What size wiring for Central A/C compressor?

stringent, but sometimes the NEC and DIN conflict and can't both be met.

My experience is with American protectorates where the facilities are the same as back home. ^_^

TDD

Reply to
The Daring Dufas
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How often do you deal with electrical and mechanical inspection services? I've done electrical and HVAC work for a living and I base my assertions on practical experience where I've worked. It may be different where you did your electrical and HVAC work for a living. Perhaps the authorities interpret the NEC differently where you have done your professional electrical and HVAC work?

TDD

Reply to
The Daring Dufas

I get along with the inspectors and since I know them and they know the quality of my work, they don't usually dig to deeply into it unless I insist in order to satisfy a customer who may have doubts. That is something they understand since they themselves worked in the field. In some places they actually have to use a stamp with their name and number for the department which can be seen inside breaker panel doors. ^_^

TDD

Reply to
The Daring Dufas

On 3/4/2013 12:50 PM, The Daring Dufas wrote: ...

...

Far more likely they apply the correct section of Code for the purpose at hand.

It would be far better to reference the specific Code in question or even the controlling jurisdiction which would likely lead to being able to find the relevant Codes in play. I strongly suspect if that were done it would be found that the installation under discussion is compliant there as well.

Reply to
dpb

I have been a certified, state licensed electrical inspector for about

20 years.

Florida and we follow the NEC state wide, unaltered, except for requiring bonding of steel studs.

I said before, this is a common question on the inspector tests and if you say 8ga on a 40a breaker for a motor circuit like this, you got that one wrong. Maybe your inspectors are not certified and it is just the mayor's nephew who learned his trade from the Time Life electrical wiring for dummies book.

Reply to
gfretwell

That's what they want around here with a disconnect at the condensing unit. I've always gone by the breaker size required by the label on the unit and sized the wiring for the breaker and that's what the inspectors want. If you were the inspector at the site, I would do what you demanded. It can't be simpler than that. Of course, different insulation types handle different currents. I don't argue with the inspector and do what their department requires. The inspectors around here would reject a 40 amp breaker on #10 copper 60°C NM/UF cable. Higher temp rated wire insulation would be different. NEC Table 310-16. I would put a 40amp breaker on #10 copper if it has 90°C rated THHN/THWN/XHHW insulation. O_o

TDD

Reply to
The Daring Dufas

It's also possible that he's basing his experience on what's required by what he's used and had passed. Of course if you use

8 gauge where a minimum of 12 gauge or 10 gauge is required, it passes because it meets code. And the inspector isn't likely to say, BTW did you know that 12 was sufficient? So, he goes on thinking that 8 gauge is what is required for it to pass.

Obviously there hasn't been any discussion with an inspector about the issue, otherwise he'd be able to give us the code section that the position is based on. He refuses to recognize that the code treats breaker requirements for general purpose branch circuits differently than it does for motors, AC eqpt, etc.

Reply to
trader4

When you can give us the section of the NEC where you can conclude that there is something wrong with Mikepier's installation, under ANY interpretation, then we can discuss differing interpretations. If an inspector is going to fail it, then he should be able to tell you that per NEC section X.Y, it's not allowed.

This isn't the first time this issue has come up. And the result is usually the same. You have some people thinking that the same rules for lights and receptacles under the NEC also apply to motors and AC equipment. They don't. I would hope that someone who installs that eqpt would understand the distinction.

Reply to
trader4

If you'll look at NEC Table 310-16 you will see the amp rating for wire size. It changes depending on the insulation on the wire. Every 40 amp circuit I've ever installed in a home using 60°C NM/UF cable has been #8 copper. If I install a 40 amp circuit in conduit using 90°C THHN/THWN insulated wire I'll use #10 copper. I don't usually run conduit in a home. The last 4 ton AC condensing unit I installed used #14 THHN/THWN copper in conduit. It was a 3ø unit that called for a 15 amp breaker. I have to install what I know the inspector will pass and the inspectors do look at the temperature rating of the wire and check if the circuit breaker is HACR rated if it's hooked to an AC condensing unit. I don't argue with the inspectors, you can if you wish. O_o

TDD

Reply to
The Daring Dufas

Every 40 amp

And if you look at that table, it shows that 12 gauge is OK for up to 25 amps. The nameplate on the AC eqpt Mike has says the minimum circuit ampacity is 24.4 amps. Therefore, 12 gauge meets the minimum requirement and is permitted.

The problem comes when you then try to tie the breaker to be installed for that AC eqpt with the wire size and treat it like it was a water heater, or a receptacle circuit. It is not. The eqpt manufacturer's rating governs and it says that a breaker of

40A max is permitted.

15 amp breaker for a 4 ton AC? That ain't right. I

It's not an issue of arguing with the inspectors. It's what the NEC says disagrees with what you say. And if an inspector fails something, he should be willing to tell you what part of the code it failed and why, without getting into an argument. Any inspector should know that motors are treated differently than resistive loads.

