XPC M90S-4S N+1 capacity at a 4.8 kW protected load

One failed 6 kW module leaves 1.2 kW of surviving margin

The M90S-4S uses 6 kW hot-swappable power modules in a four-slot enclosure and supports N+1 operation up to a 6 kW protected load. Equipment record: XPC M90S-4S12K2, companion identifier M90S-PWM6. Decision: Use two 6 kW power modules for N+1 protection only while the confirmed protected load remains at or below the 6 kW surviving-module capacity.

One module must carry the whole protected load

The same enclosure can be assembled as a 6 kW redundant system or a 12 kW capacity system. Those are different operating claims. With two power modules installed, a 4.8 kW worked load can lose one module and remain below the surviving 6 kW rating. At a 7 kW load, the same two-module frame has capacity but no module-out redundancy.

For XPC M90S-4S12K2, the applicability boundary is anchored to 6 kW/module, 12 kW and part M90S-PWM6. One worked input remains an assumption until it is recorded at the equipment.

Confirm availability and catalogue details for XPC M90S-4S12K2 or M90S-PWM6 on the UPS system catalogue page.

Figure 1. XPC M90S-4S12K2 equipment and power path

M90S-4S module and slot limits

The controlling numerical record is: Power-module rating: 6 kW/module; Maximum two-module capacity: 12 kW; Enclosure slot count: 4 slots; Applicable line-to-line class: 208 V; Published online efficiency: 93 %; Worked protected load: 4.8 kW; Published 6 kW runtime with two battery modules: 22 min. Each value has a defined source or assumption status in the engineering ledger. Values from different configurations are not combined as though they came from one installed system.

Engineering parameter	Value	Evidence status
Power-module rating	6 kW/module	Published OEM value
Maximum two-module capacity	12 kW	Published OEM value
Enclosure slot count	4 slots	Published OEM value
Applicable line-to-line class	208 V	Published OEM value
Published online efficiency	93 %	Published OEM value
Worked protected load	4.8 kW	Worked design assumption
Published 6 kW runtime with two battery modules	22 min	Published OEM value

The M90S-4S12K2 configuration uses two 6 kW power modules for 12 kW total installed capacity, but the N+1 test ignores the failed module. Surviving capacity is therefore 6 kW, not 12 kW. The 4.8 kW worked load leaves 20 percent margin on the surviving module. Battery runtime is a separate decision and does not increase module-out power capacity.

The 4.8 kW module-out calculation

The worked check uses module-out margin = 6.0 kW surviving capacity – 4.8 kW load. With one surviving 6 kW module and a 4.8 kW worked load, the result is 1.2 kW margin, equal to 20% of surviving capacity. Redundancy is lost when the protected load rises above 6 kW, even though two modules can deliver 12 kW with both available. The arithmetic is reproducible, but it remains a design check until the listed inputs are confirmed at the equipment.

The 1.2 kW margin, equal to 20% of surviving capacity result follows from module-out margin = 6.0 kW surviving capacity – 4.8 kW load. If the 4.8 kW input changes, this check is repeated rather than carrying the earlier result into a different operating state.

Figure 2. Quantified basis for the XPC M90S-4S12K2 decision

Capacity build versus redundant build

The four slots are shared between power and battery functions. Adding a second power module changes both power redundancy and the number of battery positions available inside the frame. Runtime and redundancy must therefore be checked together rather than quoted as independent options.

A module-out proving test observes load transfer inside the modular frame, remaining-module current, alarms, output voltage and bypass state. The test is stopped if the surviving module approaches its applicable overload band or if the protected load cannot tolerate the planned state.

The single common static bypass remains a shared path. N+1 power modules do not remove common input, output, bypass, control or distribution failures. The one-line diagram must state which risks are redundant and which remain common.

Path	Technical consequence	Disposition
Apply the stated engineering decision	Use two 6 kW power modules for N+1 protection only while the confirmed protected load remains at or below the 6 kW surviving-module capacity.	Selected basis
Generic model substitution	Select by family name or rating alone, without confirming the exact configuration.	Not selected on the stated evidence
Unverified operating assumption	Treat a design assumption as though it were a site measurement.	Reconsider only if the input changes

Confirm availability and catalogue details for XPC M90S-4S12K2 or M90S-PWM6 on the UPS selection and battery help centre page.

Confirm availability and catalogue details for XPC M90S-4S12K2 or M90S-PWM6 on the catalogue of UPS replacement batteries page.

The XPC M90S-4S12K2 decision retains part M90S-PWM6, the 1.2 kW margin, equal to 20% of surviving capacity calculation result and the manufacturer-published 6 kW/module point in one equipment record. Applicable OEM instructions, qualified electrical authority and the installed single-line or wiring record remain controlling for any executable work.

Proving a module-out state

Acceptance of XPC M90S-4S12K2 depends on five recorded checks:

• Confirm the M90S-4S12K2 bundle and two installed M90S-PWM6 power modules.
• Measure the protected load and phase or split-phase balance before the test.
• Calculate module-out loading against one 6 kW surviving module.
• Remove one module from service under the approved OEM test method and observe output and alarms.
• Record the common bypass and distribution paths that remain single points.

The XPC M90S-4S12K2 record is not accepted if part M90S-PWM6 does not match, the calculation does not reproduce 1.2 kW margin, equal to 20% of surviving capacity, or the final operating state is not recorded. The equipment returns to the approved safe state when a check stops, and the unresolved condition remains open without an invented repair result.

Figure 3. Verification sequence for XPC M90S-4S12K2

The 6 kW ceiling on N+1

At a confirmed 4.8 kW load, the two-module M90S-4S retains 1.2 kW of module-out margin. The same system ceases to be N+1 when load exceeds 6 kW, regardless of the 12 kW installed nameplate.

GDF’s UPS service page covers field measurements and service work for XPC M90S-4S12K2.

Decision rule: Use two 6 kW power modules for N+1 protection only while the confirmed protected load remains at or below the 6 kW surviving-module capacity. A different model, load, voltage, battery string, software version or operating state requires a new check against the applicable manufacturer record.

Sources

1. XPC M90S-4S product page
2. XPC M90S-4S current configuration list
3. XPC M90S power-module manual
4. GDF Technologies, internal engineering reference: DataCenter/Three-Phase and Data Center Power.md
5. GDF Technologies, anonymized field-case library, used only where the text identifies a retained field fact.