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Breaker types, and where each belongsType B or Type C. Does it change Zs?
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The type letter tells you the multiple of rating needed to trip it magnetically, and it is chosen for the load:
| Type | Trips instantly at | Where it belongs |
|---|---|---|
| B | 3–5 × In | Domestic — most of what you will meet |
| C | 5–10 × In | Loads with a higher switch-on surge, such as motors |
| D | 10–20 × In | Very high switch-on surges: transformers, X-ray machines, welding equipment |
✋Type D is not a cure for nuisance tripping. It needs far more fault current to trip instantly, so its maximum Zs is much lower and much harder to meet. Choose it for the load, and check the loop impedance will still give the disconnection time.
Where the types are listed. On-Site Guide · Table 7.2.7(ii) · p.102.
✋Changing the type changes your maximum Zs. Table 41.3 has a row per type. A question that says Type C and is answered from the Type B row is simply wrong.
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