Hobby Wiring dilemma

[mainline]

Bit of a dilemma / argument with the way the Project manager, who has supplied me with a wiring diagram that hes done for control of hot water in a block of 4 cottages.

The cottages are pme earthing, there are 2 phases split between the 4 cottages.

There needs to be a call for heat from 2 cottages which are on a different phase to the boiler, his wiring brings the supply in to a wiring centre to supply the zone valves / and tank stats.

There are 2 immersion tanks, one downstairs and one up, both zone valves are in the same location with a cable for the downstairs stat tank having to run through the house to the upstairs one.

He is adamant that i wire it the way he wants, he's installed 2 5 core cables to the wiring centre from the cottage to the wiring centre which there is totally no need to do as it only requires the call for heat to the boiler.

Wiring it his way will mean that both the tank stats, zone valves etc will all have a supply + phase on them from another location.


The prospect of not being able to isolate this wiring centre valves/stats both up and downstairs, i cant see as being right when either a no volt 2 channel programmer would do a far better job with a lot less wiring and would mean that everything apart from a single connection would be from the same supply.

There is a bit more thrown into the mix as one of the cottages has to use a wireless switch to be able to turn off the bio mass hot water but hes provided one with a SL output which is totally useless as that SL would have to be wired from the other supply along with the earth and neutral from the other location.

Im thinking of on Monday to refuse to do this am i right in doing so ?

Thoughts ?

 

[ferg]

Local isolation could be a 4 pole rotary isolator labeled with the location of the supply to it.

Warning label at DB and wiring center.
Not ideal but maybe enough of a compromise to keep things moving.

 

[mainline]

Local isolation could be a 4 pole rotary isolator labeled with the location of the supply to it.

Warning label at DB and wiring center.
Not ideal but maybe enough of a compromise to keep things moving.

It's more to do with would you do it as he's said, or would you refuse to do it his way.

 

[UKMeterman]

Ok,
That is a mess as unless relays are used to isolate the incoming call for heat then it can be possible to back feed one installation from the other. Sketch out what will happen when the double pole main switch to one installation is opened...

 

[mainline]

I've decided to refuse to do it as there are easier ways to achieve the same thing which are cheaper, easier, and safer.

 

[mainline]

Local isolation could be a 4 pole rotary isolator labeled with the location of the supply to it.

Warning label at DB and wiring center.
Not ideal but maybe enough of a compromise to keep things moving.

Not forgetting the zone valves, tank stats, isolators, 2 CUs and the 2 switches in the other 2 locations.

 

[ferg]

Not forgetting the zone valves, tank stats, isolators, 2 CUs and the 2 switches in the other 2 locations.

I misread the OP.
Having read it again it looks like my brain skipped over entire paragraphs of it.

 

[sunray]

I spent 15 years building, installing and modifying control panels, time and time I'd find voltages from multiple sources coming together in panels and even electrically connected.

One such example was a new school with something like 20 control panels with links at 24Vac between them. One part of it was a ring of cable ran around every panel, every panel provided the 24Vac and something 6 relay coils. A master panel had relays operated by the fire panel and switches to shut the system down, put it in extract only etc.
I was sent in with a box of MCBs to upgrade the 24V secondary MCBs in every panel as there had been multiple tripping problems, most were 2A or 4A for 50 or 100VA transformers and there really was nothing in each panel to get anywhere near those currents.
Isolating the first panel I quickly discovered the issue and headed down to the boiler room where the Engineer had set-up an office; asked his permission to isolate the boiler room panel 230V control circuit to demonstrate what I'd diagnosed as the issue... the gas valve remained open and most of the indicator lamps dimmed slightly but remained lit, even when the main isolator was opened.

A very much abreviated sketch showing the master control panel left, 3 random panels and the boiler panel right. The various interlocks, safety devices etc not shown for clarity. The multiple 24V's were sufficient to transform up to something below 200V in the boiler panel. All of the 24V's were ground referenced as shown by the green earth.

It didn't take many seconds to come up with an alternative arrangement.

The reason the MCBs were tripping was due to the various panels control circuits being fed from different phases and all being shorted together created significant overloads of several amps through the 7/0.2mm linking cable (0.22mm² rated at 1A and 9Ω per 100m)


Right so getting back to the point in question; there must not be any chance of the various supplies from different areas of the system being connected together. Isolation by relay is permissible but please label it carefully for the next persons safety and sanity.

 

[sunray]

Im thinking of on Monday to refuse to do this am i right in doing so ?

Thoughts ?

You are absolutely within your rights to refuse to do anything which is unsafe, and even more than that: it is your duty to not do anything unsafe.