While replacing the motor of a motorized valve in the central heating system of my house I have noticed some weird voltages that may be a problem:

Of the three cables (excluding earth) that arrive at the thermostat from the timer near the boiler, the voltage between neutral and life is 140V AC when the timer is off (it is 240V AC when the timer is on).

Also, the voltage between neutral and switched life (when not connected to life) is 90V AC. This means than when the thermostat is not asking for heat the motor is always receiving 90V AC (it does get 240V when the thermostat is asking for heat)

Should not these 140V and 90V be 0?

Perhaps this explains why this motorized valve broke. If it is permanently energized at 90V it is likely to fail earlier.

I have shorted the neutral and the life, while the timer is off (ie, when there was 140V AC ), with a 1A fuse in between, but the fuse did not blow. So, it seems that there is no big intensity behind that voltage.

I have confirmed at the junction box near the boiler that the 140V is not coming from the side of the timer.

I have also confirmed that for other zones ( I have five at home) the voltage is 0 for three of them and about 115V for the fourth one. This 115V is for a zone where the motor also failed some time ago.

Where are these voltages coming from?

Are they a problem?

How can it be fixed?

Needless to say that it is not possible to access all the wiring between timer and thermostats and motorized valves. Even the junction boxes near the motorized valve is very difficult to access.

Many thanks,

Antonio

On Mon, 24 Nov 2008 13:55:18 +0000, asalcedo wrote:

Where are these voltages coming from?

Your high impedance volt meter.

Are they a problem?

No.

How can it be fixed?

Nothing to fix.

--
Cheers
Dave.

On Mon, 24 Nov 2008 13:55:18 +0000, asalcedo
wrote:

some snips

While replacing the motor of a motorized valve in the central heating
system of my house I have noticed some weird voltages that may be a
problem:

Of the three cables (excluding earth) that arrive at the thermostat
from the timer near the boiler, the voltage between neutral and life is
140V AC when the timer is off (it is 240V AC when the timer is on).

Where are these voltages coming from?

You are probably using a high impedance digital meter to take readings on long
open pieces of cable. Try using a proper meter (AVO 8 etc) for the job.

Geo

asalcedo wrote:

While replacing the motor of a motorized valve in the central heating
system of my house I have noticed some weird voltages that may be a
problem:

Of the three cables (excluding earth) that arrive at the thermostat
from the timer near the boiler, the voltage between neutral and life is
140V AC when the timer is off (it is 240V AC when the timer is on).

Also, the voltage between neutral and switched life (when not

Live or Line, but not "life"...

connected to life) is 90V AC. This means than when the thermostat is
not asking for heat the motor is always receiving 90V AC (it does get
240V when the thermostat is asking for heat)

Should not these 140V and 90V be 0?

You are probably making your measurement with a meter that is very
sensitive, and places practically no electrical load on the circuit you
are testing.

When the timer is off, the wire is not connected to anything - it is
said to be "floating". So what you are seeing is a voltage induced in
the switched live wire just by its close proximity to other live wires.

Perhaps this explains why this motorized valve broke. If it is

Almost certainly not.

permanently energized at 90V it is likely to fail earlier.

If that were really the case, then perhaps, but...

I have shorted the neutral and the life, while the timer is off (ie,
when there was 140V AC ), with a 1A fuse in between, but the fuse did
not blow. So, it seems that there is no big intensity behind that
voltage.

That is the key. As you have seen with your fuse experiment, that
voltage will rapidly fall away to nothing the moment any load is placed
on the wire. In fact you will only be able to draw a few micro amps of
current from the wire before the voltage falls to nothing - hence why
your fuse did not blow.

I have confirmed at the junction box near the boiler that the 140V is
not coming from the side of the timer.

I have also confirmed that for other zones ( I have five at home) the
voltage is 0 for three of them and about 115V for the fourth one. This
115V is for a zone where the motor also failed some time ago.

Seeing half mains voltage is not uncommon on floating wires - especially
where there are noise filters present on the equipment they are
connected to (things with motors in especially).

Where are these voltages coming from?

Stray pickup, as described above.

Are they a problem?

No.

How can it be fixed?

They can't really, and there is no need to fix them. If you made the
measurements with an older moving coil volt meter then you would not
have even seen them in the first place.


--
Cheers,

John.

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Hi John and all,


Thank you for your helpful answers.

It is great to learn. This is what a forum like this is meant to do.

The meter I used is a SkyTronics 600.219, it is a modern digital one and I guess it is a high sensitivity one.


Antonio