300.20 Gone Wild

infinity

Moderator
Staff member
Location
New Jersey
I recently had someone tell me that they've been told that it's an NEC requirement to keep the conductors of a multi-conductor cable (like MC) twisted together within a panel because of 300.20. Please stop the insanity. BTW I hate the wording of this section. :eek:hmy:

Has anyone else heard of people enforcing this?

300.20 Induced Currents in Ferrous Metal Enclosures
or Ferrous Metal Raceways.
(A) Conductors Grouped Together. Where conductors
carrying alternating current are installed in ferrous metal
enclosures or ferrous metal raceways, they shall be ar-
ranged so as to avoid heating the surrounding ferrous metal
by induction. To accomplish this, all phase conductors and,
where used, the grounded conductor and all equipment
grounding conductors shall be grouped together.
Exception No. 1: Equipment grounding conductors for
certain existing installations shall be permitted to be in-
stalled separate from their associated circuit conductors
where run in accordance with the provisions of 250.130(C).
Exception No. 2: A single conductor shall be permitted to
be installed in a ferromagnetic enclosure and used for skin-
effect heating in accordance with the provisions of 426.42
and 427.47.
 

jusme123

Senior Member
Location
NY
...guess they have to start locating the ground and neutral terminations next to each breaker than...:blink:
 
There is never a time when someone, somewhere won't come up with a wacko way to make the code say something that is at odds with common sense.

Here is the part that I thought might lead to the justification to keep the conductors of a multi-conductor cable twisted together within a panel
To accomplish this, all phase conductors and,
where used, the grounded conductor and all equipment
grounding conductors shall be grouped together.
The conductors have to go where they need to go in the panel. The conductors are still grouped in the same panel. Just because they are not touching each other doesn't mean they are not grouped.

As long as the kids all come into the room through the same door why make them keep holding hands? And is there really any hope that you can force them to?
 

infinity

Moderator
Staff member
Location
New Jersey
There is never a time when someone, somewhere won't come up with a wacko way to make the code say something that is at odds with common sense.

Here is the part that I thought might lead to the justification to keep the conductors of a multi-conductor cable twisted together within a panel

The conductors have to go where they need to go in the panel. The conductors are still grouped in the same panel. Just because they are not touching each other doesn't mean they are not grouped.

As long as the kids all come into the room through the same door why make them keep holding hands? And is there really any hope that you can force them to?
I guess that we now need a clear definition of grouped. But even so if the conductors are in a cable we're being told to leave them twisted together, if they're in a raceway then it's not required. BTW this came from a few different sources including an apprentice school teacher.

Will anyone take a shot at defining the word grouped as used in the section ActionDave posted?
 

romex jockey

Senior Member
Location
Vermont
Will anyone take a shot at defining the word grouped as used in the section ActionDave posted?
It has to make sense in the electrical arena Mr Infinity , a copy/paste of some definitional analogy onto 300.20 does it no justice.

Ergo, the electric math, theory & measurement(s) become relevant......

So gentlemen, may i suggest you rev up your gauss meters ..:lol:

~RJ~
 

Fulthrotl

~~Please excuse the mess. Sig under construction~~
I recently had someone tell me that they've been told that it's an NEC requirement to keep the conductors of a multi-conductor cable (like MC) twisted together within a panel because of 300.20. Please stop the insanity. BTW I hate the wording of this section. :eek:hmy:

Has anyone else heard of people enforcing this?
well, no.... but it probably started with a networking guy who
got a job as an inspector, and all he knows about this stuff is
that you have to keep the cat 6E cable pairs twisted all the way to
punch down, to prevent NEXT....

if someone tells me that i cannot lace up a panel neatly,
and must leave it looking like a piece of chit, which this would,
then i will simply retire with my BS filter clogged. i'm done.
 

mgookin

Senior Member
Location
Fort Myers, FL
I guess that we now need a clear definition of grouped. But even so if the conductors are in a cable we're being told to leave them twisted together, if they're in a raceway then it's not required. BTW this came from a few different sources including an apprentice school teacher.

Will anyone take a shot at defining the word grouped as used in the section ActionDave posted?
To know what it means it helps to know what it doesn't mean.

On first reading I interpreted that article to mean that you don't run one pipe with all hots and another pipe with all neutrals. Same with panels & boxes; you don't have all your hots in an undersized panel and another box to join all your neutrals. Else the pipe or boxes would be unbalanced causing the heat they are intending to mitigate.

The word twisted does not appear in the article.
 
