Table 250.122

Merry Christmas

mbrooke

Batteries Included
Location
United States
Occupation
Technician
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 ConductorSize of Circuit Protective Conductor
(AWG or kcmil)(AWG or kcmil)
1414
1212
1010
88
66
46
36
24
14
1/03
2/02
3/01
4/01/0
2502/0
3003/0
3503/0
4004/0
500250
600300
700350
750400
800400
900500
1000500
1250600
1500750
1750900
20001000
 

mbrooke

Batteries Included
Location
United States
Occupation
Technician
Supporting material of consideration:

1617563365258.png


1617563448645.png




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

Senior Member
Location
Springfield, MA, USA
Occupation
Electric motor research
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

Batteries Included
Location
United States
Occupation
Technician
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.
 
Top