Different Types of Leadwire Insulating Material
There are many different types of leadwire insulating materials that we can provide with our heaters. There really isn’t any type of material we can’t use as an insulating material on the leadwire of a heater, unless it can’t fit. That’s really the only physically limiting factor.
Why select from different insulating materials? The two main factors are temperature rating and water resistance. Other factors are cost and form-factor.
At TUTCO, we used mica insulated leads as our default leadwire. It has a very good temperature rating of 450°C (842°F) and is comprised of stranded nickel conductors so it’s flexible and has a good ampacity.
We also carry Teflon insulated leads as a moisture resistant alternative, which is great for applications where water is present, but it doesn’t have such a high temperature rating of only 250°C (482° F). Unfortunately, plastic and rubber insulations (or anything made from an organic compound) that can resist water have a temperature rating that can’t exceed about 500°F. For things hotter than that you’ll have to go to non-organic insulations which are typically not water resistant. You can have one or the other, but not both.
That’s where leadwire protection comes in. We can provide mica insulated leads with heat-shrink sleeving over them, or convoluted armor, both which will keep water away. If you’re looking for an inexpensive insulation you might want to try PVC. It has a rating of only 105°C (220°F) but it can keep water away. You need to be careful in how these leads are connected to heaters. They can’t be too close to a hot part of a heater, such as if they’re internally connected inside a cartridge heater, because the insulation will get damaged from excessive heat.
SJO Cord is a popular option when you want all the conductors (power leads and groudwire [if called for]) to be held in the same outer jacket that provides good protection from water. It’s also handy if you want to attach a plug to the end of the leads. The insulating material is neoprene rubber (polychloroprene) and has a temperature rating a little lower than PVC of 90°C / 194°F so similar precautions must be taken.
If used on a cartridge heater you’ll want an unheated length of at least an inch or two to keep the heat away from the rubber insulation. SJO Cord can’t be used on all our heaters because the conductors are held together in a single outer jacket, so the connecting points can’t be too far apart, like with an Ultima Strip Heater, for example.
At the other end of the temperature scale there are some conductors that are insulated with a high temperature material able to withstand 550°C (1020°F) for those applications where the leads need to run through very hot spaces. The insulation is a proprietary mica/glass composite, is not the least bit water resistant and the leadwires are quite thick in diameter, sometimes 50% thicker than our default mica insulated wires. That makes them unsuitable for some heater where they simply won’t fit. These leads with a very high temperature rating are also quite expensive. We do have a few sizes of the wire in stock, but not all of them.
In the case of this exotic leadwire, don’t assume we can build you something without a conversation first. In some of these cases where we don’t normally carry a specific leadwire in-house, customers have provided the leadwire to us to use in their heaters. We have one particular customer that doesn’t like the texture of one of our leadwires, so they provide their own when they place an order.
Another customer wants the most flexible leadwires imaginable, so they provide us a17 ga rubber insulated wire with 210 strands(!) when placing an order. Another point to consider is the seal called for on the heater. If you’re going to want a moisture resistant heater built with Teflon leads (for example) don’t forget that you’ll probably need to go with an epoxy or RTV seal in the heater. Our default seal is cement, which is porous, so using it in a moist environment isn’t a great idea, especially when you’ve gone to the effort of specifying moisture resistant leadwires.
Here’s a table that summarizes the details above:
