Minimum size wire for loop wiring

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Npstewart

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I work for an engineering firm in Florida. Im designing a RV park, approximately 120 Sites total over (3) buildings.

The NEC has specific requirements for these parks per Article 551 (Revised in NEC 2008). Each Site with a 30A receptacle is REQUIRED to be calculated as 3600VA/Site. I am dropping distribution panels evenly spread out for voltage drop purposes, and each distribution panel will have 12 sites, the distribution panels will be 200A each with (2) 125A breakers feeding a group of 6 sites, (2) breakers total.

I found a charging station for RV''s made by Midwestern electric, and are capable of being loop fed. My REAL question is for this entire post, is for each group (6 sites) if I am loop feeding with a 125A breaker, I know I need to use (2) #1 (1) #6eg, but do I need to carry that through out the entire loop system? That wouldnt make sense because at my last site I would be feeding a 30A site with #1's when I only need #10's.

(OR) :confused::confused:

Should I Start at the beginning of the loop with #1's and decrease the wire size as I move past each site (subtracting 3600 watts) ea time.

PS> The voltage here is 240V-1 phase
PSS> Wire sizes above are assuming less then 3% VD.
PSSS> Any other suggestions on designing this would be greatly appreciated.!
 
raider1

raider1

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Welcome to the forum.:)

The wire must be protected by an overcurrent protective device that is sized to protect the wire. So if the breaker protecting these feeders is 125 amps you can't down size the wire below the #1 or #2 copper provided that the calculated load does not exceed 115 amps.

Chris
 
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Npstewart

Senior Member
Thanks for the quick response radier1!

Your reply makes a lot of sense, I just wanted to mention one other thing. Each "Site" is protected by a 30A breaker. So basically, at the last site down the line, it would be impossible for someone to plug in and use more then 30A or the breaker flip.

So to recap, the 125A breaker is feeding (6) 30A "Sites" that is protected by a 30A breaker, and each site is fed from the last site (loop fed).
 
don_resqcapt19

don_resqcapt19

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Electron_Sam78 said:
technically the pedestals are tapping off the feeders coming from your distribution panels so tap rules would apply to the whole run
Click to expand...
The only part that is a tap is the bus from the double lugs to the 30 amp breaker, with the exception of the conductors to the last pedestal from the previous one...the rest is a feeder.
 
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Npstewart

Senior Member
OK so just so just to recap. , the tap rules apply to this installation, and specifically NEC 2008 210.19 A.2. "Multi outlet branch circuits",

conductors of branch circuits supplying more than one receptacle for cord and plug connected portable loads shall have an ampacity of not less than the rating of the branch circuit

I suppose you guys are right, the only thing that was confusing me was that the 30A breaker at the pedestal... I will size the entire run with #1's for the 125A branch circuit all the way through. Thanks for your help guys!!!:)
 
augie47

augie47

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raider1 said:
Welcome to the forum.:)

The wire must be protected by an overcurrent protective device that is sized to protect the wire. So if the breaker protecting these feeders is 125 amps you can't down size the wire below the #1 or #2 copper provided that the calculated load does not exceed 115 amps.

Chris
Click to expand...

Chris, No one has ever asked and I never thought of it untill this thread, but could one not use 240.21(B)(5) for the last pedestal. (AHJ as to USE being "protected from physical damage")
 
jwjrw

jwjrw

Senior Member
Seems like it says so but I dont know if anything in 551 or anywhere else would prevent it as long as you meet the 4 requirements.
 
Electron_Sam78

Electron_Sam78

Senior Member
Location
Palm Bay, FL
by the way jwjrw how long are the runs going to be? We have some 1150+ ft. runs in our parks. The other day I just traced and wheeled out a couple that were over 1600 ft. Those are way too long and I wrote up a scope of work to have the distribution panel relocated to a more central location. As it is now the panel is over 600 feet away from the first pedestal on the closest circuit.
 
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stew

Senior Member
Location
federal way,washington
why do you feel that the pedastels need ground rods? I have never been required to install one on a looped pedastel system. I have done 4 of these type installs and the pedastels have never been require to have rods.
 
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winnie

Senior Member
Location
Springfield, MA, USA
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Electric motor research
I know that the general understanding of tap rules is that you 'cannot have a tap of a tap'.

Why not?

As long as the _total_ conductor length from the first point of conductors being undersized to the fed OCPD is less than the length restrictions, and as long as the ampacity of the smallest conductor meets the requirements relative to the feeding OCPD, then why can you not have multiple smaller conductor sizes 'in series'.

As applied to the original post, what rule says that you cannot start reducing the conductor sizes right after the first pedestal, as long as the conductors are large enough for the load served?

-Jon
 
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stew

Senior Member
Location
federal way,washington
I do not feel that the pedastels are "built or constructed" and nethier have the inspectors which have inspected my projects. your thread specifically concerns buildings and structures which thes pedastels are clearly not. Yes the are manufactured and installed but constructed? Not in my most humble opinion. O f course the panel feeding these pedastels where installed would require ground rods.
 
don_resqcapt19

don_resqcapt19

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Location
Illinois
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retired electrician
winnie said:
I know that the general understanding of tap rules is that you 'cannot have a tap of a tap'.

Why not?
Click to expand...
The tap rules provide for the use of conductors that are not protected at their amapcity. A tap of a tap would result in a smaller conductor being protected by an OCPD larger than what is permitted by the tap rules.

As long as the _total_ conductor length from the first point of conductors being undersized to the fed OCPD is less than the length restrictions, and as long as the ampacity of the smallest conductor meets the requirements relative to the feeding OCPD, then why can you not have multiple smaller conductor sizes 'in series'.
As applied to the original post, what rule says that you cannot start reducing the conductor sizes right after the first pedestal, as long as the conductors are large enough for the load served?
Click to expand...
You can start reducing as soon as you want as long as the smaller wire is still protected at or below its ampacity. In this installation the only parts of the circuit that meet the tap rules in the connection between the supply lugs and the breaker in each pedestal and, maybe, the feeder conductor to the last pedestal.
 
L

lostinspace

Member
Location
Florida
Volta said:
They are a structure.
Click to expand...

if you mounted a subpanel on a post at each location would you consider this a "structure" and also install ground rods. the pedestal is essentially a subpanel mounted to the ground, it will have an egc looped through them all, i don't see a reason for ground rods.

from the original post, watch the voltage drop, around here the parks will be at max capacity on holiday weekends and stress the system, i've had to install new feeders more than once in these that weren't sized correctly
 
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