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Discussion Starter #1
Read, and re-read section 10. Can't seem to find a clear answer on the sizing of the neutral (XO) to case bond when running paralleled secondary wires.

I always thought the XO bonding jumper was sized to the output of the transformer or equivalent/total wire size of the paralleled runs. But by reading over the rules it seems that the jumper only needs to be sized the to largest conductor (not equivalent)?

10-624 (2) - Use 10-814 to size XO bonding conductor

10-814 (1) (a) - Says use T16a and size to largest conductor (secondary)

Am I missing something here? When the runs are paralleled the neutral to case bond would still need to carry back the same (total paralleled or not) fault current back to the XO. So what good would sizing the XO bond to only the largest conductor (in a paralleled run) do? would it not be undersized?



Another related question. Does the transformer ground (#6) need to be directly connected to the XO of the transformer? or can it be just connected to the case? (as it will be connected to the XO by the bonding jumper)

10-206 (1) (a) - Does not say ground has to be on XO just "at the transformer"

10-206 Appendix B - "A neutral of each transformer is bonded to the transformer enclosure (see Rule 10-624) and connected to (a) the grounding electrode of the system that supplied the facility"

Whats the purpose of rule 10-206 (3)?

Reading these rules leads me to believe I can just connect the ground anywhere to the case of the transformer. Am I correct?


Thanks!
 

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..............................................................................
10-814 (1) (a) - Says use T16a and size to largest conductor (secondary)

Am I missing something here? When the runs are paralleled the neutral to case bond would still need to carry back the same (total paralleled or not) fault current back to the XO. So what good would sizing the XO bond to only the largest conductor (in a paralleled run) do? would it not be undersized?

!
Good question. I also can't find where the code says to use equivalent
ampacity for parallel secondaries. None the less, I think the secondary
should be grounded based on the equivalent. That appears to be what
you were thinking as well.
All I'm doing these days is residential so hopefully my recollection
isn't too poor. Last transformers I wired I think I grounded the
secondary with single piece of wire coming from the electrode and
passing through the case lug before ending at the X0 lug. Lots of guys
on here do this all the time so I'm sure they'll correct me if I've
mis-remembered.
Good Luck,
P&L
 

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Discussion Starter #3 (Edited)
Good question. I also can't find where the code says to use equivalent
ampacity for parallel secondaries. None the less, I think the secondary
should be grounded based on the equivalent. That appears to be what
you were thinking as well.
All I'm doing these days is residential so hopefully my recollection
isn't too poor. Last transformers I wired I think I grounded the
secondary with single piece of wire coming from the electrode and
passing through the case lug before ending at the X0 lug. Lots of guys
on here do this all the time so I'm sure they'll correct me if I've
mis-remembered.
Good Luck,
P&L
The last transformer you wired was probably done based off the 2009 code that required larger ground wires for transformers, so the ground wire was also large enough to used for bonding the XO.

Both the 2012 and 2015 code now only require the ground wire to be #6 for a transformer no matter the size (under 750v), and on larger transformers #6 is not large enough to bond the XO so you must bond/size as per 10-624

I checked my 2012 code book and under the old (2012) Table 16 it says "Ampacity, A, of the largest ungrounded conductor in the circuit or equivalent for multiple parallel conductors not exceeding"...

But it seems they excluded that explanation in the new 2015 book because the Table 16 bonding conductor size is no longer based on the amperage of the largest conductors it is now based on the wire size of the largest conductors.

Just trying to figure out where it actually says in the new book that you must size to the equivalent/output. My boss is claiming that the XO bond only needs to be sized to the largest conductor based on the new 2015 book. Still doesn't seem right to me and I can't find anything to prove him wrong..
 

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So I'm 2 code cycles behind.....kinda pathetic. Thanks for the update.

If you don't get your answer here, you could submit your question to the ESA
FAQ page at: http://www.esasafe.com/faq-esasafe/electrical-code
It takes up 2 weeks to get an answer, but you get a definitive answer.

Cheers,
P&L
 
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Discussion Starter #5
So I'm 2 code cycles behind.....kinda pathetic. Thanks for the update.

