3 phase motor

[The electron man]

So we know when it comes to a 3 phase motor that if we want to reverse motor ration we just have to switch 2 of the phase's

But there was this one time we had a temp construction hoist and it was working fine but when the utility brought in the power we hand an issue with it since the utility doesn't match there cables to our phase's

So we switch 2 phase's and it still did not work so we switch it again

For example

Black and red

And then

Blue and black

We had to do this a few times till it worked
Each time using a different combination

Why did this happen

 

[Eddie702]

i have no explanation

 

[hillbilly1]

Wasn’t connected to a frequency drive? With those you change on the load side, or flip it in the program.

 

[zbang]

Any one swap would change the phase rotation, what does "had an issue" or "did not work" really mean? Did it turn the wrong way or not function at all (and are electronic controls involved)? Did someone swap the phases at both ends of feed? That moves the color but doesn't change anything else.

The phase rotation to a VFD should not matter at all.

 

[TwoBlocked]

Nah, if it was powered by a VFD, it would not have been a problem to start with. Maybe confusion as to which button was up, and which button was down on the hoist control.

 

[hillbilly1]

One of my customers just got a deal on five bridge cranes that I have to hook up now, $836 each. $5000 in freight. Everybody is moving out of California, so no one bid on them.

 

[petersonra]

One of my customers just got a deal on five bridge cranes that I have to hook up now, $836 each. $5000 in freight. Everybody is moving out of California, so no one bid on them.

I have started to hear about all kinds of deals coming out of California and NYC as the mass exodus continues.

A couple decades ago there was a mass exodus of companies out of the area I live in. Lots of industrial equipment to be had for pennies on the dollar. Some of the closed buildings are still empty.

I have also seen reports that there are serious deals in used cars at the auto auction sites right now. If you know someone with access to buy there and are looking for a used vehicle, might want to consider going that route. There are even brokers that will handle the transaction for you.

 

[Jraef]

So we know when it comes to a 3 phase motor that if we want to reverse motor ration we just have to switch 2 of the phase's

But there was this one time we had a temp construction hoist and it was working fine but when the utility brought in the power we hand an issue with it since the utility doesn't match there cables to our phase's

So we switch 2 phase's and it still did not work so we switch it again

For example

Black and red

And then

Blue and black

We had to do this a few times till it worked
Each time using a different combination

Why did this happen

Another possibility, revolving around the definition of "didn't work", could involve the use of a Phase Monitor Relay that is looking for a SPECIFIC and EXACT phase sequencing. I have run across this before. They look for A, followed by B, followed by C, relative to the first time it was hooked up. So until you get that exact sequence correct, it will not engage to enable the machine to work. I have no idea of the value of this feature, maybe it was just an unintended consequence of how they chose to design the monitor, but I have run into it twice. VERY frustrating because you don't expect that to make any difference, i.e. A-B-C is the same as B-C-A is the same as C-A-B... Yet, there it was. Move the machine and reconnect the leads B-C-A and it wont work. It said it right in the instruction manual, but who the heck reads that?

 

[kwired]

Another possibility, revolving around the definition of "didn't work", could involve the use of a Phase Monitor Relay that is looking for a SPECIFIC and EXACT phase sequencing. I have run across this before. They look for A, followed by B, followed by C, relative to the first time it was hooked up. So until you get that exact sequence correct, it will not engage to enable the machine to work. I have no idea of the value of this feature, maybe it was just an unintended consequence of how they chose to design the monitor, but I have run into it twice. VERY frustrating because you don't expect that to make any difference, i.e. A-B-C is the same as B-C-A is the same as C-A-B... Yet, there it was. Move the machine and reconnect the leads B-C-A and it wont work. It said it right in the instruction manual, but who the heck reads that?

Rotational sequence shouldn't matter and it shouldn't know any difference. Now if there is a corner ground or high leg that possibly could matter if not in the correct position, if designed to detect that.

Otherwise to know what is actually "A" it would need a reference to some known "A", wouldn't it?

