Apprentice path · Stage 8: Equipment and faults · Lesson 27

Reading a nameplate

The nameplate tells you what the equipment is built for, and connecting it to anything else is not your decision to make.

Why this matters on the job

The supply that is closest and most convenient is not automatically the supply the equipment is rated for, and the equipment will not refuse it.

How to think about it

  1. Identify the supply type and the rated voltage first -- AC or DC, and how many volts.
  2. Read the current, the power and the other listed ratings.
  3. Use the manufacturer's instructions alongside the nameplate, not instead of it.

Worked through

A plate reading 24 V DC, 2 A tells you two things. It is a direct-current device, and it is built for twenty-four volts. Both have to match the supply. The 2 A tells you what it draws when it is working normally, which is what the circuit feeding it has to be able to deliver.

Check yourself: A nameplate reads 24 V DC. Can you connect it to a 120 V AC supply?

Answer: No. A 24 V DC rating does not authorize connection to 120 V AC.

Two things are wrong at once: the supply type is different (alternating instead of direct) and the voltage is five times the rating. Either one alone would be enough to rule it out.

Watch out for: Reading the number and skipping the letters. 24 V DC and 24 V AC are not the same rating, and the difference is two characters on a plate.
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Written from the owner's poster for this lesson. Nothing added beyond what the poster states.

Written for Texas apprentices as free study material. The Texas apprentice licence is an application, not an exam (Occupations Code 1305.161), and nothing here counts as apprenticeship hours or continuing-education credit. VoltMark is not affiliated with, endorsed by, or sponsored by NFPA, PSI, TDLR, or any state or local licensing authority. Always follow your employer's safety programme and your supervising electrician.