Relevance of Table 41.3 where Additional Protection is present? Discussion ThreadRelevance of Table 41.3 where Additional Protection is present? Electrical Advice
Reading of 411.3.2 and following suggests that compliance for disconnection <400ms may be obtained using either MCB or RCD. Where an RCD (RCBO in this case) is used for Additional Protection, is compliance with Zs specified in Table 41.3 still necessary?
The situation: new installation by A.N.Other in a timber shower/toilet block on a camping facility. Initially 8 no. hand dryers on a B20 wired in 2.5 T&E radial, 1.25mm flex drops from local FCU to each dryer. Repeated tripping found even with only a single dryer activated led to installer converting radial to ring, protected by C32/r30mA RCBO, and moving 2 of the dryers to a different circuit. The tripping persisted. When I was asked to look at it, I was unable to identify cause of tripping, as nothing showed up in any tests. I concluded it to be an initial burn-in problem, as no more tripping was reported after a couple of months in service.
The problem: while rectifying other poor work, I found the highest R1+R2 reading at the most remote dryer to be 0.51Ω, which with Ze of 0.42Ω puts the Zs well above the Table 41.3 limit for a C32 device.
The question: does this matter?
Thanks for your thoughts.
Relevance of Table 41.3 where Additional Protection is present? for the original thread on Electricians Forums
Reading of 411.3.2 and following suggests that compliance for disconnection <400ms may be obtained using either MCB or RCD. Where an RCD (RCBO in this case) is used for Additional Protection, is compliance with Zs specified in Table 41.3 still necessary?
The situation: new installation by A.N.Other in a timber shower/toilet block on a camping facility. Initially 8 no. hand dryers on a B20 wired in 2.5 T&E radial, 1.25mm flex drops from local FCU to each dryer. Repeated tripping found even with only a single dryer activated led to installer converting radial to ring, protected by C32/r30mA RCBO, and moving 2 of the dryers to a different circuit. The tripping persisted. When I was asked to look at it, I was unable to identify cause of tripping, as nothing showed up in any tests. I concluded it to be an initial burn-in problem, as no more tripping was reported after a couple of months in service.
The problem: while rectifying other poor work, I found the highest R1+R2 reading at the most remote dryer to be 0.51Ω, which with Ze of 0.42Ω puts the Zs well above the Table 41.3 limit for a C32 device.
The question: does this matter?
Thanks for your thoughts.
Relevance of Table 41.3 where Additional Protection is present? for the original thread on Electricians Forums
