Time delayed trip

[tonyelectric]

(re signing) Not always they don't design the installations, we do that, they check our designs which is a requirement of the council, a lot of red tape to be honest. They insisted on 100A to a caretakers shed with a light and 1 13A socket!!!!

(re-DBs) Mostly the boards are custom built MEM glasgow or in all the older places Simplex ironclad, don't think they make RCBos for the main distribution kit but I stand to be corrected - never seen one though.

 

[Adam_151]

I understood it as you were saying that if wiring say a new classroom block in a school which for the sake of argument included a computer lab, that you'd have to fit either an earth shunt trip to the MCCB at the panel board, or take the circuit through a separate TD RCD mounted on the switch room wall, and then you'd have to protect every circuit at the final dist board by either a 30ma rcd incommer, or individually, etc (since I can't imagine a computer lab for example would be happy all running through a single 30ma RCD) ?

The point I was making was if you had an arrangement with the TD RCD at source and then standard SP rcbos in the final dist board, then the first neutral to earth fault will take out the circuit RCBO and then half a second later, the whole dist board as the TD device disconnects the neutral earth fault still in place...

And its a bit bizarre, does the engineer have an electrical background? or is he more mechnaical services biased and blagging the electrical side with bits and pieces he has picked up from various places?

 

[tonyelectric]

Questions I too have asked the engineer, he talks a good job but hasn't got much practical experience, his way of doing it involved putting a DP 32A 30mA RCD on each final ring in IT rooms, I know, I know, mad mad mad.

 

[Adam_151]

Conventional wisdom would lead me to try and avoid RCDs to computer labs, but I'm not 100% sure I'd apply that to a school...where students might be plugging any maner of things they shouldn't be into the computer sockets

Though most designs wouldn't have any RCD protection to the submains, so SP RCBOs can be used if it is deemed necessary to protect the computer circuits.

*Though I'm not convinced the risk is massivly great, expessly these days with shrouded pins, but its more an issue for the schools risk assessment

 

[tonyelectric]

Agreed, RCds in computer labs can be a pain and avoiding is best if possible, we tend to fit non standard 13A sockets in the schools, one in every room for a vacuum cleaner and the vacs with non standard plugs, this stops cleaners unplugging computers etc to plug in the vac! (not an original idea, I nicked it from london underground they in turn...)

 

[Adam_151]

None standard plugs on the vacuum cleaners?

Surely it would be better to have the non standard plugs on the computers... that way, the students cant be plugging telepphone chargers, etc into the non RCD computer points.. and the RCD protected cleaners sockets can be used by the maintenance crew for power tools etc

 

[Deansplit]

It's a single phase system. The mains in 100amp fuse in black box is a sealed box - this had t be reset a while back as the workmen hit the 16mm black cable when piling - it wasn't fused at the board!!! Tripped the whole house!

 

[bernardgreen]

Surely it would be better to have the non standard plugs on the computers... that way, the students cant be plugging telepphone chargers, etc into the non RCD computer points

Much better,

And also permits the use of "clean" local earths for the computor equipment instead of the noisy CPC earth. Starts getting complicated then.

 

[tonyelectric]

It's a single phase system. The mains in 100amp fuse in black box is a sealed box - this had t be reset a while back as the workmen hit the 16mm black cable when piling - it wasn't fused at the board!!! Tripped the whole house!

OK so you have single phase, but where does your earth wire go to, that tells us the kind of supply you have. Better still post a picture.

 

[Deansplit]

Better still post a picture.

Ok will take pic when at house today, cheers.

 

[Deansplit]

Thanks for the explanation - so a bit OTT for my house where the kitchen (where the 2nd consumer board was due to go) is 10m from the main board!??