failed inspection

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eljefetaco

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Fanwood, NJ
Note using my phone to post. On a job and failed an AC motor compressor inspection. Nameplate calls for min circuit ampacity of 18amps. Max circuit breaker 30a minimum 25a. I used 12g rx on 30amp breaker. Inspector failed because I didn't use 10g. Idont have code book with me. Pretty sure I amcorrect. Any input. Or code I can site?
 
I agree with Bob, a #14 AWG would be code permissible.

Steve Beranek said:
You should have 10g installed, not 12.
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When sizing motor circuit conductors and branch circuit short circuit and ground fault protection you don't have to follow 240.4(D) the small conductor rule.

Chris
 
I agree with Bob and Chris. It's a common misconception though and can be frustrating and agravating when an inspector mistakenly calls it as a violation.

Roger
 
I agree with Bob & Chris & Roger. Specifically, 240.4(G) would direct you to Article 440 Parts III & IV for the sizing of the branch circuit conductor sizing and OCPD sizing for AC & Refrigeration Equipment.
 
I stand corrected. However if the breaker panel is not located in immediate proximaty of the unit, any Junction box between the panel and the unit, could be opened up by a maintainance person to tie some receptacles into, easily causing the amperage to go above what the intended use is.

And also, I would be ok with a disconnect at the unit, and the wire between the disconnect and the unit to be sized at the ampacity.

Let us know how the inspector turns out.
 
Steve Beranek said:
I stand corrected. However if the breaker panel is not located in immediate proximaty of the unit, any Junction box between the panel and the unit, could be opened up by a maintainance person to tie some receptacles into, easily causing the amperage to go above what the intended use is.

And also, I would be ok with a disconnect at the unit, and the wire between the disconnect and the unit to be sized at the ampacity.

Let us know how the inspector turns out.
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The code can not anticipate what some future person might do. What the original poster has is code compliant and the inspector should pass it.

Chris
 
david luchini said:
I agree with Bob & Chris & Roger. Specifically, 240.4(G) would direct you to Article 440 Parts III & IV for the sizing of the branch circuit conductor sizing and OCPD sizing for AC & Refrigeration Equipment.
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In 440.32 Single Motor-Compressor. Branch circuit conductors supplying a single motor-compressor shall have an ampacity not less than 125 percent of either the motor compressor rated-load current or the branch-circuit selection current, whichever is greater.

Maybe I am mis-inturpreting, but wouldn't this cause the 18 amps to be multiplied by 1.25, and then conductor sized? In which case a #14 would not be large enough.

And what is the branch-circuit selection current, is that not 30 ?

Thanks for the insight.
 
Steve Beranek said:
In 440.32 Single Motor-Compressor. Branch circuit conductors supplying a single motor-compressor shall have an ampacity not less than 125 percent of either the motor compressor rated-load current or the branch-circuit selection current, whichever is greater.

Maybe I am mis-inturpreting, but wouldn't this cause the 18 amps to be multiplied by 1.25, and then conductor sized? In which case a #14 would not be large enough.

And what is the branch-circuit selection current, is that not 30 ?

Thanks for the insight.
Click to expand...

The minimum circuit ampacity already has the 125% built in it. All he needs to go by is that
 
Steve Beranek said:
In 440.32 Single Motor-Compressor. Branch circuit conductors supplying a single motor-compressor shall have an ampacity not less than 125 percent of either the motor compressor rated-load current or the branch-circuit selection current, whichever is greater.

Maybe I am mis-inturpreting, but wouldn't this cause the 18 amps to be multiplied by 1.25, and then conductor sized? In which case a #14 would not be large enough.

And what is the branch-circuit selection current, is that not 30 ?

Thanks for the insight.
Click to expand...

The branch circuit selection current is sometime labeled "Minimum Circuit Ampacity" on the A/C unit nameplate.

For an A/C unit you do not need to multiply the minimum circuit ampacity by 125% that is already done by the manufacture when comming up with the MCA.

The 30 amp would be the maximum overcurrent protective device size.

Chris
 
mcclary's electrical said:
The minimum circuit ampacity already has the 125% built in it. All he needs to go by is that
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Ok, just to get clarification, I seen another post you made, and decided to look up feeder. Would the circuit not fall under a feeder since from the breaker it goes to a disconnect located next to the unit?

Feeder. All circuit conductors between the service equipment, the source of a separately derived system, or other power supply source and the final branch-circuit overcurrent device. And the branch circuit is from the equipment to the final overcurrent device protecting the circuit?

Just want to make sure the inspector isn't correct, I'm trying to stand on the inspector side of the table.

Steve
 
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Steve Beranek said:
Ok, just to get clarification, I seen another post you made, and decided to look up feeder. Would the circuit not fall under a feeder since from the breaker it goes to a disconnect located next to the unit?

Feeder. All circuit conductors between the service equipment, the source of a separately derived system, or other power supply source and the final branch-circuit overcurrent device.

Just want to make sure the inspector isn't correct, I'm trying to stand on the inspector side of the table.

Steve
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If the disconnecting means is non-fused then it would be a branch circuit.

Chris
 
Steve Beranek said:
Would the circuit not fall under a feeder since from the breaker it goes to a disconnect located next to the unit?
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Not necessarily. The disconnect need not contain any OCP at all if the panel breaker is sized accordingly.

If you choose to use an OCP/disco, it could be considered supplementary, and the circuit still be a BC.
 
Most electrical people are fixated on the parent paragraph of 240.4. They rarely read the other subsections of 240.4.

A/C units are motor driven, and that is one of the reasons why the larger size overcurrent protection for what we call standard ampacity of conductors can be larger. This is similar to the way we can increase the size of the overcurrent device for motor branc circuits or feeders.

The difference between motors and A/C compressors is, the manufacturer of A/C unit know what the intended usage of their product is, and motor manufacturers generally do not. Hence A/C manufacturers provide all of the calculations, which is pretty handy for installers. I have seen contractors apply the 125% rule for sizing their conductors to A/C units...which generally results in oversized conductors - and costs.
 
To add a little to this.

The sizing of conductors for general purpose branch circuits have to take into account that they can be over loaded, so it is required to have protection rated at what the conductors can handle under an over load, this is more long term type of over load, But when it comes to motors and A/C units, they already protect the conductors with a built in overload device, and since nothing else should be placed upon this circuit (like a range or a dryer:roll:) they will be protected.

So since the conductor is already protected by the overload in the compressor, the conductors can be sized for just fault current, so in essences a 14 AWG conductor will still be protected from a short circuit by a 30 amp breaker because of the available current in a bolted fault will still clear the breaker within the require time, now if the circuit is long then this has to be taken into account as the added resistance can cause a longer tripping time and this can cause conductor damage.

Rule of thumb is wire for the minimum and breaker for the max.
 
Steve Beranek said:
Ok, just to get clarification, I seen another post you made, and decided to look up feeder. Would the circuit not fall under a feeder since from the breaker it goes to a disconnect located next to the unit?

Feeder. All circuit conductors between the service equipment, the source of a separately derived system, or other power supply source and the final branch-circuit overcurrent device. And the branch circuit is from the equipment to the final overcurrent device protecting the circuit?

Just want to make sure the inspector isn't correct, I'm trying to stand on the inspector side of the table.

Steve
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Feeders supplying motors can be permitted to have larger overcurrent devices than they would for non motor loads see 430.62
 
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