Stray Voltage
- Thread starter edw
- Start date
- Status
- Location
- Lockport, IL
- Occupation
- Semi-Retired Electrical Engineer
Re: Stray Voltage
Stray voltage is voltage from one point in the dirt to another. It comes from the earth being used as a conductive path for transmission voltages, and from some connection not being properly connected. If there is enough voltage from one point in the dirt to another for you to illuminate a light bulb, then that same voltage would kill any person or animal that attempted to walk in that area.
Stray voltage is voltage from one point in the dirt to another. It comes from the earth being used as a conductive path for transmission voltages, and from some connection not being properly connected. If there is enough voltage from one point in the dirt to another for you to illuminate a light bulb, then that same voltage would kill any person or animal that attempted to walk in that area.
luke warmwater
Senior Member
Re: Stray Voltage
Here are two sites that address the issue:
http://www.bassengineering.com/SV_Cause.htm
http://www.emfrelief.com/stray.htm
Here are two sites that address the issue:
http://www.bassengineering.com/SV_Cause.htm
http://www.emfrelief.com/stray.htm
Re: Stray Voltage
If I can be more specific...I had a small transformer in an apartment building which was 208/24 volt. The problem came in when the 24V hot leg was sent to a thermostat where it would return to energize a heating or a cooling valve actuator. In a perfect world, these return lines say H and C would not have any voltage on them until they were connected to the hot leg by the thermostat when cooling or heating were needed. Since we do not live in said perfect world...I witnessed the following. The hot leg 24V was connected at the transformer and sent to the stat however the H and C lines were not connected to anything, yet there was 21V on the end of the wire which would be normally hooked up to the actuator motor... If this is a stray voltage where does it come from and if I grounded the secondary side of the transformer would it have dissapeared?? How can I make it dissapear??
If I can be more specific...I had a small transformer in an apartment building which was 208/24 volt. The problem came in when the 24V hot leg was sent to a thermostat where it would return to energize a heating or a cooling valve actuator. In a perfect world, these return lines say H and C would not have any voltage on them until they were connected to the hot leg by the thermostat when cooling or heating were needed. Since we do not live in said perfect world...I witnessed the following. The hot leg 24V was connected at the transformer and sent to the stat however the H and C lines were not connected to anything, yet there was 21V on the end of the wire which would be normally hooked up to the actuator motor... If this is a stray voltage where does it come from and if I grounded the secondary side of the transformer would it have dissapeared?? How can I make it dissapear??
physis
Senior Member
Re: Stray Voltage
It sounds like the old using a high impedence DVM senario.
If you are using one of those you'll also see voltage in the air.
It takes next to no current to get those meters to read a voltage. However there isn't enough current to drive any kind of a load and if connected across one nothing would happen.
If that is in fact what's happening you can put a 100k or a 1 megaohm resister across the meter's probe leads and the reading will go away.
They're just really sensitive.
It sounds like the old using a high impedence DVM senario.
If you are using one of those you'll also see voltage in the air.
It takes next to no current to get those meters to read a voltage. However there isn't enough current to drive any kind of a load and if connected across one nothing would happen.
If that is in fact what's happening you can put a 100k or a 1 megaohm resister across the meter's probe leads and the reading will go away.
They're just really sensitive.
Re: Stray Voltage
I would agree and that's probably part of it except one thing. I connected the stray voltage leg to a load and it did drive the motor of the actuator. That's really what the problem was, the actuator motor would drive open a heating valve when there was no call to do so.What I ended up doing was putting a 1K Resistor from the from control input wire of the acutator to the common side of the transformer. This bled off the excess current back to the transformer when there was no call to open the valve.I just can't figure out where this voltage was comming from???
I would agree and that's probably part of it except one thing. I connected the stray voltage leg to a load and it did drive the motor of the actuator. That's really what the problem was, the actuator motor would drive open a heating valve when there was no call to do so.What I ended up doing was putting a 1K Resistor from the from control input wire of the acutator to the common side of the transformer. This bled off the excess current back to the transformer when there was no call to open the valve.I just can't figure out where this voltage was comming from???
wirenut1980
Senior Member
- Location
- Plainfield, IN
Re: Stray Voltage
Could it be some kind of emf? It seems strange that there is 21 V on a 24 V circuit, not surprised that it is causing the motor to start. Hard to tell without seeing the setup and routing of the circuits.
Could it be some kind of emf? It seems strange that there is 21 V on a 24 V circuit, not surprised that it is causing the motor to start. Hard to tell without seeing the setup and routing of the circuits.
physis
Senior Member
Re: Stray Voltage
Aren't those actuators 50 mA.
Even that's significant for stray juice coming out of where ever it's coming from.
I'd be curious, if you measured the current, how much it is.
If there is a leak somewhere I'd be interested in finding it.
Inductive coupling Wirenut? It's possible.
Aren't those actuators 50 mA.
Even that's significant for stray juice coming out of where ever it's coming from.
I'd be curious, if you measured the current, how much it is.
If there is a leak somewhere I'd be interested in finding it.
Inductive coupling Wirenut? It's possible.
Re: Stray Voltage
I put a 1K resistor in series with the wire while it was connected to the actuator and it measured 30 ma
It was just a stray voltage running around the building. This was a 30 story apartment building. I'm sure there are all kinds of things running around there.
If I grounded the common side of the transformer would that have drained off the excess current??
I put a 1K resistor in series with the wire while it was connected to the actuator and it measured 30 ma
It was just a stray voltage running around the building. This was a 30 story apartment building. I'm sure there are all kinds of things running around there.
If I grounded the common side of the transformer would that have drained off the excess current??
physis
Senior Member
Re: Stray Voltage
I'm pretty sure you mean paralell, beacuase at 24v you'll get no more 24 mA through a 1k.
