Table 250.122

[mbrooke]

Should the proposal for 250.4 (A) 5 be "unsubstantiated", this revision would at least eliminate the risk of EGC fusing where disconnection times exceed 5 seconds. However, this will not solve or mitigate the danger of touch potential.


Table 250.122

Size of Largest Ungrounded Conductor		Size of Circuit Protective Conductor
(AWG or kcmil)		(AWG or kcmil)
14		14
12		12
10		10
8		8
6		6
4		6
3		6
2		4
1		4
1/0		3
2/0		2
3/0		1
4/0		1/0
250		2/0
300		3/0
350		3/0
400		4/0
500		250
600		300
700		350
750		400
800		400
900		500
1000		500
1250		600
1500		750
1750		900
2000		1000

 

[mbrooke]

Supporting material of consideration:

https://ultracad.com/articles/reprints/stauffacher.pdf

Where 5 seconds are not exceeded the EGC is permitted to be less than full size or less than half size respectively. Where 5 seconds are exceeded Table 54.3 must be applied as to guarantee integrity of the EGC whereby adiabatic limits are not exceeded during fault clearing times in excess of 5-10 seconds.

 

[winnie]

IMHO you first need to substantiate that this is a practical problem, meaning one that has actually caused issues in the field as opposed to a theoretical problem.

Next if this is a problem I would suggest that the solution include several mitigation options, including increasing the size of the EGC, increasing the size of all circuit conductors, and using ground fault detection.

There are purely electromagnetic RCD systems which would easily trip on a 1A fault, without electronics or quiescent power consumption, in addition to more conventional powered GFCI and GFPE devices.

 

[mbrooke]

IMHO you first need to substantiate that this is a practical problem, meaning one that has actually caused issues in the field as opposed to a theoretical problem.

Next if this is a problem I would suggest that the solution include several mitigation options, including increasing the size of the EGC, increasing the size of all circuit conductors, and using ground fault detection.

There are purely electromagnetic RCD systems which would easily trip on a 1A fault, without electronics or quiescent power consumption, in addition to more conventional powered GFCI and GFPE devices.

I think the best solution is defining effective ground fault current path.

EM RCDs could be a solution since there are no electronics to fail, however the above solution makes use of existing OCPDs.

 

[mbrooke]

An example of smaller wire coupled with the delayed operation of an OCPD:

 

[romex jockey]

An example of smaller wire coupled with the delayed operation of an OCPD:

that.......is some serious substantiation!

~RJ~

 

[mbrooke]

that.......is some serious substantiation!

~RJ~

6mm2 is just a hair larger than 5.26mm2 cable ie 10 AWG.