"Hot" wire...

[weressl]

This happened some time ago.

We were troubleshooting an MCC starter because we had difficulty with stopping a motor. Had regular three wire Start/Stop and integral 480/120V control transformer.

Got the Fluke out and found that there were about 81Volts on the open STOP return wire. To test the meter, both before and after testing the control wires, I had touched the secondary of the CPT and read the 118-120V as expected.

Being confident with the wiring, since I have checked the ciruit out and to mess with the head of my buddy, I confidently proceeded to grab the wire with the indicated voltage on it. Then, looking straight into my buddy's bewildered eyes, I grabbed the MCC enclosure with the other.

So anyone would be willing to guess of what happened?

Hint: don't beleive your lying eyes.

 

[Dennis Alwon]

So is willing to guess of what happened?

Hint: don't beleive your lying eyes.

I am guessing nothing happened. We had the same situation with a dimmer switch in the off position and we read 120 volts. This was after my guy already cut it with his pliers. No sparks nothing.

You must be reading some current thru a coil or something. Not my area of expertise to explain it. I am sure you know.

 

[RayS]

nada, because the secondary wasn't grounded?

 

[realolman]

.....So anyone would be willing to guess of what happened?.....

.

Someone who seems immensely intellegent revealed doing something that seems immensely un-intellegent:smile:

 

[weressl]

Someone who seems immensely intellegent revealed doing something that seems immensely un-intellegent:smile:

See!

How looks can fool ya....!:grin:

 

[kspifldorf]

yea I told a buddy we can make a delayed circuit by running a longer wire to the other pump contactor,

 

[weressl]

yea I told a buddy we can make a delayed circuit by running a longer wire to the other pump contactor,

...actually that is true, but ridiculously impractical.

 

[kspifldorf]

True but very funny, he went for days on it.

 

[celtic]

Induction.............

 

[realolman]

I'm afraid I'm not getting the point of all this.

 

[HighWirey]

Realolman, I concure wholeheartly. Maybe we both are so old that we missed the point.

Kinn'a reminds me of the joke about that oldtimer who needed to wet his fingers to check 120, no need for wet fingers on 277!

 

[weressl]

Induction.............

...and the winner is!

 

[wwhitney]

Induction.............

So I'm familiar with the idea that the electronic multimeters will read induced voltages that "go away" when you try to draw a significant current through them (e.g. to power a test lamp). But can they still provide enough current to deliver a perceptible shock?

For an example, on a 240/120V residential installation, if you disconnect one of the load side phase conductors at the meter, could you get a shock between that disconnected phase conductor and a ground? There may be many feet of premise wiring where the two phase conductors are parallel.

Cheers, Wayne

 

[weressl]

So I'm familiar with the idea that the electronic multimeters will read induced voltages that "go away" when you try to draw a significant current through them (e.g. to power a test lamp). But can they still provide enough current to deliver a perceptible shock?

For an example, on a 240/120V residential installation, if you disconnect one of the load side phase conductors at the meter, could you get a shock between that disconnected phase conductor and a ground? There may be many feet of premise wiring where the two phase conductors are parallel.

Cheers, Wayne

Yes.

Two ways:
1./ It is one leg of a 240V circuit.:grin:
2./ Open ground bond to the grounded conductor.

 

[wwhitney]

Two ways:
1./ It is one leg of a 240V circuit.:grin:
2./ Open ground bond to the grounded conductor.

Neither of these ways involves induced voltage, though, so are you saying that induced voltage from straight parallel runs can't provide enough current to shock a person?

BTW, I'm not sure I follow #2.

Thanks, Wayne

 

[celtic]

Here is a prime example of induction.....take a fresh roll of 14/3 ....connect ONLY the black and white conductors....like so:

Here is the link to a previous thread that lead to this "experiment":
Scientific Test



(I haven't forgotten your request George....time and location are at issue).

 

[weressl]

Neither of these ways involves induced voltage, though, so are you saying that induced voltage from straight parallel runs can't provide enough current to shock a person?

BTW, I'm not sure I follow #2.

Thanks, Wayne

When we connect one of the service wires to a ground electrode at the service point we "force" that voltage to be at the ground reference voltage level that is designed as "0 Volts". As there is potential difference exist all times between two points that are isolated from each other, if the bond between the ground and the "grounded service wire" - aka neutral - is open, you will read "a" voltage difference. That may or may not have sufficient energy and voltage difference to be harmful to a person.

Induced voltages on open wires would seldom if ever have sufficient energy to cause harm. MV and HV cables connected to motors or transformers are suspected to store or even induce sufficient energy to cause electrocution, although this is little more than anecdotal. (In most cases it was discovered that the electrocution was caused by back feed from another power source.) Regardless when working on MV and HV wires?, grounding each wire is mandatory.

 

[celtic]

Induced voltages on open wires would seldom if ever have sufficient energy to cause harm. MV and HV cables connected to motors or transformers are suspected to store or even induce sufficient energy to cause electrocution, although this is little more than anecdotal.

I GOT my azz kicked by the induced voltage in a 25kv catenary line....definitely a "little more than anecdotal".


EDIT:
I said something that wasn't remotely english.

 

[wwhitney]

If the bond between the ground and the "grounded service wire" - aka neutral - is open, you will read "a" voltage difference. That may or may not have sufficient energy and voltage difference to be harmful to a person.

Right, but I wasn't clear initially on a floating neutral could cause a shock from the situation I described, where one phase conductor is disconnected at the load side of the service. But I see now that if there is any load connected between the floating neutral and that phase conductor, then the phase conductor is set to the potential of the floating neutral once it is disconnected from the service.

Thanks, Wayne

 

[RayS]

So I'm familiar with the idea that the electronic multimeters will read induced voltages that "go away" when you try to draw a significant current through them (e.g. to power a test lamp). But can they still provide enough current to deliver a perceptible shock?

Cheers, Wayne

Oh, yeah. We did some runs of tray cable that were parallel to some energized runs for a couple hundred feet. Could actually draw a spark from the induced current.