NEC: Air Conditioning and Refrigeration Equipment – Part 3

Clause 440, Chapter 3 supplies necessities for department circuit quick circuit and earth fault safety utilized in HVAC and refrigeration tools. That’s, it supplies the necessities for overcurrent safety gadgets (OCDPs) for airtight motor circuits.

Nonetheless, these necessities are usually not impartial. They complement or change the overcurrent safety necessities relevant to non-hermetic motor circuits. [440.21]. This reality could make compatibility a bit tough. This is a professional tip: Proceed as when you had been putting in a non-hermetic motor, then Artwork. 440, Chapter 3, to see if there are a sound set of necessities.

For instance, as an instance you’re sizing the OCPD for a separate motor-compressor. You proceed as if you’re sizing the OCPD for a single non-hermetic engine. You begin with the necessities within the article. 430. However it is a nice Article – how are you going to discover the necessities shortly? Go to Determine 430.1. Within the fourth step of the drawing you will notice “Motor department quick circuit and earth fault safety”. Chapter 4 is true throughout the road. Bingo.

Whenever you go to Artwork. 430, Chapter 4, Sec. 430.52 “Ranking or Adjustment for Particular person Motor Circuit.” That is Sec. 440.32 “Single Engine Compressor.” Part 430.52 has undergone a large overhaul with the 2023 cycle and is now Sec. 440.32. Earlier than studying by Sec. 430.52 necessities, Sec. It has 440.32 necessities. And you’ll discover that they’re much easier. You do not have to hassle with Desk 430.52(C)(1) and the grading guidelines that observe. All it’s important to do is use the bigger of the 2 values:

1. 125% of motor compressor rated load present.
2. 125% of the department circuit choice present.

However there is a caveat – score guidelines aren’t the one guidelines that you must observe. You need to return to Sec. 430.52, if the producer has an overload relay desk, you’re utilizing a surge breaker, you’re utilizing a really quick motor, or you’ve got one of many three gadgets listed in Part 2. 430.52(C)(5), (6) or (7). There is no such thing as a point out of those within the sec. 440.32, ie Artwork. 430 manages.

Now there’s a good larger shortcut that could be out there to your specific setup. Usually, the producer has designed a “ready-to-use” bundle. When you set up a Make X Mannequin 123XYZ HVAC unit, the producer has most likely specified which disconnect and OCPD to make use of. The producer does this for a lot of causes, corresponding to lowering assist tickets and guarantee claims. If you’re getting ready a invoice of supplies for putting in such a system, test the set up directions to see if it does the job for you.