Outdoor NON-service transformer

[electrofelon]

another related question... I'll need a disconnect switch prior to the transformer at this second building, according to section 225.31 (2008 NEC). This will be my disconnecting means. Section 225.36 requires this switch to be suitable for service equipment, meaning i have to bond the neutral and grounding terminals (which seems useless from what i've been reading)... BUT, since i'm running the primary feeder to the delta-wye transformer, my primary feeder won't have a neutral conductor since the delta terminals of the transformer don't require a neutral... only 3 phase conductors and an EGC. how do i call for this disconnect switch, located on the line side of the transformer, to be service rated if i have no neutral going through it?

SUSE doesn't mean the N-G has to be bonded.

 

[Grouch1980]

SUSE doesn't mean the N-G has to be bonded.

you got me there. what does SUSE mean then?

 

[electrofelon]

you got me there. what does SUSE mean then?

Suitable for use as service equipment

 

[Grouch1980]

Suitable for use as service equipment

and in the case of section 225.36, it doesn't require a bonding connection between neutral and ground?

 

[Grouch1980]

Now that I think about it, let me see if i can take a stab at this... 225.36 doesn't say "suitable for use ONLY as service equipment". so it gives you flexibility, as in my case where a neutral wire is not brought to the second building along with the phase wires (since we're feeding a delta-wye transformer); so i have the option of not making that bond connection, since there is no neutral. Do I have this correct?

 

[kwired]

All correct. And the transformer and most of the distribution is located outside that second building, right up against it; the 8 ft. ground rod would be right next to the transformer. And there are some regular breaker panels inside that second building. What would be this change you mention?

The transformer is a separate building/structure. The building you are supplying is also a separate building and would have it's own required grounding electrode system. If the separately derived system were inside the building then you only need to bond it and then make a connection to the building GES. Inside you wouldn't drive a rod, connect it to transformer and call it good, you must connect to the building GES.

 

[kwired]

and in the case of section 225.36, it doesn't require a bonding connection between neutral and ground?

Lost me on exactly what point in the system you are referring to.

Once you are past the main/system bonding jumper you don't bond the grounded conductor (most times the neutral conductor) again, even at separate buildings/structures.

If feeding 480 to the separate building but then transforming to 208/120 for all utilization you don't need the 480/277 neutral at that building. You still need to connect the EGC to a grounding electrode system at that building. You also would need to bond the secondary neutral and connect it to the same GES

If the transformer is not in the building then you only enter with the 208/120 system. If that system already is bonded at source then you must run separate neutral and EGC to the building and the building GES would be connected to the EGC.

If transformer is not in the building but is adjacent to it, you likely can have the first disconnect also be the main disconnect for the building, put your bonding jumper in that disconnect, connect the GES at that disconnect, but would still need a SSBJ back to the transformer housing.

 

[Grouch1980]

All noted, and thanks! Now, would I still need an unfused disconnect on the line side of the transformer, based on 225.31? That section states "Means shall be provided for disconnecting all ungrounded conductors that supply or pass the building or structure." For this same switch, assuming its needed, section 225.36 throws me off by saying this line side switch needs to be SUSE, which doesn't make sense.

 

[electrofelon]

Now that I think about it, let me see if i can take a stab at this... 225.36 doesn't say "suitable for use ONLY as service equipment". so it gives you flexibility, as in my case where a neutral wire is not brought to the second building along with the phase wires (since we're feeding a delta-wye transformer); so i have the option of not making that bond connection, since there is no neutral. Do I have this correct?

Right. You could not use equipment "suitable for use ONLY as service equipment". SUSE means it has provisions for a N-G bond, not that it must be bonded

 

[Grouch1980]

The transformer is a separate building/structure. The building you are supplying is also a separate building and would have it's own required grounding electrode system. If the separately derived system were inside the building then you only need to bond it and then make a connection to the building GES. Inside you wouldn't drive a rod, connect it to transformer and call it good, you must connect to the building GES.

which section defines the transformer as a separate building / structure? i imagine it's because it needs its own GES... but where does it say this specifically that it's considered a separate structure?

 

[augie47]

which section defines the transformer as a separate building / structure? i imagine it's because it needs its own GES... but where does it say this specifically that it's considered a separate structure?

Seldom disagree with kwired but in this case, if we use 2017 NEC as a reference I would say the transformer would not be a separate structure:
Structure. That which is built or constructed, other than equipment

 

[Grouch1980]

I'm on the 2008 NEC code. NYC is way behind.

 

[kwired]

Seldom disagree with kwired but in this case, if we use 2017 NEC as a reference I would say the transformer would not be a separate structure:
Structure. That which is built or constructed, other than equipment

May not be, but is not a part of the other structures either, unless immediately adjacent to one of them then probably up to AHJ to determine if it is considered a part of that structure. So if stand alone it may not require a GES at the transformer, but each building still does. You also are still creating a separately derived system and need to ground it. Does it need grounded at the transformer in such case or can it be grounded at first disconnect - even if that is in a separate structure? Regardless the transformer enclosure should still need a SSBJ run back to it if is allowed to bond at the first disconnect. I'd say NEC does not want you to ground it at transformer and at the separate building - that is consistent with other situations when supplying a separate building

 

[Grouch1980]

I think I may have explained one part incorrectly, as I'm reading everything again. The disconnect on the secondary of the transformer will be adjacent to the transformer, right outside the building.... the disconnect will not be inside the building, but rather it will be next to the transformer, outside. The disconnect will be feeding panels inside the building. Will this work?.... Based on the top half of the diagram that I attached from the 2008 NEC (maybe in another 50 years NYC will get to the 2017 version ), I'll run a SBJ from the secondary disconnect back to the transformer neutral terminal (again, both are together outside). From that transformer neutral terminal, i'll ground it to 2 ground rods... and since the building's metal frame will act as a GES, I would bond the ground rods to the building's metal frame, and therefore have one GES for the entire installation. Does this also work?

 

[kwired]

I think I may have explained one part incorrectly, as I'm reading everything again. The disconnect on the secondary of the transformer will be adjacent to the transformer, right outside the building.... the disconnect will not be inside the building, but rather it will be next to the transformer, outside. The disconnect will be feeding panels inside the building. Will this work?.... Based on the top half of the diagram that I attached from the 2008 NEC (maybe in another 50 years NYC will get to the 2017 version ), I'll run a SBJ from the secondary disconnect back to the transformer neutral terminal (again, both are together outside). From that transformer neutral terminal, i'll ground it to 2 ground rods... and since the building's metal frame will act as a GES, I would bond the ground rods to the building's metal frame, and therefore have one GES for the entire installation. Does this also work?

As I have tried to mention, sort of depends on what AHJ may allow. NEC doesn't say anything about how far away from the building something like this can be before not considered a part of the building.

If considered part of the building do things pretty much the same way you would if it were inside. If not considered part of the building then the building must have it's own disconnect in/on the building and it's own GES. The transformer may or may not be considered a separate structure per NEC (especially with change mentioned earlier in 2017 that exempts "equipment") but regardless if it is stand alone equipment it is still separate from the other "building".

Since you said you were on 2008, you pretty much still have the separate grounded and grounding conductor rule for separate buildings that was first year there it was required that way as the general rule, if you were on 2005 you could still run just a grounded conductor (no separate EGC) to a separate building and then connect that to the GES at the separate building, with some conditions.

 

[Grouch1980]

Understood. What I may do is try to take a look at other installations around NYC and see what was done. The downside to that is.... just because it was done that way doesn't mean it's right I'll see what I'll do. I appreciate all the feedback from everyone. As always it's great help.