Yes, I usually get my Hager bits from them.
Or http://www.sparkydirect.co.uk/product/412/9912/VAN00/Hager-Neutral-Link/index.html
Or http://www.sparkydirect.co.uk/product/412/9912/VAN00/Hager-Neutral-Link/index.html
Overcoming RCD discrimination
- Thread starter paul1972
- Start date
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Clearly that approach does not comply with BS7671.
A HRC fuse would be more appropriate than a BS EN 60898 circuit breaker for discrimination.
The largest load on the sub main is a 20A radial. I rather think that a 63A MCB would provide plenty of discrimination!
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If by plenty you mean absolutely none then you would be correct.
As a general rule a fault current will NOT discriminate between BS EN 60898 circuit breakers of any rating.
I am sorry, but you will have to explain that statement. Maybe I was asleep at electricians' school that day but AFAIK discrimination of 60898 MCBs is used extensively.
Indeed many manufacturers of said product produce discrimination tables to help those who cannot understand time/trip graphs
eg 3047 WA discrimination tables cover.indd - Eaton
Its true that in the old days dsicrimination between MCBs was unreliable (so fuses were used upstream) but modern electronic trips have resolved a lot of the 'old' problems associated with grading energy let through of the downstream device against the tripping threshold of the upstream device. In my experience the first stage 'Long Short' element for MCCB's has never really been an issue, it's always been the 2nd stage 'short circuit' instantaneous element that causes grading problems. This is where the energy let-thru charts came in use....
Maybe we need to consider if we are arguing about discrimination in the event of overload, or of short circuit.
Indeed many manufacturers of said product produce discrimination tables to help those who cannot understand time/trip graphs
eg 3047 WA discrimination tables cover.indd - Eaton
Its true that in the old days dsicrimination between MCBs was unreliable (so fuses were used upstream) but modern electronic trips have resolved a lot of the 'old' problems associated with grading energy let through of the downstream device against the tripping threshold of the upstream device. In my experience the first stage 'Long Short' element for MCCB's has never really been an issue, it's always been the 2nd stage 'short circuit' instantaneous element that causes grading problems. This is where the energy let-thru charts came in use....
Maybe we need to consider if we are arguing about discrimination in the event of overload, or of short circuit.
If I understand those tables correctly, they do not consider the case in which both upstream and downstream MCBs are Type B (which is probably the situation being discussed in this thread). Can reasonable discrimination be achieved in terms of fault (i.e. "short circuit") current when both are Type Bs?
I think he was clear in saying that he was talking/arguing about discrimination in relation to fault (i.e. "short circuit") currents. As you say, the nature of the curves is such discrimination is unlikely to be a problem (given appreciably different In) in terms of overload currents.
Kind Regards, John
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