AC disco Wiring? [RE-wrenches]

[Matt Lafferty]

Sunny Greetings from Sacramento!  (Yeah, I've been here, just keeping my
mouth shut for awhile...lucky you!)

Graham wrote:

Is it best to land the wires from the inverter or the wires from the
service panel on the top of the switch?

All:

It is important to land the wires from the service panel on the "top",
or "line-side" of a disconnect.

This is important for several reasons....1) "Hots on Top" has been the
electrical industry standard for disconnect termination for many years;
2) Many disconnect switches have arc-shields or other provisions that
prevent inadvertent contact with the energized terminals when in the
"Open" or "Off" position;  3) If the disconnect is fused, landing the
"Hot" wires on the top allows replacement or testing of the fuses when
the disconnect is in the "Off" position without either end of the fuse
being energized;  4) It's required by NEC..."Hots on Top", "Top to
Bottom" and "Left to Right" are some of the common-language principles
and references that apply.

It is important to apply the same principle to the DC Disconnect as
well.  PV landed on top lugs, Inverter on the bottom.

The single most "confusing" area of this principle I've encountered is
when there is a PV Production Meter installed in the system.....As Keith
pointed out with his "spanking reference", the Main Service "Revenue"
Meter should have the Utility / Line Side terminated on "Top".  The
"concept" or "principle" originates from the "Top to Bottom"
principle....."Power in on Top, Out on Bottom".  This was established
many years ago in an effort to standardize (a good thing in general) the
application within the industry.  Power consumption is measured "Top to
Bottom" through a standard kWH meter as a result.

In the case of a PV Production meter, we are measuring the "consumption"
of the grid and the attached Customer Load......The grid and the
Customer comprise the load, the PV is the source.  In the case of a PV
Production meter, the Inverter(s) should be connected to the top lugs of
the Socket, with the Interconnection wiring connected to the bottom
lugs.  This leaves the "Bottoms Hot" with the meter removed, presenting
a "Not-Normal" conddition for anyone working with the Meter Removed.  As
Brother Bill stated, a sign or placard is recommended stating the
presence of this condition....Remember, it's "not normal" anymore.

Glad to hear Keith still has two coconuts,

Matt Lafferty
mlafferty at universalenergies.com


 

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