18 awg in appliance - ceiling fan/light

[electricpete]

I installed a cheapo ($25) ceiling fan and light fixture in my home yesterday.

There are four wires (blue, black, white, green) that go up from the fan through the downrod to the connection with home wiring at the top.

blue is the fan, black is the light, white is common return for both fan and light, green is ground. All 4 wires are 18 AWG.

I looked at that 18AWG Cu and saw how tiny it was and something tells me it just has to be wrong.

Wires says 105C insulation. Bulb fixture says no more than 60W which I guess means 0.5A at 120v. The fan I'm not sure but it's 4 52" blades that go pretty fast at full speed and put out a good breeze. I looked in a table in standard handbook for engineers (probably based on NEC) and saw 18AWG 90C actually has an ampacity of 14A in 30C ambient when routed three wires in a conduit. (the downrod is sort of like a conduit, although it's short 6" so maybe not as restrictive as a conduit?). I guess it might be marginal if NEC applied since 15A breaker might not protect those wires for overload.

The point of all this rambling, I guess I don't know sure how to evaluate it but I have never seen such a small wire in an appliance like this. What do you guys think?

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[mpparent]

Hey pete,

Section 402 of the NEC (402.5 gives the ampacity table)talks about fixture wires. 18AWG is good for 6A. I guess it's going to depend on water the fan motor draws.

Mike

 

[itsmoked]

Well I'm holding the entrails of one of those do-everything fans in my hand. All the wires are 18AWG. So you aren't being the path finding guinea pig.

Hmmm 9 transistors, 31 caps, 4 MOVs, 2 triacs, 5 diodes, 2 chokes, 33 resistors, 1 full bridge, 1 res net, 2 ICs, 2 relays [12A 120VAC], 1 relay [1A, 125VAC].

I was kind of expecting a fuse on this that would drive a stake through your concerns. Three of the resistors are 1 watts that could be performing the fuse function but I don't think so since they are half submerged in waxy goo.

NEC allows smaller wire {then expected}inside machines because it usually has air around it. Perhaps 6 inches of the pipe is concidered "in the machine" still.

The fan probably doesn't draw more than 120Watts in fact most draw less than 100W, after all why try to cool a place down with a large wattage fan, doh!

So you have 2 or 3 60W bulbs and a 100W fan. 280W = 2A@ 120V.

The 18 has that covered being 14A as you say.

Have you looked at your electric range wires lateley? You'd swear they are all 3 sizes too small!! You run 6AWG to the range then inside a bunch of 12 and 14AWGs continue!!

I guess the fans are UL tested and they find that the slow overload results in, say, the triac blowing[fuse] and a high current fault[short] can be handled by the 18Awg longer than the typical 15A breaker. I would expect an 18AWG to take 30A for maybe thirty seconds before getting scary hot.

 

[jraef]

You can't apply the NEC rules for wire in conduit to appliances and other NTRL listed pieces of equipment. The NTRL (Natioally Recognized Testing Lab such as UL, ETL etc.) has their own rules, and once the entire system is labeled, it is allowed per the NEC. If your fan is not listed, all bets are off.

From an engineering standpoint, the18ga is most likely fine, even when protected by a 15A breaker. The appliance mfgr knows that the appliance has some other form of overload protection, such as a thermal switch or even a specifically designed fuse wire, and is always going to be some distance from the breaker so that the voltage drop will not allow an internal overload to exceed the rating of that 18ga wire even if it has to rely upon that 15A breaker tripping. The reason why you can only use 14ga wire on a 15A breaker is that the NEC has no way of knowing that distance, drop etc. in advance, so the rules must assume the worst. Remember, the NEC is for the INSTALLATION, not the specifc device.

I know that under UL508a for control panels, 18ga wire is rated for 7A, however it appears as though under UL62 for appliance hook-up wire, it may be rated for 10A (I don't have access to UL62 directly, but it references that within UL508). Either way, the point is that you don't know what rule the appliance mfgr. tested to, but they do test based on knowing that it will be fed from a circuit protected by a minimum 15A breaker or fuse, because that is the smallest available in the US. Again, no NRTL label = cause to worry.

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[mpparent]

water = what



Mike

 

[itsmoked]

Aren't you just using the water = amps comparison?

 

[OperaHouse]

Hey, I have no larger than #10 wires feeding 220 volts into my house. Can't get the utility to replace them even though the insulation has fallen off!

Look at it this way. An overload causes the wires to melt. That causes a short that will either clear itself or pop the breaker. UL doesn't promote good design, just that any fire is self contained and does not propagate.

 

[petronila]

Hello Electricpete,
For electric motor appliances some manufactures use hypalon´s wires this are class A (105 C)and have excellents
heat resistance and electrical properties. I don´t know who is the fan manufactured but I think the wires could be made with hypalon, in this case the maximun ampacity value for single conductor in free air at 30 C is 20 Amps, the NEC is righ for the 14 Amps for three conductors at duct and I think the AWG Stranding for the wires (fun and Lamp) is OK.The other factor is how to protect this electrical installation? I think too a 15 Amps breaker is high, the better way could be by fuses. With the Lamp on and the Fan RunningTake a reading with a clamp to know the Full amps then calculate the fuse using 1.15 factor (Fuse= 1.15 Amps reading).

Regards

PETRONILA

 

[itsmoked]

Hi petronila,
Don't need a clampon, I just said the fan doesn't draw more than 2 or 3A.

No they don't use Hapalon! It would've been cheaper to use 14AWG than the very expensive Hapalon.


jraef is exactly correct; If another organization (like UL) determines that the fan is safe with what people think is too small a wire then that trumps NEC.

Just like if you are building a house and you have some part done by a structural engineering firm. The building inspector won't even look at the engineered part! This is because it is no longer in his purview. Further OperaHouse is correct, NEC is only concerned about preventing fire. Nothing more. They don't really care if something could "work better".