Just do some googling. This whole issue has come up many times. Some homeowner or inspector raises the issue of the breaker for an AC being larger than would normally be permitted for a light circuit, etc. that uses a given wire gauge. Or some home inspector flags it. Then a lot of discussion follows and the folks most knowledgable about the actual issues and code say it's perfectly normal. In this case, you have gfretw, an actual electrical inspector, telling you how it works and that what Mike has is code compliant.

Reply to
trader4

This is interesting stuff guys. I never knew there were a different set of codes for motors and A/C's. I'll leave the existing wiring for now. What I'll do is run a drag line in the ceiling joists so if i ever had to run another line, I can do it easily by pulling the new wire attached to the drag line.

I have another question regarding central Vac systems wiring requirements. Please see upcoming seperate post.

Reply to
Mikepier

Right.

It's pretty cold outside ! A couple of things. My memory is bad. The unit is in fact 2.5 tons. The installer quoted price for 3 ton unit !

Gsc130301a goodman.

13.7 minimum amp Max fuse amps 20 Compressor 9.7 amp 1.5 hp fan.

The reading have been stable last 2-3 summers. 6.5 amp draw. Could low r22 cause reduced reading ?

Im happy with the performance, low bills. I even drop the temp down to 68 degrees in summer nights.

Greg

Reply to
gregz

Did you look at the notes from the table? They are at the bottom of the table and will show what I use and what the inspectors go by. You will see a little note reference next to the 25 amp figure. ^_^

TDD

It is a 240 volt three phase unit and 15 amps 3ø power is what it calls for. It has run without a problem for 10 years in three different locations. I installed it at a pizza place which has moved twice after I installed at their first location. I also use test equipment to check the current draw and phase rotation on all three phase equipment. ^_^

TDD

If gfretw was the inspector in charge I would do what he said but I have to go by what the inspectors here and now require. I also go by the manufacturers requirements unless they clash with the inspector who has final say. The city here actually has stricter guidelines in some areas than the NEC. Here, they want the circuit and wire gauge to match no matter what the load is with the only difference being that HACR rated breakers be used on AC and refrigeration units. Understand that the temperature rating of the insulation also determines the amp carrying specification of the wiring for both copper and aluminum. ^_^

TDD

Reply to
The Daring Dufas

You have to look at the whole code, in context, you can't just cherry pick one article and believe that is the way it works in every situation. When you are looking at an AC unit you start in 440 if you are sizing the breaker, not using the label.

440.22 Application and Selection. (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, provided that, where the protection specified is not sufficient for the starting current of the motor, the rating or setting shall be permitted to be increased but shall not exceed 225 percent of the motor rated-load current or branch-circuit selection current, whichever is greater. 12 ga wire has an ampacity of 25a in the 60c column so you can start with a 45a breaker and you might end up with a 60 if you use the round up rule at 225%. The label is actually rounding down to get to 40a.

The label is very unambiguous. It tells you can use 12ga wire and a

40a breaker. If an inspector is confused about that, he is incompetent. I am not saying there are not incompetent inspectors out there but at a certain point they need to be educated. That probably does not happen on an active job but you can send a letter to the state licensing authority asking for a ruling. Fix it for everyone, not just that job.

What is your jurisdiction? I may actually know someone there.

Reply to
gfretwell

Absolutely. That note takes you to 240.4(D) which references 240.4(G)

G) Over current Protection for Specific Conductor Applications. Over current protection for the specific conductors shall be permitted to be provided as referenced in Table 240.4(G).

which references 440 part III & IV and 430 part III, IV, V, VI & VII where we get this permission for larger OC devices and the ability to use 310.16 at the listed rating.

Like I said, you need to read the whole code, not just the first thing you see.

Reply to
gfretwell

It's Birmingham in Jefferson County Alabamastan. I noted the 25 amp rating in the 60°C column too but I also read the notes at the bottom of the chart and those jive with what has always been told to me. The city code does differ a bit from NEC and that's what I've been told by the inspectors I've dealt with. Now in your experience are you also considering LRA of the compressor? Is that part of the 225% overload? O_o

TDD

Reply to
The Daring Dufas

I'll defer to you on it then but I'll continue to install what I know will pass inspection not what I think I can get away with. ^_^

TDD

Reply to
The Daring Dufas

The 225% is the max O/C device based on FLA but usually 175% will be plenty. When you even start approaching that is after the compressor gets old and they put a hard start kit on it.

Reply to
gfretwell

Whatever you need to do. You are just oversizing wire but as long as you keep getting the bid, rock on.

You probably should have the conversation tho. I am curious how your inspectors can ignore that label.

Reply to
gfretwell

I remember one who would not pass a job unless the HACR sticker was on the breaker for the AC. It didn't matter what the paperwork from the manufacturer stated. O_o

TDD

Reply to
The Daring Dufas

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