Need help quick correct wire size for a 1200kw 440 volt generator

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hurk27

Senior Member
Ryandumas
You have been given enough information to design this job. The conductor must have at least the ampacity of the 2000 amp breaker. I believe
1. You must get the local inspector involved
2. Will he allow the use of table 310.17 for this installation
3. If any of the conductors are in conduit the information given will not be valid.
4. How are you going to manage all of these conductors w/o conduit
5. If not in conduit does close grouping of the conductors require further adjustments

I think it was said this is on a barge, on the water, see post 1

so not in NEC territory I think?

also I would think the cable would have to be flexable fine stranded type hard use.
 

nakulak

Senior Member
it occurred to me to check the book (lol), noone here seems to be looking at table 610.14 A for the correct wire ampacities ? (if it applies) (including me) However, OP has not provided crane details either. OP I suggest you brush up on article 610.
 
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hurk27

Senior Member
Whoops forgot 445.13

Also I'm confused at the caculation, 1200000/440/1.732=1574.6*115%=1810.8?

I have never used PF in calculating the source, just the load?:confused:

3 500Kcmil@75deg Coulomb free air = 1860 table 310.17
the 2ka breaker is for short circuit as it is the next available size breaker
 
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bob

Senior Member
Location
Alabama
I am working on a crane that is run by a 440 volt 60\hz 1200 kw generator. The company wants a backup generator on the deck ready to wire in. The electrician above me says we only need 350 mcm the length of the leads will be 120' in thru a barge and up inside the crane in free air with an ambient temperature of 100 degrees F.

Does thru a barge mean its on the water? I did not read it that way. Maybe the OP will tell us if an inspector is involved. If this is an N EC installation, 240.4C would require the conductors to match the ampacity of the breaker. Does 240.4C trump 445.13?

hurk27 said:
3 500Kcmil@75deg Coulomb free air = 1860 table 310.17 the 2ka breaker is for short circuit as it is the next available size breaker

OP said temp was 100 degrees.
 
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hurk27

Senior Member
Does thru a barge mean its on the water? I did not read it that way. Maybe the OP will tell us if an inspector is involved. If this is an N EC installation, 240.4C would require the conductors to match the ampacity of the breaker. Does 240.4C trump 445.13?

Not sure as this is an area I'm kind of learning, not wanting to go on the "what I been told over the years" kind of thing

If we look at 240.3 it directs us to the table which list generators in article 445 for the protection of the equipment (the generator) now 240.21(G) also allows the same breaker required in 445.12 to serve as the protection of the conductors connected to the generator if they are sized to the requirements in 445.13, which to me would mean if the conductors are sized at 115% of the rating of the generator it's good to go?

and the only reason I can figure for this allowance is the inherent inability of a generator to produce a high level of current above its rating for any length of time enough to damage the conductors. most generators will stall or bog down way before you reach the 115% over it's rating, so by design it protects the conductors as stated in 445.12(A)




OP said temp was 100 degrees.




I agree I should have used the derating factor at the bottom of the table 310.17
 
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ryandumas

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The barge is on the water no inspectors. ambient temp is between 95 and 110. I was told to size the temp generator to the breaker which is 2000 amps (first I was told to wire to the max of the gen) The cables will be run thru the air in the barge then up the pedestal to the crane. Yes it needs to be flexible. Not the ideal installation. Thanks for your help
 

hurk27

Senior Member
I was just trying to get to the bottom of what the NEC really requires, as I said this is one of those areas I was always told what to run based upon the above, Maybe someone would chime in if I'm mistaken.

I know copper is expensive and running the right cable for the job is more money in my bank. but sizing upon the 2ka breaker you should be definitely good to go for the voltage drop part of the equation.:D
 
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