Pinouts for T1/E1 crossover cable WAS "RE: [Asterisk-Users] what cable to connect a legacy PBX to a TE410P ?"

[Rich Adamson]

Kevin P. Fleming wrote:
> Rich Adamson wrote:
> 
>> Oh, and if shielded T1 cable is used, the shield at each end of the
>> cable must be grounded. (Let's see how many can figure out how to do
>> that via an rj45 plug. ;)
> 
> You use shielded plugs and jacks, of course :-) That is why the
> TE405P/TE410P have shielded jacks (as of about a year ago, IIRC). The
> retail packaged cards even ship with four shielded cables included!

Excellent!

> Minor point: isn't it safer to only ground the shield on one end?

Best practices suggests IT/telco equipment racks throughout a building 
share a single grounding system (and not with 24 ga cable). Likewise, 
grounding of both ends of a T1 (eg, shield) is considered best practice. 
Treat a T1 cable as no different then a transmission line with a 1.5mhz 
RF signal.

If rack grounding is totally ignored (which probably happens 
frequently), there is a possibility of a ground loop created through the 
T1 shield. But, the root-cause is the lack of rack grounding, not 
leaving one end of a T1 cable ungrounded.

For safety, also think about the number of devices that are produced 
with poor power supplies, hot chassis, etc. Seen (and felt) several of 
those. ;)

R.