AC wire sizing
- Thread starter binney
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websparky
Senior Member
- Location
- Cleveland, Ohio
Re: AC wire sizing
Bob,
If the fuse is 40A, and the disco is rated at 30A, you say that this is acceptable?
Bob,
If the fuse is 40A, and the disco is rated at 30A, you say that this is acceptable?
- Location
- Massachusetts
Re: AC wire sizing
Dave it is obvious that we can not put a 40 amp fuse in a 30 amp switch with out the use of a hammer.
I took your question to mean if we already had the 40 amp fuse at the distribution panel and ran 12 out to the unit what size disconnect would we need to use at the unit.
In this case a 30 amp disconnect would cover it.
It would be impossible to overload any conductor or switch in this circuit because the overloads in the unit will prevent it.
Dave it is obvious that we can not put a 40 amp fuse in a 30 amp switch with out the use of a hammer.
I took your question to mean if we already had the 40 amp fuse at the distribution panel and ran 12 out to the unit what size disconnect would we need to use at the unit.
In this case a 30 amp disconnect would cover it.
It would be impossible to overload any conductor or switch in this circuit because the overloads in the unit will prevent it.
websparky
Senior Member
- Location
- Cleveland, Ohio
Re: AC wire sizing
Bob,
OK, let me see if I got this right.
Start with a 40A fuse or proper type breaker at panel. Run 12AWG to outside service disconnect. The outdoor disconnect is not fused, just a disco or a switch. The disco only needs to be rated at 30A.
Do I have it correct?
Bob,
OK, let me see if I got this right.
Start with a 40A fuse or proper type breaker at panel. Run 12AWG to outside service disconnect. The outdoor disconnect is not fused, just a disco or a switch. The disco only needs to be rated at 30A.
Do I have it correct?
- Location
- Massachusetts
Re: AC wire sizing
Dave that is what I believe to be correct.
I have been wrong before and will be again.
If we agree that we can use 12 awg for the supply conductors what would be the logic in requiring a 60 amp switch?
We would not think twice about putting a 30 amp fused switch on a tap of a 200 amp feeder because we know the current through the switch will be limited by the fuse we install.
This is the same thing happening in this circuit, the units overloads will prevent to much current from passing through the switch or conductors.
In the case of a short circuit or ground fault the 12 awg will carry enough current to open the 40 amp breaker.
This is the same as using 8 awg EGC for a 100 amp OCPD, for the short duration of a ground fault the 8 awg can tolerate the current from the 100 amp breaker.
Dave that is what I believe to be correct.
I have been wrong before and will be again.
If we agree that we can use 12 awg for the supply conductors what would be the logic in requiring a 60 amp switch?
We would not think twice about putting a 30 amp fused switch on a tap of a 200 amp feeder because we know the current through the switch will be limited by the fuse we install.
This is the same thing happening in this circuit, the units overloads will prevent to much current from passing through the switch or conductors.
In the case of a short circuit or ground fault the 12 awg will carry enough current to open the 40 amp breaker.
This is the same as using 8 awg EGC for a 100 amp OCPD, for the short duration of a ground fault the 8 awg can tolerate the current from the 100 amp breaker.
websparky
Senior Member
- Location
- Cleveland, Ohio
Re: AC wire sizing
Bob,
OK........ How does this fit into the scheme?
Bob,
OK........ How does this fit into the scheme?
- Location
- Massachusetts
Re: AC wire sizing
Dave I am not sure I get the question.
The opening post had a minimum circuit ampacity of 23 amps.
23 amps x 1.15 = 26.45 amps.
Looking more closely we should be on 440.12(B) for this unit as we probably have a fan along with the compressor.
We do not have the individual motor ratings to figure it out.
Dave I am not sure I get the question.
The opening post had a minimum circuit ampacity of 23 amps.
23 amps x 1.15 = 26.45 amps.
Looking more closely we should be on 440.12(B) for this unit as we probably have a fan along with the compressor.
We do not have the individual motor ratings to figure it out.
websparky
Senior Member
- Location
- Cleveland, Ohio
Re: AC wire sizing
Bob,
OK, I thought maybe the 40A circuit came into play?
Bob,
OK, I thought maybe the 40A circuit came into play?
Re: AC wire sizing
the 1.25 factor has been included. In this case the actual load is 23/1.25 = 18.4 amps. The #12
is adequate for this load.
440.22 lists the max rating of the OC device at
175% of the FLA. 1.75 x 18.4 = 32.2 amps. The next size is a 40 amps OC device.
440.12A.1 lists the disconnect rating at 115% of the FLA or 1.15 x 18.4 a = 21 amps. Since the OC device is listed at 40 amps we will need a 60 amp disc.
