SMA SSM-U-2410, SSM-U-1615, SSM-U-3210, SSM-U-3215, SSM-U-1610 Technical Information
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TechnicalInformation
SMA STRING-MONITOR SSM-U-XX10 / SSM-U-XX15
SSMUXX1015-TI-en-10 | Version 1.0
ENGLISH
1 Overview of Product Details
Product Description
• The SMA String-Monitor is a PV array junction box for outdoor areas to which several strings can be connected in
parallel. The SMAString-Monitor collects, measures and monitors the input currents of the strings, assists in
detecting failures, thus helping to minimize power and yield losses.
• The measured values are transmitted from the SMA String-Monitor via Ethernet to the next SMA String-Monitor in
the communication bus up to the inverter. Distances of up to 100m between the nodes are possible when using
copper cables. Greater distances of up to 2,000 m between two nodes are possible via optical fibers (see
Section8, page24).
• The number of SMA String-Monitors connectable to an inverter depends on the DC inputs of the inverter. One
SMA String-Monitor per DC input can be connected to the inverter.
• Up to ten SMA String-Monitors can be connected in line topology to each string monitoring communication
terminal of the inverter (for information on the number of string monitoring communication terminals, see the
inverter manual).
• The SMAString-Monitor is equipped with a DC load-break switch. The DC load-break switch can disconnect the
PV array connected to the SMA String-Monitor from the inverter.
• The SMA String-Monitor may only be operated if the strings are protected with fuses. SMA Solar Technology AG
guarantees the safe operation of the SMA String-Monitors in combination with inline fuse connectors as string
fuses and when the inline fuse connectors are connected directly to the DC connectors of the string cables of the
SMA String-Monitor. Using a different type and location of fuses for the strings does not guarantee the safe
operation of the SMA String-Monitor and the observance of the thresholds by SMA Solar Technology AG. The
inline fuse connectors are available as an accessory (see Section8, page24).
• There are six SMA String-Monitor models available depending on the system voltage and on the number of PV
inputs to be monitored:
– The SSM-U-XX10 is suitable for voltages of up to 1,000 VDC and is available with XX = 16, 24 or 32 PV
inputs.
– The SSM-U-XX15 is suitable for voltages of up to 1,500 VDC and is available with XX= 16, 24 or 32 PV
inputs.
Equipment and Equipment Options
• Depending on the product option, the SMA String-Monitor is equipped with 16, 24 or 32 measuring channels.
Different numbers of string inputs and string fuses can be assigned to the measuring channels. This allows you to
achieve the optimum design for your PV system and to protect the PV array from reverse currents.
• The interior of the SMA String-Monitor is equipped with protective covers for the lower DC input area and for the
upper DC output area. This facilitates working on the disconnected lower DC input area in the SMA StringMonitor without having to disconnect the DC output area from voltage sources on the inverter side.
• The string fuses are attached on the outside of the enclosure of the SMA String-Monitor. This prevents additional
heat in the enclosure caused by the waste heat of the string fuses.
Inline fuse connectors of the SUNCLIX plug-in system by Phoenix Contact with internal gPV fuse are available as
an accessory. The inline fuse connectors are connected to the pre-installed DC connectors of the string cables of
the SMA String-Monitor.
The inline fuse connectors can be connected to the positive and/or negative terminal of the PV inputs and are
available in different electrical current strengths.
• The SMA String‑Monitor is equipped with a type II overvoltage protection. This protects the inverter against
overvoltage. The SMA String-Monitor can be additionally equipped with a type II overvoltage protection for the
communication connection and for the 230 VAC voltage supply of the SMA String-Monitor.
1 Overview of Product Details
SMA Solar Technology AG
Technical InformationSSMUXX1015-TI-en-102
• The SMAString-Monitor is equipped with a double-bit key for the switch cabinet. Profile half-cylinders are
available upon request from the manufacturer of the SMA String-Monitor enclosure.
• DC connection:
– You can connect up to two DC main cables per terminal by default.
– You can connect DC main cables from 70 mm2 to 400 mm2 made of aluminum or copper to the busbar in
the SMA String-Monitor by means of terminal lugs. Only tin-plated copper tube terminal lugs for copper
cables or bimetal tube terminal lugs for aluminum cables are permitted.
– You can connect DC main cables from 70 mm2 to 300 mm2 made of aluminum or copper to the V-box
terminals in the SMA String-Monitor. The V-box terminals are available as an accessory.
– For connecting the tube terminal lugs or the V-box terminals, the required material for the bolted connection is
pre-mounted on the busbars.
• DC load-break switch:
– The DC load-break switch is equipped with a viewing window for the contacts.
– To receive feedback on the switching state of the DC load-break switch, an alarm contact is available as an
accessory (see Section8, page24).
1 Overview of Product Details
SMA Solar Technology AG
Technical Information 3SSMUXX1015-TI-en-10
2 Product Description
2.1 Circuitry Options with Inline String Fuses
The string fuses for the SMA String-Monitor are integrated as so-called "inline string fuses" on the outside of the
enclosure in the string connection. The string terminals of the SMA String-Monitor are equipped with DC connectors
from the SUNCLIX product range of Phoenix Contact. Suitable for the SUNCLIX plug-in system, inline fuse connectors
(see Section2.2, page6) and Y adapters are available from SMA Solar Technology AG as accessories (see
Section8, page24).
