Wye to wye questions

[tortuga]

I like the sketch but in Option B there is a bond from H0/Xo terminal in the LV side to the ground pad.
that should be clearly shown in the sketch.
as synchro and others have pointed out
we need that for fault clearing and to comply with 250.4(A)(5) and 250.122.

The question becomes does 250.184(C)(1) allow it?

250.184 modifies 250.24(A)(5) and
250.142(B).

250.180 General. Where systems over 1000 volts are grounded,
they shall comply with all applicable provisions of the preceding
sections of this article and with 250.182 through 250.194, which
supplement and modify the preceding sections.

250.184(C) Multigrounded Neutral Systems. Where a multigrounded
neutral system is used, the following shall apply:
(1)The neutral conductor of a solidly grounded neutral system
shall be permitted to be grounded at more than one point.
Grounding shall be permitted at one or more of the fol-
lowing locations:
a. Transformers supplying conductors to a building or
other structure

I addressed exactly this point in post #132

In post #132

MGN only applies to MV. So you are into a game of where you ground the neutral and where that point of demarcation is.

I agree its murkey but as soon as you hit 250.180 code is modified including the entire transformer.
The demarcation is noted on the option B drawing.
The H0/X0 --> G connection is in the 'transformer' and is allowed on either side.
As option B shows in the sketch.
http://thinkelectric.org/continuingEd/wye-wye2.pdf

All the 'ground pads' in the transformer do get bonded together within the transformer.
[I should add the pass thru ground pad on the HV side and the three concentric.]

All references 2014 NEC

 

[electrofelon]

NOTE: Their is no one X0 termnial and no another separate H0 terminal. Their is One H0/X0 terminal on LV side only. There are two gnd pads one each compartment.

Sorry, I think was confusing you. When I was talking about making the bond to the neutral on the MV side in the MV compartment, I was assuming the HO was accessible there. It seems on your unit, the ONLY point where HO/XO is accessible is in the LV compartment. I kept skipping over that, sorry. Attached is a picture of what I was thinking of.

 

[electrofelon]

I like the sketch but in Option B there is a bond from H0/Xo terminal in the LV side to the ground pad.
that should be clearly shown in the sketch.
as synchro and others have pointed out
we need that for fault clearing and to comply with 250.4(A)(5) and 250.122.

The question becomes does 250.184(C)(1) allow it?

250.184 modifies 250.24(A)(5) and
250.142(B).









In post #132


I agree its murkey but as soon as you hit 250.180 code is modified including the entire transformer.
The demarcation is noted on the option B drawing.
The H0/X0 --> G connection is in the 'transformer' and is allowed on either side.
As option B shows in the sketch.
http://thinkelectric.org/continuingEd/wye-wye2.pdf

All the 'ground pads' in the transformer do get bonded together within the transformer.
[I should add the pass thru ground pad on the HV side and the three concentric.]

All references 2014 NEC

I like it. I agree with your interpretation of the MGN provision applying to the entire transformer. MV/LV MGN snuggle fest :hug:

So hhsting make the following changes to you sketch post #160:

1. Remove EGC going from 13.2 gear to transformer
2. Bond HO/XO to ground pad (there is probably a strap like in my recent HO picture).


Also, GEC connection to 13.2 neutral and gear frame, GEC connection to transformer as shown, not GEC connection to LV EGC bus.

Only sticky thing is you do have a parallel path for neutral current between the 13.2 gear and the tranny due to them using the same ground ring. Not sure anything can be done about that and I cant point to a specific code violation.

 

[hhsting]

I like it. I agree with your interpretation of the MGN provision applying to the entire transformer. MV/LV MGN snuggle fest :hug:

So hhsting make the following changes to you sketch post #160:

1. Remove EGC going from 13.2 gear to transformer
2. Bond HO/XO to ground pad (there is probably a strap like in my recent HO picture).


Also, GEC connection to 13.2 neutral and gear frame, GEC connection to transformer as shown, not GEC connection to LV EGC bus.

Only sticky thing is you do have a parallel path for neutral current between the 13.2 gear and the tranny due to them using the same ground ring. Not sure anything can be done about that and I cant point to a specific code violation.

Slight problem with removal of EGC 13.2kV going from gear to xfmr:

Nec 2014 Article 250.190(C)(2) "the metallic insulation shield encircling the current carrying conductor shall be permitted to be used as EGC if its rated for clearning time of ground fault protrective device operation without damaging the metallic shielding......"

metallic insulation shield if you read blue commentary handbook further down is concentric neutral cable.

I think designer maybe provided 13.2kV EGC because concentric neutral cannot clear ground fault without damaging concentric neutral.

