Can't test RCBO as main RCD trips first - what to do?

[spark 68]

What the hell does it matter which RCD trips for the purpose of the cert?....If there is a requirement for RCD protection on the circuit installed and a test operates at least one within the required time jobs a goodun innit?....Whats all this nonsense about falsifying certs and legal action?????????........confused.

Exactly WP!, it is the disconnection time that counts, the only non compliance is that the up-front RCD trips first which should be noted on the cert.

 

[Jimmy Boy]

Hole ? no hole here sunshine, I believe what I said is true, and I will stick to it, if you have a different opinion that's your entitlement, I can respect others opinions without agreeing with them.
J

 

[Guest55]

^^^Good , i like a man who sticks to his guns.
no hard feelings

 

[Jimmy Boy]

None taken fella robust discussion is the heart and soul of a good forum
ATB J

 

[Engineer54]

As you are totally relying on a RCD device for your earth fault protection on a TT system, it makes perfect sense to have an up-front 100mA S type RCD as your ''Additional'' means of protecting against faulty down stream RCD(s). Far better to have a decent back-up, when your TT system is an unstable 200 ohm Ra set-up using a twig as the earth electrode!!... lol!!

 

[terminator]

Terminator please quote the reg that tells us we have to have an upfront RCD if all circuits have 30mA protection, I'm not saying your wrong but I can't find that reg.
ATB J

Jimmy - I said 'ought to have' because you can never be sure that someone may come along and change or add a circuit just using an MCB - and if the main earthing resistance had deteriorated (TT is notoriously unreliable) you would lose your disconnection times. It does say in the BGB "the preferred protective device is an RCD" 411.5.2. Then Note 1 says "where discrimination between RCDs is necessary refer to Reg 531.2.9. That is about compliance with the Regs for fault protection using two or more RCD,s in series and that discrimination in their operation is necessary to prevent danger.

In this case I think you need an upfront S type RCD to meet disconnection times and downstream RCBO,s to ensure disrimination and to prevent danger by the whole installation being knocked out.

 

[Engineer54]

Jimmy - I said 'ought to have' because you can never be sure that someone may come along and change or add a circuit just using an MCB - and if the main earthing resistance had deteriorated (TT is notoriously unreliable) you would lose your disconnection times. It does say in the BGB "the preferred protective device is an RCD" 411.5.2. Then Note 1 says "where discrimination between RCDs is necessary refer to Reg 531.2.9. That is about compiance with the Regs for fault protection using two or more RCD,s in series and that discrimination in their operation is necessary to prevent danger.

In this case I think you need an upfront RCD to meet disconnection times and downstream RCBO,s to prevent danger by the whole installation being knocked out.

Not sure if i've read this right, ....but an up-front S type RCD won't meet TT disconnection times, (delayed trip time) it's there solely as additional protection to any RCD device that fails, for one reason or another to operate, (they are not the most reliable of protective devices). At the very least, it will trip out a faulty circuit, even if it is slightly outside of the set times of a TT system...

 

[terminator]

Yes, agreed Engineer - A touch of dyslexia - I meant the other way round, RCBO's to meet disconnection and and upfront for backup and discrimination, as you have pointed out. Been a long day.

 

[Jimmy Boy]

I don't disagree with extra protection I was just curious to see if it was an interpretation of the regs or a reg
Eng 54 could you explain to me how you interpret the regs on protecting tails in to an enclosure on a TT ? if the 100mA RCD is in the board, and not external to it how does/can it protect the tails that are from DNO fuse to incomer on RCD ? Not a trick question just a genuine enquiry fella.

ATB J

 

[Guest55]

I don't disagree with extra protection I was just curious to see if it was an interpretation of the regs or a reg
Eng 54 could you explain to me how you interpret the regs on protecting tails in to an enclosure on a TT ? if the 100mA RCD is in the board, and not external to it how does/can it protect the tails that are from DNO fuse to incomer on RCD ? Not a trick question just a genuine enquiry fella.

ATB J

My interpretation of this situation is that the enclosure itself cannot be metallic due to no rcd upstream of the CU main switch - ie. being fully insulated provides that extra level of protection for TT wiring prior to the rcd.
If you get my drift lol.