Three Phase Distribution Question

[Wardy1980]

Hi, I just have a quick question...
in the factory I am working in there is a 63amp Mcb feeding an 32Amp Switchfuse
which is then feeding a little distribution enclosure which has a 20amp Mcb for one
rcd socket, 20amp,16amp, 10amp and a 4 amp for machinery.
is this right because it does not seem right to me?

 

[Wardy1980]

I addressed this with the main electrician on site and he said it is fine as the machines don't pull that much current as he put his clamp meter on each machine and socket outlet and all the current was added up to 26amps
Do does this make it okay?

 

[Bobster]

Why don't you think it's right?

 

[Darkwood]

It's a tad poor design ... depends what the machine does too, is he clamping it with a low demand job on it or say it had a motor thats not anywhere near its flc, then the supply, switchgear etc should always be designed for the max demand ... the 32amp isolator should be rated to the front end device if feeding a distribution board especially if it has spare ways.
The fixed load clause seems to have been abused here to excuse a poor design, although I would need more info on loads to say if it contravenes regulations

 

[Deleted member 72666]

AS been mentioned already, what are the individual machines and loads and what was the rcd socket feeding at the time of load testing? This set-up could be okay but without much more detailed information it's impossible to tell.

 

[Darkwood]

With sockets on it then it cannot be classed as a fixed load unless the accumulative values don't exceed the switchgear in this case it is poor design IMHO and only causing no issues due to the way the machine is used and the items plugged in and not by what the machine could demand and what you could plug in.

 

[amlu]

63amp to protect the SWA or whatever feeds the switch fuse
switch fuse somewhere in other part of the building, easy to lock out when the in house spark got some work to do around there.

 

[Deleted member 72666]

It is a poor design but without knowing what the cct's feed or what they were feeding at the time of testing we wont know whether or not the system is safe for it's intended use, that's what I think the op is trying to ascertain.

 

[mojorebel]

It seems ok to me , Discrimination is fine. the MCB's protect the wiring system ( assuming max demand, diversity and correction factors have all been factored in) Cant see an issue without more details.