APPLIC ATION NOTE
APPLIC ATION NOTE
AE 500TX
(Formerly known as PVP500kW)
Integrated DC circuit breaker
based subcombiner option
A P P L I C AT I O N N O T E
Introduction
CONTENTS
•Introduction
Page 1
•Advantages of Circuit Breaker Based Subarray Combiners
Page 1
•Available Circuit Breaker Based Subarray Combiner Options
Page 2
•DC Breaker Applications Information
Page 3
•Circuit Breaker Terminal Data
Page 3
•DC Circuit Breaker Subcombiner Components
Page 3
•Conclusion
Page 3
AE Solar Energy • 20720 Brinson Blvd • Bend, OR 97701 U.S.A.
www.advanced-energy.com/solarenergy
877.312.3832 • sales.support@aei.com • invertersupport@aei.com
Please see www.advanced-energy.com for worldwide contact information.
Advanced Energy’s new AE 500TX inver ter features an integrated DC circuit breaker based
subcombiner option which features DC breakers in place of the fused subcombiner options
available on other inver ters in AE’s TX product line. The intent of this application note is to
discuss the advantages of using DC circuit breakers with respect to the National Electrical Code
(NEC) requirements, provide an overview of the DC circuit breaker configurations available from
AE and review the basic proper ties of the DC circuit breakers.
Advantages of Circuit Breaker Based Subarray Combiners
Every revision of the National Electrical Code (NEC) brings changes intended to create safer
electrical installations. The rules per taining to photovoltaic installations have been changing rapidly
as the technology evolves and sees more widespread adoption. Advanced Energy developed a
circuit breaker based subcombiner solution to specifically address 2011 NEC section 690.16(B),
which reads as follows:
690.16(B) Fuse Servicing. Disconnecting means shall be installed on PV output circuits where overcurrent
devices (fuses) must be serviced that cannot be isolated from energized circuits. The disconnecting means
shall be within sight of, and accessible to, the location of the fuse or integral with fuse holder and shall
comply with 690.17. Where the disconnecting means are located more than 1.8m (6 ft) from the over
current device, a directory showing the location of each disconnect shall be installed at the overcurrent
device location.
Previous editions of the NEC required disconnects for fuse maintenance as well. These were
contained in 690.16 in the 2008 NEC, which became 690.16(A) in the 2011 NEC. However, the
2008 NEC does not specify a location for the required disconnects. Under the 2008 NEC, it would
be permissible to have a
DC Fused fused subarray combiner
Disconnect AC Subarray located at the inver ter
Disconnect Combiner Combiner Combiner Box Box at ground level and the
disconnecting means
in the roof mounted
combiner boxes. This is
shown in Figure 1.
Combiner Box Combiner Box © Advanced Energy Industries, Inc. 2012
All rights reserved. Printed in U.S.A.
Figure 1 - Installation compliant with 2008 NEC
ENG-AE500TXBreakers-270-01 12/12
Advanced Energy is a registered U.S. trademark of Advanced Energy Industries, Inc.
AE Solar Energy is a US based company.
APPLIC ATION NOTE
APPLIC ATION NOTE
Combiner Box Combiner Box On
DC
Disconnect
On
DC
Disconnect
Off
Off
Fused Subarray Combiner DC Disconnect AC Disconnect It is impor tant to note that since the circuit breakers serve as
the load break rated disconnecting means, a single main DC
disconnect is not provided. If the circuit breaker based subarray
combiner is not installed, an external DC disconnect will be
required.
On
DC
Disconnect
Off
Combiner Box On
DC
Disconnect
Combiner Box Additional Disconnects required per 2011 NEC 690.16(B) Available Circuit Breaker Based Subarray
Combiner Options
If the roof were not easily accessible, maintenance personnel
might choose to work on live fuses rather than locating and
shutting off the disconnects. This scenario is especially likely
if roof access requires a ladder, a lift, or advanced notice to
the proper ty owner. Section 690.16(B) was added to the 2011
National Electrical Code to eliminate this potential safety
problem. If a designer wants to use subcombiner fuses, then
690.16(B) requires the addition of disconnects within sight of a
fused subarray combiner as shown in Figure 2. The definition of
within sight gives a maximum distance of 50’. Also, the final
sentence of 690.16(B) requires a directory be installed if the
disconnects are more than 6’ from the fuses they isolate. This
does not remove the requirement to install these disconnects
within sight of the fusing if a directory is installed.
