New 3 phase board

[fivestar]

Advice please. I have a customer who is converting a barninto a food grade environment and I will be installing suitable lights, socketsetc. They are also having a secondhand processing machine installed which requiresa 32A 3 phase supply. The main supply to the site is in the barn and is a 3phase TT bus bar system. The existing board is pretty rubbish it appears tosupply a lot of redundant kit, is very old and is a mess. Customer does nothave the budget to replace so my thoughts were to install new 3 phase boardwith RCBO’s for my lights and sockets, and 32A breaker for machine. Question isshould the main isolator for this board be 100ma S type RCD?

 

[philipb]

Hi There,
I wouldn't use an rcd as the main switch in this set up,if any thing trips the whole
supply will be cut off,just put the three phase machine on its own rcd and use a
normal type main switch,and use rcbo's for the single phase equipment.

 

[fivestar]

I see your point – that’s why I was thinking of having stype RCD to prevent nuisance tripping as RCBO’s would blow first. If I havemachine on separate RCD that will have to sit outside TP board or am I missingsomething?

 

[needasparks]

You must use an external Rcd as the board is metalic so the protection must be before the distrobution equipment.
It may be an idea to read up on TT requirements before you go any further on this project as there will be many areas that need upgrading in regards to bonding to steelwork, As you say large metalic machinery is to be introduced into an area with structual steel present.

An incoming RCD must be used in an insulated enclosure before entering a metalic DB, The use then of rcbo's is then permissable.

 

[fivestar]

Thanks for your comments - the situation at this site is that the main incomers go straight into a metal 200A main switch - which then feeds a bus bar system encased in metal - of which the current delapidated 3 phase board is connected along with a couple of metal switch fuses. Customer does not want to pay to upgrade this set-up hence the new board. I take your point about having the RCD before a metal enclosure.

 

[Darkwood]

Something here that no-one has picked up on, you said this a food grade environment.... you need to assertain the level of this as it may require IP rated products capable of washdown, stainless steel conduits etc etc ... if your customer is already counting pennies you may have to explain to him the legal requirements and there is no shortcuts you can take, if you fit an electrical install into a food environment that dosnt meet hygiene and IP rating of said environment you could be liable for a food poisoning outbreak if it linked to your install not meeting requirements.
I suggest research your job on this one and quote for the work.

 

[needasparks]

You say the intake is 200A. Are you saying this is a TT ? as i have never seen a TT over 100A and thought it would have to be a TN system. Perhaps i missread and its just the supply to this barn from origin thats is a TT.
So to get this straight in my head from the bussbar you have a s/fuse supply to your planned new board ?

 

[fivestar]

The supply to the barn is the main supply to the site - from here there is a sub main to the house. There is a 200A main switch but I it does appear to be a 100A supply. I am intending to feed my new board from the bus bars - but as you have pointed out it will need to go through an RCD in a insulated enclosure first. The point I was trying to make is that the current installation is all metal enclosures without an RCD in site! As far as the food grade environment is concerned - it is an egg packing plant - the machine simply grades the eggs according to size. All wiring will be behind cladding - IP rated lights fittings will be used.

 

[Darkwood]

Regards the food grade it sounds like low level so not much in the way of special requirements, jst make sure all flexes etc have chemical resistance to the likes of ammonia etc as chicken muck will be aplenty on the eggs unless they are cleaned prior to entering this barn and best run all powers in galv conduit to stop vermin attacking cabling, mice rats etc can usually get into the cladding so you've to design with this in mind.