Wiring question series/parallel

[Robooo]

Hay,



I'm learning fault finding in CH systems which I'd need help with, please.

I've been given a set example: have got hot water but heating. Measuring the resistance around the room thermostat and the motorised valve together gives a lower total resistance than measuring the individual components. The example is not going into details just shows the expected values (total and individual programmer and 3 port valve) so I worked backwards that it is actually calculating as a parallel wiring not series one. (See picture)
I thought the controls are wired in series normally.
Is parallel wiring an option with these two controls?

Thanks!

 

[fowlerboi]

It would have to be in series for the switches to work otherwise they would just be bypassed?

I am no electrician

Maybe you can enlighten me but I'm not sure resistance is the way forward for finding broken components? It would be voltage at each component to ensure they are switching properly. You can't measure resistance over a programmer for example because the circuit is normally open and you want to check the switch in the normally closed position which it can't do without power, if it has power you can't check resistance (I think.) The same applies to the motorised valve which unless energised on the brown will be normally open across the grey to orange

 

[Robooo]

It would have to be in series for the switches to work otherwise they would just be bypassed?

I am no electrician

Maybe you can enlighten me but I'm not sure resistance is the way forward for finding broken components? It would be voltage at each component to ensure they are switching properly. You can't measure resistance over a programmer for example because the circuit is normally open and you want to check the switch in the normally closed position which it can't do without power, if it has power you can't check resistance (I think.) The same applies to the motorised valve which unless energised on the brown will be normally open across the grey to orange

Unfortunately, I'm not able to enlighten anyone yet🙂
What the book says is that the room thermostat is set to high temperature so it is calling for heat but the system is isolated. So it would be a closed circuit between line and neutral from the wiring centre, room thermostat through the valve back to the wiring centre.
I know the two controls' resistance and the total resistance at the wiring centre. I'm supposed to figure out which component is faulty.
The calculation they gave it only works out if controls are wired in parallel because the total resistance is lower than the individual resistances.
It also states that it is a general fault finding which can be applied to for example to pumps etc.

 

[Robooo]

I'm supposed to be able to guess which component is faulty measuring resistance only by the wiring centre so I don't need to wonder around in the property.

 

[fowlerboi]

What terminal numbers are you using for each test?

 

[Robooo]

What colour and terminal number are you measuring for each test?

The book is not in reach at the moment but it measured the two components individually for resistance and the final resistance at the wiring terminals 2 and 4.
If I remember correctly one component gave 0.28 ohm and the other 0.36 ohm. The final resistance was 0.179 ohm. (The ohm meter was giving values the friction of 20M ohm so 0.28x20.000.000 ohm and so on).
I get the final 0.179 ohm only if the equation is 1/0.28 + 1/0.36 = 1/0.179 which would be wired parallel.
Calculating with normal straightforward addition the equation doesn't work out.

 

[Chuck]

My guess is that "I thought the controls are wired in series normally." may be the assumption that is stopping you solve the problem. You have a three-wire thermostat, not a two-terminal one. Maybe ask yourself, what are the three terminals connected to inside the thermostat? Do the same for the mid-position valve.

 

[Robooo]

My guess is that "I thought the controls are wired in series normally." may be the assumption that is stopping you solve the problem. You have a three-wire thermostat, not a two-terminal one. Maybe ask yourself, what are the three terminals connected to inside the thermostat? Do the same for the mid-position valve.

Maybe it is. I accept that. Probably the given example is wrong.
On the picture however in the first post it shows that:
The programmer connected to the wiring centre (terminal 4), this gives LIVE to the room thermostat which is calling for heat, this is coming back to the wiring centre and goes to the motor in the valve. From the valve motor the NEUTRAL is going back to the wiring centre (terminal 2). This makes me believe that there is a closed circuit present hence I can measure the total resistance at the terminal 2 & 4.
The math I mentioned above only makes sense if I do the parallel calculation.
I'll contact the study centre what they say.
Strange

 

[Chuck]

The math I mentioned above only makes sense if I do the parallel calculation.

If I've understood you correctly... The valve-motor is connected to terminals 5 and 2, the thermostat to terminals 5 and 4. So, for the resistance between 2 & 4 to equal the motor||thermostat you need terminals 2 and 4 to be linked. This would be the case if the programmer HTG terminal were neutral but you are assuming it is live.

 

[fowlerboi]

If you trace from 4 through the room stat through the nuetral through 3 port valve back to the room stat you can see you are in parallel while testing the nuetral

That may be a better way of showing it in parallel

All of the above is a giant educated guess

I still have no clue how resistance testing fits into all this. I understand how it works and have done it for things like underfloor heating mat but for this sort of thing checking voltages in the right places has been tried and tested for me.

