Can a 14 AWG pigtail be used with a smart switch with a 20 amp breaker?

Question

There are several previous questions that have been asked on this topic but they're all related to receptacles. I'm seeing that it is against code to use 14 AWG on a 20 amp circuit but when it comes to smart switches, manufacturers don't seem to follow this code.

Looking at 3 switches I have (Lutron, TP-Link, Insteon), none of them are 12 AWG. In fact, the Lutron is using 18 AWG wires. I enlarged the text in the picture to clearly see this.

My question is, how is it any different or worse to connect 14 AWG wires to a switch with the screw-in type fastener to then connect to the Romex? (bottom picture)

Essentially these are pigtails and are not soldered on like the other 3 switches.

Answer 1

but when it comes to smart switches, manufacturers don't seem to follow this code.

No. They follow UL standards, which are what apply to equipment design, and take into account design considerations for equipment. Testing labs such as UL and ETL then certify their equipment as safe.

That is the end of your query, I'm afraid.

The UL rules require certain considerations such as pigtail wires less than X inches long, or internal component arrangements that might make overcurrent impossible, or other engineer-approved methods to assure a worst-case scenario won't cause a problem.

So, seeing a #18 wire on a UL/CSA/ETL Listed device inside a junction box, is not in any way the same as seeing a #18 wire inside a wall packed in insulation.

The UL standards work because they are subject to engineering supervision. I mean you can do anything you want with engineering supervision. Get a qualified engineer to sign off on it, and you're good to go. The problem is paying for the engineering supervision and nobody wants to do that. To make house building possible, they had to come up with construction rules that non-engineers could follow without requiring review by qualified design engineers. That's the point of the NEC. Simply follow the rules and you are assured of work which meets engineering standards.

Yes, it might be overkill sometimes, but consider the alternative.

Answer 2

It is not that the 14 AWG wire will zap you. Properly insulated (just the original insulation, no need for extra tape) will protect you from being zapped.

The concern is heat, because heat leads to fires. A 14 AWG will heat up more than a 12 AWG wire, and if that wire is inside insulation and at a full 1500W then it could be a problem.

But, you may say, I am only using it for 50W of LED lighting? That's true now.

But the next owner (we see it all the time) will ask about connecting a receptacle in the same box. But wait, they may say, I only want to use it for plugging in phone chargers (low wattage, minimal heat).

But the next owner will see the receptacle and decide to plug in a space heater when the furnace is on the blink. Oops, two space heaters because it is a duplex receptacle. That's 24A - 2 x 12A - because a standard US space heater, with or without a fan, ceramic, oil-filled, whatever, uses 12A = 1500W (based on 125V).

24A = 120% of 20A (the circuit breaker) but 160% of 15A (what you should have for 14 AWG wire).

Take a look at a trip curve

Hard to tell exactly, and it is a range because of manufacturing tolerances, aging, etc. But basically it shows that at 120% you could get a trip from anywhere between 100 seconds, which would be fine, and never. The wire sizing rules factor this in - everyone knows a 12 AWG wire could handle a bit more than 20A and a 14 AWG wire could handle a bit more than 15A, but there are limits for a reason.

Now look at 160% (1.6 on the chart - i.e., a bit past 1.5). You get a trip somewhere between 20 seconds and 2 minutes. So on a 15A breaker, that double space heater on 14 AWG wire will trip the breaker in enough time to prevent a fire. On a 20A breaker it might not ever trip, even with everything functioning properly.

And that's how houses burn down.

Answer 3

Other answers here are correct. Considerable thought and testing and experience leads us to the knowledge that your switch with its #16 wire will not set your house on fire but if people use #16 wire on 15A circuits, some of them will set on fire. It's a set of principles that works when everyone adheres to them.

In this answer I'll illustrate just one possible reason these principles apply to your house. But this illustration is not the reason. The reason is pretty much what Harper said: One set of rules for people building switches, another set of rules for people wiring up houses.

The illustration:

• Your switch is labeled "Max 600W load". That's 5A. #16 wire can handle 5A.
• The switch might have a fuse or some other gizmo that prevents it from drawing more than 600W. Certainly, if you put 1800W of lighting on it something inside the switch will break before its wires or any other part of it overheat. That's why it got UL listing.
• You wrote in your question that it's #18 wire. It's not. Which further illustrates that people like you are more likely to make mistakes than people designing switches for UL approval.
• Now, what if it was ok for you to use #16 pigtails, and you use #18 because you think that's ok, and you sell the house and the next owner removes the switch, installs a receptacle on your pigtails and someone plugs in a 1500W space heater and goes to sleep?

Answer 4

This is a dimmer switch. When used with lights and not exceeding the rated spec then it's perfectly fine to use on 20 amp circuits.

Answer 5

Questions like this may give someone a better feeling about breaking the rules, when others agree, but the underlying problem is not about feelings or justifying your own electrical code. Having said that, it sounds like this is just a case of replacing a pigtail with a larger gauge pigtail. If it was soldered onto the device, I would be tempted to solder the new but non-code wire (same length). Then, it is obvious that it is not part of the structure wiring, if someone opens the box later. However, it's still at risk of not being compliant with UL (and the code, if instructions prohibited any modification or repair). I would inquire with the manufacturer. Many companies have a representative ready to answer most questions, and possibly this one.