Another 2 way switching experience (This time not domestic)

Thank heavens this one is finished. In the diagram can be seen a very standard 2 way system in brown and another in red. However SW1 & SW2 are 30A 2PCO toggle switches and wired in such a way that always one system is on and the other is off. Aditional switches shown as 'SW A' & 'SW B' [shown in orange] to select which half of the arangement the contactors 'A' & 'B' are operated by, in practice there are many tens of them dotted around the building.




The idea is the buildings lights are operated on an occupied/unoccupied basis and controlled from the 2 main entry/exit points of the building. It is very old and highly outdated/impractical, in fact I still don't understand the practicalities of it even though we've spent the best part of 30 hours fault finding and tracing cables but the customer does. That was until about 3 years ago when they got an electrician to add another control switch. They used a 4PCO to create the intermediates.



But they added it in the middle of the run which meant contactors 'B' were connected into the wrong part of the system and not working as they should, they'd lived (and struggled) with it since until recently when a fault developed blowing a fuse in some switch combinations.

I've shown different colours of wires but they are all red 7/0.029 PVC singles and completely unlabelled.

After finding the fault we were able to add 2 wires [shown pink] and make tiny changes to restore it to the way the customer requires, even though we came up with several alternatives to this horrendous system.


Edit: Not all of the 'SW A & B's' are 2 way, in that some lights can only be operated when occupied and others only when unoccupied. And the later additions are wired in 2.5mm² singles.

Sometimes you wonder if it would be better implimented with some electronic system, rather than hard wired mulipole changeovers and contactors, then you begin to wonder if thats right at all... when that fails in 30 years time and parts have long since been discontinued and there is hardly any one about who is still familar with it, it might be a lot harder to fix. Obilgatory BOFH episode: https://www.theregister.co.uk/2019/09/20/bofh_2019_episode_7/

Adam_151 said:

Sometimes you wonder if it would be better implimented with some electronic system, rather than hard wired mulipole changeovers and contactors, then you begin to wonder if thats right at all... when that fails in 30 years time and ...

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Ha, doesn't need 30 years !
At a previous job, the warehouse lighting was controlled by a programmable system - but it didn't work as well as the warehouse manager would like. it was supposed to be a combination of timed operation, daylight sensors, and manual override. It was only a few years after being built when I got asked if I'd take a look ...
Complete dead end. I couldn't find any documentation on how it worked, the system was discontinued (and nothing on the manufacturer's website), but most of all the system needed a code to get into and guess what no-one had
AFAIK, they still put up with it as it was.

But of course all the info would have been in the O&M manual .........

Adam_151 said:

But of course all the info would have been in the O&M manual .........

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The system is actually fairly simple.
Effectively there are 2 wires, lets call them occupied and unoccupied and all over the site switches can select between them. The time switches are prety much redundant but apparently used to run the extra complication of: OFF, -ve & +ve DC for day and night in addition to the occupancy control.

O&M?... oh dear.

I don't know if it did exist but this system has been significantly added to as the site has grown over the years.

There is a reasonably accurate wiring diagram (well about a dozen of them for the individual buildings) which totally made the job of finding the fault easier but of course the circuit with the fault was not on them, we updated as we went round and the changes we made but I absolutely sure there are still errors in the areas we didn't look at.

We wanted to add small MCBs around the system as some would have been very easy. We may be going back next year to replace some rubber singles (the cause of this failure) if their own maintenance guys decide thay can't do it.

I think Adam was referring to my post - where the programming setup and access codes should have been in the handover documentation. Whether there was ever such documentation, I have no idea; but I do know that if there had been any, it had been "filed away safely" where no-one knew about it The person who project managed our side of things for the build was only taken on for the duration, so realistically we had no "collective memory" about things.

When I left the company, I had been careful to hand over various documentation and one or two specialist tools to the maintenance department. A couple of years later I got asked if I'd go back in for a couple of hours - which I was happy to do as my beef had been with the previous manglement. I was able to sketch key bits from memory (the heating and A/C controls were fairly simple) - there was no trace of any of the documentation I'd left, nor the tool for servicing the control valves without draining down

SimonH2 said:

I think Adam was referring to my post - where the programming setup and access codes should have been in the handover documentation. Whether there was ever such documentation, I have no idea; but I do know that if there had been any, it had been "filed away safely" where no-one knew about it The person who project managed our side of things for the build was only taken on for the duration, so realistically we had no "collective memory" about things.

When I left the company, I had been careful to hand over various documentation and one or two specialist tools to the maintenance department. A couple of years later I got asked if I'd go back in for a couple of hours - which I was happy to do as my beef had been with the previous manglement. I was able to sketch key bits from memory (the heating and A/C controls were fairly simple) - there was no trace of any of the documentation I'd left, nor the tool for servicing the control valves without draining down

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This is why I include the post I'm replying to.
My main 'niche' since 2002 has been panel building/install/mods/repair we supply at least 2 sets of O&M which on some of the bigger systems each set has been several A4 ring binders or spiral bound books. It breaks my heart to go back 2 years later and the staff argue that we left nothing, we even tend to take pics of the folders on the customers premises. But of course an electronic copy of the O&M is always available (I used to carry a hard drive with hundreds of panel drawings which gave 90+% of the useful O&M info).
Much of my work has been replacing BMS controls (Mostly to Trend IQ3) so onsite panel partial rebuilds and sensor/valve changes. It's often at that point I've found the valves are stuck and the main reason for BMS change!
The programme is usually password protected, at least until the installation has been paid for, and a copy is kept by us. Bear in mind I'm freelance and I describe the way my various employers work. On many of the systems the program can't be read without the password but can be overwritten so the system is not 'beyond reach'. We also include a copy of the program but possibly after payment.
Some systems may include time related routines such that a visit is required after full payment to remove the routine or the system will gradually lose functions. This is particularly useful in AV/conferencing systems to remind them payment is overdue.