11kVA 3 phase supply

[snowman]

Sorry but I'm yet another noobie who needs help.
I’ve just qualified and I'm in the process of setting up on my own.
I’m quite happy with your normal domestic electrics but the in-laws have just asked me if I can sort their new 3-phase supply for them.
They’re having a 11kva 230/400 3-phase supply fitted by YEDL. I presume YEDL will fit the meter and an isolation switch and ill have the job of fitting the tails from the isolator, the consumer unit and connecting up the new machine.
I’ve had a look on 1 of the threads and think I've found the correct max phase current formula

11000/(230*3)=16A per phase

Firstly can anyone confirm this to be correct?
Secondly with the max current only been 16A do I still have to fit 25mmsq tails to the consumer unit.
Thirdly can anyone recommend a suitable consumer unit or should I just buy a 4way with 4 pole rccb mains switch and use a suitably rated 3-pole mcb for the machine

Hope you can help

 

[Chr!s]

Are you sure they are not referring to a 11kv transformer

 

[Marvo]

I would be more concerned how you would balance the load on such a small supply. You'll need to rewire certain items to 3-phase as well such as shower and stove. I don't envy you on this one, I've never seen a domestic supply less than 50 Amps per phase using 10mm tails.

Edit, In theory you could use 2.5mm, 25mm is astronomically over sized. As suggested above, I would check your figures, this doesn't sound right.

 

[snowman]

to clarify things I have a copy of the electricity suppliers quote, the wording used is.
"we shall provide a system of electricity that is 3 phase, 230/400 volts, alternating current at 50Hz and with a maximum capacity of 11kva." I took this to mean 16a per phase, which I dont understand as its so small for a new supply.
The inlaws currently have a 100a single phase supply to the home and a 60a single phase supply to the out buildings with a single to 3 phase converter to power there current machinery but this has run out of capacity so they are having a new dedicated 3 phase supply run to the out buildings.
if ive been an idiot and miss understood the quote please feel free to set me straight

 

[Chr!s]

to clarify things I have a copy of the electricity suppliers quote, the wording used is.
"we shall provide a system of electricity that is 3 phase, 230/400 volts, alternating current at 50Hz and with a maximum capacity of 11kva." I took this to mean 16a per phase, which I dont understand as its so small for a new supply.
The inlaws currently have a 100a single phase supply to the home and a 60a single phase supply to the out buildings with a single to 3 phase converter to power there current machinery but this has run out of capacity so they are having a new dedicated 3 phase supply run to the out buildings.
if ive been an idiot and miss understood the quote please feel free to set me straight

Sound about right then, best to check though.

 

[Marvo]

...The inlaws currently have a 100a single phase supply to the home and a 60a single phase supply to the out buildings with a single to 3 phase converter to power there current machinery but this has run out of capacity so they are having a new dedicated 3 phase supply run to the out buildings.

From your op I thought the whole house was to be supplied by this 3-phase installation. If it's just for small machinery in an out building then maybe it's adequate. It might still be worth just auditing the load from the machinery their using and checking there's sufficient prospects for future expansion with the 11KVA supply.
I'm sure one of the UK guys can give you good advice on a suitable CU and tail sizes.

 

[Knobhead]

I find 11KVA hard to believe 10, 12.5 or 15 are standard sizes. I’d check up on that if I were you.
As to the meter tails go for an easily obtained option, 16mm is OTT but it’s off the shelf material.
Distribution board, you’ve got to decide if you want fuses or MCCB’s

 

[Engineer54]

First things first!! have you totalled up the requirements of the 3ph machinery?? The other thing is, i've never seen a DNO or the old leccy boards, supply anything less than a 15kva supply for a commercial premises, even then, the cable will be sized for future up-grading!! Only the supply fuses will be limiting the available DNOs supply.

