atcomsystems.ca/forum Forums Other TDM Phone Systems 1A2 and Comkey Telephones & Systems Wiring help for newbie

Hi everyone!

This is my first post here. I found your site looking for information on 1A2 key systems, and it looks like you guys have just about all the information on the subject. I am a new phone technician, still cutting my teeth on wiring and installs, as my background is mostly on the IT side of things.

My question is about a 1A2 system I have acquired, as part of disposal for a new install. I have a 551C KSU (no cover) with power supply, interruptor, and 3 line cards installed. I also got a Melco K-19 R/T intercom unit and 2 2564 keysets. I can get 25-pair cable, Amphenol connectors, 66 blocks, and cross connect wire as needed. How should I wire the CO lines into the system, and ditto for the 2 keysets? Any wiring diagrams, links to manual pages, etc. would be greatly appreciated. Thanks!

Your CO lines will be on the bottom of the block in the 551. Your phones will wire on the top color for color, three pairs for each line. You didn't say anything about a ring generator, but common bell will go on your y/sl to the phones, if you don't need a common bell just put the y/sl on the tip and ring of the line you want the phone to ring on. You can get old 1A2 manuals, but they aren't cheap, there really isn't that much to it, your dial intercom should have a drawing on it. Welcome to the board, hope this helps some.

As justbill says, there are 4 pairs of pins on the lower left for the (up to) 4 CO lines in the 551C. Since you have 3 cards, you can wire up to 3 CO lines.

If you are going to wire up the intercom, I might suggest you wire the 2564 keyets directly to the 66 blocks, then run cross connects from the 551C to the 66 blocks. You can pull the 24VDC battery (talk) and the 10VAC intercom buzzer voltage (for the intercom) from the right lower side of the 551C and cross connect it out to the 66 blocks.

On my install I ran one set of cross connects out from the 551C to the first phone on the 66 blocks, then just daisy chain with bridging clips and more cross connects. That reduces the clutter on the 551C internal block itself, and you don't have to go back in there if you add more phones.

There is a large brass ground screw connection inside the 551C, better hook this up to a solid earth ground with a #10AWG solid conductor, otherwise the line cards may not pick up incoming calls.

Hope this helps, -Stryder

Good catch. I assume a lot and shouldn't common bell won't work without the external ground.

Thanks for the help guys!

Although it's been years since I put in 1A2, we would extend the blocks inside the cabinets to "B" size blocks on the backboard, sometimes even dual sets depending on how many stations, and run jumpers from there. Run jumpers to ONE side of the station blocks only, and bridge clip across. DO NOT DAISY CHAIN! It's a nightmare for trouble shooting!