# Phase Loss Relay, or Something



## TAGallagher (Sep 21, 2017)

I'm working at a location that's got quite a few motors. 
Motor control cabinets, compressors, a lot of three phase motor applications going on. 
Last week the property lost a phase coming in from utility, which consequently burnt up a few motors, fried a few contactors, etc....
What is the best way to prevent this from happening? 
Install a phase loss relay in every motor control bucket, in line with branch wiring to motors?
Or is there something more on the level of protecting whole systems?
Thanks for any input.


----------



## mitch65 (Mar 26, 2015)

If there is a central control system or plant ESD, it would be pretty easy to add something so the DCS would shut down everything if there were a phase loss or something similar.


----------



## MechanicalDVR (Dec 29, 2007)

mitch65 said:


> If there is a central control system or plant ESD, it would be pretty easy to add something so the DCS would shut down everything if there were a phase loss or something similar.


Problem with that is the more common loss of phase in a single circuit rather than the entire plant.

This is why redundancy is king in this arena.

Individual phase monitoring for critical equipment has saved many a motor, compressor, machine, and other expensive equipment.


----------



## varmit (Apr 19, 2009)

If you have MCCs, you could install one phase monitor on the power to each MCC. The phase monitor would control a relay that would break the control power. This is easier if all control power, in the MCC is on the same circuit. If you have individual starters, it is a cost vs. benefit analysis to determine what is worth adding phase monitors to. The "cost" is not necessarily motors and equipment, but potential lost production.


----------



## TAGallagher (Sep 21, 2017)

Thanks for the replies so far.
A bit more info, if it helps, there are three buildings on the property which house three different motor control centers. I will be having some fun investigating tomorrow. :biggrin:


----------



## JRaef (Mar 23, 2009)

Phase loss is worst on 3 phase motors, because any motor that is ALREADY running will continue running, but standard OL relays may not trip if the motor is lightly loaded, yet they will over heat without tripping the OL relay. 

So one thing I always like to point out is that if you *change your motor starter overload relays to Solid State*, most of those now provide CURRENT BASED phase loss protection; meaning if one (or more) phases have less than xx% of rated current flowing (usually 20%), they trip. The reason this is better is that phase loss relays that only look at voltage can be "fooled" by any motors that were spinning WHEN the phase was lost, because they will regenerate a voltage onto the missing phase, just like a Rotary Phase Converter does, and that allows the voltage sensing relay to think everything is A-OK while your motors fry.

Post your brand(s) and approximate vintage of MCC and I'll give you some ideas on what you can use.


----------



## Cow (Jan 16, 2008)

We typically install one phase monitor in front of ALL the motor starters, MCC's, etc rather than a phase monitor at each individual MCC bucket etc. 

Are your MCC buckets fused or breakered? If fused I'd probably consider putting it in each bucket. If they're breakered I'd still only put one in front of everything.

We have FAR more issues around here with incoming utility power burning things up from single phasing, etc than we do with a breaker going bad and single phasing a motor necessitating phase monitors in each bucket.


----------



## just the cowboy (Sep 4, 2013)

*Phase loss meter in main*

We just moved into a new building and I had them install phase loss monitoring in the main switchgear. We have not done anything with it yet but are thinking of putting a VERY loud air horn off of the alarm contacts. If horn sound operators start shuting down and turning off machines.


----------



## JRaef (Mar 23, 2009)

Or the horn will get mysteriously disabled...

I once put a horn system in at a Budweiser plant, because bored line workers were dropping pencils into the bottle lines, which caused jams and allowed them to go drink beer while it was fixed and cleaned up (it used to be that they got free beer in the break rooms). So the horns were programmed with different sounds indicating where the jam happened, so supervisors could immediately see who was in the area or leaving it. The horn system had an "accident" with a fork lift just a month into it's life...


----------



## TAGallagher (Sep 21, 2017)

I'm too new to post pictures, The MCC is Allen Bradley, I would guess installed in the late 90's early 2000's. The overload relays aren't electronic. After my investigating today, I've found that one of the cabinets has a Motor saver installed covering all the motor starters in that cabinet.


----------



## nolabama (Oct 3, 2007)

JRaef said:


> Or the horn will get mysteriously disabled...
> 
> I once put a horn system in at a Budweiser plant, because bored line workers were dropping pencils into the bottle lines, which caused jams and allowed them to go drink beer while it was fixed and cleaned up (it used to be that they got free beer in the break rooms). So the horns were programmed with different sounds indicating where the jam happened, so supervisors could immediately see who was in the area or leaving it. The horn system had an "accident" with a fork lift just a month into it's life...


Ahh the free beer. Lol. I heard they put many a man through rehab before they canned that policy. 

Sent from my Pixel XL using Tapatalk


----------

