3-phase protection

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Electromatic

Electromatic

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Virginia
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Master Electrician
Does anybody make some kind of all-in-one phase monitor and disconnect?

I have a customer with several different pieces of equipment that they want to shut off if they lose a phase. Some of these plug in, some hardwired, and one off a track bus. They are basically industrial/scientific ovens with no traditional motor starter type control circuit.

I could get an enclosure, a phase monitor relay, and a contactor and put them all together but wondered if there was any kind of off-the-shelf solution (with varying ratings of course).

Thanks,
 
Allen Bradley makes a Motor Circuit protector. It is a disconnect switch with GF/SC and overload protection. It should drop out on OL if you lose a phase.


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Thanks for the couple of suggestions.

The more I think about this, the more difficult it seems! If I used a phase monitor relay and either a contactor or a shunt-trip breaker, there's always the chance that the phase that should trigger the contactor or shunt-trip could be the phase that drops out! I'd be offering them 66% chance of protection!

One supplier suggested using a solid-state overload. However, since these are ovens, I don't know that their behavior while single-phasing would actually be similar to an overload (over-amperage). The customer doesn't know what exactly fails in these when they've lost a phase before; they just know it's expensive to fix.

It sure seems like it would be simple enough, but I'm going to have to keep scratching my head. Maybe I'm overlooking something simple and can give myself a dope-slap when it occurs to me.
 
Electromatic said:
Thanks for the couple of suggestions.

The more I think about this, the more difficult it seems! If I used a phase monitor relay and either a contactor or a shunt-trip breaker, there's always the chance that the phase that should trigger the contactor or shunt-trip could be the phase that drops out! I'd be offering them 66% chance of protection!

One supplier suggested using a solid-state overload. However, since these are ovens, I don't know that their behavior while single-phasing would actually be similar to an overload (over-amperage). The customer doesn't know what exactly fails in these when they've lost a phase before; they just know it's expensive to fix.

It sure seems like it would be simple enough, but I'm going to have to keep scratching my head. Maybe I'm overlooking something simple and can give myself a dope-slap when it occurs to me.
Click to expand...
You can get what's called a CTD (Capacitor Trip Device) that is connected to the Shut Trip coil of the breaker so that it still has enough power to trip the breaker no matter which phases are lost (stored in the capacitor).

https://www.alliedelec.com/m/d/ab241fcf8eea3c64733b3a9baabafd8d.pdf

The other alternative is to use an UNDER Voltage trip in the breaker, connected to the NC contacts of the Phase Monitor. The trouble with those is that they trip EVERY time there is a power fail, requiring the user to reset the breaker. I never like that option.
 
Electromatic said:
Thanks for the couple of suggestions.

The more I think about this, the more difficult it seems! If I used a phase monitor relay and either a contactor or a shunt-trip breaker, there's always the chance that the phase that should trigger the contactor or shunt-trip could be the phase that drops out! I'd be offering them 66% chance of protection!

One supplier suggested using a solid-state overload. However, since these are ovens, I don't know that their behavior while single-phasing would actually be similar to an overload (over-amperage). The customer doesn't know what exactly fails in these when they've lost a phase before; they just know it's expensive to fix.

It sure seems like it would be simple enough, but I'm going to have to keep scratching my head. Maybe I'm overlooking something simple and can give myself a dope-slap when it occurs to me.
Click to expand...

Phase monitor and energize a contactor when phase monitor is seeing "good". Lose any phase and you drop out the contactor regardless of which one supplies control power.

Does the oven have three phase convection or maybe combustion air motor? phase loss there I can see causing some damage, though one would think there would be high/low limit pressure, temperature, both switches to catch such situation as well.
 
I looked into the trip capacitor and will definitely keep that device in mind. By the time I get that, a phase relay, and a shunt trip device (Eaton makes some shunt trip disconnect switches), I'm at over $1000 in material at my cost. It's a workable solution but certainly not as simple as I initially hoped for.

I considered a contactor--closed when power is good, but I'm not overly keen on having it pulled in 24/7/365 except for outages.

I looked inside a couple of the machines last week while they weren't in use, and the controls seem pretty well laid out and accessible. I'm thinking now to just install a phase relay immediately after the control transformer and open X1. The customer is pretty sure the machines are all out of warranty, though they do need servicing sometimes. I just need to make sure that my alterations won't affect future manufacturer's support.

Thanks again for the suggestions.
 
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