wire gauge / breaker rating

Outdoor unit of a Central Forced Air Conditioner system indicates max amperage is 45 amps.

At the distribution panel (not the disconnect) there is a 40 Amp bridged breaker but the gauge of the copper conductor going into it appears to be 10 gauge (appropriate for 30 amps max).

Question: Do A/Cs system manufacturers sell their products with the conductors that run between the outdoor unit to the distribution panel attached to the unit? Or are the conductors supplied and installed separately by the installation company.

I can’t see how the Air Conditioner company (Coleman) would state max amperage at 45 and supply a 10 gauge wire.

Any insights as to why this might be okay would be considered. But for now I am putting it in my report as: “Oversized breakers within the main distribution panel should be replaced. All breaker should be sized according to wire gauge.”

Thanks in advance.


Here is an example that will confuse you more.

Sizing is an engineering issue.


Note the smaller egc size.

Thanks Mike…What’s up with that???

I think I’ll just go shoot myself in the head!

You noted the fact that it’s a Zinsco panel, didn’t you Jeff?

Sure did Jeff… Thanks for asking. I’ve recommended further evaluation for that and also for the Zinsco Main Service Disconnect breaker and the double tap and pointed cover screws in the dist. panel.

**Question for you. **What is the correct type of screw to be used in the side of the distribution panel for the ground wires. This looks suspect to me.


Without getting real technical, because the AC unit is considered a motor load it can be fused higher than you would normally see for household loads. If you look closely at the AC nameplate you will see a listing for Maximum Circuit Breaker size as well as a Minimum Allowable Ampacity. You can use this rule of thumb. Wire for the minimum and breaker for the maximum and get an allowable wire and breaker size. This doesn’t mean that you can’t use a larger conductor, just that it is not required.

The sheet metal screw that the grounding conductors are attached to is a total no-no. There should be a ground bar attached to the panel with machine screws installed into threaded holes.

Thanks Steve,

Is the reason that motor loads can be fused higher than household loads because at start up they may surge to the maximum ampacity but then settle in to run at a lower amperage?
Is installing the larger breaker with the smaller conductor an attempt to create the same kind of time delay or ‘slow blow’ found in some fuses… but for a breaker configuration?

Based on your comment I am inclined not to call out the larger breaker then. I knew there was a reason. Just had to hear it from someone else.

In regards to the grounding screw. I agree about the ground bar. This is how I normally see it. But I’m also aware that ground wires are allowed to be attached to the panel box with the correct type of connection screw.

*Paul Abernathy wrote on 3/9/06:

The termination of equipment grounding and bonding conductors must be by exothermic welding, listed pressure connectors of the set screw or compression type, listed clamps, or other listed fittings. Sheet-metal screws cannot be used to connect grounding (earthing) or bonding conductors or connection devices to enclosures.

Why it is a problem ( and personally why the wood screws and drywall screws are also wrong in my opinion even though the NEC does not call it out ) is because the threads on these types of screws to not make enough contact with the enclosure to ensure a good bond…pre-threaded holes do with at all points within the thread count…but not with the screws listed above.

In a situation where their is a fault and it travels through that "sheet metal " screw the lack of contact could provide a less efficiant bond…and could actually loose the effective bond.*

Anyone have any pictures of ‘pressure connectors of the set screw or compression type’ ?

Bus bar required. . .

I thought the smaller conductors were allowed only from the disconnect to the hvac unit. The conductors from the panel to the disconnect are always the correct size around here.

Two against one… I stand corrected. :stuck_out_tongue:

Good point Bruce…

What do you think Steve?

The “minimum circuit ampacity” is the whole branch circuit, all the way back. There may be reasons to make it bigger (voltage drop, derating in the attic etc) but that is the minimum.


Hi Bruce, the reason you may be seeing larger conductor in our area is because of the same reason a lot of electricians in our area will not use #14 in residential, they think they are doing a better job by going above code or they don’t understand the code that allows them to use smaller wire.

Does code allow for smaller than normal wire feeding airhandlers with aux heat strips?

You may wire according to the mfg. nameplate rating. If you check the nameplate and it’s lists a minimum circuit ampacity you may wire accordingly. The only ones I’ve can remember seeing were on the outside unit. The motor load on the air handler would be small compared to auxilliary strip heaters adn probabally not make a lot of difference in the total load, whereas on the outside unit the compressor is the majority of the load.

The toaster wire heat needs full circuit ampacity, based on the labelling of the air handler and the installed heat kit. The confusion is in the condenser wiring, usually smaller than the heat. You set the breaker size to the overcurrent rating and the wire size to circuit ampacity. That will not be what you usually see based on 240.4(D). (20a=12ga 30a=10ga etc)
Motors are under a different rule.

With the price of copper we will probably start seeing some creative wiring practices. I did a 3BR house the other day that only had one arc-fault breaker on a single circuit for all bedrooms.

The basic rule of thumb is 3va per sq/ft so a 20a breaker could serve 800 sq/ft of bedroom. I doubt anyone is actually measuring this in plan review and the code language is not really there but that is a guideline.


While that seems poor electrical design as I would think (4) bedrooms and only (1) AFCI circuit is rather weak.

What we see is many electricians today ( well the ones I know and teach ) are starting to put (1) AFCI on the bedroom receptacles and (1) on the bedroom Lighting outlets…that way they can get (2) rooms with a different circuit for the recepts than the lights…so the lights dont have that dim effect if a larger load is placed on it for some reason…

But again my personal feeling is on 14 AWG circuit AFCI or not…no more than 12-14 items per circuit…and 14 is my max…but we all know situations arrise…add one here " quote from the builder/buyer " and well…you know.

**210.11(B) Load Evenly Proportioned Among Branch Circuits.

Where the load is calculated on the basis of volt-amperes
per square meter or per square foot, the wiring system up to
and including the branch-circuit panelboard(s) shall be provided
to serve not less than the calculated load. This load
shall be evenly proportioned among multioutlet branch circuits
within the panelboard(s). Branch-circuit overcurrent
devices and circuits shall only be required to be installed to
serve the connected load.