TT system, RCD or RCBO

[westward10]

There is no requirement for a protective device on a TT system to be double pole just that it disconnects in the event of a fault.

 

[Deleted member 26818]

There needs to be Double Pole isolation, which is provided by the Main switch.
Is there no up front 100mA RCD in this installation?

 

[Deleted member 9648]

My interpretation is that part of the installation is on an RCD and part isn't, it's possible that a N-E fault on the RCBO circuit could result in the other RCD operating for an unrelated fault because a parallel path would remain in place even if the RCBO tripped. A DP RCBO would prevent that. I do not think it is a requirement, but if possible I would fit a DP device if I was altering the circuit protection as part of the work carried out.

 

[Welchyboy1]

My interpretation is that part of the installation is on an RCD and part isn't, it's possible that a N-E fault on a single pole RCBO circuit could result in the other RCD operating for that fault because a parallel path would remain in place even if the RCBO tripped. A DP RCBO would prevent that. I do not think it is a requirement, but if possible I would fit a DP device if I was altering the circuit protection as part of the work carried out.

In my head it sounds like a tenby split load 16th ed board with first half Circuits direct from main switch and second half 30 mA rcd protected, thats the issue i usually find

It shouldnt affect the rcd downstream with an rcbo in place on the unprotected side but if there was another rcd (e.g. 100mA s type) between the origin and the new single pole rcbo, the N-E fault on the rcbo circuit would likely effect this device even when rcbo has tripped open and also cause the rcd to trip if sufficient load was applied through it

As such a double pole rcbo would be required to completely isolate said fault

Thats my understanding for what its worth

If an N-E fault would effect downstream rcd devices then i should think we would be in trouble combining RCDs onto PME supplies?