If you don't get your answer here, you could submit your question to the ESA
FAQ page at: http://www.esasafe.com/faq-esasafe/electrical-code
It takes up 2 weeks to get an answer, but you get a definitive answer.

Cheers,
P&L
Thanks for the link will definitely submit the question if no one can figure it out.

If you want a quick update on the new code and you have some time check out this pdf

https://drive.google.com/open?id=0B6hFJ9_Fz4bsaFJDU3F5OWxaTTJCNEJDLUk4MC1Fd3UxNkw0

Goes over all the new 2015 changes.
 

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Read, and re-read section 10. Can't seem to find a clear answer on the sizing of the neutral (XO) to case bond when running paralleled secondary wires.

I always thought the XO bonding jumper was sized to the output of the transformer or equivalent/total wire size of the paralleled runs. But by reading over the rules it seems that the jumper only needs to be sized the to largest conductor (not equivalent)?

10-624 (2) - Use 10-814 to size XO bonding conductor

10-814 (1) (a) - Says use T16a and size to largest conductor (secondary)

Am I missing something here? When the runs are paralleled the neutral to case bond would still need to carry back the same (total paralleled or not) fault current back to the XO. So what good would sizing the XO bond to only the largest conductor (in a paralleled run) do? would it not be undersized?



Another related question. Does the transformer ground (#6) need to be directly connected to the XO of the transformer? or can it be just connected to the case? (as it will be connected to the XO by the bonding jumper)

10-206 (1) (a) - Does not say ground has to be on XO just "at the transformer"

10-206 Appendix B - "A neutral of each transformer is bonded to the transformer enclosure (see Rule 10-624) and connected to (a) the grounding electrode of the system that supplied the facility"

Whats the purpose of rule 10-206 (3)?

Reading these rules leads me to believe I can just connect the ground anywhere to the case of the transformer. Am I correct?


Thanks!
I think the *note* below Table 16A is what your looking for.
The way I read it, your Bonding conductor is based on the ampacity of the paralleled conductors.
 

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Yes the new code left out the sentence "or equivalent for multiple parallel conductors" on the new table 16A and B.

The new note at the bottom of the table isn't very clear either.

The bond size for the XO of a transformer is, and has always been based on the ampacity of all conductors if running parallel.

So lets say you didn't run parallel conductors, would the bond to XO be bigger because your using bigger wire to feed the same transformer? No
So lets say you ran multiple conductors, say like 4 per phase. Same transformer but smaller wires. Would the bond to XO be smaller because your using smaller wire? No

The transformer doesn't care how you wire it. The fault current will be the same and the bond to XO must be sized properly to handle the current.
 

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also .... the 10-206(3) rule you asked about ...

This is for a control transformer (ie. inside a starter or control panel) , you can bond to the metal enclosure. If it's below 1KVA.
 

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---------------stuff deleted--------------------------
Am I missing something here? When the runs are paralleled the neutral to case bond would still need to carry back the same (total paralleled or not) fault current back to the XO. So what good would sizing the XO bond to only the largest conductor (in a paralleled run) do? would it not be undersized?
---------------more stuff deleted------------------
IF the 2015 code does intend for the size of the case bond
to be based only on the size of the wires on the output and not the
equivalent size of the parallel runs, what reason might there be for
this?
If the case were to become energized, how would this happen?
If the answer to this is that it happens by one of the parallel outputs
coming in contact (due to damage to the insulation, etc) with the
case, box connector, flex, or whatever, then the available current is
dependent on the size of the individual parallel run. Not the
equivalent.

Is this their intent or reasoning? I don't know. It's just a thought.

