Interesting 2 Section Panel connection

[JAC]

The EC wired two 400 amp panels as shown on Method 1 of the attached drawing. One 400 amp breaker feeds the parallel runs of 3/0 conductors and then one set of 3/0 conductors connects the two sections together. The EC claims this effectively provides two parallel 3/0 paths from either section, however general consensus is that it doesn't meet "Code". After examining the picture, does anyone know exactly what part of the Code would be in question here? Method 2 of the drawing shows what we believe to be the proper connection method.

 

[petersonra]

It looks safe to me. Whether it is code or not is another question.

Without thinking a lot about it, I vote "OK".

<added> I looked at 310.4 and came to the conclusion there is no code violation, at least from that section.

 

[iwire]

IMO it does violate 310.4

part of 310.4

Where run in separate raceways or cables, the raceways or cables shall have the same physical characteristics.

The fact that both raceways do not enter the same enclosure means the raceways (IMO) do not have the same characteristics.

 

[infinity]

Method 1 is a violation. The two sets of feeders are really one set of parallel conductors. They must terminate at the same point as illustrated in method 2.

 

[tshea]

I vote for #2

Violation 310.4

 

[petersonra]

Method 1 is a violation. The two sets of feeders are really one set of parallel conductors. They must terminate at the same point as illustrated in method 2.

I thought about that. Does it actually say they have to terminate at the same point, or only that they have to be electrically connected at both ends? How that connection is made is not specified.

There is something I don't like about this arrangement but I am not sure it is a violation.

 

[petersonra]

IMO it does violate 310.4

part of 310.4

Where run in separate raceways or cables, the raceways or cables shall have the same physical characteristics.

The fact that both raceways do not enter the same enclosure means the raceways (IMO) do not have the same characteristics.

The raceways themselves have the same characteristics. The PB is not a raceway. IMO, the requirement regarding the raceways stops at the point they enter the panelboards. I still don't especially like it.

 

[infinity]

310.4 Exception no. 4 (5) states that they must "be terminated in the same manner". It seems that this would not include terminations in two different panelboards. Also, if one panelboard had a large load and the other had no load the effective length of the two sets of conductors would be different, which would cause one set to carry more current than the other.

 

[benaround]

Also the #4 EGC is not the proper size for a 400a, it should be #3 using

250.122, it appears that 250.66 was used (gec).

Code says conductors must be rated for the load, this setup is would only

be safe if a 200a main breaker was installed and those "jumpers" were

removed. imo

 

[petersonra]

310.4 Exception no. 4 (5) states that they must "be terminated in the same manner". It seems that this would not include terminations in two different panelboards. Also, if one panelboard had a large load and the other had no load the effective length of the two sets of conductors would be different, which would cause one set to carry more current than the other.

An argument can be made that "in the same manner" does not mean "in the same enclosure".

The two sets of conductors are tied together across the bus so I do not buy that there is an issue with "effective length". Besides, the code does not say anything about 'effective length".

 

[izak]

that setup is ridiculous
i vote that whoever thought of that method Overloaded his CRACK PIPE that day and needs to get some sleep and come back and do it right

 

[don_resqcapt19]

izak,

that setup is ridiculous

Why do you say that? I see no electrical or safety problem with the installation. The termination of the two sets of parallel conductors in different panels may result in violations of 310.4(1) and (5). Even if there is a technical violation of the rules, I don't really see an issue with the installation from a safety or performance viewpoint.
Don

 

[infinity]

I agree with Don that this appears to be a technical violation of 1 & 5, but Bob does bring up an interesting point. Neither of those sections is explicit in prohibiting this installation. IMO the use of parallel conductors is to use multiple smaller conductors in place of one large conductor therefore they should terminate at the same point. I will agree, as Bob has said, that the wording of this section makes that argument somewhat weak.

 

[petersonra]

izak,

that setup is ridiculous

Why do you say that? I see no electrical or safety problem with the installation. The termination of the two sets of parallel conductors in different panels may result in violations of 310.4(1) and (5). Even if there is a technical violation of the rules, I don't really see an issue with the installation from a safety or performance viewpoint.
Don

I still am not completely convinced I like this installation, but I don't see a violation of either 310.4(1) or (5).

(1) Be the same length

For the sake of discussion let us assume the conductors are the same length, since no one said they were not, and we have no way of knowing since the OP did not state that.

(5) Be terminated in the same manner

I just don't see that at all. They are clearly terminated the same. One could argue they are not terminated the same at both ends, but I am not sure that is what the code means. It just does not seem to cover this type of situation.

I don't see any clear code violation. If one wanted to ding this installation, I think (5) is the best shot at it, but after reading it over any number of times, I just can't convince myself it is a violation. i certainly see no hazard.

 

[infinity]

(1) Be the same length

For the sake of discussion let us assume the conductors are the same length, since no one said they were not, and we have no way of knowing since the OP did not state that.

Having installed many sets of parallel feeders I can honestly say that they almost never the same length. When you have a rack of conduits snaking through a building almost invariably the conduits will end up having different lengths. Depending on how the conductors are terminated within a switchboard, panelboard, etc., the physical conductor length can vary by several feet.

 

[don_resqcapt19]

Bob,
I said may because I can't see the installation. However, I don't think that there has ever been an installation in the history of the NEC that was in compliance with 310.4(1) as written. The section requires equal length without any tolerance.
If the panels are identical, then you should be able to comply with 310.4(5)
Don

 

[hardworkingstiff]

[quote="infinity] Depending on how the conductors are terminated within a switchboard, panelboard, etc., the physical conductor length can vary by several feet.[/quote]

Depending on the length of run, several feet could be an issue.

 

[infinity]

[quote="infinity] Depending on how the conductors are terminated within a switchboard, panelboard, etc., the physical conductor length can vary by several feet.

Depending on the length of run, several feet could be an issue.[/quote]


Although this may be true, it is a real word issue. Large racks of parallel conduits will almost always have conductors of different lengths.

 

[petersonra]

[quote="infinity] Depending on how the conductors are terminated within a switchboard, panelboard, etc., the physical conductor length can vary by several feet.

Depending on the length of run, several feet could be an issue.

Although this may be true, it is a real word issue. Large racks of parallel conduits will almost always have conductors of different lengths.

I suspect that most such installations are not exactly the same length. Hopefully the installing electrician understands the issues well enough that he/she keeps the lengths close enough so as to not overload one of the conductors.

This is one of those provisions that probably should have some kind of clarification as to intent like:

Parallel conductors shall be the same length. For purposes of this section, parallel conductors shall be deemed to be the same length if the lengths of the parallel conductors do not vary in excess of 1% between the shortest and longest conductor, but in no case to exceed 5 feet.

 

[izak]

look, i apologize for voicing my disagreement with the installation in such a negative way.

however, that is not something that i have ever seen, or thought of doing (in my limited experience), and something even more interesting is that NO-ONE on this board has come out and said, "Oh yeah, we do that all the time" or, "oh yeah ive seen that before, and they did it that way because of this or whatever"

the point is, in my opinion, code compliant or not, that installation makes NO sense what so ever

thats just my opinion tho