3com 5108M-TP Manual De Usuario

Patch panels weaken signals, thereby reducing achievable link distances. 
3Com includes the use of one patch panel in the 150 meter link distance 
calculation. However, each additional patch panel in the link reduces the 
150 meter link distance by approximately 10 meters.

In the example in Figure 2-2, if two patch panels were used between the 
top right PC and the top right concentrator, the link distance of 150 meters 
would have to be shortened to 140 meters. This is because the maximum 
allowable link distance on 22 gauge wire using 10BASE-T signaling with two 
intervening patch panels is 150 meters minus approximately 10 meters.

Note that a patch panel installed between the bottom right PC and the 
bottom left concentrator would not affect the link since it is only 20 meters.