 

[Murdoch]

I do think the OP is over thinking this. There are a few parts that can and do go wrong , namely the motorised valves, then you have the room stat(s) and tank stat. And there is the timer / controller

given all these can be at some distance apart, with cables running in unknown routes, how can you allow for the resistance of the cables?

 

[Robooo]

I'll get back with an explanation from the study centre soon. I might totally missed the point.

 

[Last Plumber]

I might be misunderstanding what you want to do here.
If you measure (as @Chuck says), 5 to 2, you are measuring the resistance through a motor winding as well as continuity/resistance through the wires to and from it. That should tell you the condition of it as well as the continuity of the wires and connections. If you measure 2 to 4 you are also measuring continuity through a stat but that won't tell you which component is faulty. It will only tell you if the circuit is complete or broken.

As I say, I may not be following your problem correctly.

 

[Chuck]

If I remember correctly one component gave 0.28 ohm and the other 0.36 ohm. The final resistance was 0.179 ohm. (The ohm meter was giving values the friction of 20M ohm so 0.28x20.000.000 ohm and so on).
I get the final 0.179 ohm only if the equation is 1/0.28 + 1/0.36 = 1/0.179 which would be wired parallel.

At the risk of piling on more 'overthinking', here are couple more thoughts:

I don't understand what you mean by this "The ohm meter was giving values the friction of 20M ohm so 0.28x20.000.000 ohm and so on."

In fact, 1/0.28 Ω + 1/0.36 Ω = 1/0.158 Ω not 0.179 Ω

The sort of general purpose DMM most plumbers carry make 2-wire resistance measurements using a low-current internal source. Unless an external current source is used, these DMMs can typically only make resistance measurements with a resolution of 0.1 Ω. You also need to account for the test leads and contact resistances, ca 0.1 Ω. This makes me wonder whether the "0.179 ohm" measurement, which would need a 4-wire method to make, should really be 179 Ω, i.e. 0.179 kΩ.

The winding resistance of a 230V zone-valve motor is likely to be around 2 kΩ. Values of less than an ohm are expected across the microswitch contacts when they are closed and a megohm or so when they are open.

The other important type of question when investigating this sort of problem is whether the system has ever worked properly. Some installation errors only get noticed years later when a new owner moves in and tries to adjust the heating.

 

[Deleted member 120897]

Which book are you being shown from? I don’t ever recall any of that. That said, I don’t recall much if any fault finding on any of my plumbing courses. Sounds good btw, just to long winded way of doing things.

 

[Robooo]

Which book are you being shown from? I don’t ever recall any of that. That said, I don’t recall much if any fault finding on any of my plumbing courses. Sounds good btw, just to long winded way of doing things.

The book is: BPEC Electricity For Plumbers, Gas Installers and Heating Engineers: chapter 8.

Finally, I spoke to my tutor and he basically said the same as you many already would think.
"Ayyy boy, you are going too deep into this. This foult finding by multimeter example is not a realistic process and I'll learn the proper way when we get to level 3."

So, I appreciate your input guys but I'm beyond help at the moment.

 

[Last Plumber]

The book is: BPEC Electricity For Plumbers, Gas Installers and Heating Engineers: chapter 8.

Finally, I spoke to my tutor and he basically said the same as you many already would think.
"Ayyy boy, you are going too deep into this. This foult finding by multimeter example is not a realistic process and I'll learn the proper way when we get to level 3."

So, I appreciate your input guys but I'm beyond help at the moment.

It's good that you're interested enough to ask. It demonstrates that you are trying to understand fully, which can only indicate to me that you could become a competent tradesman/engineer. Keep it up, this trade like many others, is a life long learning curve. Those who try to help you have all been where you are.

 

[Robooo]

It's good that you're interested enough to ask. It demonstrates that you are trying to understand fully, which can only indicate to me that you could become a competent tradesman/engineer. Keep it up, this trade like many others, is a life long learning curve. Those who try to help you have all been where you are.

Very kind, and thank you but what you just said makes you not the last plumber 🙂🙂

 

[Last Plumber]

Very kind, and thank you but what you just said makes you not the last plumber 🙂🙂

I wish it were true,
I wish I could say,
That many more Plumbers,
Would travel this way.

The truth is they're done,
Their Mole Skins are gone,
The Dressers at bay,
The Turnpins away.

So, though you may say,
There’s more on the way,
The Last one passed through,
Those Plumbers we knew.