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Old 10-23-2008, 10:52 PM   #1
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Default 800 amp service

we were given 2 al 750 kcmil for an 800 amp service, the cables don't fit the breaker. The cables were buried and taped. would you have used 3 300 kcmil awg or 2 400 kcmil awg for the job. Is the 750 to big for this job?

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Old 10-23-2008, 10:56 PM   #2
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oops, I mean 2 conductors per phase.

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Old 10-24-2008, 12:13 AM   #3
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Lugs changeable on the breaker? Can you describe what you mean by "don't fit", a little better?
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Old 10-24-2008, 12:56 AM   #4
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if the cables are already in the ground i would look at modifying the breaker, would it be possible to make up some extensions tags?

i work for a distribution company and we do this all the time but we have access to a workshop and a endless supply of copper plate.... might not be practicable for you guys
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Old 10-24-2008, 04:52 AM   #5
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Default 800 amp service parallel feeds

Well YES AND NO !! 800 amp breaker you can change out the lugs order from supply house new lugs !!!! next 800amp 2 runs of 750 mcm alu at [75 c ] column x2 =770 amps [300 mcm alu x3 =690 amps [ 400mcm alu x3 =810 amps your best is 400 mcm alu x 3= 810 amps so thats what i would run but do you actually need 800 amps ? because i cant see someone screwing up that bad ? look at the total load of your install you may not need 800 amps total ? and can use the 800 amp breaker but !!! change out the rating plug on that breaker to limit the trip rating on it to lower setting like 700 amps . whats your actual total load on your service ? but i think someone was looking at the copper side of the tables when they sized that 750 mcm and got alu wire ? 2 runs of copper 750 would do it load or no load calculation . did you say copper or alu ? but one more thing it may still maybe ok what type of insulation is on that 750 mcm jacket is it DUAL RATED WIRE if it is your fine with the 750 mcm alu ? like thwn -2 or xhhw-2 than you can use 90 c col and every one is happy ? take care best to ya

Last edited by nick; 10-24-2008 at 03:33 PM. Reason: calulate your load see if its less than 800 amps ?
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Old 10-24-2008, 06:04 AM   #6
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My guess is they oversized a wee bit for voltage drop.
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Old 10-24-2008, 06:20 AM   #7
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Default load cal service size

Well sometimes the posts are leaving out the details and its hard to fix it if your not given all needed info but we try to help out. most services in our area of work is engineered on risers and we dont design it we just do as shown by electrical drawns , we check it but they pay us if they screw up .take care best to ya .
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Old 10-27-2008, 08:15 PM   #8
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Well YES AND NO !! 800 amp breaker you can change out the lugs order from supply house new lugs !!!! next 800amp 2 runs of 750 mcm alu at [75 c ] column x2 =770 amps [300 mcm alu x3 =690 amps [ 400mcm alu x3 =810 amps your best is 400 mcm alu x 3= 810 amps so thats what i would run but do you actually need 800 amps ? because i cant see someone screwing up that bad ? look at the total load of your install you may not need 800 amps total ? and can use the 800 amp breaker but !!! change out the rating plug on that breaker to limit the trip rating on it to lower setting like 700 amps . whats your actual total load on your service ? but i think someone was looking at the copper side of the tables when they sized that 750 mcm and got alu wire ? 2 runs of copper 750 would do it load or no load calculation . did you say copper or alu ? but one more thing it may still maybe ok what type of insulation is on that 750 mcm jacket is it DUAL RATED WIRE if it is your fine with the 750 mcm alu ? like thwn -2 or xhhw-2 than you can use 90 c col and every one is happy ? take care best to ya
I dont think you can use the 90 dgree col. That breaker probably doesnt have the 90 degree rating.
Furthermore , at 800 or more , you cant use " the next size up ". The ampacity must be allowed for 800 amps , and two 750's dont make it. I think it comes to 785 or something.
Copper should be used. 500 or 600 . I dont have the book handy.
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Old 10-27-2008, 08:24 PM   #9
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Not sure if it makes a difference but our poster is in Canada. NEC or CEC (I think)? Don;t know what differences there are in the two.
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Old 10-28-2008, 05:06 AM   #10
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Default dual rated wire

