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Discuss Tt System Fuseboard For 17th Edition in the Electrical Forum area at ElectriciansForums.net

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bluecallum

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Hi,hoping Someone Can Help,going By 17th Edition,what Sort Of Consumer Unit Is Now Required When Doing A Tt System,as The New Boards Now Have 2x30ma Rcd's.thanks
 
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Had8Lives

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Arms
In theory you don't need a 100ma RCD as a main switch, but there's no harm in it as long as you don't leave in the old voltage operated one :-O In theory one of the 30ma RCDs of the consumer unit would trip before a 100ma main switch but at least if someone accidentally touched the live tails it would still trip :-D Have a read of Reg 411.5 The trip rating of the RCD now depends on the resistance of earth fault path through the earth electrode, the 17th Edition regs don't specify a specific tripping current although you could install a 300ma RCD as a main switch between the supply tails and the Consumer unit and tell the customer it is there for Fire Protection. Reg 532.1.
 
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bluecallum

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  • #3
Are You Saying That You Can Use The New 17th Edition Board With The Two Manufactured Rcds
 
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Shakey

  • Thread Starter Thread Starter
  • #4
Are You Saying That You Can Use The New 17th Edition Board With The Two Manufactured Rcds
yes, thats right, as long as the Ra is less than 1667ohms your 30mA RCD will do

protecting the tails has nothing to with it being a TT
 
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atkins_1

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  • #6
Hi just been having a read around regarding tt installations, I want to repleace my old mk 100ma rcd main switch for a up to date one. My Zs is reading 270 ohms, not too far away from the board so I'm guessing the Ra is still going to be a lot higher than 200 ohms. So whats the deal..? Do I need to get the Ra below 200ohms by installing a new earth rod or like it say above from Shakey will my new dual 30Ma rcd board be satisfactory ?
When does the below 200 ohms appay and when does the 1996 ohms apply...?
 
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MDJ

  • Thread Starter Thread Starter
  • #7
pointless post, just saw the date of the op haha
 

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