Minimum current ampacity

Master Nater said:
i used to take a continuing education class with an old-school master electrician by the name of fred bender. the guy was the president of the electrical board in the state of nebraska. he was an incredibly well-versed and super-intelligent guy.

one year, he did a motor class and was pretty spot on when someone asked him about what OCPD to install on a motor when we were given the possibility of a 250% on an inverse time breaker. he said, "which one do you install? you install the biggest one you can. why not? do you think the 40a breaker will clear slower than a 25a breaker on a short circuit? nope. do you think the breaker will protect the motor, in the event of overload? NOPE. there's no reason not to put in the biggest one that the code allows."

overlooking the possible price difference, it was hard to disagree with his logic. he was right. the breaker will still function in the event of a short circuit, and protect the insulation on the conductors. and the overload/VFD settings that provide the OL protection are the only things gonna protect the motors, if they go into overload.

the only reason i see not to go to the 25a is just stubborn pride. but, i get it. i've been there too. :)

have a good night.
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50% plus I truly think he wrong-
 
Master Nater said:
210.3 only sends you after conductor sizing requirements on a/c and refrigeration equipment in 440.6, 440.31, and 440.32. there's nothing in 210.3 about OCPD.

i gotta agree with dennis. 210.20 applies for OC protection requirements. and 20a breaks that code.

110.3(B) also still applies. so it has to be at least 125% of the continuous duty loads but can't take it beyond 25a (to 30a) because of the manufacturer nameplate.
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210.3 is basically saying go to art 440 for branch circuit requirements for air conditioning equipment.

Then there is 240.3 saying to go to art 440 for overcurrent protection requirements for air conditioning equipment.

110.3(B) also still applies.
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Art 440 does tells us not only to follow listing and instructions but also tells us what info is supposed to be on the nameplates even though we kind of have no control over what the manufacturer will put on there. Most are fairly consistent with what code requires, but my guess is because listing requires this as well.
 
kwired said:
210.3 is basically saying go to art 440 for branch circuit requirements for air conditioning equipment.

Then there is 240.3 saying to go to art 440 for overcurrent protection requirements for air conditioning equipment.


Art 440 does tells us not only to follow listing and instructions but also tells us what info is supposed to be on the nameplates even though we kind of have no control over what the manufacturer will put on there. Most are fairly consistent with what code requires, but my guess is because listing requires this as well.
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you lost me at "basically."
 
Got a Mini Split with an MCA (minimum circuit ampacity) of 23 and an MOP (Max overcurrent protection) of 25.

Well, if you had like an MCA of 18 and an MOP of 25 you could use a 20 Amp breaker but you are permitted to go to a 25 maximum if it had problems starting. Or just install a 25 to begin with.

But that thing has an MCA of 23 and an MOP of 25. That means that could use a 23A breaker if they made one and be permitted to go to 25. But there is no 23, so your only choice is to use a 25 to satisfy both requirements here. Like it was said, it's unusual for the MCA and MOP to be so close together.

-Hal
 
One point that will confuse this issue and may leave @AC\DC on the hook for a defect is the 'starts just fine' assessment.

This is probably an inverter fed unit, which means you don't have typical motor starting current but the running load will depend on operating conditions. 'Starts just fine' on a typical day won't tell you if the breaker will be stressed with >80% current for >3 hours on a particularly bad day.

That unit with the 25A recommended breaker will probably start and run just fine on a 10 A breaker... until you have a heat wave.
 
curt swartz said:
I'm still confused why you think the MCA is just a recommendation and you can choose whatever breaker size you want?

The MCA is the minimum circuit size you can feed the equipment with, period.
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Exactly,
Also 20 amp breakers are not designed for continue use unless the load is 16 amps or less. I don't see how we can be arguing whether the 20 amp breaker is compliant or not. IMO, it clearly is not for many reasons
 
B) Multimotor and Combination-Load Equipment. Multimotor and combination-load equipment shall be provided with a visible nameplate marked with the maker's name, the rating in volts, frequency and number of phases, minimum supply circuit conductor ampacity, the maximum rating of the branch circuit short-circuit and ground-fault protective device, and the short-circuit current rating of the motor controllers or industrial control panel. The ampacity shall be calculated by using Part IV and counting all the motors and other loads that will be operated at the same time…

minimum supply circuit conductor ampacity this is for the conductor is says in plain English this is not for sizing overcurrent

Going to do what he wants probably but it’s not black and white like you guys make it seem
 
AC\DC said:
B) Multimotor and Combination-Load Equipment. Multimotor and combination-load equipment shall be provided with a visible nameplate marked with the maker's name, the rating in volts, frequency and number of phases, minimum supply circuit conductor ampacity, the maximum rating of the branch circuit short-circuit and ground-fault protective device, and the short-circuit current rating of the motor controllers or industrial control panel. The ampacity shall be calculated by using Part IV and counting all the motors and other loads that will be operated at the same time…

minimum supply circuit conductor ampacity this is for the conductor is says in plain English this is not for sizing overcurrent

Going to do what he wants probably but it’s not black and white like you guys make it seem
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MCA usually means minimum circuit ampacity, and let's say it only refers to conductor size. Now how does that affect the section I posted. You still need overcurrent protection that is rated for the unit plus 125%. The unit is considered continuous so 125% must be added to the actual ampacity of the unit. The unit draws more than 16 amps so a 20 amp breaker is not compliant even though it may work for years.
 