 

[TwoBlocked]

Rotational sequence shouldn't matter and it shouldn't know any difference. Now if there is a corner ground or high leg that possibly could matter if not in the correct position, if designed to detect that.

Otherwise to know what is actually "A" it would need a reference to some known "A", wouldn't it?

For a hoist, rotation could matter.

 

[kwired]

For a hoist, rotation could matter.

rotational sequence yes, I was getting at knowing what conductor was actually designated by someone as A phase. The hoist won't care if it is connected ABC, CAB or BCA on the supply side of the controller, still same rotation from any of those.

Maybe I was misunderstanding what Jraef was trying to say?

 

[Jraef]

rotational sequence yes, I was getting at knowing what conductor was actually designated by someone as A phase. The hoist won't care if it is connected ABC, CAB or BCA on the supply side of the controller, still same rotation from any of those.

Maybe I was misunderstanding what Jraef was trying to say?

No, you’re right, it SHOULDN’T matter. But I have come across two phase monitor relays where it did. It established the sequence the first time it was connected, then had to match exactly after that. I hated them. Some foreign brand, can’t remember the name now (it was 25+ years ago).

 

[LarryFine]

"But, how do it know?"

Rotation direction I can see.

What does it use as a reference for timing of one third of a cycle relative to the applied power?

 

[ptonsparky]

I did a follow up where the PLM supposedly didn’t work. It got really quiet in the village well house when I told the installers they had it wired up wrong. Only a 60 HP, so it could have been worse.

 

[kwired]

No, you’re right, it SHOULDN’T matter. But I have come across two phase monitor relays where it did. It established the sequence the first time it was connected, then had to match exactly after that. I hated them. Some foreign brand, can’t remember the name now (it was 25+ years ago).

So if you mistakenly had it wrong the first time you energized it then is stuck with that setting?

 

[Hv&Lv]

So we know when it comes to a 3 phase motor that if we want to reverse motor ration we just have to switch 2 of the phase's

But there was this one time we had a temp construction hoist and it was working fine but when the utility brought in the power we hand an issue with it since the utility doesn't match there cables to our phase's

So we switch 2 phase's and it still did not work so we switch it again

For example

Black and red

And then

Blue and black

We had to do this a few times till it worked
Each time using a different combination

Why did this happen

I really hope you find the answer to this and let us know what you found.

No matter what it was.

 

[jim dungar]

No, you’re right, it SHOULDN’T matter. But I have come across two phase monitor relays where it did. It established the sequence the first time it was connected, then had to match exactly after that. I hated them. Some foreign brand, can’t remember the name now (it was 25+ years ago).

25 years ago I sold line of monitors that a similar issue, I think they were RK Electronics out of Cincinnati. Their A phase had to be the first rising voltage, or else they called it an error. They had other items without this quirk.

 

[Hv&Lv]

25 years ago I sold line of monitors that a similar issue, I think they were RK Electronics out of Cincinnati. Their A phase had to be the first rising voltage, or else they called it an error. They had other items without this quirk.

I don't understand how it knows the "first" rising voltage..
On a relay which ever phase is connected to the 101 terminal is considered A phase
Wouldn't the first rising voltage be dependent on what point you start measuring?

 

[jim dungar]

I don't understand how it knows the "first" rising voltage..
On a relay which ever phase is connected to the 101 terminal is considered A phase
Wouldn't the first rising voltage be dependent on what point you start measuring?

I do not know, and may have mis-remembered, the internal working of the sensing circuits. All I know is we had to replace the device monitoring the feed to a new extruder cooling pump room. We used a relay from the same company without this quirk. There was also something about not sensing at the peak of a waveform, I recall the used 70%ish point as harmonics could make locating the peak difficult if clipping occurred. All in all I avoided using the relay ever again.

There are other times where I have had issues with Rolling versus Swapping of phases, but those usually involved parallel or alternate sources.

 

[Electromatic]

I recently installed a Square D phase monitor relay that wanted its own sequence to be satisfied. It was a basic model (no under-,over-voltage, etc.), and I figured it just wanted the presence of all three phases. It wouldn't change state until I wired it a particular way.