Rules Concerning Motors/Hermetic - Electrician Talk - Professional Electrical Contractors Forum
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Old 11-03-2016, 11:46 PM   #1
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Default Rules Concerning Motors/Hermetic

Hey guys I've been poking around here unregistered and finally decided to take the bait and make it official with registering. Just to give some background info I work as an electrician in the Canadian Forces and have 2 years of on the job training but the base I work at exposes me to alot. I've taken up the ESAT a couple weeks ago and I have some conflicting issues that maybe you guys as experts could clear up for me.

Today at work we were installing a circuit for a stand up freezer, it was a normal 120V single phase with a 12A draw. Normally you would take 12A x 1.25 = 15A but I would avoid this as it's right on the 80% of a 15A breaker. So to avoid nuisance tripping I would install a 20A breaker, use the 75C column as i'm coming off a breaker which is what they're rated for and use #12AWG as we are not allowed to use any #14AWG on the base.

Now for my confusion. I've been getting alot of motor questions in the ESAT and what they do is they usually refer to Table 44 when I'm just given the Horespower and Voltage along with single or 3 phase. From there I would then take the FLA given off Table 44 and then head to table 29 to find that if i were to protect the motor with a circuit breaker that it is 250%.

Then there's the whole other avenue of hermetic motors where to protect the motor you use the FLA x 6(locked rotor current) x 50%

So now that i've expressed these other 2 confusing scenarios, i've always understood refrigeration and freezers to be hermetic but maybe they're not.
In any case would you guys use the first situation and put a 20A breaker in or would I have to do

a) 250% circuit breaker rule [28-200(a)]
FLA of 12A x 250% = 30A

b) Hermetic motor rule [28-704(1),28-708(1)]
FLA of 12A x 6 x 50% = 36A, have to use 30A breaker as you cannot go more than 50%

Really appreciate you guys taking the time cause i'm trying to get into the code and understand it as much as possible hence me buying the ESAT to prepare a year and half in advance before writing the red seal.
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Old 11-04-2016, 01:12 AM   #2
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A few points to consider...

If it's got a plug on it, Diagram 1 will dictate the receptacle.

If you can't run #14Ga, and go with #12, you can still put that on a 15A breaker, provided that coincides with Diagram 1. If you do encounter nuisance tripping, you can still throw in a 20A breaker.

Though I could be wrong, if it's 120V-12A, you might be over-thinking it.

If you're worried about hypothetical Red Seal Questions, there are specific with respect to determining a correct answer. Ie: they will state hermetic, or they won't.

If they don't give you an FLA, consult Tables. And remember Table 45 for single phase. It's an easy thing to overlook when doing lots and lots of 3 phase. Like always remembering to use 1.73, and then getting a single phase question and using the wrong Table.

With respect to writing the IP, consider the code cycle you might be writing. If you have the schooling portion done, you can always write early. There were big changes from '12 to '15. Not sure what province you're in and how soon they adopt the new code. But it's something to consider.
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Last edited by spinninwheels; 11-04-2016 at 01:16 AM. Reason: added point
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Old 11-04-2016, 08:12 AM   #3
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The plug coming from the back is the normal standard plug that we all use day to day.

Reason i suggested the 20A is because of the motor and compressor that are found in refrigeration and freezers and i was avoiding the 15A because of the inrush of current.

So then my question is when should i be using the 250% fla for circuit breaker rule cause i feel everyone just does the fla x 1.25 to account for conductors and sticks a breaker according to that. Or is it possible that those rules i listed is for when the motor states that it is hermetic or is hard wired directly from the panel?
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Old 11-04-2016, 08:36 AM   #4
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Agree with everything @spinninwheels said.
If it were direct wired I'd be considering the rules of section 28.
When it comes to plug-in equipment I don't consider the load. I'm wiring
the receptacle
and it's up to the manufacturer and the regulations they
are required to follow (CSA, ULc etc) to make sure that they're equipment
operates on a receptacle of that type wired as per the CEC. In this case I
gather it's 5-15R. This means I'd wire it with #14 on 15A breaker.
None the less, you'll be using #12 as per your workplace standard and as
spinninwheels pointed out this will give the option to change the breaker to
a 20A if needed. I'd change the the receptacle to 5-20R at the same time.
Of course you could go #12/20Abreaker/5-20R right away if you want a
higher chance of zero problems.
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Old 11-04-2016, 08:40 AM   #5
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Thank you for your insight. Where you talk about it being a plug vs. Hard wired makes alot of sense and as you said i threw in a 20A breaker with a 20A receptacle. Answers very much appreciated ^.^
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