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Old Today, 08:35 AM   #1
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I recently took a masters test in Hempstead and one question that stumped me was the following: An 18 amp hermetic compressor tripped with a 30 amp breaker. What is the largest breaker permitted. A. 35 amp B. 40 amp C.45 amp D. 50 amp I thought there was not enough information to accurately answer. Any opinions would be helpful.
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Old Today, 09:43 AM   #2
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It's a badly written question for sure. I don't have the exact code rules in front of me but off the top of my head the maximum OCPD is 175% if the RLC. In this case that would be 31.5 amps, rounding that down to the closes OCPD size would be 30 amps but rounding up would be 35. (I forgot which you're allowed to do ) In any case, I'm going with 35 amps.
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Old Today, 10:00 AM   #3
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Quote:
Originally Posted by greenlee View Post
I recently took a masters test in Hempstead and one question that stumped me was the following: An 18 amp hermetic compressor tripped with a 30 amp breaker. What is the largest breaker permitted. A. 35 amp B. 40 amp C.45 amp D. 50 amp I thought there was not enough information to accurately answer. Any opinions would be helpful.
This may not help much, but in CEC you are limited to 50% over the LRC
If it won't start, you can go to 65%.

NEC should have something similar.(specific code for hermetic compressors)
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Old Today, 10:06 AM   #4
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Here’s a quick read.



https://www.ecmweb.com/code-basics/a...on-equipment-0
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Old Today, 11:34 AM   #5
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So, that did clarify what I said. The SC and GF protection can be 175%. The breaker can be rounded up to the next size as long as it doesn't exceed 225% of the RLC. In this case, the breaker must be a 35 because 2.25 x 18 is 40.5, because the next standard size is 45 and that exceeds the allowable ampacity.
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Old Today, 01:22 PM   #6
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hermetic compressor
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It's a badly written question for sure.
Agreed, as soon as I saw "hermetic compressor", I thought nameplate.
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Old Today, 09:04 PM   #7
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Agreed, as soon as I saw "hermetic compressor", I thought nameplate.
I think the question was designed to avoid you concentrating on why a 30 amp breaker will not start a 18 amp motor.

A 18amp "bitch to get up to speed compressor" trips a 30 amp breaker. Whats the largest breaker you can throw at it by code.
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Old Today, 09:31 PM   #8
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the answer i gleamed from the CEC [canadian] with said values from the available choices given and question asked is "50 A" is the "largest breaker" permitted.
rule;28-704/1 and 28-708/1


by the numbers, 18 x 6 is 108 and then 50% is thus 54...
soooo 50A is the next best thing [always round down]

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