240cu parallel mains

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hi all

i'm having trouble calculating the maximum permissable current of parallel 240mm sq2 copper mains running a distance of 3 metres.

i have been given a high voltage 11kv to 400 volt transformer three phase to commission which is rated for 1000KVA which is rated for roughly 1400 amps

gut feeling says these 240s are too small and i will need to increase this size to be compliant with the name plate rating of 1400 amps

but with out proof of this being the case i really dont have a leg to stand on and will look like a whinning moaner that is either a.. costing the company money for over thinking the size of mains or B. doing the company a favour and getting it right.

can anyone talk me through the process of why the 240 copper parrallels are undersized??

regards steven
 

LarryFine

Master Electrician Electric Contractor Richmond VA
Location
Henrico County, VA
Occupation
Electrical Contractor
Patience, grasshopper. :)

Most of us aren't familiar with metric conductor sizes, and participation here is voluntary.

Someone who can help you will no doubt pop in and offer their assistance. Please stand by.
 

wireguy8169

Senior Member
Location
Southern Maine
Proof

Proof

How many did they spec per phase that size conductor is equivalent to a 4/0 (well 239.9) so you could be compliant just depends on how many you want to run with out doing any other math you would need 8 to get to 1400+ with derating for more than three current carring conductors per phase
 
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iwire

Moderator
Staff member
Location
Massachusetts
It is not enough for us to be able to covert his mesurments to AWG, we would need to use his ampacity tables and terminal temperature ratings.
 

wireguy8169

Senior Member
Location
Southern Maine
iwire, I thought his question was if he could use that size conductor in parallel. The numbers I gave were just an example, of the fact that he could use them I should have been more exacting. The way the question was posed I assumed he had all the other things he needed must have not understood his question. Thanks for pointing that out, I figured he would have asked that too if he did'nt know. That's why I said "with out doing any other math"
 

wireguy8169

Senior Member
Location
Southern Maine
MM size on conductors

MM size on conductors

wouldnt the mm sq of conductors be equivalent to what we use from the NEC in the US. In Chapter 9 they have them listed in Inch, MM, Inch sq, and MM sq. What I did overlook that iwire pointed out (great thing about his forum is you learn) is the poster would need to use his ampacity tables. And as someone else pointed out, there is not enough info for others to help with the calculation. Need to know if its based on the NEC or what code it is...
 

dbuckley

Senior Member
Thats my worry.

In the USA, wire for purposes covered by the NEC doesn't come measured in sqmm, but this wire does occur in Iraq and other places where American experienced electricians are working with materials designed and certified under different standards. So, the NEC may give equivalent sqmm sizes for popular wire guages, but I'm not convinced those ratings applied to wires manufactured for use under another authority are necessarily correct.

You only need look at the issues in comparing an IEC rated contactor with a NEMA specimen.

Whenever I see "foreign" terms used on tis forum, my ears instantly prick up.
 

mull982

Senior Member
Wouldn't the mm^2 be that listed under the area column of table 8 in the annex of the NEC?

If thats the case then wouldn't 250mm^2 be closer to a 500MCM?
 

iwire

Moderator
Staff member
Location
Massachusetts
Wouldn't the mm^2 be that listed under the area column of table 8 in the annex of the NEC?

If thats the case then wouldn't 250mm^2 be closer to a 500MCM?

It does not matter what it is 'close to' the NEC ampacity tables are based on the insulation and conductor temps that are used here. Where this person is they very likely have their own ampacity tables that do not match the NEC tables at all.
 
Data sheet from supplier

Data sheet from supplier

Current-carrying capacities of three single-core 0.6/1kV 110?C
(LSFLEX? R-30, LSFLEX? R-70, LSFLEX? R-80 Insulation)


Current-carrying capacity, A
Unenclosed
Spaced
Conductor size 240 mm2

MAX permissable CURRENT 845
Based on ambient temperature of 30?C,
maximum conductor temperature of 110?C

QUESTION: to calculate parallel 240s i'd just double that figure
equals 1690 amps
not taking into account length of run or load
 

kwired

Electron manager
Location
NE Nebraska
Your load side conductors need to be sized for the load being served, and not necessarily the nameplate rating of the transformer.
 

iceworm

Curmudgeon still using printed IEEE Color Books
Location
North of the 65 parallel
Occupation
EE (Field - as little design as possible)
Current-carrying capacities of three single-core 0.6/1kV 110?C
(LSFLEX? R-30, LSFLEX? R-70, LSFLEX? R-80 Insulation)


Current-carrying capacity, A
Unenclosed
Spaced
Conductor size 240 mm2

MAX permissable CURRENT 845
Based on ambient temperature of 30?C,
maximum conductor temperature of 110?C

QUESTION: to calculate parallel 240s i'd just double that figure
equals 1690 amps
not taking into account length of run or load

600V equipment manufactured for installation under the NEC won't have terminations suitable for 110C. The terminations will likely be 75C.

So, I would ask if the equipment you're connecting to has 110C rated terminations. If it does you are okay. If it doesn't --- well, you're not.
 
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