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Any system really.As per TT system.
Discuss RCBO curve in the UK Electrical Forum area at ElectriciansForums.net
Any system really.As per TT system.
True. It's down to the purpose of the RCD, I suppose.Any system really.
I’m probably going to look stupid here, but it will be worth it if I get the answer , as I can’t fathom it out.
I’ve never really thought of it before, but…..
A circuit breaker comes in curves B, C, and D. Now we all know it’s mostly to do with the in rush of current ( layman terms) but the ELI value has to be lower to achieve tripping times.
However, with a RCBO , your tripping time will be around let’s say 18 milli seconds. So why are all RCBO not at least C type? What’s the point of a B type if you have already achieved the task of the device tripping in the desired time under fault conditions?
No doubt someone will tell me what I’m missing . I look forward to it .
Thanks to all for the input, much appreciated all the views.A short circuit would trip instantaneously, provided a sufficiently high fault current flows and I previously explained this.
Take a look at thermal trip times for RCBOs and tell me why you think a 16A RCBO would trip within a few milliseconds when handling an overload current of 26A.
I'm not suggesting to do away with overload protection. I'm talking about changing a D16 amp RCBO to a C16 amp RCBO . Both offer 16 amp overload protection! , and both offer instant tripping under fault conditions..The OP is clearly misunderstanding the three different fault types under discussion here. It’s also unwise to assume that an RCD (or residual component of an RCBO) will disconnect faster than an MCB under an ADS or overload situation - type A & B RCD’s are now often in the >100mS X1n area which makes disconnection under ADS times very achievable. Yes, fault protection can be afforded by an RCD however it’s rare to be able to do away with overload protection as well.
I had in mind that, where protected for overload by an MCB, a live conductor could still exceed it's thermal limits under adiabatic conditions. I'm not 100% on that, but it's the only way I'm able to explain some of the data in table B7 in the OSG. (not that that backs up my earlier post, as it seems higher fault currents are more onerous)I think if the MCB's rating is at or below the cable's CCC then the trip time is not an issue, as they have similar/coordinated thermal overload characteristics. Meeting ADS time is a different matter of course!
What are the loads as just changing them to C type may cause further issues. D type must have been specified for a reason ..... especially 10 of them, unless the original installer got a job lot and the attitude of 'that'll do'!Apparently the RCBOs are £100 a go and he would need around 10 of them.
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