What is a per mode vs. per phase protection rating?

Product Line:
Surge Protective Devices (SPD's)

Understanding Per Mode vs. Per Phase Protection Ratings:

In surge protection terminology, per mode and per phase ratings refer to different ways of expressing the capacity of a surge protective device (SPD) to handle transient overvoltages.

Per Mode Rating

• A mode refers to a specific path between two electrical conductors where surge protection is applied.
• Common modes include:
  • Line-to-Neutral (L-N)
  • Line-to-Ground (L-G)
  • Neutral-to-Ground (N-G) (less common in some SPD designs)

A per mode rating specifies the maximum surge current (in kiloamperes, kA) that the SPD can safely divert in that particular mode.

Example:

• L-N mode: 100 kA
• L-G mode: 100 kA

Each mode is rated independently.

Per Phase Rating

• A phase refers to one energized conductor in a multi-phase system (e.g., L1, L2, L3 in a 3-phase system).
• The per phase rating is the sum of the surge current ratings for all protection modes associated with that phase.

Example: If a single phase (say L1) has:

• L1-N protection rated at 100 kA
• L1-G protection rated at 100 kA

Then the per phase rating for L1 is:

• 200 kA per phase (100 kA L-N + 100 kA L-G)

This summation gives a more comprehensive view of the total surge-handling capacity for that phase.

Why This Matters

All Schneider Electric surge protection product literature reports per phase ratings, which can appear higher than per mode ratings because they aggregate multiple protection paths.

Comparison Example:

This helps clarify that a 200 kA per phase rating doesn’t mean a single suppression component handles 200 kA, it means the combined capacity of components protecting L-N and L-G modes for that phase equals 200 kA.

Released for: Schneider Electric USA