Standards and accuracy classes: As per Bureau of Indian Standards (BIS), there are exactly six accuracy classes of electrical measuring instruments. Evaluate the statement.

Introduction / Context:
Accuracy class specifies the permissible measurement error of an instrument, typically as a percentage of full-scale or reading under standard conditions. Various BIS/IEC standards define accuracy classes for different categories such as voltmeters, ammeters, energy meters, transducers, and protection relays. This question tests whether the number of accuracy classes is a fixed universal count across all BIS instrument standards.

Given Data / Assumptions:

• BIS follows international harmonization with IEC for many instrumentation standards.
• Different instruments (indicating, integrating, protection, energy meters) are covered by distinct standards.
• Accuracy classes can include values like 0.05, 0.1, 0.2, 0.5, 1.0, 1.5, 2.5, 5 (and others), depending on the device and standard revision.

Concept / Approach:

It is incorrect to claim a single number (six) covers all instruments. The list and granularity of accuracy classes vary by instrument type and standard. For example, energy meters have classes such as 0.2, 0.5, 1.0, 2.0; indicating instruments often use 0.5, 1.0, 1.5, 2.5; protection relays and CTs/VTs have their own class schemes. Therefore, the given statement is too restrictive and false in general context.

Step-by-Step Solution:

Verification / Alternative check:

Cross-referencing BIS/IEC documents for indicating instruments, energy meters, and instrument transformers shows differing class enumerations and tolerances, confirming that a fixed count does not apply universally.

Why Other Options Are Wrong:

• “True” contradicts the variability across standards.
• “True only for …” options are misleading; even within a category, multiple classes exist and can exceed six across revisions.

Common Pitfalls:

• Memorizing a single list and assuming it applies to all instruments.
• Confusing common classroom examples with official standard scopes.

Final Answer:

False