Wire sizing calculation

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KnobnTube

KnobnTube

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I had a friend call from out west. He has a barn located 350 ft from the main highway. I ran several different calculators online and they all vary. Power company has OK'd for a 800 amp single phase service. Yes, single phase.
I am looking at what parallel runs of URD triplex will be needed.
Here is the cable specs. Which seem odd to me since it is USE-2 90 degree
I was thinking 3 sets- 400 mcm based on the table at 305 amps per

29310 WESLEYAN 350
Size 350 mcm
Neutral 4/0
Amps direct burial 415 amps
In ducts 320 amps
 
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I assume aluminum. ??350kcm alum is rated for 250 amps so depending on the calculated load you don't need to get 800 amps-- you could run 3 runs of 350kcm at 250 amps and get 750 amps. NOw to figure VD you need to know the load.
 
Dennis Alwon said:
I assume aluminum. ??350kcm alum is rated for 250 amps so depending on the calculated load you don't need to get 800 amps-- you could run 3 runs of 350kcm at 250 amps and get 750 amps. NOw to figure VD you need to know the load.
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That depends on the rating and number of Service Disconnecting Means. For a single disconnecting means, the overcurrent protection rating cannot exceed the ampacity of the [ungrounded] service conductors. If two to six disconnecting means, what you stated would be compliant under 230.90(A) Exception No 3.
 
Dennis Alwon said:
I assume aluminum. ??350kcm alum is rated for 250 amps so depending on the calculated load you don't need to get 800 amps-- you could run 3 runs of 350kcm at 250 amps and get 750 amps. NOw to figure VD you need to know the load.
Click to expand...

Well, in the beginning, he wont be using much because all the equipment is not there yet. So, I guess in the end, he could be looking at 500 amps or so when all completed.
Is there an online calculator that really works for voltage drop. I normally do small service stuff, max 400a.
What is someone just wants a service with no equipment? What would one do to determine the service? Maybe for the future?

It is one main disconnect at the service entrance from what he is thinking.

One more item.
Why does the cable company state that their 350 mcm aluminum URD cable is rated for 415 amps direct burial?
http://customcable.thomasnet.com/Asset/J-02.pdf
 
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Smart $ said:
That depends on the rating and number of Service Disconnecting Means. For a single disconnecting means, the overcurrent protection rating cannot exceed the ampacity of the [ungrounded] service conductors.
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What about 240.4(B)?
 
Smart $ said:
Doesn't apply to service conductors. See 240.3 and its Table.

Granted, OP did not state where the service is located... :rant:
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So you're saying in general that a single OCPD cannot be larger than the service conductor ampacity and that 240.4(B), next standard size up rule doesn't apply?
 
KnobnTube said:
... What is someone just wants a service with no equipment? What would one do to determine the service? Maybe for the future?
Click to expand...
Take a WAG (with load types and numbers to back it up). Then it's up to POCO and AHJ to permit it.

One more item.
Why does the cable company state that their 350 mcm aluminum URD cable is rated for 415 amps direct burial?
Click to expand...
That may well be its ampacity rating. But it doesn't consider adjustment and correction or terminal temperature limitations.
 
infinity said:
So you're saying in general that a single OCPD cannot be larger than the service conductor ampacity and that 240.4(B), next standard size up rule doesn't apply?
Click to expand...
Well that's what it was leading to... but in error. Please disregard. 230.90(A) Exception No. 2 says that 240.4(B) applies in conjunction with 240.6.
 
Ok, lets go with this.
Power transformer is at the highway. Power company said they will accommodate his 800 amp service.
Install cable from his barn (Not your usual barn,lol) to the transformer for connection. Power company making him supply this part, Dont ask, please,lol.
Cable to be URD underground to a service disconnect (single) at the barn
From there he will feed numerous disconnects , for future panels.
One 400 amp panel now.
Estimate probably 200 amp power used now.
Later additional 400 amp power used.
So total 600 amp of the 800 amp to be used for equipment etc.
240 volt, single phase
Service size conductors in URD is ????????????????
Thanks
 
I have never seen a residential service, I am assuming since it is single phase, that was 800 or 600 that did not have more than one disconnect. I have seen very few that have had one disco even at 400 amps. Much cheaper to install 2, 3 or 4 200 amp panels rather than a 400, 600 or 800 amp panel.
 
Can you get POCO to run primary underground to a closer point and install a padmount transformer? That is what I would try to do in most cases like this. 350 feet is getting close to killer distance when talking voltage drop for 120/240 single phase.

Some POCO here want you to install raceway and they will pull their primary through it. 1 2" is much easier to install than several 3 or 4 inch lines and is definately easier to pull the single HV cable than multiple 350's or larger.
 
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