cable size for 3phase

[steptoe]

my oh my,

I have put this here cos I truly feel its something I should know,

buts its very basic,

when you read it you will understand why I dont want to get it wrong.!

100m run 4core SWA (3p+N)

100kW loading

=

70mm2 70degree cable will just get me inside 3% volt drop ,

I dont have my BRB to hand and am going by what I have quickly grabbed off the internet,

Im on site trying to work out cable size for a solar PV.

thanks,

 

[steptoe]

its on my phone now,

ref D , its in a duct in places so 167A max before VD applied !

thanks anyway canoe,

looks like it may be 95mm,

on the way home now so will check when I get there,

 

[Chr!s]

Would need a little more info to give an accurate answer.

 

[steptoe]

sorry plumber,

2X50kW 3ph+N solar PV systems about 100m away from incomer , underground ducting part way.

the PV systems is actually regarded as a load for to all intents and purposes, it is on the load side of CPDs.

4% VD allowed on PV.

 

[Sidewinder]

Steps,

I am not a PV expert as you know.

I am guessing you treat PV as a balanced load.

IMHO it does not matter which end the load is really!

So you want to stuff 100kW balanced 3ph down an SWA prob gonna be 70 deg rated?

Inverters at panel end so you are shoving "a.c." down the cable?

I would think we can ignore all the spurious things that inverters create when changing d.c. to a.c.?

Thus we can let the a.c. be a pure sinusoidal a.c. waveform, this is normally the case when shoving stuff up the grid the wrong way as the HV/LV transformers act as quite a smoother, same as motors really?

Do the inverters have o.p. filters, like RLC units?

These would also smooth the o.p.?

Off shortly (again), honest!

Will pick up tomorrow.

 

[Chr!s]

What voltage is the inverter supplying at? Have we 100kw across three phases balanced at what nominal voltage?

 

[Sidewinder]

Plumber,

It will be feeding straight into the grid mate, so 230/400 V a.c.

 

[Andy™]

Plumber,It will be feeding straight into the grid mate, so 230/400 V a.c.

maybe get the inverter to put the voltage up a few volts to help VD at the end?

 

[steptoe]

sorry guys, I dont have specs to hand for the inverters yet,

SW, you are correct, it will be balanced at 230/400, 2 arrays feeding 2 inverters to 2 separate breakers then into 1 cable to main incomer,

its treated as a normal 3ph+N balanced load, in the info (which so far is very limited) I have been supplied with.

---------- Post Auto-Merged at 22:36 ---------- Previous post was made at 22:34 ----------

[quote name='Andy

 

[kerching]

I have had a word with the 'people' who installed my neighbours....they reckon twin bell wire should be enough, if not then try alarm wire... :run

:coat

 

[Andy™]

but your neighbour only has a single solar cell 50mmx50mm...

 

[steptoe]

I have had a word with the 'people' who installed my neighbours....they reckon twin bell wire should be enough, if not then try alarm wire... :run :coat

if I remember isnt it 2kW.?

then some 1mm would be fine, depending on installation of course, tho personally I use 2.5 on any I have done, or 6mm for big runs.

 

[kme]

I`m sure I`ve got a "spare" offcut of 250mm 5 core XLPE lying around - maybe about 400` long - any use to you? I was going to weigh it in for scrap & pay off my mortgage, but I`ll give it you cheap mate

(nips off to confirm substation submain sizing) :slap

 

[Chr!s]

Steptoe

By my calculations 70mm 90 C xple should be fine

 

[Sidewinder]

Plumber,

Would that be taking the cable rated at 90 or 70?

If at 90 the terminations need to be 90 also do they not, if not then the cable needs to be downrated to 70 does it not?

 

[Chr!s]

Would that be taking the cable rated at 90 or 70?If at 90 the terminations need to be 90 also do they not, if not then the cable needs to be downrated to 70 does it not?

The calculations ensure terminal temp is 70 C or less.

 

[Sidewinder]

OK cool, I did not think you would miss that one really!

 

[steptoe]

Ok thanks all,

Confirmation from smarter people than me is always good, i did my calcs on 70pvc and got it close so was going to run with xlpe to give me space.

Just glad you didnt tell me i was miles out and needed 120 or something.

 

[Chr!s]

OK cool, I did not think you would miss that one really!

Lol

I am assuming ducting being the worst case.

 

[steptoe]

Yes, sifting worst case scenario.

Scoobs will be awarded in due course, Im on the phone just now.

I have another question i will post later in a new thread, on a related topic.

Just been to price it up, IRO