4 wires to a "sub-panel"

[jasonbrozen]

Can anyone enlighten me on which NEC version (year) it became a "shall" to bond a "sub-panel" enclosure separate from the Grounded conductor? I am sure it was prior to 1947. In other words 4 wires to a "sub-panel"

I have looked and looked and cannot find a definitive answer.

I instruct a large number of home inspectors and that is a question that I have not been able to answer. Neither has my Electrical Engineer.

Thanks,

Jason

 

[jumper]

Not sure about "sub-panels", but the first time grounded receptacles were required was 1956 so maybe sometime around there.

Edit: I was incorrect. the 1947 NEC required a grounded receptacle for the laundry.

 

[Dennis Alwon]

I don't know either but perhaps Ken has some info on that. Many houses back then, at least in our area, had the main panels run in conduit from the meter- no disconnect outside or directly inside. Not sure I ever saw one from that far back that had sub panels.

 

[user 100]

Can anyone enlighten me on which NEC version (year) it became a "shall" to bond a "sub-panel" enclosure separate from the Grounded conductor? I am sure it was prior to 1947. In other words 4 wires to a "sub-panel"

I have looked and looked and cannot find a definitive answer.

I instruct a large number of home inspectors and that is a question that I have not been able to answer. Neither has my Electrical Engineer.

Thanks,

Jason

If your thinking of a same structure SP- FWIU, it has never been legal to do a 3 wire feed between main and SP in the same structure. However the rule was often not enforced years ago- there were no egcs in houses way back there, so probably a lot of ECs thought there was no real reason to pull a 4th wire just to bond the SP can. They would just bond the can off the neutral.

 

[mbrooke]

Up until recently you could have detached structures with a 3 wire subpanel provided the were no metallic paths back to the home.


Now, come reality 3 wire subpanels are very common. Was it ever legal? My understanding is no. But the rule was often broken even by electricians. There are condos around me built as late as the 90s where 3 wires were run from the meter pack disconnect to the unit panel. Passed inspection and no one thought twice.

 

[kwired]

Up until recently you could have detached structures with a 3 wire subpanel provided the were no metallic paths back to the home.


Now, come reality 3 wire subpanels are very common. Was it ever legal? My understanding is no. But the rule was often broken even by electricians. There are condos around me built as late as the 90s where 3 wires were run from the meter pack disconnect to the unit panel. Passed inspection and no one thought twice.

In such areas where that seems to be common, the inspectors were probably not necessarily aware of the requirements either.

 

[jasonbrozen]

Thanks for the replies. I appreciate your knowledge.

I wasn't sure if there was something in the code about a separate EGC to the "sub-panel". It seems that from what you guys are saying, It has always been that way.

I guess a better question would be when did the requirement change that the grounded (neutral) could not be bonded to a "sub-panel' can?

I had these dates on grounding:

1913 - Grounding of services mandatory
1923 - Ground rods
1947 - Laundry outlets grounded
1956 - outside and unfinished spaces outlets grounded
1962 - All outlets grounded