What is a three phase inspector?

[Rfsutcl]

I was assisting our facilities person recently in trouble shooting a 2 1/2 ton hoist that was broken. I determined that the three phase inspector was the problem. I am familiar with three phase systems and used to design the electrical control systems for large industrial clothes dryers, but had never used one of these. So my question is what does a three phase inspector do?

Thank you in advance for any help

 

[waross]

Is the term "Three phase inspector" translated from another language? It sounds like it may be a phase monitor. This proves that all three phases are present and in the correct rotation.
If a crane is energised to hoist up with one phase missing, the brakes may release and the load start to decend. Once the load starts the motor turning in the wrong direction, the motor will run on one phase and drive the load down.
If the incoming phases are reversed, of course, all the motors will run backwards.
Hence a phase monitor relay to prevent the crane from running unless all thre phases are present and in the correct rotation.
yours

 

[Rfsutcl]

Waross

Thanks for the reply. That is pretty much what I assumed it did, but I could not find any info on google etc. It is not translated from another language, it is called out as a three phase inspector on the electrical diagram.

 

[waross]

Interesting. What is the make and/or contry of origen?
respectfully

 

[sacem1]

Usually they only monitor if all 3 phases are energized and they usually do it by just using all 3 lines to power two contactors which are needed to be closed whenever you operate the electric hoist (L1 and L2 to contactor #1 and L2 and L3 to contactor #2) if both contactors are in series and one line fails at least one coil of a contactor becomes deenergized and the hoist will not work.

The brakes in a hoist are desig to be applied (load braked) when ever power is cut, either by a stop button, a line failure or whatever cause.

Regards

SACEM1

 

[Rfsutcl]

To waross
Here are the specs:

Make: Jet Equipment and Tools
Type: 2 Ton hoist (not 2.5 ton)
Manufacturer #: 2SS-3-10

I don't know the country of origin.

To sacem
It must monitor more than just if the phases are energized. When I jumper out the control voltage going through the 3 phase inspector the hoist works correctly. The inspector is shutting down the control voltage (24VAC) but not affecting the line voltages (240VAC) that operates the motor. The contactors function correctly using the control buttons without the inspector shutting off the control voltage.

 

[waross]

Yes, it sounds like the inspector has stepped out to lunch and should be replaced.
However, try reversing the power connections to the inspector before replacing it.
Diagram at

http://www.jetequipment.com/products/MH manuals/Electric Hoist Manual.pdf

You may find a cheap phase reversal relay at a refrigeration supply house if you have the physical room to mount it.
respectfully.

 

[jraef]

LOL, actually this is somewhat humorous. Jet equipment is made in China. Obviously they misinterpreted the word "monitor" to be the same as "inspector", not knowing that an inspector would only apply to a living person, not a device.

I do a lot of technical re-writing for a Taiwanese mfr., so I see this sort of thing a lot. Their manual translations can be very confusing, this example isn't even that bad compared to most. We call them "Chinglish versions" before I re-write them.

I would follow waross' advice, but after reversing the inputs make sure that you don't have to again reverse the motor leads to make it turn the proper direction. Phase reversal monitors like that are meant to prevent accidents after initially installed, but on first installation must be set up properly. The cheap ones just look for a specific phase sequence, usually A-B-C, then if the line is ever A-C-B, they trip. Once you set up the relay, THEN you check the motor rotation.

Eng-Tips: Help for your job, not for your homework Read faq731-376

 

[waross]

As jraef says, the incoming phases may be reversed and the monitor just doing it's job.
respectfully

 

[Rfsutcl]

I doubt that the phases are reversed and the monitor is doing it's job. The hoist is being used in the same location and power connections as before. And given that the hoist functions correctly with the monitor jumpered out, I'm leaning toward the monitor being broken. The replacement part is just over $300.00. Fortunately it's not my money, or I would be tempted to leave it jumpered out or solve it another way.