Combiner Box Combiner Box Circuit Breaker Based Subcombiner AC Disconnect Combiner Box Combiner Box Figure 3 - Circuit breaker based subarray combiner
In response to this change in the National Electrical Code,
Advanced Energy is offering circuit breaker based inver ter
integrated subarray combiners on its AE 500TX inver ter. Moving
from the fuse based inver ter integrated subarray combiners to
circuit breaker based subarray combiners eliminates the need
for additional, external disconnecting means. Because there are
no fuses, there is no need for fuse servicing disconnects. This
is shown schematically in Figure 3. This change maintains the
advantage of having an inver ter integrated subarray combiner
while complying with the latest code revision. In addition,
Page 2
DC Breaker Applications Information
Circuit Breaker Thermal Derating
Advanced Energy offers a number of options for inver ter
integrated circuit breaker based subcombiners on the AE 500TX.
There are two frame sizes available, 225 A and 400 A. Different
factory installed trip units give a selection of trip settings within
each frame size. The mix of trip settings can be specified based
on the array design. The available options
are listed in the table below.
Option
Monitoring
Available Trip Units
8 x 400 A
Available
400 A, 350 A, 300 A, 250 A, 200 A,
150 A, 100 A
16 x 225 A
Available
225 A, 200 A, 175 A, 150 A, 125 A,
100 A, 80 A
Not Available
225 A, 200 A, 175 A, 150 A, 125 A,
100 A, 80 A
20 x 225 A
Note: The sum of all overcurrent protection must be 3500 A or less.
When a mix of breaker trip settings is used, the breakers will
be installed with the highest ampacity setting at the top of the
subarray combiner and the lowest value at the bottom. If fewer
than the standard number of breakers are specified, the bottom
position(s) will be left vacant. There will be empty spaces at the
bottom of the enclosure. Breaker positions and settings are not
field configurable.
The circuit breaker based subcombiner is optional for the
AE 500TX. It is not necessary to order the inver ter with
an integrated subcombiner. However, the breakers serve as
both overcurrent protection and disconnecting means. If a
subcombiner is not included with the inver ter, external DC
disconnects must be installed.
DC Circuit Breaker Subcombiner
Components
The DC circuit breakers used in Advanced Energy’s integrated
subcombiner are not rated for continuous operation at 100%
duty. Therefore, when selecting the appropriate circuit breaker,
the 125% safety factor given in NEC 690.8(B)(1) must be used.
This is in addition to the 125% safety factor given for high
irradiance required by NEC 690.8(A)(1).
Off
Figure 2 - Disconnects added per 2011 NEC
the DC circuit breakers serve as load break rated disconnect
switches. They can be used to disconnect DC power from the
inver ter for routine maintenance or for an emergency response.
After installation, the terminals are covered by a dead front
cover, leaving only the operating handles accessible.
Circuit Breaker
Thermal Derating
ASHRAE 2% Temperature
Breaker Derating
39 °C or less
1.00
40 °C to 44 °C
0.96
45 °C to 49 °C
0.92
50 °C or greater
0.88
In addition, consideration must be given to the inver ter’s thermal
environment. At elevated temperature circuit breakers will trip
at a lower current level. To prevent nuisance tripping, circuit
breakers should be derated based on the expected ambient
temperature. For inver ters installed outdoors, the use of
American Society of Heating, Refrigeration, and Air Conditioning
Engineers (ASHRAE) 2% dry bulb temperature data for the
hottest month is recommended. The breakers should then be
derated based on the table on the values in the table above.
The thermal derating is multiplied by the nominal trip setting
to give the effective breaker ampacity. For example, a 200 A
circuit breaker installed in Barstow, CA with a July ASHRAE 2%
temperature of 43 °C, would have an effective ampacity of
200 A x 0.96 = 192 A.
Circuit Breaker Terminal Data
Breakers
Breakers
DC
+ bus
bus bar
DC+
bar
400 A (frame)
circuit breaker
Dead front removed
for access
Bus bar for
conductor landing
Deadfront
front
Dead
Subcombiner
monitoring
I/O unit
Figure 4 - Subcombiner components - 8 x 400 A option
Conclusion
The AE 500TX continues Advanced Energy’s tradition of
innovative products and solutions for PV applications. By
introducing a DC circuit breaker based subarray combiner
option, AE provides a path for simple, low cost compliance
with the 2011 National Electrical Code.
The allowable wire range and terminal temperature rating vary
depending on the selected subcombiner option. The table below
shows the terminal characteristics for all options.
Option
Allowable Wire
Size
Conductor
Material
Terminal Temp
Rating
8 x 400 A
Direct to Bus bar
Cu/Al
90 °C
20 x 225 A
4-4/0 AWG
Cu/Al
75 °C
Direct to Bus bar
Cu/Al
90 °C
None
The 8 x 400 A and 16 x 225 A breaker options simply present
the installer with a shor t piece of bus bar containing a 3/8” hole
for landing conductors. The installer provides an appropriate
crimp on a mechanical lug based on the desired wire size. This
allows the installer to use any reasonable conductor size. If
parallel conductors are required, it is possible to mount one on
each side (front/back) of the bus bar.
Page 3