Is this a good practice? My old supervisor told me to use my fluke 87 3 meter and get a reading for A phase. measureing AC volts with my meter leads from the load side of A phase and the other lead on the line side of the A phase and if i read more than 1 volt there is a problem. he said this is common for motorstarters, relays, breakers. Is this a common practice for trouble shooting?
Measureing voltage across A phase line ,load
- Thread starter khixxx
- Start date
- Status
bphgravity
Senior Member
- Location
- Florida
Re: Measureing voltage across A phase line ,load
In order to obtain a voltage reading, the leads of the meter must be connected between two points of different potential. What you are suggesting is taking a readng of two points on the same conductor. This does not make much sense to me.
Any reading that you may get is most likely some sort of ghost voltage or a false reading from neighboring conductors.
In order to obtain a voltage reading, the leads of the meter must be connected between two points of different potential. What you are suggesting is taking a readng of two points on the same conductor. This does not make much sense to me.
Any reading that you may get is most likely some sort of ghost voltage or a false reading from neighboring conductors.
Ed MacLaren
Senior Member
Re: Measureing voltage across A phase line ,load
This is one way to check for higher than normal resistance in a component or connection, providing it is done with the load in operation.
The voltage drop across a switch contact or connection is proportional to it's resistance.
I would suggest that, when using a digital voltmeter, you compare the no-load reading with the full-load reading.
Why just phase "A"? This test could be useful on any phase.
Ed
[ May 18, 2005, 06:42 AM: Message edited by: Ed MacLaren ]
This is one way to check for higher than normal resistance in a component or connection, providing it is done with the load in operation.
The voltage drop across a switch contact or connection is proportional to it's resistance.
I would suggest that, when using a digital voltmeter, you compare the no-load reading with the full-load reading.
Why just phase "A"? This test could be useful on any phase.
Ed
[ May 18, 2005, 06:42 AM: Message edited by: Ed MacLaren ]
Re: Measureing voltage across A phase line ,load
It depends what you're looking for. I've used this practice to determine if a breaker has high resistance internally without shutting things down. A voltage drop, (more than 1 volt) through that leg would indicate a possible problem. Contacts on starters or relays will build up resistance over time due to arcing.
It depends what you're looking for. I've used this practice to determine if a breaker has high resistance internally without shutting things down. A voltage drop, (more than 1 volt) through that leg would indicate a possible problem. Contacts on starters or relays will build up resistance over time due to arcing.
brian john
Senior Member
- Location
- Leesburg, VA
Re: Measureing voltage across A phase line ,load
This is a very common practice often referred to as FOP or Fall of Pontenial Test Met hood,, of course there must be a load, and balanced loads make it easier to determine if the results are a problem. I usually lok for problems with balanced loads with a 20%-30% difference between the poles. I think at 1 volt you are into problems.
Of course this depends on size of equipment and type of equipment.
BP due to voltage drop there is always a difference of potential, along the length of any conducting body carryinig current.
This is a very common practice often referred to as FOP or Fall of Pontenial Test Met hood,, of course there must be a load, and balanced loads make it easier to determine if the results are a problem. I usually lok for problems with balanced loads with a 20%-30% difference between the poles. I think at 1 volt you are into problems.
Of course this depends on size of equipment and type of equipment.
BP due to voltage drop there is always a difference of potential, along the length of any conducting body carryinig current.
Re: Measureing voltage across A phase line ,load
hey ed A phase was used just to keep my post short. any phase will do. i used 1 volt because thats what my old supervisor told me to use as a rule of thumb. i'm not sure if there is a fomula or a better number to use. yeah i mostly see mv to. thanks guys for the input. another question would be is there any range limit as far as amps that you can do this test safely. ex. less than 60 amps or can you do this test up to 600 amps ect. thanks again.
hey ed A phase was used just to keep my post short. any phase will do. i used 1 volt because thats what my old supervisor told me to use as a rule of thumb. i'm not sure if there is a fomula or a better number to use. yeah i mostly see mv to. thanks guys for the input. another question would be is there any range limit as far as amps that you can do this test safely. ex. less than 60 amps or can you do this test up to 600 amps ect. thanks again.
- Location
- Illinois
- Occupation
- retired electrician
Re: Measureing voltage across A phase line ,load
Most likely the level of PPE required to do this test will increase with the amp rating of the circuit being tested.
Don
Most likely the level of PPE required to do this test will increase with the amp rating of the circuit being tested.
Don
bphgravity
Senior Member
- Location
- Florida
Re: Measureing voltage across A phase line ,load
I am reading a relay spec sheet as I write that states, "Voltage drop of 1V - 1.6V should be expected through this device." There goes the 1 volt theory. I would think IR readings would be more reliable, unless you know the manufacturered resdistance of the device in question.
I am reading a relay spec sheet as I write that states, "Voltage drop of 1V - 1.6V should be expected through this device." There goes the 1 volt theory. I would think IR readings would be more reliable, unless you know the manufacturered resdistance of the device in question.
- Status