Conductor sizing

[Devin Hanes]

That was my interpretation as well.

Anyone want to take a stab at explaining Note 2?

Here's my stab, based on my bias of what I thought the Code allowed. Like I said before though, I don't think it is clear either.

Note 2. Where there are no service-entrance conductors, the grounding electrode conductor size shall be determined by the equivalent size of the largest service-entrance conductor required for the load to be served.

"Where"=Physical Location-"the service", "the separate structure", "or at a separately derived system"
Based on 250.66

250.66 Size of Alternating-Current Grounding Electrode
Conductor. The size of the grounding electrode conductor at
the service, at each building or structure where supplied by a
feeder(s) or branch circuit(s), or at a separately derived system
of a grounded or ungrounded ac system shall not be less than
given in Table 250.66, except as permitted in 250.66(A)
through (C).

now for the "largest" issue

Note 2. Where there are no service-entrance conductors, the grounding electrode conductor size shall be determined by the equivalent size of the largest service-entrance conductor required for the load to be served.

This is the exact language used in the tables column heading

2017



What do you think?

 

[Devin Hanes]

As I said, IMO, that is there for services that do not have SEC's which is fairly common. Besides, what comes after "where there are no SEC's...." doesn't really seem to be worded like it applies to a feeder.

Service-Entrance Conductors, Overhead System. The service conductors between the terminals of the service equipment and a point usually outside the building, clear of building walls, where joined by tap or splice to the service drop or overhead service conductors. (CMP-4)

Service-Entrance Conductors, Underground System. The service conductors between the terminals of the service equipment and the point of connection to the service lateral or underground service conductors. (CMP-4)
Informational Note: Where service equipment is located outside the building walls, there may be no service-entrance conductors or they may be entirely outside the building.

Were you thinking of the non-NEC definition? Or what type of installation? I'm drawing a blank.

 

[Devin Hanes]

1971 Proposed Amendments. Although it's not very clear either

Table 250-94(a): Hold on Docket PROPOSAL NO. 31:
I. Revise the heading over the two left-hand columns of Table 250-94(a) to read: · Size of Service "Entrance" Conductor or Equivalent for Multiple Conductors

2. Add Footnote to bottom of Table to read:
FINE PRINT NOTE: Where there arc no_service-entrance conductors, grounding conductor size to be determined by equivalent rating of the service equipments.

SUBMITTER: Electric Light and Power Group, J.P. Markey.

SUPPORTING COMMENT: The purpose of a service grounding cond_uctor_ (electrode conductor) is to limit the voltag_e abo_ve ground, winch might occur upon the circuit as a result of hghtnmg or actual breakdown of a supply transformer. The location of this grounding conductor is such that it drains off at the service equipment the surge currents resulting from the abnormal voltage thus maintaining the interior wiring system al a safe voltage. Its size, therefore, must be sufficiently large enough 10 carry as much current as any other source of the abnormal voltage and the resulting current .would flow via the service-entrance conductor and since the service grounding conductor is joined to the grounded conductor on the load side of the service-entrance conductor,_ the service grounding conductor should be sized according to the service-entrance conductor. Theoretically, the service grounding conductor size should be based on the smallest service conductor in the c!rcuit which would include the service drop or service lateral, but since the drop or lateral is usually of smaller size than the service entrance conductor and since the drop or lateral can be increased without any change in the service-entrance conductor, we believe it is more practical to base the groundin_g conductor size on the size of the service-entrance conductor. The footnote will cover the few cases where there arc no service-entrance conductors by sizing the service grounding conductor on a fictitious service-entrance conductor of comparable size to the size of the service equipment.

PANEL RECOMMENDATION: Hold on Docket for further study.

 

[Devin Hanes]

1971 NEC

250-24. Two or More Buildings Supplied From Single Service Equipment.
Where two or more buildings are supplied from a single service equipment, a grounding electrode at each building shall be connected to the AC system grounded conductor on the supply side of the building disconnecting means of a grounded system or connected to the metal enclosure of the building disconnecting means of an ungrounded system.

Exception: A grounding electrode at a separate building supplied by a feeder or branch circuit is not required where either of the following conditions are met:

a. Only one branch circuit is supplied, there is no noncurrent-carrying equipment in the building that requires grounding, and no livestock is housed in the building; or

b. An equipment grounding conductor is run with the circuit conductors for grounding any noncurrent-carrying equipment, water piping, or building metal frames in the separate building and no livestock is housed in the building. If the separate building has an approved grounding electrode and~or interior metallic piping system, the equipment grounding conductor shall be bonded to the electrode and~or piping system.

 

[electrofelon]

I still disagree.

Were you thinking of the non-NEC definition? Or what type of installation? I'm drawing a blank.

I am not sure what you are asking. There are services that do not have service entrance conductors.

 

[Devin Hanes]

I still disagree.

I am not sure what you are asking. There are services that do not have service entrance conductors.

I now agree with you. I think it reads that way but it's probably not the intent of the panel, I'm working on a proposal to remove the references in 250.66 and 250.64 related to the Original Posts installation. To leave 250.32(B)(1) requiring the use of the equipment grounding conductor. I will post it in the code proposal forum. Thank you.
250.32(B)(1)

......An equipment grounding conductor, as described in 250.118, shall be run with the supply conductors and be connected to the building or structure disconnecting means and to the grounding electrode(s)......

In the 2008 cycle (ROC 5-116 Log #1523 NEC-P05 (250.66)) the Correlating Committee added theses references to "at each building or structure where supplied by a feeder(s) or branch circuit(s), or at the source of a separately derived system " into those sections to exclude IT and communication system electrode conductors.