When it comes to wires, there is quite a lot of confusion. Especially regarding the acronyms. Case and point: What is a THWN wire? What is the difference between THHN and THWN wire? Let’s address both of these questions to get a little clearer vision about wires.
THWN stands for Thermoplastic Heat and Water-resistant Nylon-coated wire. Basically, THWN wire is a wire that can be used in high heat situations (up to 75°C or 167°F) and in both dry and wet conditions. This wire is insulated by thermoplastic wrap and is additionally coated with nylon to give it high heat and water resistance.
In conjunction with the THWN wire, you might have also heard about the THWN-2 wire. This is basically a THWN wire with extra heat protection and it can be used in very high heat situations (up to 90°C or 194°F).
So, what’s the difference between THHN and THWN wires?
Let’s look at what THHN wire is as well:
THHN stands for Thermoplastic High Heat resistant Nylon-coated wire. The key here is high heat resistance; THNN has the same high heat resistance as THWN-2 wire (up to 90°C or 194°F). In fact, it has a higher heat resistance than the THWN wire. Unlike THWN and THWN-2 wires, the THHN wire cannot be used in wet conditions.
That ‘W’ that is present in the THWN and THWN-2 wires is not found in THHN wire because THHN wire doesn’t have water (W) resistance.
In many cases, all three wires – THWN, THWN-2, and THHN – are used for connecting branch circuits and electric appliances.
When To Use THWN, THWN-2, Or THHN Wires?
Now that we know the difference between THWN vs THHN vs THWN-2 wires, we can easily see when it’s best to use one of these wires.
Namely, it all comes down to what kind of conditions we have regarding heat (temperature) and moisture (humidity levels).
Let’s cover the high heat situation first:
1. High Heat Situations (Above 75°C or 167°F)
If you expect the heat to be below 75°C or 167°F, you can use any of these wires. In high heat situations, however, you would do much better going with high heat wires like THHN or THWN-2. Both of them have high heat resistance and can function adequately in temperatures us to 90°C or 194°F.
2. High Humidity Situations
When working in a wet environment, you can’t use THHN wire because it doesn’t have wet resistance.
Your choices are THWN and THWN-2 wires. In most cases, we just go with THWN wire for wet conditions since it’s cheaper than THWN-2 wire.
3. High Heat + High Humidity Situations
This is the most extreme case. Example: In the summer, both heat and humidity levels rise. If you live in Florida, you should have wires that are both heat and water-resistant.
Therefore, the THHN wire is not suitable for such conditions; no ‘W’ in the abbreviation means no water resistance.
You could potentially use the THWN wire since it is water-resistant if the temperatures are not too severe. THWN is a heat resistance wire but to a point (up to 75°C or 167°F)
The best choice among THWN vs THHN vs THWN-2 is the THWN-2 wire. It has both water resistance and high heat resistance.
All in all, if you are ever in doubt, use the THWN-2 wire. It might be a bit more pricy but it has both superb qualities of the other two wires:
- High heat resistance like THHN wire.
- Water resistance like THWN wire.
Hopefully, now the understanding behind this wire abbreviations and their characteristics (with uses) is a bit clearer.
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