N+1 generator redundancy
N, N+1 and N+2 in plain numbers: what each level installs, what it protects against, and how to choose for a temporary power plant.
What does N+1 redundancy mean?
N is the number of generators needed to carry the load. N+1 adds one standby generator, so the plant keeps full capacity if any one unit trips or is taken out for service. N+2 adds two, covering one unit in maintenance and one unplanned trip at the same time.
How many 1,250 kVA generators does each redundancy level need?
Add one module for N+1 and two for N+2 to the number of running modules. The table uses the full rating of about 1 MW per module; plants planned with a loading margin need more running modules.
| Load | N | N+1 | N+2 | Installed at N+1 |
|---|---|---|---|---|
| 1 MW | 1 | 2 | 3 | 2.5 MVA |
| 2 MW | 2 | 3 | 4 | 3.75 MVA |
| 3 MW | 3 | 4 | 5 | 5.0 MVA |
| 5 MW | 5 | 6 | 7 | 7.5 MVA |
| 10 MW | 10 | 11 | 12 | 13.75 MVA |
How do you choose between N, N+1 and N+2?
Compare the cost of an outage with the cost of an extra module. Where a trip only stops non-critical work, N may be enough; where a trip stops production, safety systems or a customer, N+1 is a common starting point. The final level follows the consequence of an outage, the maintenance strategy and project requirements.
| Level | Protects against | Often chosen for |
|---|---|---|
| N | Nothing: any unit out reduces capacity | Short, non-critical supplies; loads that can be shed |
| N+1 | One unit tripped or in service | Construction, industrial and utility support, most rental plants |
| N+2 | One in service plus one trip | Long continuous duty, remote or island sites, critical loads |
| 2N | Loss of a complete supply path | Data centres and other loads with dual (A/B) supplies |
Redundancy in generators does not remove single points of failure elsewhere: the bus, the transformer, the fuel supply and the controls also need a plan. That is part of the temporary power plant design, together with synchronisation and load sharing.
Redundancy FAQ
What does N+1 mean for generators?
N is the number of generators needed to carry the load. N+1 installs one more, so the plant still carries the full load if any single generator trips or is stopped for maintenance.
Is N+1 the same as 2N?
No. 2N duplicates the whole capacity: two complete, independent systems. For a load that needs three generators, N+1 means four units, 2N means six units in two separate groups. 2N is common in data centres with separate A and B supplies.
When is N+2 worth it?
When one unit may be out for planned maintenance while the plant must still survive an unplanned trip, for example on long continuous-duty contracts, remote sites where repairs take time, or critical loads.
Does the standby generator run all the time?
It depends on the control philosophy. The standby unit can be stopped and start automatically on a trip (hot standby with auto-start), or all units can run and share the load at a lower loading. Running units at a very low load is poor for diesel engines, so this is set per project.
Technical content prepared and reviewed by the SINTAQA Engineering Team, Dubai. Last updated September 2026. Configurations shown are indicative; every project is engineered to its own load, site and standards.
Size your plant with the right redundancy
Send the load and how critical it is. We will propose N+1 or N+2 and the unit count.