300.20 violation

[yesterlectric]

Panelboards at times only have 1 neutral bar on one side. So if the rule were applied too literally, nothing would be acceptable. I think an understanding of the reason for the rules might help. 300.20 deals with the fact that an imbalance of current in a metal raceway or enclosure can cause heating, and can thus present a fire hazard. Other sections (300.3B, 376.20, 392.20C&D just to name a few) have to do with concerns over the increased reactance that is present when conductors of the same circuit are separated over a long distance, and the increased risk of overcurrent protective devices not functioning properly as a result.

Sometimes, it's easy to find a bunch of similar NEC sections, and think they are all trying to mitigate the same risk. Despite similar wording about grouping, 300.20 is there to deal with a different risk than what 300.3B (and other sections) are intended to deal with.

300.20 is one of the NEC sections that tells you the goal of the rule: it is to avoid heating.
300.3B does not have anything stating the goal of the rule. You (hopefully) are taught the goal of the rule in trade school.

If there is a revision to the NEC to reduce the possibility of improper interpretation of 300.20, perhaps the real solution would be to add a statement to 300.3B, so that it states that the conductors shall be grouped so as to reduce circuit impedance and facilitate overcurrent protective devices. Then, it could go on with its language about grouping in the same tray, conduit, trench, etc. In certain cases I think NEC rules could be better implemented if the code stated its intent more often, because otherwise we get requests to pepper it with all kinds of exceptions and clarifications that may cause more confusion when applied to even further unanticipated questions that arise in the real world.

Hope I'm not called out by one of the better experts here as wrong............

 

[kwired]

Panelboards at times only have 1 neutral bar on one side. So if the rule were applied too literally, nothing would be acceptable. I think an understanding of the reason for the rules might help. 300.20 deals with the fact that an imbalance of current in a metal raceway or enclosure can cause heating, and can thus present a fire hazard. Other sections (300.3B, 376.20, 392.20C&D just to name a few) have to do with concerns over the increased reactance that is present when conductors of the same circuit are separated over a long distance, and the increased risk of overcurrent protective devices not functioning properly as a result.

Sometimes, it's easy to find a bunch of similar NEC sections, and think they are all trying to mitigate the same risk. Despite similar wording about grouping, 300.20 is there to deal with a different risk than what 300.3B (and other sections) are intended to deal with.

300.20 is one of the NEC sections that tells you the goal of the rule: it is to avoid heating.
300.3B does not have anything stating the goal of the rule. You (hopefully) are taught the goal of the rule in trade school.

If there is a revision to the NEC to reduce the possibility of improper interpretation of 300.20, perhaps the real solution would be to add a statement to 300.3B, so that it states that the conductors shall be grouped so as to reduce circuit impedance and facilitate overcurrent protective devices. Then, it could go on with its language about grouping in the same tray, conduit, trench, etc. In certain cases I think NEC rules could be better implemented if the code stated its intent more often, because otherwise we get requests to pepper it with all kinds of exceptions and clarifications that may cause more confusion when applied to even further unanticipated questions that arise in the real world.

Hope I'm not called out by one of the better experts here as wrong............

Or on the opposite end, not so much with typical "loadcenters" but I have seen several old switchboards with the main conductors feeding the top end and the neutral bus being on the bottom end. But if you think about it if you were able to clamp ammeter around all the current carrying components at any cross section you probably still have net zero nearly all the time.