Hi there, I deal with a lot of low voltage and controls, so my confidence shrank a bit when i discovered that my voltmeter in fact wasn't broken, and i was dealing with corner grounded 480. And furthermore that the 120 in the old equipment is actually from a local transformer. This is part of an industrial animal cage cleaning system of which we're adding a component. Our add-on is 480 also, but the controls are ran on a separate 120 circuit. I attempted to interface our 2 control panels, assuming that the 120 was actually from a panel, and ran into a problem attempting to trip a relay using the generated 110 hot leg with my neutral. From that line to neutral or ground, I get a small burst of about 48v AC that dissapates to nothing on one meter, and on another, i get a sustained 48. Yet across its own neutral its 120. My question is, aside from modifying the old panel with more relays etc, and running more wires, is there any long term solutions where I can use that one transformer 120 hot leg as a relay coil trip in my panel? The PLC I'm using will only sense DC so even that's out. Basically, there's no more access for more modifications and no more money for add-ons, so either I make it work with what's there, or concede that it can't be done as is. Any thoughts, input , or corrections would be greatly appreciated. Thanx
delta 480 and 120
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My apologies, I think I did use the wrong terminology though. I said corner grounded when i think I meant center grounded, I'm not 100% sure though as there was a lockout on the disconnect, paper labeling in a damp/wet location, and some space constraints. So i wasn't fully able to "investigate"
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It's far more likely that whatever is deriving that 120V in the other sytem is too small to handle both your additional load and the votlage drop across the distrance from their panel and yours. Why don't you just put in your own Control Power Transformer and be done with it?
I'm operating my controls off of a separate 120 service. The existing panel is operating off a local transformers 120 off of the 480 service. In particular, I am trying to tap and break the existing 120vac emergency stop circuit, which is off of that transformer. Tapping so my PLC knows the status, and break if there's a fault on the new equipment side. I can break the circuit just fine. However, when i attempt to throw a relay with it, it wont. I tried putting the opposite side of the coil to neutral and ground, nothing. Sorry if I'm not explaining the situation well as its a little confusing to me. Like I said, I'm not greatly experienced with this kind of stuff. I understand some of it in principal but don't have the experience. Shouldn't the 120 flow to ground no matter what its source? And the distance between the two control panels is only about 30 feet, so shouldn't it flow enough to pull in just a relay coil? And how would you suggest incorporating another transformer and to what voltage?
I did a reply, but I don't see it coming up. I'm basically trying to tap and break the emergency stop circuit for the old equipment. I can break it fine. But tapping it to just throw a 120v relay won't work. Again, my 120 is a seperate service, and the 120 on that system is via what I'm assuming is a delta-wye transformer, so its creating its own neutral, right? But now as I sit here typing this, here's a thought. In theory... couldn't I just trip a 48vac relay with it? If I get 120 between their black and white but it halves to ground (near 48), it could work right? Would it be safe/legal? Because of location, that one wire is all I have access to. It would take a lot of man hours that no one wants to pay for to do anything more. I'm assuming that when the job was planned, this wasn't accounted for. So its either find a way with just the one wire, or it cant be done. At least thats my direct order anyways. And as for the transformer, how would u suggest implementing it? Would it be better if I somehow got a sketch up?
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It can't be done in a code compliant way. You can't use a hot from one system with a neutral from another system.
If this was something other than a control circuit you could use a current switch on the hot conductor and the contact on the current switch for your control circuit.
If this was something other than a control circuit you could use a current switch on the hot conductor and the contact on the current switch for your control circuit.
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3,099 Posts
Why don't you just pull another wire in and do it right?:blink:
Thanx for the replies! I appreciate the input. :thumbsup: Basically just confirms it can't be done the right way as is. I'm sure it will end up as an up sell later on or something. But just for my own sake, grounding the transformer would fix the fluctuating voltages, right? Again, its a 480/120 delta/wye transformer. All the hook ups and jump outs are correct, yet no ground wire. So I'm assuming it has no "reference point", right? :001_unsure:
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