Is all wire the same for a given size no matter whether its intended for marine or land use. Its been a really long time since ive put that much thought towards the math of it all so if someone wants to double check my numbers please do.

Alumaflex Simpull Thhn Cable Vs Xhhw
Automotive wire vs thhn. This thermoplastic heat and water resistant nylon coated wire is designed to operate in the same environments as thhn without the addition of installation accessories for use in harsher environments. Thhn is a code for thermoplastic high heat resistant nylon coated wire which is allowed for use in dry to damp location and rated for a maximum temperature of 90ºc 194ºf. Thwn is considered an evolution of thhn although both are still widely used. It is usually rated to 80ºc 176ºf. The most common type of insulation used for simple parts store wire is a thhn thermoplastic high heat resistant nylon a pvc covered wire mostly used in the industrial and housing markets. Im planning on doing some major re wiring on my boat over the winter.
As its name implies it is a good general purpose automotive wire. Mtw and thhn can both feature a bare copper conductor however thhn is available with an aluminum conductor depending on size and mtw wire is available with a tinned copper conductor. 1gpt or primary wire. A friend and i have been arguing about whether there is a difference between automotive wire and marine grade wire. It features a multi stranded core and flexible insulation making it ideal for pulling through tight spaces. This is the most common wire you find at auto stores.
As always the decision between using thhn or xhhw comes down to weighing performance versus budget. Thhn and other types of stranded wire is rated to be used in situations where the wire does not move during use automotive wire uses much finer stranded wire that allows many more movement cycles before wire fatigue and breaking of the strands. Although some is also rated to 105ºc 221ºf. On the other hand xhhw has the additional features that provide increased efficiency and extended longevity. Lead free thin wall automotive wire rated to 105 degrees celsius. Entering the known numbers for the 4awg thhn wire it says it can handle 51000 watts 600v 85a 51000w.
Thwn is a code for thermoplastic heat and water resistant which is suitable for use in both dry and wet locations with a maximum temperature rating of 75ºc 167ºf. At the core mtw offers a higher strand count in the conductor making it more flexible than thhn which also features a nylon coating that further restricts movement. Pvc is insulation is extruded and created by heating pvc and then extruding it through a die on the stranding. Heavy wall automotive wiring rated to 80 degrees celsius. Its counterpart is called thwn or thwn 2. Our customers often express that the more popular and less expensive thhn wire is perfectly suitable for what they need.
This insulation can be melted with a heat source changing the form.