300.20 Gone Wild

[al hildenbrand]

Al,
We are not going to agree on this issue...there is just no way that wires run down one wireway are grouped with the wires in the opposite wireway (my opinion and it is not going to change).

:?:blink:
Don, I agreed with you on this "issue" in Post # 109. AND, if there actually was a panel with ONLY one conductor down one side, and ONLY one conductor down the other side, AND the ferrous metal, at a point or area, WAS HEATING, then you have a failure of arrangement per 300.20(A).

HOWEVER, the NFPA Glossary of Terms makes the arrangement, so described (one wire this side, one wire that side), as "grouped" if they share the same ferrous metal container, be the container a raceway or a panel box.

It might be nice if the Rule was prescriptive, but at present, the presence of HEAT is the performance basis for failure to comply, . . . as written, in my opinion.

The complex summing of magnetic fields in open air and in ferrous metal, where the magnetic fields arise from alternating currents in many conductors and where the ferrous metal is of unknown shape, size and orientation relative to the currents, will elude verbal prescription because of the difficulty of measuring and interpreting the magnetic field information, and reducing that to a sentence or two.

 

[don_resqcapt19]

:?:blink:
Don, I agreed with you on this "issue" in Post # 109. AND, if there actually was a panel with ONLY one conductor down one side, and ONLY one conductor down the other side, AND the ferrous metal, at a point or area, WAS HEATING, then you have a failure of arrangement per 300.20(A).

I don't agree that the second part applies only if there is actually heating.

HOWEVER, the NFPA Glossary of Terms makes the arrangement, so described (one wire this side, one wire that side), as "grouped" if they share the same ferrous metal container, be the container a raceway or a panel box.

Again we don't read the words the same way.

It might be nice if the Rule was prescriptive, but at present, the presence of HEAT is the performance basis for failure to comply, . . . as written, in my opinion. ...

The rule is prescriptive as it tells you what to do. It doesn't say that you only have to do that if there is heating of the ferrous metal.

 

[al hildenbrand]

Again we don't read the words the same way.

Hence the discussion.

The rule is prescriptive as it tells you what to do. It doesn't say that you only have to do that if there is heating of the ferrous metal.

OK. Have it your way. The rule is "prescriptive" as it tells us "to avoid heating. . . by induction." The results= no heat by induction. The performance is an absence of heating.

 

[jim dungar]

The rule is prescriptive as it tells you what to do. It doesn't say that you only have to do that if there is heating of the ferrous metal.

But if there is no heating doesn't that mean, whatever the actual physical grouping, it is sufficient? The NEC does not have a maximum separation distance in its definition of grouping.

 

[Smart $]

But if there is no heating doesn't that mean, whatever the actual physical grouping, it is sufficient? The NEC does not have a maximum separation distance in its definition of grouping.

I say yes.

However, we are talking about how inspectors enforce this section... and I would say the inspection is during rough in, before energizing and loading... impossible for either party to determine actual heating at that point in time.

Now if you can get these "group it" inspectors to come back without extra charge at a later date to prove/disprove heating, we might get somewhere... but it is probably going to be easier to change the Code wording.

 

[mgookin]

I say yes.

However, ...... but it is probably going to be easier to change the Code wording.

+1

And this is the venue to initiate that.

Not sure how the process works but I'd guess it requires a reason, a cost analysis, etc. All that should be easy to generate.

 

[Strathead]

the correct spelling of the German word is "dummkopf," and it roughly translates to a stupid person, a blockhead.

Stupid head, actually. And I only studied it for two years. Sorry, I just couldn't help myself. I am anal after all.

 

[don_resqcapt19]

Hence the discussion.

OK. Have it your way. The rule is "prescriptive" as it tells us "to avoid heating. . . by induction." The results= no heat by induction. The performance is an absence of heating.

The rule is prescriptive because it tells us to group the conductors. The requirement applies to all installations, not just those were inductive heating would be expected.

 

[don_resqcapt19]

+1

And this is the venue to initiate that.

Not sure how the process works but I'd guess it requires a reason, a cost analysis, etc. All that should be easy to generate.

Code change proposals (public inputs) do not require a cost analysis.

 

[don_resqcapt19]

But if there is no heating doesn't that mean, whatever the actual physical grouping, it is sufficient? The NEC does not have a maximum separation distance in its definition of grouping.

If you eliminate the second part of the rule, I would agree. I read the current rule as requiring the "grouping" for all installations in ferrous metal enclosures, no matter if inductive heating is possible or not.

