Table 250.102 (C) (1)

[ohmboyz]

Hi all

Last night, one of my students asked me a question about the above-referenced table in Article 250. He was confused by the boldface heading the right column which reads: Size of Grounded Conductor or Bonding Jumper (AWG or Kcmil). This is followed by an asterisk which sends one to the bottom of the table notes and it reads: For the purposes of this table, the term bonding jumper refers to main bonding jumpers, system bonding jumpers, and supply side bonding jumpers.

His question was why does it say Grounded Conductor and not just Bonding Jumper. I told him I thought it was because this table refers to supply side conductors and that there are times a utility will size a grounded conductor differently than one might if using article 220. That's just a guess. I promised I would post the question on the forum.

Anyone care to weigh in?

Thanks

 

[david luchini]

Hi all

Last night, one of my students asked me a question about the above-referenced table in Article 250. He was confused by the boldface heading the right column which reads: Size of Grounded Conductor or Bonding Jumper (AWG or Kcmil). This is followed by an asterisk which sends one to the bottom of the table notes and it reads: For the purposes of this table, the term bonding jumper refers to main bonding jumpers, system bonding jumpers, and supply side bonding jumpers.

His question was why does it say Grounded Conductor and not just Bonding Jumper. I told him I thought it was because this table refers to supply side conductors and that there are times a utility will size a grounded conductor differently than one might if using article 220. That's just a guess. I promised I would post the question on the forum.

Anyone care to weigh in?

Thanks

See 250.24(C)(1).

 

[ohmboyz]

Hmmm. Kinda like a circle, no? 250.24 (C) (1) simply refers back to the table I originally asked about. My question is based on an understanding that on the load side, we calculate the size of the grounded conductor according to Article 220. For a single phase delta, it is rare for the grounded conductor to be more than two sizes smaller than the ungrounded ones. In the 250.102 table, the first row would indicate a grounded conductor could be as much as four times smaller than the ungrounded conductor. I'm wondering why this is. I'm wondering why the table doesn't just say in the right hand column, "size of bonding jumper" and simply exclude the term "grounded conductor."

 

[infinity]

Hmmm. Kinda like a circle, no? 250.24 (C) (1) simply refers back to the table I originally asked about. My question is based on an understanding that on the load side, we calculate the size of the grounded conductor according to Article 220. For a single phase delta, it is rare for the grounded conductor to be more than two sizes smaller than the ungrounded ones. In the 250.102 table, the first row would indicate a grounded conductor could be as much as four times smaller than the ungrounded conductor. I'm wondering why this is. I'm wondering why the table doesn't just say in the right hand column, "size of bonding jumper" and simply exclude the term "grounded conductor."

That table is also used for sizing the minimum size grounded conductor.

250.24(C) Grounded Conductor Brought to Service Equipment. Where an ac system operating at 1000 volts or less is
grounded at any point, the grounded conductor(s) shall be routed with the ungrounded conductors to each service dis-
connecting means and shall be connected to each disconnecting means grounded conductor(s) terminal or bus. A
main bonding jumper shall connect the grounded conductor(s) to each service disconnecting means enclosure. The
grounded conductor(s) shall be installed in accordance with 250.24(C)(1) through (C)(4).
(1) Sizing for a Single Raceway. The grounded conductor
shall not be smaller than specified in Table 250.102(C)(1).

 

[packersparky]

Hmmm. Kinda like a circle, no? 250.24 (C) (1) simply refers back to the table I originally asked about. My question is based on an understanding that on the load side, we calculate the size of the grounded conductor according to Article 220. For a single phase delta, it is rare for the grounded conductor to be more than two sizes smaller than the ungrounded ones. In the 250.102 table, the first row would indicate a grounded conductor could be as much as four times smaller than the ungrounded conductor. I'm wondering why this is. I'm wondering why the table doesn't just say in the right hand column, "size of bonding jumper" and simply exclude the term "grounded conductor."

220.61 is for calculating the load of the grounded conductor. The size of the grounded conductor would be the larger size of that required by your load calculation or of that required by table 250.102(C).

 

[ohmboyz]

okey dokey, thanks

 

[kwired]

220.61 is for calculating the load of the grounded conductor. The size of the grounded conductor would be the larger size of that required by your load calculation or of that required by table 250.102(C).

+1

 

[LarryFine]

For a single phase delta . . .

What is a single phase delta? :?

 

[jumper]

What is a single phase delta? :?

Lonely......

 

[ActionDave]

What is a single phase delta? :?

Lonely......

:thumbsup:

 

[ohmboyz]

what is a single phase delta

what is a single phase delta

not clear why you're asking the question? surely you know the answer. if on the other hand you're trying to make a particular point, please let me in on what that would be.

thanks

 

[jumper]

not clear why you're asking the question? surely you know the answer. if on the other hand you're trying to make a particular point, please let me in on what that would be.

thanks

Your terminology, a pun. A delta by its make up is three phase. You were referring to the tranny that is center tapped for single phase from a delta set up.

There is no such thing as a single phase delta tranny.

See?

 

[ohmboyz]

well dang if i haven't been wrong all these years

well dang if i haven't been wrong all these years

i've worked as a licensed sparktrician for more than thirty years. Whether in Chi-town, the western North Carolina mountains, Pennsylvania, Michigan and Ohio, a single family residential service was commonly understood to be fed from a three phase delta transformer,hence the 240/120/ voltage and the peculiar 240/120/plus c leg stinger for a three phase panel.

now, come to find out me and a bunch of other fools been swallowed up by a bermuda triangle. :lol:

 

[jumper]

i've worked as a licensed sparktrician for more than thirty years. Whether in Chi-town, the western North Carolina mountains, Pennsylvania, Michigan and Ohio, a single family residential service was commonly understood to be fed from a three phase delta transformer,hence the 240/120/ voltage and the peculiar 240/120/plus c leg stinger for a three phase panel.

now, come to find out me and a bunch of other fools been swallowed up by a bermuda triangle. :lol:

Wow, they really call a single center tapped tranny a delta? Totally incorrect.

While the properties of the two are similar in regards to deriving 120/240V, the term delta is only appropriate to the three phase system.

Deltas with one tranny center tapped for 120/240. Note that corner grounded and ungrounded deltas exist also, but no 120V is derived from those set ups.

 

[LarryFine]

not clear why you're asking the question? surely you know the answer. if on the other hand you're trying to make a particular point, please let me in on what that would be.

If you're asking me, no, I don't know the answer and I'm not trying to make a point.

 

[kwired]

now, come to find out me and a bunch of other fools been swallowed up by a bermuda triangle. :lol:

Open delta triangle obviously

 

[charlie b]

OK guys, let's please not let language get in the way of communication. :happyno: