Methods / Single Point of Failure
How RokBench checks this
Single Point of Failure
A node is a single point of failure when losing it alone de-energizes a critical load.
1. What this check does
RokBench takes each in-service node out of service, one at a time, and checks which loads remain energized with automatic transfers allowed. Every node whose loss de-energizes at least one critical load other than itself is reported, with the loads it affects. User-defined scenarios are evaluated the same way with their own outage lists and transfer rules.
2. Inputs used
- The model topology: nodes, connections, normally open or closed, statuses.
- Critical flags. If no node is marked critical, every load and motor is treated as critical.
- Scenarios: out-of-service list, kind (failure, maintenance, utility loss, user-defined) and whether transfers are allowed.
3. Formulas and assumptions
For each node X (in service):
energized(X out, automatic transfers)
lost(X) = critical loads energized normally but not with X out
X is a SPOF if lost(X) contains a load other than X
Scenario transfer rules
failure, utility loss automatic transfers only (ATS, STS)
maintenance, user automatic transfers + planned switching
transfers not allowed normally closed connections only
- One outage at a time for the automatic search. Combinations are covered by the scenarios you add.
- Transfers are assumed to succeed. Transfer switch failure is covered by the transfer switch itself being a node.
- The weakest point shown for each load is the single point of failure that affects the most critical loads, nearest the load when tied.
4. What is NOT checked
- Whether the surviving path has enough capacity for the transferred load.
- Transfer time and whether the load rides through it.
- Hidden common dependencies not drawn in the model (controls, cooling, shared enclosures).
5. Reference standards
Pointers only; consult the edition adopted by your authority having jurisdiction.
- NFPA 70 (NEC) 2023 Article 700, 701, 708 — emergency, standby and critical operations power (context)
- IEEE Std 3006.7 (background)
6. Validation cases
Hand-calculated cases run on every change. See Validation.