90v back from pipe stat?

LostInLM

Currently pipe stat connected to stove is wired with 4 core flex back to a junction box. When I check the voltage readings between the wires and earth at the junction box with a multimeter I get the following :

• Brown - common live 230v.
• Black - connects on to circulation pump. 0v to earth when temp is lower than setting on stat, 230v when temperature rises above set level.
• Grey - terminated at junction box, not connected to anything else. 230v when temp is lower than setting on stat. However 90v when temperature rises above set level.

Wondering what that 90v on the grey wire is all about when the thermostat closes? Would have expected it to be zero. Is that normal or safe or is the stat faulty? Is it an induced voltage, or something else?

Zarco

LostInLM wrote: »

Currently pipe stat connected to stove is wired with 4 core flex back to a junction box. When I check the voltage readings between the wires and earth at the junction box with a multimeter I get the following :

• Brown - common live 230v.
• Black - connects on to circulation pump. 0v to earth when temp is lower than setting on stat, 230v when temperature rises above set level.
• Grey - terminated at junction box, not connected to anything else. 230v when temp is lower than setting on stat. However 90v when temperature rises above set level.

Wondering what that 90v on the grey wire is all about when the thermostat closes? Would have expected it to be zero. Is that normal or safe or is the stat faulty? Is it an induced voltage, or something else?

What are u reading the voltage with

LostInLM

Zarco wrote: »

What are u reading the voltage with

A bog standard multimeter, nothing special. Measuring between various terminals and earth terminal. Also notice the grey wire gives a low glow on a phase tester when the stat is calling the pump.

Zarco

LostInLM wrote: »

A bog standard multimeter, nothing special. Measuring between various terminals and earth terminal. Also notice the grey wire gives a low glow on a phase tester when the stat is calling the pump.

It's probably just induced

You'll get 0v on the black because of the connection through the pump when off

It all seems to be operating correctly, dunno if there's an RCD or not on the pump circuit, multimeter prob wouldn't trip it when you're taking those readings

LostInLM

Zarco wrote: »

It's probably just induced

You'll get 0v on the black because of the connection through the pump when off

It all seems to be operating correctly, dunno if there's an RCD or not on the pump circuit, multimeter prob wouldn't trip it when you're taking those readings

Thanks. Good question about RCD. There's one in the CU but not sure if CH goes through it. Must check as it's an older installation.

Bruthal

The usual capacitive/induced voltage detected with very high impedance multimeter on a line parallel and close to a live conductor.

Bruthal

Bruthal wrote: »

The usual capacitive/induced voltage detected with very high impedance multimeter on a line parallel and close to a live conductor.

My thinking too.

Add a parallel load like a 1kohm resistor and a fiver says it disappears.

longgonesilver

Are there any situations where an induced current can be dangerous?

2011

longgonesilver wrote: »

Are there any situations where an induced current can be dangerous?

Yes, many!

It is also desirable that this phenomenon exists. If not we wouldn’t have transformers or motors.

DC's day is coming.

Tuco88

Not with transmission.

You betcha it will. What's 50kVDC peak to peak?

..and frequency compatibility?

2011

Tuco88 wrote: »

Not with transmission.

Too late, it is already used for transmission. Example:
http://www.mutual-energy.com/trading-across-the-moyle-interconnector-isem/

Plenty of HVDC transmission going on.

HVDC lines have lower power losses than HVAC. No induction losses and no dielectric losses. This extends the life span of the conductors used.

Tuco88

Learning something new everyday.

Bruthal

Sir Liamalot wrote: »

My thinking too.

Add a parallel load like a 1kohm resistor and a fiver says it disappears.

Yes although it probably wouldnt last too long when 230v switches onto it.

Restrooms

longgonesilver wrote: »

Are there any situations where an induced current can be dangerous?

I heard first hand of major equipment damage from ELV or Data( can't remember) in close proximity to LV wiring

Not sure if it happens much

adrian92

Bruthal wrote: »

The usual capacitive/induced voltage detected with very high impedance multimeter on a line parallel and close to a live conductor.

As suggested, looks like an induced voltsge.

Try connecting a small load, like a light bulb between the two points and see if the voltage goes to zero to confirm. Just my suggestion. Others may advise if I am incorrect

Restrooms

adrian92 wrote: »

As suggested, looks like an induced voltsge.

Try connecting a small load, like a light bulb between the two points and see if the voltage goes to zero to confirm. Just my suggestion. Others may advise if I am incorrect

What voltage would it read with the phase tester lit

Would the phase tester bring it down I wonder

Tuco88

It's a problem with instrument loops... A good example lets say a RTD (PT-100) any mV induced to the loop distorts the true PV measurement. If its cabled back over a distance with large motors driven from VSDs in the room and cable segregation, cable spec and correct grounding of screens is not correct. Its awful commissioning.

adrian92

Restrooms wrote: »

What voltage would it read with the phase tester lit

Would the phase tester bring it down I wonder

I do not think a phase tester would be good. The OP has a multimeter.
Neither would work , I think, to discharge some micro Amps for measurement purposes, assuming it is an induced voltage with no power .

That is why I gave my suggestion.

I may be wrong, of course.

2011

adrian92 wrote: »

I do not think a phase tester would be good. The OP has a multimeter.
Neither would work , I think, to discharge some micro Amps for measurement purposes, assuming it is an induced voltage with no power .

A low impedance multimeter will do the trick. For example one of these:

https://www.fluke.com/en-ie/learn/blog/digital-multimeters/dual-impedance-digital-multimeters

For the love of God avoid the “phase tester” screwdriver type devices.

Restrooms

2011 wrote: »

A low impedance multimeter will do the trick. For example one of these:

https://www.fluke.com/en-ie/learn/blog/digital-multimeters/dual-impedance-digital-multimeters

Good article that

Bruthal

A simple diagram shouid be drawn explaining this "ghost voltage" thing with regard to high and low impedance meters. It's so simple that anyone who wants to unravel the mystery, can see it.

Restrooms

The old solenoid tester brings back memories

You'd be lucky if the mains could drive it sometimes

Bruthal

Restrooms wrote: »

The old solenoid tester brings back memories

You'd be lucky if the mains could drive it sometimes

Yes had one for years. They would trip rcds and all