SMA Automatic 3-Phase Backup Box BU-STPH-4P63B
SMA Backup BU-STPH-4P63B: wall-mounted box for automatic three-phase backup in systems with the Sunny Tripower Hybrid X hybrid inverter. During a blackout it disconnects the home from the grid and supplies it from battery and PV, up to 63 A per phase.
4-pole version: it also switches the neutral. Switchover adjustable from 1 to 600 s, IP65 for indoor and outdoor use, 506 x 260 x 236 mm, 6.6 kg. Requires a battery and an SMA Energy Meter.
The SMA Backup BU-STPH-4P63B is the automatic transfer switching device that brings three-phase backup to systems with the Sunny Tripower Hybrid X hybrid inverter. When the grid fails it disconnects the installation from the utility and runs it off-grid on battery and PV energy; when the grid returns it reconnects automatically, with no manual intervention.
Why the 4-pole version
SMA makes the same device in two variants: 3P units switch only the three line conductors, 4P units provide all-pole disconnection that also opens the neutral. This matters at design stage, because in off-grid mode the neutral reference has to be re-established locally, and how this is done depends on the earthing system.
In TT systems, where the consumer's earth electrode is separate from the utility's, as is common in several European countries, a solution that also switches the neutral is usually the first one to consider. SMA states that the variant must be chosen and installed according to the applicable standards and the local grid operator's connection conditions: the final choice belongs to the designer who signs the wiring diagram, not to the installation site.
BU-STPH-4P63B technical specifications
| Function | Automatic grid / off-grid transfer, three-phase |
| Poles switched | 4 (L1, L2, L3, N), all-pole disconnection |
| Rated current | 63 A (max. continuous) |
| Voltage / frequency | 230 / 400 V, 50 Hz |
| Backup overload | 150% of inverter rated power for less than 100 ms, 125% for less than 30 s |
| Switchover time | Adjustable from 1 to 600 s, 5 s factory setting |
| Recommended upstream protection | 50 A |
| Consumption | 4 W in backup mode, 0 W in grid-parallel mode |
| Compatible inverters | STPH5-60, STPH6-60, STPH8-60, STPH10-60, STPH12-60, STPH15-60, STPH20-70, STPH25-70, STPH30-70 |
| System requirements | Hybrid X as System Manager with a battery connected, SMA Energy Meter |
| Degree of protection | IP65, indoor or outdoor, wall mounting |
| Operating temperature | -40 °C to +45 °C (+35 °C with additional components in the box) |
| Maximum altitude | 3,000 m |
| Dimensions (W x H x D) | 506 x 260 x 236 mm |
| Weight | 6.6 kg |
| Warranty | 2 years |
It is not a UPS
Switching is done by contactors and the minimum delay is 1 second, with 5 seconds as the default: when the blackout hits, the house goes dark for a moment and then restarts off-grid. Computers, NAS units and electronics reboot; fridges, pumps, boilers and lighting resume without consequence. The delay, adjustable up to 600 s, is useful on lines with frequent micro-interruptions, to stop the system from entering and leaving island mode at every disturbance.
In off-grid mode the inverter handles short peaks of 150% of rated power (under 100 ms) and 125% for under 30 seconds: enough for compressor and pump inrush, not for starting several large motors at once.
What it needs to work
- A Sunny Tripower Hybrid X set as System Manager, with a battery connected: with several Hybrid X units, the System Manager is the one with the highest rated power and storage capacity
- An SMA Energy Meter to detect grid failure and grid return
- Upstream protection, recommended at 50 A
- Updated grid connection documentation: off-grid operation changes the configuration declared to the grid operator
Frequently asked questions
Does it supply the whole house or only some circuits?
The box is installed upstream of the distribution board and switches the entire installation up to 63 A per phase, so no separate backup-loads board is needed. The real limit in off-grid mode is inverter and battery power, so heavy loads still need to be managed sensibly during a blackout.
Does it work at night?
Yes, because in off-grid mode the energy comes from the battery. The System Manager must have a battery connected: backup is not intended without one. During the day PV contributes and extends autonomy.
Can I use it with several inverters?
Yes. The datasheet specifies parallel operation of up to three hybrid inverters, and the manual allows other compatible SMA inverters to feed into the off-grid network. The inverter controlling the backup must be the Hybrid X with the highest rated power and the largest battery.
How does it differ from the inverter's SPS output?
The Sunny Tripower Hybrid X already has a 3,680 W single-phase SPS emergency socket with manual switching. The BU-STPH-4P63B makes backup automatic and three-phase, for the whole installation: the difference between a socket that works if someone activates it and a house that keeps running on its own.
Can it be mounted outdoors?
Yes. The B version comes in an IP65 enclosure for indoor and outdoor use, operating from -40 °C to +45 °C. The K version (BU-STPH-4P63K) is a DIN-rail kit for the meter cabinet, for indoor use only.
