This has probably been asked before. Apologies if it has. I want to replace some Merlin Gerin multi 9 C60 mcb's with rcbos. It appears that the replacement is only available as a Type C. Two questions. 1. Why is there not a Type B available. 2. Is there another manufacturers rcbo that will fit that I can get in a Type B? Square D maybe? Thanks
Why do you need a type B when its an RCBO you are using -------------------- Could you explain that question please waz?
I think the op is getting at the max earth loop value for RCBO's when its not really relevent, he should be looking at table 41.5 for max Zs. I had this problem at a university job I carried out when we had high Zs values at sockets, we changed the merlin type C for square D type B. It did not sit well with me or the clarke of works at the time, I checked with merlin who advised me to look at the correct table.
So what you are saying Waz is if you have an rcd in the circuit then max values of Zs are irrelevant. I don't think so. This may be ok for a TT system but for a TN-S (which is what I have here)then a Type C device may not comply if Zs is not low enough. Discuss.......
I don't come on this site now (once in last 18 months) because of idiots like you JP. Sod of and leave it to people with something constructive to say. I might not agree with Waz but at least he's replied with something relevant and a point worth discussing.
The rcbo does not behave any different because of the earthing system. In a TT we are allowed upto 200 ohm for a stable reading we are putting our faith for the rcd to do its part because the earth loop is high. What I am saying for some poorly designed installations its a acceptable to use an rcd for excessive earth loop, Merlin dont make a type B because its not required a 30mA will operate within limits at 1667ohm.
I would have thought that as long as the Zs fits into the lower end of the table, then all is well with a Type C RCBO. Merely an observation and not saying that this is correct.
Wouldnt worry about Zs with but you could use square d is the lower breaking capacity does not worry you, just rip the ****** quickline adaptor off the top of the breaker
I dont like mixing peoples switch gear in the same pannel(even if its from the outfit). Its a bit rough and not required in this case, I take it its a commercial job?
Waz, the type b,c,d has nothing to do with the rcd properties of an rcbo, it's the characteristics of the overcurrent part of the device.
So you are saying that an rcd a Merlin in this case is non compliant in TN system but a TT its fine? Im very interested in peoples opinions on this because we've had many an argument with sparks on site about this.
What makes you think i'm saying it doesn't comply in a TN system then Waz, i'm not saying anything of the sort!
Once again... Have a look here at NDQ36 http://www.esc.org.uk/forum/forum_ndthread.html Low Zs requirements are for disconnection times and an RCD will disconnect in time under earth fault conditions even where high Zs conditions exist in either TT or high R1+R2 TN. The only consideration for using RCD to overcome high R1+R2, is where the possibility of a high R1+Rn will mean too long disonnection times for a short circuit fault L/N. Some other info here as well http://www.esc.org.uk/forum/index.html