What was wrong with this table?

[mbrooke]

This was in the first draft of the 2020. Why didn't it make its way through? This is genius and makes a LOT more sense.

 

[tortuga]

From the meeting:

The FR should be rejected on lack of need, lack of technical substantiation, and the
resultant decrease in safety. There is no reason given or implied that making such a
drastic change is needed. No information is provided to indicate the existing Table
250.122, based on the size of the overcurrent device, is wrong, inadequate, or
confusing, or that this change will be an improvement. In fact, the existing Table is
simple and straightforward and has been proven safe for decades.
The Panel statement only says that the Table is being changed but does give any technical reason for doing
so. The use of a UL Standard for MC cable and TC cable is not representative of all
installations or conditions: it addresses a specific, tightly controlled factory
manufactured wiring method, in which the equipment grounding conductor is installed
within a jacket in a determined location/configuration. This concept cannot possibly be
valid for all configurations where the proximity of the EGC to the phase conductors is
random, as in a trench, wireway, or raceway. The physics of these installations should
not be assumed to be the same as for construction of specific cables. It needs to be
noted that these standards were not made available to the Panel at time of the Public
Input, nor during the deliberations during the PI hearings; only a few minutes was
offered to a few CMP-5 members. This in itself should disqualify the change due to lack
of ability to review the standards for relevancy. The comment that this action is
consistent with sizing of supply-side bonding conductors and grounded conductors in
Table 250.102(C)(1) is not accurate, as those conductors generally do not have an
known overcurrent protection. Only the protective device applied by the utility is
applicable, and is not controlled by the NEC and often will not come close to protecting
a conductor sized per the NEC. The hope is that the supply-side bonding jumper will
survive long enough to open some device on the utility side of the premises wiring, or
possibly until the shorted conductor burns through.

I'd say personally that 250.122 is a waste of resources, the current table is a result of a UL effort in 1969 that also had no technical substantiation, no data.
There is vast technical substantiation that our neighbors to the north whom rejected the UL table don't have any problems with their CEC table which seems way more reasonable:

 

[mbrooke]

So I'll put on my NFPA hat.

This concept cannot possibly be
valid for all configurations where the proximity of the EGC to the phase conductors is
random, as in a trench, wireway, or raceway. The physics of these installations should
not be assumed to be the same as for construction of specific cables.

So what proof does he have to make such a confident statement? When we cite physics or theory it gets shot down as unsubstantiated. Yet he can make such statements without anything to back them up.


With that said I'd ask the code making panel to look at Preece calculations, in particular just how little current it takes to fuse an EGC...

 

[romex jockey]

The hope is that the supply-side bonding jumper will
survive long enough to open some device on the utility side of the premises wiring, or
possibly until the shorted conductor burns through.


good lord....i just realized i've survived the trade for 4 decades on 'HOPE' ..... ~RJ~

 

[mbrooke]

The hope is that the supply-side bonding jumper will
survive long enough to open some device on the utility side of the premises wiring, or
possibly until the shorted conductor burns through.


good lord....i just realized i've survived the trade for 4 decades on 'HOPE' ..... ~RJ~

It is all hope. CMP 5 does not understand the physics, theory or concept of grounding, bonding or loop conduction.

 

[mbrooke]

From the meeting:


I'd say personally that 250.122 is a waste of resources, the current table is a result of a UL effort in 1969 that also had no technical substantiation, no data.
There is vast technical substantiation that our neighbors to the north whom rejected the UL table don't have any problems with their CEC table which seems way more reasonable:
View attachment 2556330

Do you have the page number and what ROP/draft that is? I want to read more of this- very interesting.

 

[tortuga]

Do you have the page number and what ROP/draft that is? I want to read more of this- very interesting.

Sure here you go, check NFPA website under 2020 NEC also;
Page 39
I think its great people are interested in how the code is made.
As your our official Mike Holt Code Forums Industry lobbyist, most of us would rather you stay focused on getting together a peer review study of AFCI's with some engineering undergrads of Gars.
I personally think the canadian table is fine (only two differences) but thats mostly becasue I have seen allot of 14 AWG on 20A breakers/fuses that trip fine, even the old 18 AWG bond that was in early cloth romex trips a 20.
and Ill admit I am jealous that the Canadians have cooler romex colors than us, like 12/2 and 10/2 with a red and a black for 240 stuff.

 

[romex jockey]

It is all hope. CMP 5 does not understand the physics, theory or concept of grounding, bonding or loop conduction.

neither do I MBrooke
ergo the crux of the problem
~RJ~

 

[mbrooke]

neither do I MBrooke
ergo the crux of the problem
~RJ~

Right, because we are only as smart as what the code tells us. That and to many people are taught "do not question authority or else"


But I am willing to teach you and anyone else.

It boils down to ohms law- primarily:


1. Zs=Ze+(R1+R2)

2. R1+R2+R3+R4

 

[romex jockey]

But I am willing to teach you and anyone else.

plz keep it simple then MBrooke, methinks the payoff will be far better here ~RJ~

 

[mbrooke]

neither do I MBrooke
ergo the crux of the problem
~RJ~

Ditto for every conscious thought:

http://minerva.union.edu/newmanj/physics111/chapter16.pdf

Translating into:




Be it electricity, electronics, nature, the sun, our universe, space time, ect all function on this most fundemtnal equation:





The NFPA has a fairly good grasp of I and V, but nothing even remotely tangible regarding "R"

 

[mbrooke]

plz keep it simple then MBrooke, methinks the payoff will be far better here ~RJ~

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