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Can the smaller RJ11 jack be plugged into an RJ45 (technically a 8P8C) socket?

I've seen the plug be plugged into the socket, but have not seen it used to transmit data.

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You have to be very careful when plugging the RJ11 into the RJ45 jack becuase you are responsible to make sure that the plug is centered and lines up with the connectors. It will work, but it's not recommended, and certainly not recommended if you will have end users trying to plug and unplug these things. –  Richard West Jun 26 '09 at 14:48
    
I have to use a machine that uses a telephone line and the cable I've been given to use and that I've been told works, is BT jack to RJ11. Lining up the connectors to the pins is actually sorted by the top of the socket. Luckily I'm not responsible for any more users. It's surprising and interesting that there's not a 1 to 1 relationship of jack types to socket types (not including the different types of RTS jacks), but I had assumed that that identity of physical dimensions would be a constraint of sorts. You learn something new every day! –  StuperUser Jun 26 '09 at 15:14

7 Answers 7

up vote 13 down vote accepted

Yes it can. I have my home ADSL modem line (RJ-11) plugged into an RJ-45 socket, which goes back to my BT master socket.

They are fiddly to unplug though.

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+1 - Yes, you can. We've done this in a production environment before. It's more likely that you'll need RJ45 in the future than than RJ11, so might as well run the CAT5e or CAT6 now to save running cable again. –  Andy May Jun 26 '09 at 14:59
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At this point, I'd be hard pressed to stop myself from making an 11->45 cable just because I can... –  Kara Marfia Jun 26 '09 at 16:48
    
+1 for ghetto rigging –  theman_on_osx Jun 26 '09 at 17:29
    
Wouldn't the socket be damaged if we accidentally misalign the RJ-11 to it? –  Pacerier Sep 7 '13 at 20:06

Yes, you could do this. You can wire RJ-45 to handle RJ-11 signals.

Personally I'd tend to look at just a few jacks with this setup as a bit unprofessional, but I've seen installations where they did everything as RJ-45 to avoid needed two kinds of connectors/cabling/etc.

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That's what we do - network and phones are both RJ-45, both use the same structured (ha!) cabling, and get separated at the patch panel. –  RainyRat Jun 26 '09 at 14:47

Sometimes there are sockets available which fit both connectors. I had a surge protector for a while that allowed both to fit in, to supress surges on either ethernet or phone.

That said, just because you can plug an RJ11 plug into an RJ45 socket doesn't mean you should. RJ11 sockets fit RJ11 plugs. RJ45 sockets fit RJ45 plugs. Right tool for the right job. I would only try to put an RJ11 plug into an RJ45 socket if:

  • Someone paid me to and didn't care if it was all goofy + wierd, and I wouldn't be held liable if the connection didn't work right.
  • I'm fiddling around in the lab, it's 1AM, RadioShack is closed, and I need to jury-rig something now because if I don't it won't work by 9AM tomorrow when The Boss is coming, and I can't find an RJ45 plug to use.
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RJ45, RJ11, and RJ12 are designed for this, though. 5 years in the future, it's still common to find RJ12 jacks on phones, but only RJ45 jacks are commonly used in building wiring. –  Falcon Momot Aug 18 at 7:46

Like others have said about alignment problems, be mindful of this. The outer edges of the RJ11 cable end are thick plastic and will push the copper connectors in positions 2 and 7 down further then they are supposed to go which can cause a later issue with a RJ45 in it's place.

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You can plug an RJ11 plug into an RJ45 jack, but I'd make or buy an adapter in order to prevent damage and alignment problems.

By the way, in your question you use "jack" when you should use "plug". And, though "socket" works, it's more commonly referred to as a "jack".

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Yes, you can, but due to the inconsistency in getting the pins lined up, I usually end up cutting the RJ-11 end off and crimping on an RJ-45.

Cannot recommend the other way, I have had to replace RJ-11 jacks (female) where a user tried to plug in an RJ-45(male) cable. Not sure how, but he managed to get it part way inserted, and I could not get it out without damaging the receptacle.

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Ooh err missus! –  StuperUser Jun 26 '09 at 16:24

Yes, can you physically plug an RJ11 jack into an RJ45 socket, as you have seen before.

Standard Cat5 cabling uses twisted pairs for pins 3&6 and 4&5 this is going to give you decent signal propagation too because RJ11 generally pairs 2&5 and 3&4.

Edit: Changed RJ11 pin numbers. I tend to forget about pins 1&6 because they aren't usually used...

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I believe the 1&2, 3&6, 4&5, 7&8 set up ethernet was specifically designed so that the same cabling could be used for phone and ethernet. –  freiheit Jun 26 '09 at 14:56

protected by Falcon Momot Aug 18 at 8:37

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