I am trying to settle an issue I'm having with a Chinese factory we do importing from. We import Christmas lights. There is a debate between SPT-1 wire and SPT-2 wire. My understanding is that the only difference is SPT-2 has more insulation. However, just because it has more insulation, does not mean it can handle more wattage.

For example, if you have 16 gauge SPT-1 wire and 16 gauge SPT-2 wire, they can handle the same amount of wattage, no more, no less than the other. Is this correct? If not, can someone explain how insulation would allow the same gauge wire to handle more wattage.

Many thanks in advance for your help.

Best Regards,
Ben

16ga is 16ga unless the material is different. Copper vs Aluminum for example.
Not an expert by any means but, I don't see what diff. the insulation makes.

I think you need to understand what wattage is... versus voltage and current.

Insulation is temperature rated. However, in your low amperage case, it is meaningless. If you search http://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=1&cad=rja&uact=8&sqi=2&ved=0CC8QFjAA&url=http%3A%2F%2Fwww.cerrowire.com%2Fampacity-charts&ei=Ki8sVLy0H9OXgwSTsIL4Aw&usg=AFQjCNEtd13nBCA84w6wAEa4oAT9hw00VQ&sig2=aDcvs9HMZ2veondrJhycVw
you will see that with different rated wiring insulation, higher amperage rating can be achieved for the same AWG

ma0641 - that chart only talks about wire gauge size and current-carrying ability - it doesn't address insulation type or thickness.

celticdiablo: you are correct - thicker insulation does not mean the conductor can carry more current (and hence provide more power). In theory you may be able to design a circuit that runs at a higher voltage, assuming the thicker insulation is rated for a higher breakdown. But for Christmas lights I would expect that you are carrying standard household 110 VAC, and so can't actually take advantage of that - correct? So no - you're only freedom for providing more power is to carry more current, and that means switching to a larger gauge wire (such as moving from 18AWG to 16AWG wire).

celticdiablo: Assuming you are in the USA, the national electrical code will be likely need to be followed. There are tables in Article 400 that will detail many properties, such as insulation thickness and voltage ratings, of flexible cords and cables (such as SPT-1 and SPT-2). Individual conductors are detailed elsewhere.
How you use the cords or cables, the number of cords or cables installed together or as a group and the number used as current carrying...etc. determine the ampacity or amount of power a conductor can safely conduct.
For products imported into the USA for use I expect that UL or other testing agency will be involved. There testing may adjust or effect conductor ratings and ampacities.
...and you thought this was a simple question...