Three Phase Electrical question

[MstrCarpenter]

I had to do some field repairs on a big vacuum cleaner last week. We typically run it of a 70 KVA gen. set. The repair (which I don't think matters, but here it is anyway) was to tighten all the connections and delete one jumper that fried the contact. Both the momentary on and off switches (same except for color) have have three terminals; N.O., N.C., and Common. The on switch had a jumper connecting the the N.O. and N.C. terminals and there was a wire on each of them. The only thing I could think it could possible accomplish is if there was another "start" switch. Similar but smaller vac.s have a coil around one of the "load" lines that will start the vac when the equipment is started. (This vac does not have an on/off/auto switch.) With that modification, it started right up. Except.... the phases were wired to the gen set in the wrong order. Got huge dust clouds real fast! I bet it cleaned the HEPA filters too. I swapped two leads and all was well.

So that's the background, and it works as it should. Now the Contractor who owns this rig says that it never would run backwards before. If the phase were wrong it would illuminate a red light and it wouldn't start.

I cannot figure out how a circuit could prevent the coil from being energized when there are still three (correct) possible variations of how the 3ph line can be connected and still maintain correct rotation. An' how in the helll does it know when to turn that light on?

[fixtureman]

If it runs backward just switch any 2 wires

[MstrCarpenter]

Yea, did that. "I swapped two leads and all was well." The problem is that it (supposedly) shouldn't have started.

[Roly]

Yea, did that. "I swapped two leads and all was well." The problem is that it (supposedly) shouldn't have started.

Phase rotation relays like THESE will prevent reverse rotation.    The jumper you installed may have bypassed the permissive contacts from that relay so it always had permission to run.  Roly

[MstrCarpenter]

Phase rotation relays like THESE will prevent reverse rotation.    The jumper you installed may have bypassed the permissive contacts from that relay so it always had permission to run.  Roly

Actually I deleted a jumper because the contacts were shot. I'll have to look at the switch again to confirm the function of the two terminals, but at the time it seemed redundant. (IIRC it may have been a mom. dbl. pole, dbl. throw?) It is a basic momentary on for start, momentary off to stop, circuit with an extra "emergency switch" on the stop wire controlling the relay. The relays and any other electronics are pretty well buried but there must have been a reason to send additional conductors to this simple circuit.

So I just spent some time reading about Phase Monitoring Relays. I'm thinking the "permissive" contacts might have been momentarially bypassed when the start button is pushed. There's a duplicate vac i can put my meter to, but the two of them are not usually on the same jobsite. 

I try to learn something new every day. This was a good day. Thank-you Roly!

[Roly]

Actually I deleted a jumper because the contacts were shot. I'll have to look at the switch again to confirm the function of the two terminals, but at the time it seemed redundant. (IIRC it may have been a mom. dbl. pole, dbl. throw?) It is a basic momentary on for start, momentary off to stop, circuit with an extra "emergency switch" on the stop wire controlling the relay. The relays and any other electronics are pretty well buried but there must have been a reason to send additional conductors to this simple circuit.

So I just spent some time reading about Phase Monitoring Relays. I'm thinking the "permissive" contacts might have been momentarially bypassed when the start button is pushed. There's a duplicate vac i can put my meter to, but the two of them are not usually on the same jobsite. 

I try to learn something new every day. This was a good day. Thank-you Roly!

Since the contacts are momentary they are controlling a contactor,  The relay that would prevent starting would be in the relays coil circuit most likely near the relay it self.  Roly

[MstrCarpenter]

Got a chance to sneak a peek at the other Vac. It does have a phase monitoring relay. I didn't have time to snip the cable ties, but there does appear a few conductors run up tp the on off switch. The fault lamp module is physically located between the N.O. and N.C. contact modules. The N.C. contact module is a siemens 3su1400-1aa10-1ca0 . Any idea what a part number for the same thing but N.O. would be? I'd have to take three of these modules out and separate them to see any identifying marks on the defective one. I'd perfer to have the replacement in hand when I did that.

P.S. I snapped a photo and E-mailed it to myself. Too large to post it. Couldn't figure out how to make it work. That'll remain a lesson for another day. Maybe before my 15 year anniversary.

[Roly]

Does the unit have a schematic ?   It may say on that.  Sometimes the manufacturer may have it online or have the info.   Other than that Contact Seimens as I am sure they could help.
Roly I would think it will have the same basic number except the last four digits but would need conformation before ordering

[MstrCarpenter]

Found it! Only one letter different; the "C" is a "B". Both are already ordered.

Here's a link to the Vac. The filter purge works great. I've been thinking about an easy way to incorporate that principal to a shop vac.
https://ermatorusa.com/product/t8600-3-p...extractor/

This is the grinder its used with. Those handles are at eye level, and I'm 6' tall. Even with the weights in the rear position (they're in the forward position in the photo) I have to stand on them and put my skinny butt as far back as possible to tilt the machine back for access to the diamond tooling. 
https://www.husqvarnacp.com/us/machines/...967977802/

[Roly]

Found it! Only one letter different; the "C" is a "B". Both are already ordered.

Here's a link to the Vac. The filter purge works great. I've been thinking about an easy way to incorporate that principal to a shop vac.
https://ermatorusa.com/product/t8600-3-p...extractor/

This is the grinder its used with. Those handles are at eye level, and I'm 6' tall. Even with the weights in the rear position (they're in the forward position in the photo) I have to stand on them and put my skinny butt as far back as possible to tilt the machine back for access to the diamond tooling. 
https://www.husqvarnacp.com/us/machines/...967977802/

Great.   I had no ides Husqvarna made floor grinders.   Roly