Voltage Drop on a 120mm 4 core.....

[JakeSpark]

Please someone help me.....

Im trying to work out a cable size for a new Sub Main at our warehouse. The cable is going to be pulling 320A and is going to be a total lengh of 120m, (give or take a little). Whilst doing my calculations i came across Voltage drop. For this table 4E4B, pg 348 of bs7671 uses 'r,x&z' values for the calculation of voltage drop. I am lost as to how i use these values correctly to ensure my Voltage drop complies.

Anyone have any ideas!!

P.S. apart from burying the cable between the two installs, (the main warehouse and the new one, to which the sub main will be feeding) which is going to rapidly reduce my current carring limits, can anyone recommend a different installion method.

thanks

Jake

 

[m4tty]

Ive taken a few guesses at the information you havent supplied ie, fuse/breaker type etc etc but this may help

Cable ID / REF number : JakeSpark

Supply voltage = 400 Volts

Ib - design current = 230 Amps

Protective device type = BS88

In - protective device rating = 250 Amps

Length of run of cable = 120 metres

Power factor = 1

Cable Type : Thermosetting 90

 

[kerching]

Ib = 320A not 230A................or is Senor Merlot visiting me early tonight................ :innocent

 

[m4tty]

Oops I'll redo it later sorry

 

[Manator]

If you can clip direct/surface, then your cable will be at least 185mm. If you bury it then your looking at well over 240mm

 

[m4tty]

Try no 2 sorry

Supply voltage = 400 Volts

Ib - design current = 320 Amps

Protective device type = MCCB

In - protective device rating = 350 Amps

Length of run of cable = 120 metres

Power factor = 1

Cable Type : Thermosetting 90

 

[park1]

320 Amp per phase?

 

[park1]

Im in a sweat thinking about it.

 

[Jono Pashley]

Off prepping a 2000mm2 rod ready

 

[batty]

You are going to need a very low loop at the supply end for a 320 amp supply is it suitable?

 

[steptoe]

Good, go back to your T&E and let the men take over :slap ROTFWL :slap Hopefully its not TT !!!! Steps where are you :innocent

here boss :Salute

now, who borrowed me BIG sledge hammer, Im gonna need it for this rod.

 

[timgdean]

why not in a duct between the buildings ?

reference method d

T.

 

[JakeSpark]

M4tty,

Thanks for that, regarding the Installation method it will be running on a tray/ladder system thoughout the existing warehouse then as said before it has to pass between the oldand new warehouse. Is there a better way of doing this other then to bury the cable.

RE $park comment, this '320amp' current is a total current draw on all 3 phases, should i split the currents over the 3 phases before choosing a cable size.

Excuse my ignorance this is the first 'big' job i have done.

 

[Manator]

320 amps should be split over all phases and will effect the size of cable required. Remember that each phase is only 230 volts, giving you the required 400v at point of demand. 320amp is an odd end demand and I would think the design would have to be rounded up as it is 106.66666 amps per phase.

 

[park1]

For cable sizing you would use line current per phase not total current of all three phasesSo as per Manator 320/3 for cable size

Or just stick 400mm in as per Contolboy and be a "Man". ROTFWL

---------- Post Auto-Merged at 09:04 ---------- Previous post was made at 09:01 ----------

Id disagree with Manator and Canoeboy, design to the largest load any any given Phase, i expect the load to be unbalanced.

 

[park1]

M4tty,Thanks for that, regarding the Installation method it will be running on a tray/ladder system thoughout the existing warehouse then as said before it has to pass between the oldand new warehouse. Is there a better way of doing this other then to bury the cable.

RE $park comment, this '320amp' current is a total current draw on all 3 phases, should i split the currents over the 3 phases before choosing a cable size.

Excuse my ignorance this is the first 'big' job i have done.

May be as stated it would be better showing how you have calculated a MD of 320amp.

You need to explain the transition between the to buildings for advise on installation methods.(Inside, Outside, Traffic etc)

You need to assess the types of loads within the installation including any Harmonic content and applying diversity where needed. Distribute the loads as evenly as possible, don't worry to much about balancing you wont be on a Maximum demand tariff.

Id suggest you enlist the help of someone more learned, it it will help you to understand and ensure your client gets what is required.

 

[JakeSpark]

May be as stated it would be better showing how you have calculated a MD of 320amp.You need to explain the transition between the to buildings for advise on installation methods.(Inside, Outside, Traffic etc)

You need to assess the types of loads within the installation including any Harmonic content and applying diversity where needed. Distribute the loads as evenly as possible, don't worry to much about balancing you wont be on a Maximum demand tariff.

Id suggest you enlist the help of someone more learned, it it will help you to understand and ensure your client gets what is required.

The client is my boss... we orginally thought this could be done in house, however it appears it would be best to get the design done by a exturnal contractor.

thanks for all your help guys.

 

[park1]

The client is my boss... we orginally thought this could be done in house, however it appears it would be best to get the design done by a exturnal contractor. thanks for all your help guys.

May be for the best, hard to say without more info.

 

[Manator]

As canoeboy said above given a final demand of 320 amps is all we can go from on the design so we can only do 320/3. We would also need to know if there is any room in the design and if diversity can be applied.

 

[m4tty]

Any help ??? lol

Supply voltage = 400 Volts

Ib - design current = 107 Amps

Protective device type = MCCB

In - protective device rating = 125 Amps

Length of run of cable = 120 metres

Power factor = 1

Cable Type : Thermosetting 90