 

[al hildenbrand]

I read the current rule as requiring the "grouping" for all installations in ferrous metal enclosures, no matter if inductive heating is possible or not.

The rule says absolutely nothing about the presence, absence or location of magnetic fields. The rule only instructs us to pay attention to the absence of HEAT.

Where the conductors ARE carrying alternating current the arrangement of conductors is "grouped" if the ferrous metal heating is avoided. The NFPA Glossary of Terms definition of "grouped" does nothing to alter that being the result of the conductors being "arranged".

The key, then, that conflicts with your assertion of "no matter if", is that the second sentence of 300.20(A) ties its subject ("To accomplish this") invoking "arranged to avoid inductive heating".

The rule requires alternating current happening and says nothing about invisible magnetic fields AND says nothing about currents that are, or are not induced IN ferrous metal. . . ONLY the heat. We, as installers and inspectors, can envision the invisible magnetic fields and the invisible currents, but that is no matter to this rule. . . only "avoid heating the surrounding ferrous mental."

 

[don_resqcapt19]

The rule says absolutely nothing about the presence, absence or location of magnetic fields. The rule only instructs us to pay attention to the absence of HEAT.

Where the conductors ARE carrying alternating current the arrangement of conductors is "grouped" if the ferrous metal heating is avoided. The NFPA Glossary of Terms definition of "grouped" does nothing to alter that being the result of the conductors being "arranged".

The key, then, that conflicts with your assertion of "no matter if", is that the second sentence of 300.20(A) ties its subject ("To accomplish this" invoking "arranged to avoid inductive heating".

The rule requires alternating current happening and says nothing about invisible magnetic fields AND says nothing about currents that are, or are not induced IN ferrous metal. . . ONLY the heat. We, as installers and inspectors, can envision the invisible magnetic fields and the invisible currents, but that is no matter to this rule. . . only "avoid heating the surrounding ferrous mental."

Al, we are not going to come to agreement on this.

 

[al hildenbrand]

:dunce: Woof! Didn't mean "mental."

 

[al hildenbrand]

Al, we are not going to come to agreement on this.

It's been a good discussion, Don. Thanks for entering the NFPA Glossary of Terms with the meaning of "grouped" into the discussion.

 

[charlie b]

Al, We are not going to agree on this issue...there is just no way that wires run down one wireway are grouped with the wires in the opposite wireway (my opinion and it is not going to change).

I agree with Al on this issue. My interpretation of the actual words, as written, is that two wires within the same panelboard are "grouped," in the context of this article, even if they run on opposite sides of the enclosure. Don, I acknowledge that you don't agree with this interpretation. So be it.

 

[mivey]

I also have respect for Don, and I agree with what Don said: the conductors do have to be grouped within an enclosure. At issue is the meaning of "grouped." As others have also said, I don't interpret "grouped" as meaning "touching or twisted together." I say they are "grouped" if they enter the enclosure from the same conduit, and either they are terminated within the enclosure or they exit the enclosure within the same conduit.

That makes sense. Unless the conductors are passing through additional holes in the enclosure, there should not be the inductive heating we would normally try to avoid and eddy currents would be small and "normal".

 

[mivey]

I learned a little bit of German when I was a kid too, but not in school. It was from watching Hogan's Heroes after school.

I still watch it at nights on ME TV. Werner Klemperer refused to play Clink unless he would be portrayed as incompetent. Silly show but still fun to watch.

 

[mivey]

For most part, I cannot remember seeing much in the way of mathematical formulas that are to be used to determine the magnetic field strength between conductors internal to a common 'ferrous' enclosure.

Agreed, and I'm sure SqD would have a bulletin about it if they thought it was a problem.

I suppose we could model it but I see no point without of ferrous loop anyway. Perhaps there might be some issue with high fault current mechanical stress but that would be a stretch for smaller panels.

 

[mivey]

It's been a good discussion, Don. Thanks for entering the NFPA Glossary of Terms with the meaning of "grouped" into the discussion.

Al, I went back through the thread and you have made some good points and wholesome discussion. I won't quote them all but I agree with you.

 

[al hildenbrand]

I agree with Al on this issue.

I agree with you.

:thumbsup: The NFPA Glossary of Terms definition of "grouped" ( you can download it for free at the NFPA by clicking here) was new to me, in this discussion. It finally solidified the meaning of "grouped."