parallel conductors AC and DC

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69gp

Senior Member
Location
MA
hi Just a couple questions on some parallel conductors for both AC and DC. This is from a project that I was recently on.


First of all I know that for parallel conductors the cable needs to me the following.

[FONT=Georgia, Times, Times New Roman, serif]- Be the same length.[/FONT]
- Have the same conductor material.
- Be the same size in circular mil area.
- Have the same insulation type.
- Be terminated in the same manner.
[FONT=Georgia, Times, Times New Roman, serif]- Have the same physical characteristics, where run in separate raceways or cables.[/FONT]

[FONT=Georgia, Times, Times New Roman, serif]My question on the AC parallel conductors is the following. I have 4 sets of 250 MCM Aluminum and only 3 conduits can 2 sets be installed in 1 conduit and 1 set in the other conduits or is this a violation? There is a 800 amp breaker protecting the circuit.[/FONT]

On the DC parallel conductors I was under the impression that we follow the same as AC.

The picture below shows 2 different terminations techniques for Parallel DC Conductors. First of all you have 750 MCM ALUM with a piece of 4/0 Copper type MTW/ THHW spliced via a split lug and then the wire is terminated to the lug. This is a fine cable, almost a welding type cable. The other method of termination is a 750 MCM Aluminum wire that has a solid offset pin that is terminated under a lug. Does this meet the code?

The way I see it this is a code violation. but I am being told that it is a good install.

IMG_20140906_103553983.jpg
 

GoldDigger

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Retired PV System Designer
I would be inclined to say that two sets in one raceway would be OK provided that no derating is applicable to the wires in the double set.
If derating is required just for the double set, or for both double and single with different percentages, I would call the two types of path different.
Putting two sets in each of two raceways, for a total of four, on the other hand, seems fine to me.
 

iwire

Moderator
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Location
Massachusetts
My question on the AC parallel conductors is the following. I have 4 sets of 250 MCM Aluminum and only 3 conduits can 2 sets be installed in 1 conduit and 1 set in the other conduits or is this a violation?

In my opinion that is a violation.

Having different numbers of conductors in each conduit means they do not have the same characteristics.


you have 750 MCM ALUM with a piece of 4/0 Copper type MTW/ THHW spliced via a split lug and then the wire is terminated to the lug. This is a fine cable, almost a welding type cable.

There may be other issues but I doubt those terminals in the equipment are rated for fine stand cable, and then there is the question if the split bolt is rated for fine strand and copper to aluminum.


The other method of termination is a 750 MCM Aluminum wire that has a solid offset pin that is terminated under a lug. Does this meet the code?

Again hard to see but a pin adapter could be fine.
 

69gp

Senior Member
Location
MA
thanks for your replies.

the picture below is of the 4 sets of conductors in 3 conduits. the Front conduit is the one that has the 2 sets.

also I forgot to mention the lack of a ground in the conduits. not sure how that plays into it all

IMG_20140906_102948013.jpg
 

GoldDigger

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Location
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Occupation
Retired PV System Designer
If you are using the raceway as the EGC, that is one more asymmetry between the set of two and the single sets, in terms of the ratio of CCC to EGC size.
 

jumper

Senior Member
Here is the code section of the violation that is referred to above regarding unequal distribution of the paralleled conductors in the conduits:

310.10(H)(3) Separate Cables or Raceways. Where run in separate
cables or raceways, the cables or raceways with conductors
shall have the same number of conductors
and shall have the
same electrical characteristics. Conductors of one phase, polarity,
neutral, grounded circuit conductor, or equipment
grounding conductor shall not be required to have the same
physical characteristics as those of another phase, polarity,
neutral, grounded circuit conductor, or equipment grounding
conductor.
 
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