I think you should invesigate it. What if it wont start? What if it wont stop?
If it is a 50 mA valve I think the reason for the small current is that you don't want sparks. Not that the thing doesn't have a fire in it already.
I would at least want to know how much current you're fending off. I think you've only put a bandaid on it.
I'm pretty sure you mean paralell, beacuase at 24v you'll get no more 24 mA through a 1k.
I think you should invesigate it. What if it wont start? What if it wont stop?
If it is a 50 mA valve I think the reason for the small current is that you don't want sparks. Not that the thing doesn't have a fire in it already.
I would at least want to know how much current you're fending off. I think you've only put a bandaid on it.
- Location
- Illinois
- Occupation
- retired electrician
Re: Stray Voltage
Is the low voltage cable running physically parallel to and power conductors?
Don
Is the low voltage cable running physically parallel to and power conductors?
Don
Re: Stray Voltage
I agree but what else could I do. The voltage was there and the only thing I could think of was bleed it back to common.
I still do not unerstand were it was coming from.
It was a small isolated transformer not grounded and the secondary 24 volts went out to the stat and came back on another wire without even being connected. It seemed to be induced. It was not running in any other conduit to pick up the voltage. The wire was shielded control wire which had already been replaced by the building tech. We ohmed it out to check for shorts but there were none found. It was either Gremlins or somekind of bad ju ju...I just don't know
I agree but what else could I do. The voltage was there and the only thing I could think of was bleed it back to common.
I still do not unerstand were it was coming from.
It was a small isolated transformer not grounded and the secondary 24 volts went out to the stat and came back on another wire without even being connected. It seemed to be induced. It was not running in any other conduit to pick up the voltage. The wire was shielded control wire which had already been replaced by the building tech. We ohmed it out to check for shorts but there were none found. It was either Gremlins or somekind of bad ju ju...I just don't know
wirenut1980
Senior Member
- Location
- Plainfield, IN
Re: Stray Voltage
How many and which wires do you have going out to the T-stat?
How many and which wires do you have going out to the T-stat?
Re: Stray Voltage
3 wires running out to the stat. a hot wire went to R on the stat which by the way was a T 87 simple mechanical stat. The other 2 wires were W and Y obviously one for heat and one for cooling. Again without the stat wires even being connected to the stat, during the troubleshooting phase the wires were just hanging at the stat waiting to be connected. At this time we connected the hot wire R to 24V a 21V signal was picked up and could be read with a meter between W and the common side of the transformer.
3 wires running out to the stat. a hot wire went to R on the stat which by the way was a T 87 simple mechanical stat. The other 2 wires were W and Y obviously one for heat and one for cooling. Again without the stat wires even being connected to the stat, during the troubleshooting phase the wires were just hanging at the stat waiting to be connected. At this time we connected the hot wire R to 24V a 21V signal was picked up and could be read with a meter between W and the common side of the transformer.
wirenut1980
Senior Member
- Location
- Plainfield, IN
Re: Stray Voltage
This is not my area of expertise by any stretch, but does anyone think that running a ground wire out there like edw has suggested would help? Are these low voltage transformers typically grounded?
This is not my area of expertise by any stretch, but does anyone think that running a ground wire out there like edw has suggested would help? Are these low voltage transformers typically grounded?
Ed MacLaren
Senior Member
Re: Stray Voltage
If the T87 is used with the switching sub-base, there is a cooling anticipator resistor permanently connected in parallel with the cooling contact.
With power to the R terminal, there would be a voltage on the W terminal even if the contacts were open.
However, there shouldn't be enough current through the resistor to run the valve motor.
Ed
If the T87 is used with the switching sub-base, there is a cooling anticipator resistor permanently connected in parallel with the cooling contact.
With power to the R terminal, there would be a voltage on the W terminal even if the contacts were open.
However, there shouldn't be enough current through the resistor to run the valve motor.
Ed
petersonra
Senior Member
- Location
- Northern illinois
- Occupation
- engineer
Re: Stray Voltage
I would suspect the the tstat has some kind of surge suppressor built in across the tstat contacts.
Re: Stray Voltage
Sorry, the stat wires were not connected at all they were just hanging out of the sub-base stripped and in thin air. When voltage was connected from the hot side of the transformer to the R wire and the R wire was not connected to anything on the other end, there was still a 21V signal on the output of the W wire which was read on a meter from W to the common side of the transformer back in the box where the transformer was mounted. I worked in the field doing HVAC work for a long time and have never seen anything like it before???
Sorry, the stat wires were not connected at all they were just hanging out of the sub-base stripped and in thin air. When voltage was connected from the hot side of the transformer to the R wire and the R wire was not connected to anything on the other end, there was still a 21V signal on the output of the W wire which was read on a meter from W to the common side of the transformer back in the box where the transformer was mounted. I worked in the field doing HVAC work for a long time and have never seen anything like it before???
Ed MacLaren
Senior Member
Re: Stray Voltage
Edw, is the cable between the thermostat and valve location visible? in other words, can you trace it?
This happened to me once. The customer complained that when she turned up the thermostat her apartment got colder. In order to get any heat, she had to turn the thermostat down.
We discovered that the heating system installer had mixed up the thermostat cables going to this customer and the next apartment. When she turned up her thermostat, the neighbor got too warm and turned her's down.
Any possibility of this?
Ed
Edw, is the cable between the thermostat and valve location visible? in other words, can you trace it?
This happened to me once. The customer complained that when she turned up the thermostat her apartment got colder. In order to get any heat, she had to turn the thermostat down.
We discovered that the heating system installer had mixed up the thermostat cables going to this customer and the next apartment. When she turned up her thermostat, the neighbor got too warm and turned her's down.
Any possibility of this?
Ed
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