So he has in 13.2kV swbd service disco their is neutral bar where concentric neutral lands from POCO and customer concentric neutral connected and ground bar, their is neutral to ground bond MBJ and separate EGC from the ground bar to 13.2kV xfmr. Customer concentric neutral also goes to 13.2kV xfmr with phase conductor.

Engineer says he is using MGN 13.2kV side. Would keeping the 13.2kV separate EGC be problem and would it still be MGN?

 

[electrofelon]

I think designer maybe provided 13.2kV EGC because concentric neutral cannot clear ground fault without damaging concentric neutral.

I dont see how that could be. Even if cables are 1/3 neutral, you then have an EGC same size as phase conductors.

So he has in 13.2kV swbd service disco their is neutral bar where concentric neutral lands from POCO and customer concentric neutral connected and ground bar, their is neutral to ground bond MBJ and separate EGC from the ground bar to 13.2kV xfmr. Customer concentric neutral also goes to 13.2kV xfmr with phase conductor.

Engineer says he is using MGN 13.2kV side. Would keeping the 13.2kV separate EGC be problem and would it still be MGN?

Yes it would still be an MGN if the neutral is grounded. I cant think of a violation in keeping that EGC.

 

[Hv&Lv]

Nec 2014 Article 250.190(C)(2) "the metallic insulation shield encircling the current carrying conductor shall be permitted to be used as EGC if its rated for clearning time of ground fault protrective device operation without damaging the metallic shielding......"

metallic insulation shield if you read blue commentary handbook further down is concentric neutral cable.

I haven’t read the handbook but I can tell you there are “metallic insulation shield encircling the current carrying conductor” that is NOT concentric neutral cable.

metallic tape shielded cable is not capable of clearing a fault. It is a shielding only. A separate neutral must be pulled if it is wye.

concentric neutral cable is different.

 

[hhsting]

I haven’t read the handbook but I can tell you there are “metallic insulation shield encircling the current carrying conductor” that is NOT concentric neutral cable.

metallic tape shielded cable is not capable of clearing a fault. It is a shielding only. A separate neutral must be pulled if it is wye.

concentric neutral cable is different.

Yes there are two kinds: 1. . metallic insulation tape, or 2. drain wire shield encircling conductor according to NEC 2014 Article 250.190(C)(2). Metallic Tape and Drain wire shield insulation cannot be used as EGC solidly grounded systems.

However handbook 2014 Article 250.190(C)(2) blue commentary says "...A metallic insulation shield encircling the conductor (bottom cable shown), commonly called concentric neutral cable...."

I thought concentric neutral cable can be used as EGC as long as it is not damaged during time it takes to clear fault by protrctive device operation. Are you saying concentric neutral are not permitted to be EGC?

 

[electrofelon]

Yes there are two kinds: 1. . metallic insulation tape, or 2. drain wire shield encircling conductor

No, those are one type. Concentric neutral is the 2nd type.

 

[Hv&Lv]

Yes there are two kinds: 1. . metallic insulation tape, or 2. drain wire shield encircling conductor according to NEC 2014 Article 250.190(C)(2). Metallic Tape and Drain wire shield insulation cannot be used as EGC solidly grounded systems.

However handbook 2014 Article 250.190(C)(2) blue commentary says "...A metallic insulation shield encircling the conductor (bottom cable shown), commonly called concentric neutral cable...."

I thought concentric neutral cable can be used as EGC as long as it is not damaged during time it takes to clear fault by protrctive device operation. Are you saying concentric neutral are not permitted to be EGC?

No. I’m saying the handbook isn’t always 100% correct in the way things are written in it...

concentric neutral cable can be used for your application. The CN is no different than any other CU conductor you would pull.

 

[hhsting]

I like it. I agree with your interpretation of the MGN provision applying to the entire transformer. MV/LV MGN snuggle fest :hug:

So hhsting make the following changes to you sketch post #160:

1. Remove EGC going from 13.2 gear to transformer
2. Bond HO/XO to ground pad (there is probably a strap like in my recent HO picture).


Also, GEC connection to 13.2 neutral and gear frame, GEC connection to transformer as shown, not GEC connection to LV EGC bus.

Only sticky thing is you do have a parallel path for neutral current between the 13.2 gear and the tranny due to them using the same ground ring. Not sure anything can be done about that and I cant point to a specific code violation.

The sticky thing that you mention parallel path between13.2kv swbd and tranny can it be problem for proper functioning of fuses and breakers?

 

[electrofelon]

The sticky thing that you mention parallel path between13.2kv swbd and tranny can it be problem for proper functioning of fuses and breakers?

No