water contact

[puckman]

I was in a class 1 div ? to day when i seen a no#12 thhn single wire going to the top of a glass container of some sort that fills with water. it had a sta kon ring attached to the treaded screw about 1/4/-20 on top of glass. i ask the operator what it was and he said it a ground wire. and when the water came incontact with a rod inside the glass the motor started. he also took the wire off the glass connection and motor stopped, then touched the motor with the wire and the motor started and ran untill he took it off the motor. he insist the rod is only a piece of metal and not a switch of any kind. i took a votage reading from ground to the sta kon and got 24vac. any ideas what this is and is it a violation/

 

[walkerj]

I guess they never heard of a float switch:-?

 

[dbuckley]

It cant be a ground wire, so its a sensor wire. Something connected to that wire is measuring the resistance from that wire to ground and using that to control a relay that powers the motor.

My opinion is it is outside the scope of the NEC.

 

[hillbilly1]

They use something like that for water level control on large municipal water towers, the control powers a dry contact to signal the pump(s) to turn on and off to fill the tank. More reliable than a float switch, because all that's in the tower are the electrode(s) and easier to service since the controller is not at the top of the tower.

 

[gar]

081210-2150 EST

The Charles F. Warrick Co. manufactured liquid level controls using a moderate voltage AC source in series with a relay starting a very long time ago. This may have been in the 30s. Moderate means up to maybe 600 V. This was a very simple reliable conductive liquid level control.

I did some consulting with them in the early 60s on the development of some electronic units, both capacitive and conductive. I obtained several patents for them in this area. Warrick was a family business started by Charles and was run by Woodward when I has contact with them. Later the business was sold to a larger company, and now appears to be part of GEMS.

You can see some infromation on the product that is the evolution of the original concept that started the company at
http://www.gemssensors.com/content.aspx?id=2258

This product is really an isolated transformer secondary of some adequate voltage, somewhat high leakage inductance, in series with a relay coil, and a probe. Note that the transformer is made from separately molded coils and this provides very good input to output isolation and ease of changing or initially building different voltages on the primary and secondary.

.

 

[ELA]

081210-2150 EST

The Charles F. Warrick Co. manufactured liquid level controls using a moderate voltage AC source in series with a relay starting a very long time ago. This may have been in the 30s. Moderate means up to maybe 600 V. This was a very simple reliable conductive liquid level control.

I did some consulting with them in the early 60s on the development of some electronic units, both capacitive and conductive.
.

Thats some real old school stuff Gar!

 

[weressl]

I was in a class 1 div ? to day when i seen a no#12 thhn single wire going to the top of a glass container of some sort that fills with water. it had a sta kon ring attached to the treaded screw about 1/4/-20 on top of glass. i ask the operator what it was and he said it a ground wire. and when the water came incontact with a rod inside the glass the motor started. he also took the wire off the glass connection and motor stopped, then touched the motor with the wire and the motor started and ran untill he took it off the motor. he insist the rod is only a piece of metal and not a switch of any kind. i took a votage reading from ground to the sta kon and got 24vac. any ideas what this is and is it a violation/

It could be a crude level switch and the power is feed by an intrinsically safe power supply. As weird as this sounds, it may be perfectly 'legal' and safe in a hazardous location.

 

[gar]

081211-1056 EST

ELA:

In the electronic on-off circuit I developed for Warrick I used a bridge circuit. Excitation across the bridge was 10 V AC. AC is important because it avoids a time varying polarization problem that with time shows an increase in resistance from the probe.

Some quick results I just ran on a 1961 sample of this device. The set-point resistor is 4990 ohms. The resulting balance resistances at the threshold point are:

0 capacitance across the probe resitance
AC in ---- Resistance
90 V ---- 5540
135 V --- 5170

0.1 mfd in shunt with the probe resistance, equivalent to over 1400 ft of 8723 wire
AC in ---- Resistance
90 V ---- 4700
135 V --- 4200

0.33 mfd in shunt with the probe resistance, equivalent to over 4600 ft of 8723 wire
AC in ---- Resistance
90 V ---- 3400
135 V --- 2800

The results would be different if the set-point resistor was on the opposite side of the bridge.

There is no internal voltage regulation, the circuit is a very simple circuit, and integrated circuits did not exist.

.

 

[gar]

081211-1129 EST

Some comments on water conductivity. Currently our air is quite dry and many years ago I gave up on furnace humidifiers. I am use an ultrasonic room type unit now, and also a big pot on the stove.

I really need to use pure water in the ultrasonic unit to avoid calcium dust on everything.

I am not sure of the calibration factor for my test probe, but I am guessing at 10. The resistance measurements are at 1 kHz and the probe capacitance in free air is about 34 pfd including the leads. In distilled water it is about 117 pfd and D=20.

The resistivity measurements are:

800,000 ohm-cm for distilled water
90,000 ohm-cm for recent rain water
44,000 ohm-cm for recent snow water
1,400 ohm-cm for room temp tap water
170 ohm-cm for boiled and hot --- may be about a days worth of cooking and refill several times
310 ohm-cm for the same water but at room temperature
85 ohm-cm after another day's worth of cooking and at room temperature

An interesting reference on water purity:
http://www.lenntech.com/deionised-demineralised-water.htm

Thus, it looks like my grocery store distilled water is what might be expected for ordinary distillation.

My resistivity measurement of tap water would be useful in the discussion with the person and his horse watering problem, but he has not responded with more information. Critical to that discussion is what is the voltage variation from different points in the water in the bowl to the wall of the stainless bowl. My off hand guess it is near zero and the problem is really the voltage between the earth and the bowl.

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