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I dont think you can use the 90 dgree col. That breaker probably doesnt have the 90 degree rating.
Furthermore , at 800 or more , you cant use " the next size up ". The ampacity must be allowed for 800 amps , and two 750's dont make it. I think it comes to 785 or something.
Copper should be used. 500 or 600 . I dont have the book handy.
Well in the usa you can use the 75/90 if its has a (-2 )read your code book note (4) table 310.13 and 750 alu 310.16 at 90 thwn-2 is rated for 435 a x2 =870 amps,next read article 240.4 ( b)device rated 800amps or LESS the next higher shall be permitted if the conductors do not correspond to standard breaker . DUAL RATED WIRE IS THE KEY POINT HERE and thats alu wire . Thats why they made dual rated wire to connect to a 75 deg brks since 90 deg brks are rare . and you can go up in brk size if you read that article in the nec code ,well i looked at the cec tables now Nap had a good point ,but could only fined 2002 tables and its almost the same ampacity as most of ours its fine . but were is the guy who posted this he can give us the correct amps since hes from canada what happened op? take care

Last edited by nick; 10-28-2008 at 06:08 AM. Reason: as cold as it is up there any wire would work it never gets to 30c
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Old 10-28-2008, 07:57 AM   #11
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I was thinking of the lug rating on the breaker being 75 dgree.
I guess 90 degree pin connectors might be acceptable to some .
i dont have my book here , but I thought it was less than 800 amps,then you can go to the next highest ocp. Being at 800, I thought you needed the 800 ampacity

Got to go and wire a house, later
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Old 10-28-2008, 04:54 PM   #12
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Default canada yearly temp

Well Ralph good issue , Nap had a good point both of you guys got me thinking ? lets look at it in another way , service feeder outside location canada its yearly temperature is below 70 deg.f and mostly lower than that lets say between 35 and 65 degs average year round , thats pretty cool and cold ambient . Lets use the NEC as to its intents meaning the main purpose fully! article 310.16 table 75 deg f column says 750 mcm = 385 amps ampacity , now go to the correction factors below 310.16 table multiply 385 x 1.05 % = 404.25 amps x 2 runs = 808.50 amps the boys up in Canada are fine both copper or alum. and dual rated wire if they have it they dont derate they uprate for yearly ambient temperatures but i dont like the cold so ill just stay down here in florida ? I looked up Canadas code tables for wire ampacity and its the same as we have and ieee charts pretty much the same . But its just my thinking i maybe out of line. comments take care best to ya

Last edited by nick; 10-28-2008 at 04:58 PM.
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Old 10-29-2008, 07:48 AM   #13
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Well Ralph good issue , Nap had a good point both of you guys got me thinking ? lets look at it in another way , service feeder outside location canada its yearly temperature is below 70 deg.f and mostly lower than that lets say between 35 and 65 degs average year round , thats pretty cool and cold ambient . Lets use the NEC as to its intents meaning the main purpose fully! article 310.16 table 75 deg f column says 750 mcm = 385 amps ampacity , now go to the correction factors below 310.16 table multiply 385 x 1.05 % = 404.25 amps x 2 runs = 808.50 amps the boys up in Canada are fine both copper or alum. and dual rated wire if they have it they dont derate they uprate for yearly ambient temperatures but i dont like the cold so ill just stay down here in florida ? I looked up Canadas code tables for wire ampacity and its the same as we have and ieee charts pretty much the same . But its just my thinking i maybe out of line. comments take care best to ya
Good point. I didnt think of the ground temp
I hate ground temp ( when its frozen ). Thats why im here in Savannah
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Old 06-12-2010, 09:44 PM   #14
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Question 600 amp panel with parallel feeds

i have a 600 amp panel with parallel feeds in two different runs of conduit.
one run of conduit has 3 500 kcmil and a 4/0 for ground.
second one has 3 3/0 thhn and a 1 awg for ground.
(IS THIS CODE) can you run different size wire on a parallel feed.
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Old 06-13-2010, 05:24 AM   #15
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Originally Posted by industrialboy View Post
i have a 600 amp panel with parallel feeds in two different runs of conduit.
one run of conduit has 3 500 kcmil and a 4/0 for ground.
second one has 3 3/0 thhn and a 1 awg for ground.
(IS THIS CODE) can you run different size wire on a parallel feed.

No


and this is a 2 year old thread.

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