RCD BS4293 ok or not

[jackdor]

Hi all, I installed an outside security light the other day and utilised an existing switched fused spur which was off the down stairs ring. The ring was protected by a 32amp breaker and a 30mA RCD (BS4293 type). When tested the rcd did not meet the 40ms disconnection time as per bs7671 regs. There for i installed a separate 30mA rcd unit(Bs61008) and connected the ring circuit to it, fed from the 32amp breaker on 6mm cable. Was i right to do this as in the updated version of the "Electrician's Guide To The Building Regulations" page 96(6.4.2) it says that rcd's to bs 4293 should open in less than 200ms. Have i read the regs right on done the right thing or just made the job more expensive. Thanks in advance for your feed back.

 

[scotsparky]

whats the 5x disconnection time?

 

[electricAl]

The 40ms is the max allowable time in which the device should operate @ 5x I^n

As you read, for a 4293 the 200ms is @ 1x I^n

 

[jackdor]

At 5x the discon times was 45 ms and at 1 times it was 41ms so hence doing what i did.

 

[electricAl]

At 5x the discon times was 45 ms and at 1 times it was 41ms so hence doing what i did.

Well, strictly speaking it failed on the 5x test then - even if only marginally. Did you repeat the test? If so, what was the result. Did you carry out testing to the letter - 1/2 times, 1x, 5x, test button? All loads disconnected...blah, blah

 

[jackdor]

Sorry the cu is a split load board with 1 half protected by the 80amp 30mA rccd (crabtree). i installed a new separate rcd unit and put ring off this to make sure the circuit was under or equal to 40ms as per reg bs7671. the 6mm t & e fed this from the 32 amp mcb. R1+R2 =0.26 and measured Zs=0.36

 

[electricAl]

Well, unless someone`s complaining, i wouldn`t worry about it Jackdor. It failed the allotted test...

Sleep easy

 

[jackdor]

Yea all test carried out Megger1552 was set to 30mA and auto test all plugs removed and and equipment isolated. tested it 3 times tester is only 6 months old and is tested regularly. building only 15 years old.