The string terminals are located outside of the enclosure of the SMA String-Monitor. This offers several options for the
circuitry and fuse protection of the strings.
One-Sided Fuse Protection with Inline Fuse Connector on the Positive or Negative Terminal
Figure 1: One-sided fuse protection with inline fuse connector on the positive terminal (example)
Two-Sided Fuse Protection with Inline Fuse Connector on the Positive or Negative Terminal
Figure 2: Two-sided fuse protection with inline fuse connector on the positive or negative terminal (example)
Two Strings on One Fuse via Y Adapter
Figure 3: Two strings on one fuse via Y adapter (example)
2 Product Description
SMA Solar Technology AG
Technical InformationSSMUXX1015-TI-en-104
Two Fuses on One String via Y Adapter
Figure 4: Two fuses on one string via Y adapter (example)
Connection of Pre-Fabricated Cable Harnesses with Integrated String Fuse
Figure 5: Connection of pre-fabricated cable harnesses with integrated string fuse (example)
Position Designation
A PV module
B DC connector (positive terminal)
C Inline fuse connector
D DC connector (negative terminal)
E Y adapter
F Integrated string fuse
G SMA String-Monitor
2 Product Description
SMA Solar Technology AG
Technical Information 5SSMUXX1015-TI-en-10
2.2 Inline Fuse Connector as Inline String Fuse
The DC connectors and the inline fuse connectors are from the SUNCLIX plug-in system by Phoenix Contact and can
be installed by easily plugging them together. For further information on this subject, see the Technical Information
"IFCON Inline Fuse Connector Set16".
Design of the Inline Fuse Connector by Phoenix Contact
Figure 6: Design of the inline fuse connector by Phoenix Contact
Position Designation
A Plug-in contact (pin) from the SUNCLIX plug-in system
B Enclosure
C Electronic string fuse
D Connection of the plug-in contact with the fuse
E Plug-in contact (pin connector) from the SUNCLIX plug-in system
2.3 DC Load-Break Switch
The SMAString-Monitor is equipped with a multi-terminal DC load-break switch with a viewing window for the
contacts. The DC load-break switch disconnects the PV array connected to the SMA String‑Monitor from the inverter.
Disconnection takes place at all poles.
An alarm contact for the switching status of the DC load-break switch is available as an accessory (see Section8,
page24).
Upstream LV/HRC fuses required
Use of the DC load-break switch is only permissible if LV/HRC fuses with gPV characteristic are installed upstream
in the inverter or the main DC distribution box.
2 Product Description
SMA Solar Technology AG
Technical InformationSSMUXX1015-TI-en-106
3 System Design
3.1 Design Considerations
When designing an SMAString-Monitor, take the following aspects into account:
• Maximum current values
• Fuse rating
• Specifics for installation altitudes over 2,000m
• Ambient temperatures over 50°C
3.2 Maximum Current Values
The following current values must not be exceeded:
• Rated current (I
DCmax
) up to 50°C: 315 A
DC
• Rated current (I
DCmax
) over 50°C: reduction by 2.5% per K
• Rated current per measurement input: 17.5 A
DC
The following applies:
I
String_max
= I
DC_max
/ number of string inputs ≤ 17.5A
The rated current applies for a maximum irradiation of 1,200W/m2 (hourly average value of the horizontal global
radiation). In case the irradiation is higher, the rated current must be adapted linearly downwards.
3.3 Fuse Rating
If you are using the inline fuse connectors offered by SMA Solar Technology AG, you can find information on the fuse
rating in the Technical Information "IFCON Inline Fuse Connector Set16".
If you are using other fuses, you can find information on the fuse rating in the datasheet of the fuse manufacturer.
When selecting the fuse nominal values (I
nom
), a reduction factor according to the manufacturer specifications for the
short-circuit current of the connected PV array under standard test conditions (I
SC_STC
) needs to be applied.
The following applies:
I
SC_STC
≤ I
nom
x reduction factor or I
nenn
≥ I
SC_STC
/ reduction factor
3.4 Specifics for installation altitudes over 2,000m
3.4.1 Reduction of Maximum Fuse Current
When installing at altitudes over 2,000 m, an additional reduction factor for the fuse rating needs to be taken into
account (when using the inline fuse connectors offered by SMA Solar Technology AG, see the Technical Information
"IFCON Inline Fuse Connector Set16"; when using other fuses, see the datasheet of the fuse manufacturer).
3.4.2 Reduction of the Electrical Parameters of the DC Load-Break Switch
The current is not being reduced.
The rated voltage is reduced as follows:
• For installation altitudes of 2,001 m to 3,000 m = reduction by 1.0% per 100 m
• For installation altitudes of 3,001 m to 4,000 m = reduction by 1.2% per 100 m
3.4.3 UV Radiation
UV radiation increases by approximately 1.5% for every 100m of altitude. For example, the UV radiation at an
altitude of 4,000m is approximately30% stronger than at an altitude of 2,000m.
UV radiation has damaging effects on plastics.
3 System Design
SMA Solar Technology AG
Technical Information 7SSMUXX1015-TI-en-10
However, the UV radiation does not impact the functionality and the insulation of the plastic enclosure of the SMA
String-Monitor. Over time, merely the color and condition of the enclosure surface might change slightly.
3 System Design
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Technical InformationSSMUXX1015-TI-en-108
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