 

[davelerave]

the existing single phase sub-main from a house

supplying 3-phase machinery through a convertor isn't usually a great setup anyhow



i doubt the uk dno's provide anything that small in 3-phase ? you'd be leaving yourself no spare capacity anyhow

 

[somersetsparks]

Working for a DNO, I have never known a 3 Phase supply to be under 60A per phase, infact we wouldn't even carry fuses below 80A generally.
I imagine they might have given yoiu that figure as that is the maximum safe figure available from the grid without overloading in your area without major uprgrades to trandformers etc.
They will probably supply you with a normal 80A setup cable and fuse wise anyways, i imagine the 11kva is an arbitary figure, if you requested a 50kva supply they would probably ask you to pay towards transformer upgrades.

 

[snowman]

Thanks for all your advice.
Somersetsparks may be right, Ill wait till its installed and get back to you all if i need more help.

 

[ian.settle1]

Sorry but I'm yet another noobie who needs help.
I’ve just qualified and I'm in the process of setting up on my own.
I’m quite happy with your normal domestic electrics but the in-laws have just asked me if I can sort their new 3-phase supply for them.
They’re having a 11kva 230/400 3-phase supply fitted by YEDL. I presume YEDL will fit the meter and an isolation switch and ill have the job of fitting the tails from the isolator, the consumer unit and connecting up the new machine.
I’ve had a look on 1 of the threads and think I've found the correct max phase current formula

11000/(230*3)=16A per phase

Firstly can anyone confirm this to be correct?
Secondly with the max current only been 16A do I still have to fit 25mmsq tails to the consumer unit.
Thirdly can anyone recommend a suitable consumer unit or should I just buy a 4way with 4 pole rccb mains switch and use a suitably rated 3-pole mcb for the machine

Hope you can help

Whats this in red,

230*3 gives 690?

 

[snowman]

sorry might be the way i typed it

11000 / (230 x3) = 16A
or
230 x 3 = 690

11000 / 690 = 15.94 A per phase.

 

[ian.settle1]

sorry might be the way i typed it

11000 / (230 x3) = 16A
or
230 x 3 = 690

11000 / 690 = 15.94 A per phase.

OK but what is the 690?

 

[snowman]

its the single phase voltage times the number of phases.

I got this formula off one of the forum pages. I didnt know if it was correct thats why i asked about it. Ive since talked to an industrial electrician who told me its the correct formula to use.

 

[Guest123]

It's there or there abouts.

11000/(400 x 1.732 x PF (unknown)) = 15.88A.

 

[ian.settle1]

its the single phase voltage times the number of phases.

I got this formula off one of the forum pages. I didnt know if it was correct thats why i asked about it. Ive since talked to an industrial electrician who told me its the correct formula to use.

to find the 3 phase voltage from single phase you multiple the single phase voltage by the square root of 3 (1.732) not by 3.

 

[Engineer54]

It's there or there abouts.

11000/(400 x 1.732 x PF (unknown)) = 15.88A.

That's the correct calculation to use Lenny... root 3 rules!! lol!!

 

[ian.settle1]

It's there or there abouts.

11000/(400 x 1.732 x PF (unknown)) = 15.88A.

Confused by your answer Lenny as

400 x 1.732 = 692.8

400/1.732 = 230

230 is single phase voltage if your 3 phase voltage is 400

 

[Guest123]

Confused by your answer Lenny as

400 x 1.732 = 692.8

400/1.732 = 230

230 is single phase voltage if your 3 phase voltage is 400

Sorry Ian, what are you confused by??

The calc is correct the sum is 15.88A per phase.

 

[ian.settle1]

Sorry Ian, what are you confused by??

The calc is correct the sum is 15.88A per phase.

So what you are saying that he has a single phase voltage off 400 and a 3 phase voltage of 692 that is what I am saying from your calculation.

 

[snowman]

to find the 3 phase voltage from single phase you multiple the single phase voltage by the square root of 3 (1.732) not by 3.

ian it was the max current per phase i was after not the phase to phase voltage but thanks anyway.
The formula i found must be a rule of thumb or something cos it works out just about the same as the formula lenny gave.
thanks for the input.