Would 4 1/0 be same as 1 4/0?

Status
Not open for further replies.
G

Gounded

Member
Location
washington dc
I tried looking for an answer to this question, but couldn't find easily.

Somewhere I read that 4 1/0 might be better as far as current carrying capacity since it gives more surface area (so heat dissipation is better). But then, if you use this for, say ground conductor, and fault happens, will the integrity and strength of the ground conductor be same to withstand that fault? Since fault could travel any path, is it possible it only goes through the first conduct (1/0) and not the rest, thus damaging the conductor?
 
See NEC Table 8 for the properties of conductors - compare the cross sectional area of 4 - #1/0 vs 1 - #4/0.

BTW what is a "ground conductor"? (Engineers need to be a bit more precise)

Welcome to our community.
 
Gounded said:
I tried looking for an answer to this question, but couldn't find easily.

Somewhere I read that 4 1/0 might be better as far as current carrying capacity since it gives more surface area (so heat dissipation is better). But then, if you use this for, say ground conductor, and fault happens, will the integrity and strength of the ground conductor be same to withstand that fault? Since fault could travel any path, is it possible it only goes through the first conduct (1/0) and not the rest, thus damaging the conductor?
Click to expand...

4/0 is not 4 times larger than a 1/0. It is close to twice as large by cross sectional area.

Ability to curtail voltage drop is generally proportional to the KCMIL, but ampacity (a local factor that doesn't depend on length) is disproportionate. Small conductors have more ampacity per kcmil than their counterparts. So conductors in parallel, where allowable, allow you to have more ampacity for less conductive material.
 
Gounded said:
I tried looking for an answer to this question, but couldn't find easily.

Somewhere I read that 4 1/0 might be better as far as current carrying capacity since it gives more surface area (so heat dissipation is better). But then, if you use this for, say ground conductor, and fault happens, will the integrity and strength of the ground conductor be same to withstand that fault? Since fault could travel any path, is it possible it only goes through the first conduct (1/0) and not the rest, thus damaging the conductor?
Click to expand...

Do you mean the groundING conductor or the groundED conductor? The rules are different, depending.
 
Gounded said:
.. is it possible it only goes through the first conduct (1/0) and not the rest ... ?
Click to expand...
No. Current travels across all paths simultaneously, dividing proportionally to the impedance of each path. With four identical conductors, the impedances will be essentially identical and the current will divide equally.
 
drcampbell said:
No. Current travels across all paths simultaneously, dividing proportionally to the impedance of each path. With four identical conductors, the impedances will be essentially identical and the current will divide equally.
Click to expand...

But it seems to me that if there is a fault on one conductor near the supply end, the section of the faulted conductor between the supply and the fault will get a lot more of the fault current than the other conductors since the path through the others to the fault is a lot longer (all the way to the other end and back up the faulted conductor). Likewise, the other part of the faulted conductor is fed by all three of the others from the other end and gets more than the others as well. It looks to me like the single faulted conductor gets all the fault current - some of it from one end and the rest from the other.
 
ggunn said:
But it seems to me that if there is a fault on one conductor near the supply end, the section of the faulted conductor between the supply and the fault will get a lot more of the fault current than the other conductors since the path through the others to the fault is a lot longer (all the way to the other end and back up the faulted conductor). Likewise, the other part of the faulted conductor is fed by all three of the others from the other end and gets more than the others as well. It looks to me like the single faulted conductor gets all the fault current - some of it from one end and the rest from the other.
Click to expand...
Absolutely true for a fault directly affecting one of the parallel conductors rather than a fault at the load end of the cable.
There will be current (in a loop) on the other wires and the other end of the faulted wire, but that may be small in comparison.
The NEC just accepts that for a short or ground fault the single conductor will carry enough current for a magnetic trip and will not be damaged.
Of greater concern for current sharing would be an overload in the thermal range of the breaker. And that will almost always be on the load side of the parallel set.
 
Checked the table, thanks.

I meant grounding conductor in a general sense, but I was thinking about a temporary grounding conductor that we use in a distribution/transmission substation. It could even be the grounding conductor used in a ground grid in a substation.
 
ggunn said:
Yes, but the effect is frequency dependent. At 60Hz it doesn't do much.
Click to expand...

A more complete statement would be that is does not do much except for very large conductors.
Look at where the AC impedance starts to differ noticeably from the DC impedance in the NEC tables.
 
GoldDigger said:
A more complete statement would be that is does not do much except for very large conductors.
Look at where the AC impedance starts to differ noticeably from the DC impedance in the NEC tables.
Click to expand...
Well, even with huge conductors the effect at much higher frequencies would be very much greater. In those terms, it still doesn't do much. :D
 
ggunn said:
Yes, but the effect is frequency dependent. At 60Hz it doesn't do much.
Click to expand...


Does the stranding pattern make a difference as well? For instance, if you compare standard class C wiring and fine stranded DLO wiring in the same size and conductive material, and same frequency, which one would you expect to have a greater AC resistance
 
Carultch said:
Does the stranding pattern make a difference as well? For instance, if you compare standard class C wiring and fine stranded DLO wiring in the same size and conductive material, and same frequency, which one would you expect to have a greater AC resistance
Click to expand...

At first glance, without looking at the result of magnetic field from adjacent strands in addition to the field of the current in that strand itself, I would say that the fine stranding would have a lower skin effect multiplier for any given frequency.
That is part of the motivation behind using stranded conductors (and, in fact, flat braid rather than round bundles) for lightning protection down conductors.
But a second look, taking into account that the strands are both touching each other, allowing loop currents in the cross section plane of the wire, and always in the same orientation within the bundle the benefit is greatly reduced and the stranded wire has a comparable skin effect penalty.

This skin effect in stranded wires, very significant at higher frequencies even in small wires, has led to some elaborate weaving patterns of individually insulated strands, known as Litz wire.
 
Status
Not open for further replies.
Top