P&L
 

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Both the 2012 and 2015 code now only require the ground wire to be #6 for a transformer no matter the size (under 750v), and on larger transformers #6 is not large enough to bond the XO so you must bond/size as per 10-624
This is a common misconception. 10-204 says you must use Table 16A to size the system ground. When you bring a neutral (wye) the ground needs only be #6. When there isn't a neutral present, the grounded circuit conductor (which is the grounding circuit conductor in this case) must be able to carry a larger amount of current.
Nothing in the code is ever simple.
10-204 Grounding connections for ac systems (see Appendices B and I)
(1) When a consumer’s service is supplied by an ac system that is required to be grounded in accordance with
Rule 10-106(1), the system shall
(a) be connected to a grounding conductor at the transformer or other source of supply;
(b) be connected to a grounding conductor at each individual service, with the connection made on the
supply side of the service disconnecting means either in the service box or in other service
equipment; and
(c) except as provided for in Rule 10-208, have no connection between the grounded circuit conductor
on the load side of the service disconnecting means and the grounding electrode.
(2) Where the system is grounded at any point, the grounded conductor shall
(a) be run to each individual service;
(b) have a minimum size as specified for bonding conductors in Rule 10-814;
(c) also comply with Rule 4-024 where it serves as the neutral; and
(d) be included in each parallel run where the service conductors are run in parallel.
(3) Notwithstanding Rule 12-108, the size of the system grounded conductors in each parallel run shall be
permitted to be smaller than No. 1/0 AWG.
 

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This is a common misconception. 10-204 says you must use Table 16A to size the system ground. When you bring a neutral (wye) the ground needs only be #6. When there isn't a neutral present, the grounded circuit conductor (which is the grounding circuit conductor in this case) must be able to carry a larger amount of current.
Nothing in the code is ever simple.
OK there are a lot of misunderstandings here.
Table 41 sizes the bonding jumper based on the largest service conductor or equivalent for multi conductor (parallel runs) not Tables 16
T 16A is for sizing bond wires and correctly references only the wires in the cable or raceway but is not for sizing the bond jumper.
The neutral is the grounded circuit conductor and carries the load in 10-204 (2) and must be run to each subdivision of the service to ensure the bonding jumper will transfer fault current to the neutral for the OC protection to work.
Bond wires carry fault current. Ground wires do not, except in DC systems.

Ground wires are sized under 10-812 for AC systems only and it is #6 if copper for all low voltage services (750v or less).
 

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OK there are a lot of misunderstandings here.
Table 41 sizes the bonding jumper based on the largest service conductor or equivalent for multi conductor (parallel runs) not Tables 16
T 16A is for sizing bond wires and correctly references only the wires in the cable or raceway but is not for sizing the bond jumper.
The neutral is the grounded circuit conductor and carries the load in 10-204 (2) and must be run to each subdivision of the service to ensure the bonding jumper will transfer fault current to the neutral for the OC protection to work.
Bond wires carry fault current. Ground wires do not, except in DC systems.

Ground wires are sized under 10-812 for AC systems only and it is #6 if copper for all low voltage services (750v or less).
Table 41 is for service raceways no?
Can you direct me to the code that says we use Table 41 to size a bonding jumper? Like in a transformer as per the OP's question.


Here is all I got.
10-614 Bonding jumpers shall be
(1)(b) of sufficient size to have an ampacity not less than that required for the corresponding bonding conductor, except that for service raceways this ampacity shall be permitted to be determined on the basis of
(i) Table 41
 

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OK there are a lot of misunderstandings here.
Table 41 sizes the bonding jumper based on the largest service conductor or equivalent for multi conductor (parallel runs) not Tables 16
T 16A is for sizing bond wires and correctly references only the wires in the cable or raceway but is not for sizing the bond jumper.
The neutral is the grounded circuit conductor and carries the load in 10-204 (2) and must be run to each subdivision of the service to ensure the bonding jumper will transfer fault current to the neutral for the OC protection to work.
Bond wires carry fault current. Ground wires do not, except in DC systems.

Ground wires are sized under 10-812 for AC systems only and it is #6 if copper for all low voltage services (750v or less).
Thanks for that Mshea. My CE code handbook is old -> 2002.
Still has valid info, like the following:
"Rational for Rule 10-614 Bonding jumpers are essential links in the
bonding path and shall be mechanically secure and electrically
capable of carrying any available fault current. They are used for
bonding the identified conductor or neutral to the enclosure or
service electrical equipment, for bonding grounding electrodes
together, for bonding sections of raceway or cable trays together,
for bonding hinged or removable covers, and for many other
purposes. "

I think I knew about this rule and T41 10 years ago. Thanks for
the reminder.