440.22(A) Rating or Setting for Individual Motor-Compressor








“The motor-compressor branch-circuit short-circuit and ground-fault protective device shall be capable of carrying the starting current of the motor. A protective device having a rating or setting not exceeding 175 percent of the motor-compressor rated-load current or branch-circuit selection current, whichever is greater, shall be permitted.


It starts it compliant.
I’ll change it but don’t see a black and white
Plus manufacturer says recommended it doesn’t say mandatory they said there’s no minimum because the way I read it as long as it starts it’s comp
 
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Dennis Alwon said:
MCA usually means minimum circuit ampacity, and let's say it only refers to conductor size. Now how does that affect the section I posted. You still need overcurrent protection that is rated for the unit plus 125%. The unit is considered continuous so 125% must be added to the actual ampacity of the unit. The unit draws more than 16 amps so a 20 amp breaker is not compliant even though it may work for years.
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Kwired showed were it changes what you posted
 
AC\DC said:
440.22(A) Rating or Setting for Individual Motor-Compressor








“The motor-compressor branch-circuit short-circuit and ground-fault protective device shall be capable of carrying the starting current of the motor. A protective device having a rating or setting not exceeding 175 percent of the motor-compressor rated-load current or branch-circuit selection current, whichever is greater, shall be permitted.


It starts it compliant.
I’ll change it but don’t see a black and white
Plus manufacturer says recommended it doesn’t say mandatory they said there’s no minimum because the way I read it as long as it starts it’s comp
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ok, you're 100% right. 440.22(A) states that the OCPD on refrigeration equipment shall be capable of carrying the starting current of the motor. so let's ask the next logical question. why don't you install it on a 15a 2p breaker? how about a 10a 2p?

I GUARANTEE that 15a breaker will make start-up. especially considering it's probably on a VFD. it will only run for a few minutes, depending upon how hard the unit is calling for the compressor. but this 15a 2p, this satisfies your 440.22(A) requirement, correct?

the fact is, that 15a breaker does not satisfy the 210.22(A) requirement. minimum OCPD size is 125% of continuous loads. neither does your 20a 2p breaker. it is required to be a 25a breaker. your inspector was wrong. it is a code violation.
 
now this equipment is in 440- I don’t have my book I am at an event.. it this by default consider continuous use?? For the over current protection device. if it doesn’t state it in 440 this overrides 220.
General rules are chapter 1 through three apply and 400 can modify
 
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Here is my rundown:
-> 210.11 says Branch circuits for motor-operated appliances, shall
be provided to supply the loads calculated in accordance with
220.10.

-> 220.10 General tells us Branch-circuit loads shall be calculated as
shown in 220.14.

-> 220.14(C) Tells us the branch circuit must have a 'rating' equal to the required
ampacity of conductors you come up with working thru 440.6.
This is key as 440.6 alone does not cover the branch circuit minimum rating.


-> 210.18 Rating. Says Branch circuits recognized by this article shall
be 'rated' in accordance with the maximum permitted ampere rating or setting of the overcurrent device
And Where conductors of higher ampacity are used for any reason,the ampere rating or setting of the specified overcurrent device shall determine the circuit rating.
 
AC\DC said:
now this equipment is in 440- I don’t have my book I am at an event.. it this by default consider continuous use?? For the over current protection device. if it doesn’t state it in 440 this overrides 220.
General rules are chapter 1 through three apply and 400 can modify
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440 does not override 220. even if it did, your code in 440.22(A) only pertains to the MAXIMUM size of the breaker. not the minimum.

enjoy your event. there is plenty of time for discussion later.
 
tortuga said:
Here is my rundown:
-> 210.11 says Branch circuits for motor-operated appliances, shall
be provided to supply the loads calculated in accordance with
220.10.

-> 220.10 General tells us Branch-circuit loads shall be calculated as
shown in 220.14.

-> 220.14(C) Tells us the branch circuit must have a 'rating' equal to the required
ampacity of conductors you come up with working thru 440.6.
This is key as 440.6 alone does not cover the branch circuit minimum rating.


-> 210.18 Rating. Says Branch circuits recognized by this article shall
be 'rated' in accordance with the maximum permitted ampere rating or setting of the overcurrent device
And Where conductors of higher ampacity are used for any reason,the ampere rating or setting of the specified overcurrent device shall determine the circuit rating.
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Well I thought all those thumps up were for me guess I lost one..

Well I guess I am wrong. Or misunderstood lol
 
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