I guess that we now need a clear definition of grouped. But even so if the conductors are in a cable we're being told to leave them twisted together, if they're in a raceway then it's not required. BTW this came from a few different sources including an apprentice school teacher.

Will anyone take a shot at defining the word grouped as used in the section ActionDave posted?
I'm staying with Grouped means what I said, in the same room i.e. the same panel, same cable, same raceway. Like mgookin said, grouped in no way means twisted. You can be grouped in the same room and not have to be touching shoulders.
 

al hildenbrand

Senior Member
Location
Minnesota
I recently had someone tell me that they've been told that it's an NEC requirement to keep the conductors of a multi-conductor cable (like MC) twisted together within a panel because of 300.20. Please stop the insanity. BTW I hate the wording of this section. :eek:hmy:

Has anyone else heard of people enforcing this?
I have only experienced this kind of mania with X-Ray technicians, "high end" stereo installers and electrical engineers. Never with an AHJ or a local inspector.

I guess that we now need a clear definition of grouped. But even so if the conductors are in a cable we're being told to leave them twisted together, if they're in a raceway then it's not required. BTW this came from a few different sources including an apprentice school teacher.

Will anyone take a shot at defining the word grouped as used in the section ActionDave posted?
I'm not sure that "grouped" is directly related, as a stand alone term, to the heart of this passage. My emphasis on the text below is intended to show what I think is already there.

300.20 Induced Currents in Ferrous Metal Enclosures or Ferrous Metal Raceways.

(A) Conductors Grouped Together.
Where conductors carrying alternating current are installed in ferrous metal enclosures or ferrous metal raceways, they shall be arranged so as to avoid heating the surrounding ferrous metal by induction. To accomplish this, all phase conductors and, where used, the grounded conductor and all equipment grounding conductors shall be grouped together.
Exception No. 1: Equipment grounding conductors for certain existing installations shall be permitted to be installed separate from their associated circuit conductors where run in accordance with the provisions of 250.130(C).
Exception No. 2: A single conductor shall be permitted to be installed in a ferromagnetic enclosure and used for skin-effect heating in accordance with the provisions of 426.42 and 427.47.
Understanding induced currents (their direction and magnitude) requires a certainty of the instantaneous results of the generator principle. Only magnetic field, moving relative to the ferrous enclosure or raceway, is active in generating the current in the conductive paths of the ferrous material.

And, once created, the "eddy current" is affected by the resistance of its path in the ferrous material, so orientation of the magnetic field originating current relative to the plain of the ferrous construct greatly influences the density of the induced current and the subsequent I squared R heat creation.

The reality of that sentence is not for the beginner theorist. And, in my opinion, it is the person who thinks they get "magnetic field induced current" who sees them as everywhere. They aren't. Orientation of causal current and ferrous material is everything.

To me, being confronted by someone making such a Code claim, a common sense "poser" rebuttal question would be, why are many, if not most, NM cable conductors from manufacturers UN-twisted. All two conductor with ground NM cables are untwisted, UF and some NM three conductor with ground are untwisted. If this were a manufacturer affectation that gave rise to induced current heating of surrounding ferrous metal, the Code would instruct us to twist the conductors together.

The Code is silent about "twisting" or "untwisting" or "not twisted."
 

al hildenbrand

Senior Member
Location
Minnesota
300.20 Induced Currents in Ferrous Metal Enclosures or Ferrous Metal Raceways.

(A) Conductors Grouped Together.
Where conductors carrying alternating current are installed in ferrous metal enclosures or ferrous metal raceways, they shall be arranged so as to avoid heating the surrounding ferrous metal by induction. To accomplish this, all phase conductors and, where used, the grounded conductor and all equipment grounding conductors shall be grouped together.
The second sentence of (A), beginning with "To accomplish this," is referring, in whole, to "conductors. . . shall be arranged to as to avoid heating the surrounding ferrous metal by induction." Given the complexity of the causal magnetic field and the orientation of the induced current in the ferrous material, I submit that:

Grouped conductors = conductors arranged to avoid heating the surrounding ferrous metal by induction.

Avoiding defining, as a physical twisting or grouping, permits the continued use of cut slots between the individual entry holes for wiring methods such as K&T that require one conductor per hole.
 

brnring

New User
Location
US
If i remember correctly it says multiwire branch circuits have to be tied together in panel,,,,Unless otherwise obvious or something like this....if it is a 3 wire coming into the panel, thats pretty obvious to me....Never have been called on this. As long as it is hooked up to a proper 2 pull breaker!