P&L
 

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Thanks for that Mshea. My CE code handbook is old -> 2002.
Still has valid info, like the following:
"Rational for Rule 10-614 Bonding jumpers are essential links in the
bonding path and shall be mechanically secure and electrically
capable of carrying any available fault current. They are used for
bonding the identified conductor or neutral to the enclosure or
service electrical equipment, for bonding grounding electrodes
together, for bonding sections of raceway or cable trays together,
for bonding hinged or removable covers, and for many other
purposes. "

I think I knew about this rule and T41 10 years ago. Thanks for
the reminder.

P&L
That code tells us table 41 is for bonding a metal service conduit. It doesn't say table 41 is used for sizing a bond wire.

Check out 10-200 in your handbook. Look at Figure 10-5. (I will try and scan a pic and put it up) It shows how the service conduit (metal) is bonded as per table 41 and the bonding conductor is as per 10-624(2)

10-624(1)and (2)
(1)Where the system is grounded at any point, the metal enclosure of the service box, or equivalent where a service box is not provided, shall be bonded to the grounded conductor bus with a bonding screw or strap supplied with the equipment.
(2)where a bonding screw or strap is not provided, a bonding jumper sized in accordance with rule 10-814 shall be used.

10-814 Says use table 16
 

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Discussion Starter #19
Ok, where to start...

Yes the new code left out the sentence "or equivalent for multiple parallel conductors" on the new table 16A and B.

The new note at the bottom of the table isn't very clear either.

The bond size for the XO of a transformer is, and has always been based on the ampacity of all conductors if running parallel.

So lets say you didn't run parallel conductors, would the bond to XO be bigger because your using bigger wire to feed the same transformer? No
So lets say you ran multiple conductors, say like 4 per phase. Same transformer but smaller wires. Would the bond to XO be smaller because your using smaller wire? No

The transformer doesn't care how you wire it. The fault current will be the same and the bond to XO must be sized properly to handle the current.
It was always my understanding that the XO bond was sized to the parallel equivalent but if you read the 2015 code book as is, it only says "size based on largest conductor" So my boss says do it that was because thats what the code book says! ...Im trying to find something *in the code book* that says use the equivalent, not just common sense.

The note on T16a only says "Where multiple ungrounded conductors are used in parallel runs, parallel bonding conductors should be used " and just clarifies that each bond wire needs to be run in each conduit/next to the conductors "to minimize increased impedance in the bonding conductor". At least thats my understanding of the note..


As for where to land the ground conductor, inspectors want to see it on XO.

ESA has a bulletin with a nice picture showing where to land what on a transformer. Bulletin 10-21-2 Diagram B-1
Can you screenshot and upload that bulletin/diagram?

IF the 2015 code does intend for the size of the case bond
to be based only on the size of the wires on the output and not the
equivalent size of the parallel runs, what reason might there be for
this?
If the case were to become energized, how would this happen?
If the answer to this is that it happens by one of the parallel outputs
coming in contact (due to damage to the insulation, etc) with the
case, box connector, flex, or whatever, then the available current is
dependent on the size of the individual parallel run. Not the
equivalent.

Is this their intent or reasoning? I don't know. It's just a thought.

P&L
Not really sure. If you think about it, what would happen if there was a ground fault/short from the lugs (where the parallel conductors are terminated) to the case. The conductors played no part in the fault so if would definitely make sense to size the XO bond based on the output.

This is a common misconception. 10-204 says you must use Table 16A to size the system ground. When you bring a neutral (wye) the ground needs only be #6. When there isn't a neutral present, the grounded circuit conductor (which is the grounding circuit conductor in this case) must be able to carry a larger amount of current.
Nothing in the code is ever simple.
I believe 10-204 (2) (b) only states that If you are using a neutral/grounded conductor it must be at minimum (the grounded conductor) sized to 10-814.

The rule you are looking for is 10-812 (see Appendix B) from sizing transformer grounds

Table 41 is for service raceways no?
Can you direct me to the code that says we use Table 41 to size a bonding jumper? Like in a transformer as per the OP's question.


Here is all I got.
10-614 Bonding jumpers shall be
(1)(b) of sufficient size to have an ampacity not less than that required for the corresponding bonding conductor, except that for service raceways this ampacity shall be permitted to be determined on the basis of
(i) Table 41
Yes T41 is for bonding service raceways, bonding bushings, floating sections of pipe as per 10-614 (1) (b)
 
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