Cable Size for 3 phase 1250A breaker

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aqeelpk

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I have a 3 phase main breaker of 1250A and voltage supplied is 110V, what will be the size of main cable needed and how many pairs, any one illustrate.
 

Dennis Alwon

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Location
Chapel Hill, NC
Occupation
Retired Electrical Contractor
you cannot have a 3 phase breaker and only have 110v. It is 208V, 240V or possibly 480, etc.

To supply 1250 amps you would have to parallel conductors. How many parallel runs will you have. Also look at T. 310.15.

Also 1250 amps is not a standard size breaker. Where did you get this question from.
 

Hameedulla-Ekhlas

Senior Member
Location
AFG
I have a 3 phase main breaker of 1250A and voltage supplied is 110V, what will be the size of main cable needed and how many pairs, any one illustrate.

First of all, please correct your question
second, Are you using NEC
Third, If not please see the company cable catalog which you order the cable.
 

bob

Senior Member
Location
Alabama
It will depend on which code you are using. If you use the NEC you can check the ampacity of conductors at this site.
http://www.houwire.com/products/technical/article310_16.html
If you did have a 1250 amp breaker, look at 600 mcm copper under the 75C column. The ampacity is 420 amps. Three conductors per phase would give
you 3 x 420 = 1260 amps per phase. There are some other factors that come into play. Distance, temperature, metric wire sizing and maybe you local code requirements.
 

aqeelpk

Member
Yes ofcourse breaker is 3 phase and also 1250AF (at full load) with L, S, I and G functions made by ABB.

We are using here IEC codes.

In my opinion 300mm2 cable is enough but how many parallel conductors and how many cores?
 

aqeelpk

Member
Sorry, one thing i forget;

the voltage is 110V (or 127V, this is phase voltage) or 230V (line voltage).
 

Dennis Alwon

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I am here in Riyadh, Saudi Arabia.
كيف حالك؟


Well for starters I am not sure our wire sizes are equivalent. i don't think a 300mm2 cable is equivalent to our 300kcm. The circular mils on that wire is 300,000. In fact our 300 kcm is equal to 201mm2. The 2 being squared, of course. The closest we have to 300mm2 is 500kcm which is 336mm2
 

Hameedulla-Ekhlas

Senior Member
Location
AFG
Yes ofcourse breaker is 3 phase and also 1250AF (at full load) with L, S, I and G functions made by ABB.

We are using here IEC codes.

In my opinion 300mm2 cable is enough but how many parallel conductors and how many cores?

Oh, you are using IEC code and do you have any cable catalog or have you requested any company to send you their cable catalog.

what type of IEC cable you are using have you noticed this. In NEC there is ThHHN, THWN and many others.

IEC also has NYY and many other types which current capacity differs per type.

You should have IEC cable catalog from a company.
you can not gues like this 300m sq is enough and how many.
There are many other factors to be considered like voltage drop, derating and etc.
Try to you use NEC as a guide book for factors.

I will give one IEC cable catalog please do not just take cable ampere capacity also consider voltage drop, derating factor, and others.
If you still have any farther question please let us know.

By the way, you are working in Sudia and you are from Pakistan. Which part of pakistan you are
 

aqeelpk

Member
IEC 60502 we use.

Cable type we are using is three core XLPE/STA/0.6-1KV rated at 85 degree centigrade, by Saudi-American Cable (Riyadh Cable is the other name). The catalogue on the website of Riyadh Cable doesn't contain the ampacities of the Cables.

Actually we are using the cables in our construction project, our consultant has given us the approved size (3*300mm2+150mm2) of the cables to be used for connecting the two main distribution panels of main breaker 1250A.

But i want to know how we used this and what's the reason behind this.

By the way I am from Abbottabad District of N.W.F.P and i have graduated from U.E.T Peshawar in 2008.

I will be grateful for reply of my question, from anyone.
 

charlie b

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Location
Lockport, IL
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Retired Electrical Engineer
I am here in Riyadh, Saudi Arabia.
. . . the voltage is 110V (or 127V, this is phase voltage) or 230V (line voltage).
Now you have me confused. I was part of the design team for a very large project in Thuwal, Saude Arabia. The voltages there are 220 line to ground, and 380 line to line. Is it really that different in Riyadh?


 

Hameedulla-Ekhlas

Senior Member
Location
AFG
Now you have me confused. I was part of the design team for a very large project in Thuwal, Saude Arabia. The voltages there are 220 line to ground, and 380 line to line. Is it really that different in Riyadh?


now line to line voltage is 400volt and per phase is 230 volt. I am also confused with his question and method of design.
 

aqeelpk

Member
Supply is 500KVA supply, Primary voltage 380V line to line or 220 line to ground but secondary is 220V line to line and 127V line to ground. This voltage (127V, i will always talk about phase voltage here in secondary, for that not to be confused because there are two types of 220V, one is line to line in case of secondary and other is line to phase in case of primary) is used for further supplying the equipments through the main distribution panel of 1250A.
 

charlie b

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Location
Lockport, IL
Occupation
Retired Electrical Engineer
Primary voltage 380V line to line or 220 line to ground but secondary is 220V line to line and 127V line to ground.
OK, I see. Thanks for clarifying. In my project, all equipment to be installed on site was required to be rated for either 220 or 380. But I see you are allowing for equipment at other voltage ratings.


I'll take a quick look through the project files, and see if I can find any ampacity information for the sizes of cables you are working with.
 

Hameedulla-Ekhlas

Senior Member
Location
AFG
Supply is 500KVA supply, Primary voltage 380V line to line or 220 line to ground but secondary is 220V line to line and 127V line to ground. This voltage (127V, i will always talk about phase voltage here in secondary, for that not to be confused because there are two types of 220V, one is line to line in case of secondary and other is line to phase in case of primary) is used for further supplying the equipments through the main distribution panel of 1250A.

ok, any way doest matter what voltage is but select the cable carefully.
 

aqeelpk

Member
Here in Saudia, the main supply for any type of equipment (secondary voltage is used ofcourse for equipments) is 110V which is line to ground but any equipment which requires 220V, we combine two 110V (two different phases) and don't install the neutral, so automatically the phasor sum of 110V (with different phase angles, here point to be noted that neutral may or may not be needed when we are dealing with two different phases simultaneously) becomes 220V, that's how we create 220V for end user equipments but the main supply is always 110V.
 

charlie b

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Location
Lockport, IL
Occupation
Retired Electrical Engineer
I am not sure I can give you the best solution for your particular question. The closest "standard" overcurrent device setting (per the NEC) to your situation is 1200 amps. For a 1200 amp breaker, I would use four sets of 350 MCM conductors in parallel. That gives you a total ampacity of 1240 amps. The closest metric equivalent to 350 MCM is 150 mm2. So four sets of 150 mm2 might be your answer.
 

aqeelpk

Member
So it means ampacity of one conductor (3 core) of 150mm2 is 310A. Is it so? What will happen if we use three conductors each of ampacity 400A (what will be the size in metric?)

Thanks for the answer.
 

Dennis Alwon

Moderator
Staff member
Location
Chapel Hill, NC
Occupation
Retired Electrical Contractor
So it means ampacity of one conductor (3 core) of 150mm2 is 310A. Is it so? What will happen if we use three conductors each of ampacity 400A (what will be the size in metric?)

Thanks for the answer.
Here we would use 3 runs of 600mcm which is equivalent to 420 amps * 3= 1260amps. 600 kcm=404mm2. So perhaps 3 --400mm2 would work.
 
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