buck boost
Silver Member
Since to original topic has faded... who cares! Keep discussing....
:laughing:
Here's another example:
When we bought our house, the power went pole to meter to main panel. The neutral and ground were bonded in the main panel.
The next year we had the house resided and moved the meter to a different side of the house. This made the length of the run from the meter to the main panel more than X feet (I don't remember the exact distance code states), so we had to put in a service disconnect below the meter and move the neutral/ground bond to that service disconnect box. The service disconnect is now considered the main panel, as it is now the first panel after the meter. Any panel after that would now be considered a sub-panel, and the neutral and ground has to be isolated in any sub panel. So the original main panel became a sub-panel. See the diagram below. I posted this in another wiring discussion a couple days ago. Its the schematic of my house...
^^ A very good diagram there Sir!
The meter socket to the primary disconnecting means is a local utility code (not NEC), where I'm at it has to be six ft or less for a non-disconnecting meter socket.
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Metal underground water pipe is permitted for use as a grounding electrode as long as it has 10' or more in contact with the earth and is electrically continuous. The NEC also states, that if it is present, it SHALL be used.
It also requires one [ground] rod 5/8" x 8' for a grounding electrode.
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It is common practice now to also install a concrete encased electrode on new installations.
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The only place the neutral (grounded) conductor should be bonded to the grounding wire (bare or green wire) is at the main disconnecting means. Think primary panel in a house, or Main Switch Board in a commercial/industrial structure. This tie is referred to by the NEC as the MBJ or main bonding jumper. There are a few exceptions in the code, and the most common would be if the structure had a separately derived system (think a step up or step down transformer). An example of that would be a 277v/480v Y system to a 120v/208v Y system done with a step down transformer.
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Article 250.32 of the 2005 NEC (I have a newer code book, it is not accessible at the moment)
building or structure supplied by a branch circuit, shall have a grounding electrode or grounding electrode system.
That means, if one were to add a sub panel to a garage, it requires a ground rod to be bonded to the ground at the sub panel. There are other methods instead of ground rod, but that is probably the easiest and cheapest.
The neutral is not to be bonded to the ground at a sub panel.
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As far as voltage drop should be figured, there is an easy formula (copper conductors only):
(2*K*I*L)/Acm=VD
K=12.9
I=current in amperes
L=distance of branch circuit in feet
Acm=area of circular mills
VD=volatge drop in volts
Example: I want a 240v 100 amp sub panel in my garage. I need three cuts of 135' of wire, termination to termination. Voltage drop not to exceed 3% as recommend by the NEC. 120/240v 3 wire, single phase service.
What is the appropriate wire size?
2*12.9*100*135 all divided by 7.2
That gives me 48,375. That is the wire size I need in circular mill area to not exceed my 3% voltage drop.
#4AWG has a circular mill area 41,740. Too small. #3AWG 52,620 for the two hots and neutral. And a #8 AWG is sufficient for an a equipment ground. Perfect.
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If anyone has any code or load calc or general electrical question, I would be happy to try to help. Probably best to shoot me a PM.
Cheers!