First of all there is no such thing as not being able to pull a new cable; it's just a matter of cost!

Now with that said, splicing CAT-5 is never a great idea but there are times where it is the only solution that makes sense. Usually this happens when you working with existing cables and the termination point has changed.

The problem usually is that you do not have easy access to the path that a cable takes, like in a house. In the case of a house or some offices in order to run a new cable you may have to cut holes in sheetrock. Now add up the cost of patching, paint and cabling labor cost and the splice idea starts to look like a better idea. So, now that you have made your mind up to splice. How should it be done?

A Good Way

There are two methods to splice a CAT-5 that usually works out with good results. One is to simply, put a plug on one cable and a jack on the other, connect the two together.

A Better Way

The other way is to strip both ends of the CAT-5 back and then stager cut each wire on one cable. For instance cable "one" the Blue wire is the longest, the Blue / White is the second longest. On cable two the Blue would be the shortest and the Blue / White would be the next longer wire.  Once all the wires are stagger cut then solder the corresponding colors together trying to keep the twist in the pairs.  If there is a correct way to splice CAT-5 this has to be it, but it takes a lot of time.

The Wrong Way

By far the most common way I see CAT-5 spliced is to use regular crimp splices. This in no way comes close to meeting the CAT-5 standards. Nor will it pass a scanner test, however it will usually pass the continuity test.

When I run across this I usually replace it with the Plug / Jack method. If left in place then you may see collisions and 10 / 10 - 100 negotiation type problems.

The best method is not to splice, but if you must use the solder method or the plug and jack method.