One point not mentioned is the the question listed
the OC device as a 40 amp FUSE not a CB.
[ December 16, 2003, 02:04 PM: Message edited by: bob ]
When the mfg. lists the minimum circuit capacity
the 1.25 factor has been included. In this case the actual load is 23/1.25 = 18.4 amps. The #12
is adequate for this load.
440.22 lists the max rating of the OC device at
175% of the FLA. 1.75 x 18.4 = 32.2 amps. The next size is a 40 amps OC device.
440.12A.1 lists the disconnect rating at 115% of the FLA or 1.15 x 18.4 a = 21 amps. Since the OC device is listed at 40 amps we will need a 60 amp disc.
One point not mentioned is the the question listed
the OC device as a 40 amp FUSE not a CB.
[ December 16, 2003, 02:04 PM: Message edited by: bob ]
pierre
Senior Member
- Location
- Westchester County, New York
Re: AC wire sizing
Bob
The answer to your last question is 12 AWG and a 40 amp fuse. The 12 AWG is sized according to Part IV of 440 and 310.16, not by dividing 23 by 125%. The nameplate permits the larger fuse based on testing by the manufacturer and a Recognized testing laboratory.
Pierre
Bob
The answer to your last question is 12 AWG and a 40 amp fuse. The 12 AWG is sized according to Part IV of 440 and 310.16, not by dividing 23 by 125%. The nameplate permits the larger fuse based on testing by the manufacturer and a Recognized testing laboratory.
Pierre
aceofdiamond
Member
Re: AC wire sizing
The branch circuit conductor size can be sized as a minimum circuit conductor size by using the MCA [minimum circuit ampacity=[RLA x 1.25] + all connected loads or full load current of all other loads in that unit carried on that branch circuit].This name plate says the ampacity must equal or exceed 23 amps. Look in Table 310-16 in the 60 degree column as required in 110-14 for conductors smaller than a 1 awg conductor regardless of the insulation on that conductor. The minimum branch circuit conductor size for this name plate is 12 awg copper branch circuit conductor size.
The maximum over-current protection is determined by the manufacturer and is usually found marked ?maximum fuse or HACR type breaker? This data is found on the name plate. It is determined as follows; RLA OR BCSC whichever is greater x 175%] or if that overcurrent device size won?t carry the load without tripping then you may calculate as a maximum [RLA x 225%] but only if required for the equipment to work reliably without the overcurrent device tripping. See Article 440-22 This breaker or fuse is used only for short circuit protection. So minimum disconnect23-fan Amp)x1.75~40Amp
The branch circuit conductor size can be sized as a minimum circuit conductor size by using the MCA [minimum circuit ampacity=[RLA x 1.25] + all connected loads or full load current of all other loads in that unit carried on that branch circuit].This name plate says the ampacity must equal or exceed 23 amps. Look in Table 310-16 in the 60 degree column as required in 110-14 for conductors smaller than a 1 awg conductor regardless of the insulation on that conductor. The minimum branch circuit conductor size for this name plate is 12 awg copper branch circuit conductor size.
The maximum over-current protection is determined by the manufacturer and is usually found marked ?maximum fuse or HACR type breaker? This data is found on the name plate. It is determined as follows; RLA OR BCSC whichever is greater x 175%] or if that overcurrent device size won?t carry the load without tripping then you may calculate as a maximum [RLA x 225%] but only if required for the equipment to work reliably without the overcurrent device tripping. See Article 440-22 This breaker or fuse is used only for short circuit protection. So minimum disconnect
23-fan Amp)x1.75~40Ampaceofdiamond
Member
Re: AC wire sizing
benny; I think 110-14(c)(1)and (2)clearly states that for termination provision of less than 100 circuit 60 degree columb is used and over 100 amp 75 degree columb. that's the way I read it
benny; I think 110-14(c)(1)and (2)clearly states that for termination provision of less than 100 circuit 60 degree columb is used and over 100 amp 75 degree columb. that's the way I read it
pierre
Senior Member
- Location
- Westchester County, New York
Re: AC wire sizing
Ace
The second sentence of 110.14(C)(1) states:
Unless the equipment is listed and marked otherwise, conductor ampacities used in determining equipment termination provisions shall be based on Table 310.16 ...
This is where using higher ratings as listed is permitted.
Pierre
Ace
The second sentence of 110.14(C)(1) states:
Unless the equipment is listed and marked otherwise, conductor ampacities used in determining equipment termination provisions shall be based on Table 310.16 ...
This is where using higher ratings as listed is permitted.
Pierre
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