Sent from my SM-G900P using Tapatalk
 

kwired

Electron manager
Location
NE Nebraska
If i remember correctly it says multiwire branch circuits have to be tied together in panel,,,,Unless otherwise obvious or something like this....if it is a 3 wire coming into the panel, thats pretty obvious to me....Never have been called on this. As long as it is hooked up to a proper 2 pull breaker!

Sent from my SM-G900P using Tapatalk
Yes, that was new in either 2008 or 2011, but if it leaves the panel via a cable assembly that is enough to identify them. Where that requirement kicks in the most is with raceways that contain multiple circuits, then you need some method to identify which conductors are part of the same circuit, which can be individual markings or tying all the conductors of an individual circuit together somehow, or just about anything you can concoct to somehow distinguish them by circuit. The fact they land on multipole breakers is enough to distinguish them - except any associated neutral conductor that lands on a separate bus is just there and is not so easy to determine which ungrounded conductors it goes with if there are multiple circuits in same raceway or cable without further methods of identifcation.
 

charlie b

Moderator
Staff member
Location
Seattle, WA
My answer is that if the A, B, C, N, and G are in the same conduit, they are "grouped," in the context of this NEC article. Enclosures are a bit trickier. Let's talk about a panelboard. I can run 6 wires in a conduit leaving the panelboard, with an A & N, a B & N, and a C & N. I can connect the A to a breaker on the top left, the B to a breaker on the top right, the C to a breaker on the bottom left, and all the Ns on the bar at the bottom, and I would still say they are "grouped," in the context of this NEC article. I say that because, even though the three phase conductors are physically separated from each other within the panelboard, they are not going to result in measureable inductive heating of the panelboard's enclosure.
 

don_resqcapt19

Moderator
Staff member
Location
Illinois
My answer is that if the A, B, C, N, and G are in the same conduit, they are "grouped," in the context of this NEC article. Enclosures are a bit trickier. Let's talk about a panelboard. I can run 6 wires in a conduit leaving the panelboard, with an A & N, a B & N, and a C & N. I can connect the A to a breaker on the top left, the B to a breaker on the top right, the C to a breaker on the bottom left, and all the Ns on the bar at the bottom, and I would still say they are "grouped," in the context of this NEC article. Isay that because, even though the three phase conductors are physically separated from each other within the panelboard, they are not going to result in measureable inductive heating of the panelboard's enclosure.
I agree, but the wording of the code section seems to require grouping within the enclosure itself.
 

kwired

Electron manager
Location
NE Nebraska
300.20 says enclosures or raceways.

If you pulled a whole bunch of 14 AWG into 4 inch RMC, do you need to group conductors of same circuit together within the conduit so they are close to one another? I certainly hope not. Magnetic effects on the raceway shouldn't matter as long as all conductors of all the circuits are within the conduit. Same for a cabinet, wireway, etc.
 

charlie b

Moderator
Staff member
Location
Seattle, WA
I agree, but the wording of the code section seems to require grouping within the enclosure itself.
I don't think so, Don. The rule is not talking about individual circuits. It does not say that each circuit has to have its phase, neutral, and ground conductors grouped. We can't do that within a panel, because the neutral and ground buses are at the bottom, nowhere near the breakers. Rather, it speaks of all phase conductors being grouped. A 42 circuit panelboard is going to have up to 42 phase conductors within the same enclosure. The rule cannot be telling us to group all 42 together.

 

al hildenbrand

Senior Member
Location
Minnesota
We can't do that within a panel, . . .
More important than the "grouping", to me, is the emphasis that "heating" is to be avoided in the "surrounding" ferrous material.

The magnetic field on any one current carrying conductor is a very complex physical thing that is summing and cancelling the magnetic fields of all the other conductors, depending upon their relative strength and the orientation of individual fields to other fields. These magnetic fields, inside a ferrous enclosure, are in air and are diffuse and generate no heat at all in the air.

The collection of magnetic fields from individual currents expand through air and impinge upon the ferrous metal surrounding the conductors. The magnetic field, in the ferrous metal is concentrated, and is a resultant of all the individual magnetic fields. The summing to a resultant field is the "canceling of the field" that can, and does, "avoid" the heating of the ferrous metal.

Quite simply, if the heating is avoided, the conductors ARE grouped.

300.20 Induced Currents in Ferrous Metal Enclosures or Ferrous Metal Raceways.

(A) Conductors Grouped Together.
Where conductors carrying alternating current are installed in ferrous metal enclosures or ferrous metal raceways, they shall be arranged so as to avoid heating the surrounding ferrous metal by induction. To accomplish this, all phase conductors and, where used, the grounded conductor and all equipment grounding conductors shall be grouped together.
 
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