is a fault.



For this message the author OnlyMe has received gratitude : tonk
Top
 Profile  
Reply with quote  
 Post subject: Re: dISCONNECTION TIMES
PostPosted: Tue Jul 17, 2018 5:36 am 
Offline
Senior Member
User avatar

Joined: Tue May 10, 2011 3:43 am
Posts: 2672
Location: North Wales
Has thanked: 64 times
Been thanked: 542 times
MCB's come as B, C, and D, it was 5x, 10x and 20x so a 5A B type MCB will need 5 x 5 = 25 amp to trip in 0.1 seconds, now we add 5% so 230/25 = 9.2 ohms plus 5% = 8.74 ohms earth loop impedance. It seems the 5% was added because of volt drop, a B type magnetic part should trip between 3 and 5 times rating. The thermal part is far slower there are graphs.

Today the RCD means the ELI is in real terms less important, however since often the volt drop is exceeded before the tripping times are exceeded it is only to comply with regs we measure ELI I seem to remember to be within volt drop the loop impedance line - neutral is around 0.95 ohms for a ring final but ELI is 1.366 so it should never be limiting factor with a TN-C-S supply.



For this message the author ericmark has received gratitude : tonk
Top
 Profile  
Reply with quote  
Display posts from previous:  Sort by  
Post new topic Reply to topic  [ 3 posts ] 

 

 




Similar topics
   

Time zone: Europe/London [ DST ]


Who is online

Users browsing this forum: No registered users and 0 guests


You cannot post new topics in this forum
You cannot reply to topics in this forum
You cannot edit your posts in this forum
You cannot delete your posts in this forum
You cannot post attachments in this forum

Search for:
Jump to:  
Visit Solent plastics


 

 

 

News News Site map Site map SitemapIndex SitemapIndex RSS Feed RSS Feed Channel list Channel list
ultimatehandyman privacy policy

Contact

 

Powered by phpBB® Forum Software © phpBB Group

phpBB SEO