New installation work.

[Groundedforlife]

Dear Forum,

I have a rather lengthy question. Please bare with me. I am installing a
complex distribution system. Admittedly, it is beyond my normal scope of
daily duties. It is my hope to make this clear as can be when describing the
task at hand.

From and at a pad mount xfmr's secondary of 480v I will be installing a 200
amp fused safety switch. The conductors will travel underground 225' to a
new wood frame single story bldg. Inside the building I will install an
additional 200A fused safety switch then to a 150kva xfmr that will be in
close proximity and have a secondary of 120/208. From this new SDS
transformer I will be installing a 400 amp MB panel then to a ML sub panel
rated at 200A. All components will be in close proximity <10'. This is all
specked out in the drawings. There is a note stating that "Connections shall
be neutral/ground bonded". I understand the terms "System bonding jumper",
"Equipment ground conductor" & Parallel path potential.

My question: Where should I Neutral/ground bond and where should I not?
This is a commercial building and will be 3 ph. throughout. The new
transformer must be neutral/ground bonded as per manufacturers
recommendation.

Thanks
Rich

 

[maghazadeh]

Dear Forum,

I have a rather lengthy question. Please bare with me. I am installing a
complex distribution system. Admittedly, it is beyond my normal scope of
daily duties. It is my hope to make this clear as can be when describing the
task at hand.

From and at a pad mount xfmr's secondary of 480v I will be installing a 200
amp fused safety switch. The conductors will travel underground 225' to a
new wood frame single story bldg. Inside the building I will install an
additional 200A fused safety switch then to a 150kva xfmr that will be in
close proximity and have a secondary of 120/208. From this new SDS
transformer I will be installing a 400 amp MB panel then to a ML sub panel
rated at 200A. All components will be in close proximity <10'. This is all
specked out in the drawings. There is a note stating that "Connections shall
be neutral/ground bonded". I understand the terms "System bonding jumper",
"Equipment ground conductor" & Parallel path potential.

My question: Where should I Neutral/ground bond and where should I not?
This is a commercial building and will be 3 ph. throughout. The new
transformer must be neutral/ground bonded as per manufacturers
recommendation.

Thanks
Rich

Base on the priviously posting of similar question, you have 2 choices for the system bonding jumper location.
1) at the transformer to bond GEC and neutral together. or
2) at the first disconnect which in your case is the 400A MB panel.
I prefer at the tranny, but my undrestanding of other posts is your EGC from tranny to 400A panel must be sized equal to GEC.
You bond neutral and ground only once at either locations, no more bonding there after.
Hope this helps.

 

[jwelectric]

Base on the priviously posting of similar question, you have 2 choices for the system bonding jumper location.
1) at the transformer to bond GEC and neutral together. or
2) at the first disconnect which in your case is the 400A MB panel.
I prefer at the tranny, but my undrestanding of other posts is your EGC from tranny to 400A panel must be sized equal to GEC.
You bond neutral and ground only once at either locations, no more bonding there after.
Hope this helps.

Depending on which code cycle you are on this conductor would be either the “equipment bonding conductor” (2008) or the “supply side bonding conductor” (2011 cycle) but whatever you call it, it must be sized by Table 250.66 or the 12 ?% rule. See 250.30(A)(2)

 

[infinity]

As Mike has pointed out in the 2011 NEC they've attempted to clean up some of these definitions when they apply to a service or a separately derived system. By using the proper terminology it puts us all on the same page. Although the new stuff makes sense I still want to use some of the old terminology.

One other note if you're using parallel raceways you could size the supply side bonding jumper(s) according to the size of the conductors in each raceway with Table 250.66.

 

[jwelectric]

Rob,
I did a class yesterday on the Analysis of Changes 2011 for electrical contractors. While addressing the rewriting of section 250.30 and talking about 250.30(A)(2) and its reference to 250.102(C) I got a loud roar from the audience.

Are you ready for this?????

I went on to say that section 250.102(C) would refer one back to 250.94. I suppose old habits are hard to break. How many years has it been since it was moved to 250.66?
It was an embarrassing moment but I got through it. It wasn?t until we were talking about NM cable and twice I made a reference to 336 that my face really got red. I caught myself both times but still it was a very embarrassing moment to foul so badly so many times in one day.

What made it all livable was the fact that at break time a couple of the older electricians came to me and said I was keeping the young bucks on their toes making references to older code cycles.

I understood what he was saying about the EGC but wanted to point out the proper way to size it.