Phase monitor relay

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jim dungar

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What is your actual issue?

The wiring diagram on page 4 shows all of the terminals.
The control diagram on page 5 shows the sequencing of the output contacts based on the input voltages and the relay settings.
Simple explanation:
For this product the the output relay contacts will change state after it has gone through its startup routine. The contacts will maintain their energized state until the voltage drops below the pickup point for the programmed time.
For a motor control circuit where the incoming line is being monitored, I might consider placing the 'de-energized NO' contact in series with the Stop button, in order to shut down the motor during an event.
 

fatuus

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Location
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What is your actual issue?

The wiring diagram on page 4 shows all of the terminals.
The control diagram on page 5 shows the sequencing of the output contacts based on the input voltages and the relay settings.
Simple explanation:
For this product the the output relay contacts will change state after it has gone through its startup routine. The contacts will maintain their energized state until the voltage drops below the pickup point for the programmed time.
For a motor control circuit where the incoming line is being monitored, I might consider placing the 'de-energized NO' contact in series with the Stop button, in order to shut down the motor during an event.

I'm missing something here. L1, L2,L3 is line voltage-the output contacts should also be line voltage, in this case 480vac, but terminal 14 is normally open. Dammit, I hate it when my brain shorts out.
 

Jraef

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I'm missing something here. L1, L2,L3 is line voltage-the output contacts should also be line voltage, in this case 480vac, but terminal 14 is normally open. Dammit, I hate it when my brain shorts out.
The relay contacts are only rated for 250VAC max, you cannot do what you want to do if you are using 480V control.
 

jim dungar

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I'm missing something here. L1, L2,L3 is line voltage-the output contacts should also be line voltage, in this case 480vac, but terminal 14 is normally open. Dammit, I hate it when my brain shorts out.


The line voltage to the relay and the control circuit have nothing to do with each other.

Think of the output relay as being nothing more than a light switch. You bring a 'hot wire' (250V max) to terminal 11 and then take a switch leg from terminal 14 and go to your 'normal control circuit'.

The open contact will close after there is sufficient Line voltage to the L1, L2, L3 terminals.
 

Tony S

Senior Member
Why do you need a phase failure relay?

Phase rotation only needs to be checked on initial commissioning with the belts/coupling removed. Thermal O/L’s have single phase protection.

I dread to think where the 208V is coming from. If it’s from outside the cubical I hope you know what you’re doing.
 

Tony S

Senior Member
Just thinking about it in 40 years I’ve used phase failure relays twice.

Each time it was due to external control supplies. Each time it could have ended in a fatality. I’d get called in after the event to sort the mess out.

With proper design and there’s no need for PFR’s
 

Tony S

Senior Member
It’s not uncommon here but I’ve always used add on side contacts to the cubical isolator.

One of the incidences I mentioned a MCC feeder was well and truly overloaded. A genius idea from the engineering manager “cut the busbars feeding the 400HP fan at the end of the panel and put a separate supply in.”

Pity he forgot the control was from the other side of the board.

The plant operator pressed the start button, nothing happened, he radios the shift electrician. He was a young lad just out of his time, he soon spotted the fan feeder was off and turned it on. All the contactors were closed by then. As he described it “there was a ******* big bang and all the lights went out.” This is when I get called in.

We bodged a PFR that night out of what we could find.


Guess who got the job of reinstating the busbars and upgrading the MCC feeder.



Bodged = jury rigged
 
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Tony S

Senior Member
That is an absolutely false statement. Sometimes the proper design is a PFR.

Most PFR’s are also phase reversal which should never happen after commissioning.

Unless you’re using an external control supply why would you need a PFR for a compressor? With the 480V and 208V mentioned in the OP would seem likely. Panel isolator control supply interlocks should take care of that.


Something I forgot when saying I’ve only used PFR’s twice. Crane and lift (elevator) control, a single phasing motor isn’t bothered which way it goes, unfortunately usually down, rapidly. Lift’s are weird, they go up ;-)

So OK all EOT cranes and lifts had them. But I didn’t design them.
 

Tony S

Senior Member
We don't know if there is even an MCC involved, I wire a lot of three phase motors but rarely get to touch an MCC.

I’ve given up trying to get all relevant information from most OP’s.

No criticism of the MH forum or any other. The site I help run in the UK is just as bad. If you’re lucky you get drip fed information, it has me tearing my hair out at times.
 
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We use phase loss relays frequently. Almost every pump panel. They are wired into the control with the POCO. POCO opens one phase to the control. We use that open phase to drop out the control. A delay restart ensures pumps, pivots, etc are not restarted to soon. Phase reversal is just a side benefit. Low voltage sensing has worked on LR & faults because some of these systems are 1500 feet away with marginally sized transformers. Voltage drops before current gets high enough to blow fuses or trip overloads.
 

iwire

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Staff member
Location
Massachusetts
That’s a bit of a tenuous use of PFR’s when the supply OCPD and cable should be rated for fault currents.

The OCPD and cable are not the issue, it is the smoke leaking from the motor windings.

Keep in mind out many currently used motor OLs do not protect against single phase conditions.
 
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