3 Phase wiring in industrial office.

[Maxi]

Hi all,

I am doing a piece of design coursework involving full wiring for a garage and attached offices. The premises has 3 sub DBs, one of which is located in the upstairs office. Since all the lights and power outlets are single phase here, should I just take one of the phases from the main supply to this DB, or supply it with all three phases and balance out the loads across all phases? My tutor it is advisable to only use one phase per floor in practice, because this would limit shock risk to 230V. Or would it be acceptable to use one same phase per area on each floor (i.e offices, kitchen, store rooms, etc).

Opinion would be much appreciated.

 

[Spoon]

Hi Maxi,
I don't fully understand the layout of the install from your description. How many floors are there? How many kitchens? What are in them? Are they all the same?
IMO your tutor is correct in that it would be nice to limit the shock to 230V. Also its good practice to balance the loads.
It's best to distribute the loads about, so that if a phase goes down you don't loose all the light for the entire premises.
More info is needed.

 

[Maxi]

Hi Maxi,
I don't fully understand the layout of the install from your description. How many floors are there? How many kitchens? What are in them? Are they all the same?
IMO your tutor is correct in that it would be nice to limit the shock to 230V. Also its good practice to balance the loads.
It's best to distribute the loads about, so that if a phase goes down you don't loose all the light for the entire premises.
More info is needed.

Thanks Spoon. The setup is an industrial type building used as a vehicle maintenance depot which also houses a two story office setup, with small to large office rooms, store rooms, and a rest area with 9kw cooker, as opposed to a kitchen, and toilets with fcu's. The only possible 3 phase load would be a passenger lift from ground to first floor. But this could also be a single phase motor in theroy, otherwise it would be supplied from another db if I keep the db in question as a single phase. This db is on upper floor. The two others are in intake room on ground floor in workshop area.

So... does the whole floor have to be one phase... or just limit to one phase per room ie brown for lights and sockets in small office, black for medium office, grey for rest area, etc, but keeping load balance in mind.

 

[Spoon]

Have you drawn up the plans of the building. Maybe you can post them on here, where the db's are and your intensions. I'm being a dumb --- and still can't get it fully.
So there is no 3 phase needed in the vehicle maintenance depot? What power is needed for this area? You are also selecting what lift system motor to use?

 

[Maxi]

Have you drawn up the plans of the building. Maybe you can post them on here, where the db's are and your intensions. I'm being a dumb --- and still can't get it fully.
So there is no 3 phase needed in the vehicle maintenance depot? What power is needed for this area? You are also selecting what lift system motor to use?

Attached is upper and lower floors in one image. Again, I am only concerned about DB3 located in upper office, and whether to supply this with 3ph or 1ph, as all circuits here are 230V.

 

[Darkwood]

I disagree with your tutor, most shock risk is received when you become the earth path, if an install is layed out correctly then having 3ph on a floor poses no more risk than 1ph. Having 3ph has more benefits too, balanced loads, phase down would only affect approx 1/3 of the floors power.
Aircon and similar systems can be run using 3ph and reducing the required CSA as well as improving the efficiency of the units, another advantage is you have 3phase available if ever required on that floor.

I know of little if any incidents of anyone receiving the full 400v shock and would say 99% are <230v or equivalent to.

Feel free to copy and show your tutor, I would be interested on his/her response although if this is what you are been taught which I disagree with, then your design needs to reflect your teachings or you may be graded down for it.

 

[Andy78]

Load balancing across phases could be achieved more evenly and easily with TP+N supplies to each floor. Also, as Spoon says, the loss of a phase would cause less danger and inconvenience. Use these reasons as your justification. Is this for 2396 ?

 

[Maxi]

I disagree with your tutor, most shock risk is received when you become the earth path, if an install is layed out correctly then having 3ph on a floor poses no more risk than 1ph. Having 3ph has more benefits too, balanced loads, phase down would only affect approx 1/3 of the floors power.
Aircon and similar systems can be run using 3ph and reducing the required CSA as well as improving the efficiency of the units, another advantage is you have 3phase available if ever required on that floor.

I know of little if any incidents of anyone receiving the full 400v shock and would say 99% are <230v or equivalent to.

Feel free to copy and show your tutor, I would be interested on his/her response although if this is what you are been taught which I disagree with, then your design needs to reflect your teachings or you may be graded down for it.

I guess the worry is if someone simultaneously touches two phases... which would be less likely if each room is limited to one phase only.

Not blowing my own trumpet but I'm not worried about being marked down with the effort I'm putting in... and compared to some of last year's ridiculous designs (e.g. all lights on one circuit) and they still passed... but thats for another thread.

 

[Maxi]

Load balancing across phases could be achieved more evenly and easily with TP+N supplies to each floor. Also, as Spoon says, the loss of a phase would cause less danger and inconvenience. Use these reasons as your justification. Is this for 2396 ?

This is for 2365 level 3, but I tend to over analyse, and try to go above and beyond what is required. Plus for my own benefit, and others seeing this thread.

 

[Spoon]

Thanks for the plan Maxi. It looks like you need 20A TP&N for the lift supply, so supplying 3 phase to DB3 is best. Also if you just supply it with one phase that is a very large area to go down if that phase is lost.

 

[davesparks]

Can you ask your tutor to explain exactly how having more than one phase on a floor will increase the shock risk please and post the answers up here? I think we could all do with a bit of a giggle!

 

[davesparks]

Which DB is feeding the workshop lighting? I might be being very old fashioned and outdated here, but I was taught that to spread workshop lighting across the three phases is one of the available methods of reducing/eliminating the stroboscopic effect of discharge lighting (other methods being lead/lag pairs or HF fittings)

 

[PEG]

Also,is that a single phase compressor? Them fitters will have to draw lots to pick who can use their windy-guns...

 

[davesparks]

Also,is that a single phase compressor? Them fitters will have to draw lots to pick who can use their windy-guns...

If you zoom in and put your glasses on you can just about make out that it has a 32A TP&N supply for the compressor.

That plan is not helping with my bid to convince myself that I don't really need glasses yet!

 

[Spoon]

From what the OP is saying, he is only concerned about DB3 on the upper floor.
I had to size the screen up to 200% dave to see it properly.