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Keeping up with the requirements of the Code should be the goal of
everyone involved in electrical safety. Following is what I feel is an
important rule in the 2020 NEC®, complete with
graphics and a video. I encourage you to use it as a training resource for
your organization, and share it with your colleagues.
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Marking on Hermetic Refrigerant
Motor-Compressors and Equipment [440.4] |
The content below is extracted from
Mike Holt's Understanding the National Electrical Code, Volume
1, based on the 2020 NEC.
Click on the image to watch the
video.
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(B) Multimotor and Combination-Load
Equipment.Multimotor and combination-load
air-conditioning and refrigeration equipment must
have a visible nameplate marked with the
manufacturer's name,
rating in volts, number of phases, minimum conductor
ampacity, and the maximum rating of the
branch-circuit short-circuit and groundfault
protective device. ▶Figure 440-3
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▶Figure 440-3 |
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▶ Multimotor Equipment Example 1
Question: What size conductor and short-circuit and groundfault protective device is required for a multimotor air-conditioning compressor? The nameplate minimum circuit ampacity is 31.40A,
the maximum circuit breaker amperes are rated 50A, and all terminals are rated 75°C. ▶Figure 440-4
(a) 10 AWG, 50A breaker (b) 10 AWG, 30A breaker
(c) 8 AWG, 50A breaker
(d) 8 AWG, 20A breaker
Solution:
Conductor: Since the terminals are rated 75°C, we can use 10 AWG rated 35A at 75°C [110.14(C)(1)(a)(3) and Table 310.16].
The circuit breaker protection for air-conditioning compressor equipment
must have a rating of not more than the 50A marked on the nameplate [440.4(B)]. Use a maximum 50A breaker in accordance with 240.6(A).
Answer: (a) 10 AWG, 50A breaker |
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▶Figure 440-4 |
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▶ Multimotor Equipment Example 2
Question: What size NM cable and short-circuit and ground-fault protective device is required for a multimotor air-conditioning
compressor? The nameplate minimum circuit ampacity is 24.50A, the maximum circuit breaker amperes are rated 40A, and the terminals
rated 75ºC. ▶Figure 440-5
(a) 10 AWG, 40A breaker (b) 12 AWG, 35A breaker
(c) 8 AWG, 40A breaker (d) 8 AWG, 35A breaker
Solution:
Conductor: The conductor must have an ampacity of not less than
24.50A as marked on the air conditioner nameplate [440.4(B)]. 12
AWG is suitable since it is rated 25A at 75°C [110.14(C)(1)(a)(3)
and Table 310.16]. In this example however, the wiring method
is Type NM cable and its allowable ampacity is restricted to the
60°C Column of Table 310.16 [334.80]. Therefore, even though
the terminations are rated 75°C, the conductors must be sized to
the 60ºC ampacity as listed in Table 310.16. This will require a 10
AWG conductor rated 30A at 60°C.
Overcurrent Protection:The circuit breaker must have a rating of
not more than 40A as marked on the air conditioner nameplate
[440.4(B)]. Use a maximum 40A breaker in accordance with 240.6(A).
Answer: (a) 10 AWG, 40A breaker
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▶Figure 440-5 |
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• • •
We'd
love to hear from you about this series, and the ways you're using it.
Send us your comments and feedback by clicking on Post a Comment
below. Look out for the next part in this series a month from now, and
please share with your colleagues.
This content is extracted from Mike Holt's Illustrated Guide to
Understanding the National Electrical Code, Volume 1, based on the
2020 NEC Program.
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