Length of Conductor

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Mike01

Mike01

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If I install a grounding conductor on the outside of conduit according to article 3003..b.2 it cannot exceed more than 6?-0? is that correct. What about when you ground a transformer to building steel can that exceed more than 6?-0? because it is not installed with circuit conductors?
 
First you have to figure out what kind of "ground" we are talking about.
Is it an EGC ~ Equipment Grounding Conductor
Is it an GEC ~ Grounding Electrode Conductor
 
electrode

electrode

grounding electrode conductor from a panel to the derived system of the upstream drytype transformer.
 
An external bonding jumper has a higher impedance than an internal bonding jumper, but by limiting the length of the bonding jumper to 6 ft and routing it with the raceway, the increase in the impedance of the equipment grounding circuit is insignificant. (from the commentary following 250.102(E) )
 
GEC's can be longer than 6' and may not require protection if run along the surface of the building construction. Look at 250.64(B)
 
Mike01 said:
If I install a grounding conductor on the outside of conduit according to article 3003..b.2 it cannot exceed more than 6?-0? is that correct. What about when you ground a transformer to building steel can that exceed more than 6?-0? because it is not installed with circuit conductors?
Click to expand...


300.3(B)(2) is referening to an equipment ground conductor or a equipment bonding Jumper. The connection between the transformer XO and building steel is an grounding electrode conductor which does not have a specific length however it is too be connect to the closest building steel
 
Rich Elec. said:
Celtic,
Why does an external equip. bonding jumper have a higher impedance than an internal?
Click to expand...

Here's the entire commentary following 250.102(E):
In many applications, equipment bonding jumpers must be installed on the outside of metal raceways and enclosures. For example, it would be impractical to install the bonding jumper for a conduit expansion joint on the inside of the conduit. For some metal raceway and rigid conduit systems and conduit systems in hazardous (classified) locations, installing the bonding jumper where it is visible and accessible for inspection and maintenance is desirable. An external bonding jumper has a higher impedance than an internal bonding jumper, but by limiting the length of the bonding jumper to 6 ft and routing it with the raceway, the increase in the impedance of the equipment grounding circuit is insignificant. Exhibit 250.43 illustrates a bonding jumper run outside a length of flexible metal conduit. Because the function of a bonding jumper is readily apparent, color identification is not necessary.
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(NOTE: Exhibit 250.43 just shows a motor and disco w/a#10 6' external bonding jumper)

That goes back to 300.3(B)....here's the commentary following that article:
This general rule remains consistent with electrical theory; that is, to reduce inductive heating and to avoid increases in overall circuit impedance, all circuit conductors of an individual circuit must be grouped. Similar requirements are found in 300.5(I).
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The "general rule" (300.3(B) ) being ~
All conductors of the same circuit... shall be contained within the same raceway..
unless otherwise permitted in accordance with 300.3(B)(1) through (4).


If your asking me to do the math on a #10 60' long run externally vs. a #10 60' long run internally...that'll take a little more time ;)
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