System Grounding

[Babybearjs]

I want to know if it is good to have a "common" ground on a ktu system.... when I opened up my 101G, all the ground terminals are common.... can the ktu's be wired that way too? (EG: on a 207C ktu, the system uses batteries A, B, C, and Lamp power... can they all have a common ground?) terminals 9 is LB, terminal 10 is LG, terminal 20 is ground, along with terminal 30, and 40..... can these all be tied together so you only have 1 ground wire for the whole KTU....    the same goes for other ktu's that use multiple voltages..... should they all only have 1 ground wire across all the ground terminals??

[dsk]

I would have been happy to answer yes, or now to this, but it will always be one designer thinking another way than others.
Usually yes should be the answer. If there are connections to the cabinet, the ground should be common.
What may be the reason for grounding?  1) safety?  If it is a risk of electrocuting, grounding are the most common protection, and will probably be the solution.
2) noise reduction, elimination of statics? A relatively high ohm resistor to ground does the job, and will not do any harm.

Remember a good grounding may result in fault current traveling from one unit to another, not often but it may happen. (Usually at error no 2 in a system.)

dsk

[Dave F]

One good reason for NOT combining all grounds into a single wire is the current-carrying capacity of those thin wires.  Each KTU (and each lamp) draws a certain amount of current from the power supply.  If you combine all the ground wires into one, the total current from all the KTUs and lamps will have to pass through that single wire.  In addition to the possible fire hazard from wires overheating, this can cause a voltage drop to the key system if the wire-runs from the power supply are particularly long.  Erratic operation of KTUs is sometimes the result.  In the case of the lamps in the phones, combining the grounds sometimes results in dimming when several lamps are on at the same time.  The longer the wires between the KTU rack and the phones the more severe the problem, as the voltage drop in a single ground wire can be substantial.  When one line is on hold, the steady lamps on other active lines will dim as the lamp of the held line winks on and off.  It is always better to keep the grounds separated and home-run back to the power supply whenever possible.  More labor, but much superior.

DF

[Babybearjs]

well this is what I needed to hear....thank you, you just confirmed my concern. For right now, I have the grounds common, once I get the 20B2 power plant, then I'll change things back the way they should be.... as for erraticness, yes the system is acting funny, but on one phone only right now.... for some reason I'm not getting the wink signal on my 5th line and when I change lines the lights dim... just for a moment but there is still issues... what I did, was I pulled my 202B KTU and wanted to put in a 208.... wound up putting the 202 back in and the control signal is not working right.... (LK, CO, HA, and TO) also when the phone goes to hold the light wont wink... even though I have terminals 9 and 10 connected to my 210.... I guess I'm going to have to almost start all over with my wiring.... I wish there was a way of "Modularizing" all these connections so if I ever have to make changes, all I have to do is to unplug my connections and plug in the different KTU... but that's hard because of the different wiring schemes in the 1A1 system.... no wonder they upgraded to the 1A2.....I guess I need to invest in some 400 series adapters.... that way I can upgrade to a 1A2 without having to change out the whole system.....it never stops does it??

[Dave F]

Yup, the tedious amount of manual wiring, coupled with the difficulty of making changes and additions, was one of the motivations for the switch from 1A1 to 1A2.  Not to mention that all those wirespring relays and their associated metal frames, terminal boards, and internal hand wiring were vastly more expensive than the new small 400-series circuit boards.  But, from the standpoint of a collector of vintage phones and equipment, nothing compares to the elegance of a nice working 1A1 system.  There is great satisfaction in hearing the clicking of those wonderful old relays.

Don't give up!

Dave

[Babybearjs]

Thanks Dave, you know your phones! Getting this system back up and running  was a bit frustrating, but it is working.... and a 20B2 power plant is on its way to update the system... I found a decent deal at deep surplus.com, some Cat 5E 25 pair cable. got 45 ft. of it for $20.00! was pricing it and the average price for cat 3 was .86/ft.  I'm trying to get all my wiring in 1 bundle instead of 3 or 4 runs... now I just need to figure out how to plan this out. I picked up a 66 block at a electronics thrift store here in Boise, and that with the cable has got me started.... now, I have all this IW wiring under my mobile home and right now am using #44 Blocks to make my splices.. can I continue to use these or should I upgrade to #66 blocks? right now, I have 4 pair cat 5 cable in a home runs setup for my internet wiring..  the phone lines are spliced at various locations...  once I start to use the 25 pair, it can support the internet too... what do you suggest? use the 25 pair for both phone and dsl, or just phone and leave the internet wiring the way it is...  dsl already is degraded just from the distance from the CO... I'm signed up for 20 Meg, but only get 18 meg at the house. Centurylink can't provide the 40 Meg at my location because their system isn't wired for it in my area... so I'm worried about making splices in the wiring from the router to the jacks.   John