Need wiring advice from RPC to 3-phase sub-panel. Problems with single phasing?

[Ltk]

I am feeding a 3 phase sub-panel with T1, T2, and T3 from my American Rotary AD20. 220v single phase input voltage going into terminals L1 and L2.

Wiring 1 machine at a time directly to the phase converter works just fine but when I wire the phase converter to the 3-phase panel and turn on the breakers, the start/stop switch on my 3hp grinder is buzzing, with the phase converter OFF.

With the phase converter being off and the start/stop switch on the grinder buzzing, am I hurting that machine? I would like to leave the phase converter on while I'm in the shop working and not have to worry about harming the motors on my machinery.

Is directly running ground, T1, T2, and T3 straight to the 3 lugs and main ground of the 3-phase panel the correct way to do this? Thanks

 

[EmGo]

I am feeding a 3 phase sub-panel with T1, T2, and T3 from my American Rotary AD20.

Wiring 1 machine at a time directly to the phase converter works just fine but when I wire the phase converter to the 3-phase panel and turn on the breakers, the start/stop switch on my 3hp grinder is buzzing, with the phase converter OFF.

Depends on what you mean by OFF. When off, do you cut the power to the phase converter or is it just not rotating ? If there is no power going to the phase converter, then how can anything be buzzing, since there's no current on any leg to your breaker box ?

If it just isn't rotating but there is current to it, then you are feeding single phase to three phase devices, which is probably not a great idea. The rotation just creates a third leg, but the other two exist independently.

 

[JST]

" Phase converter off" would normally be with the switch or starter powering it also "off", which should remove all power both to it, and to the downstream machines.

it should not be possible to turn on a 3 phase unit when the RPC is not producing output.

 

[J_R_Thiele]

http://www.wolfautomation.com/media/pdf/phaseconverters/amerrotary/ar-adx-ownersman-2020.pdf

Look at page 11 figure 3.2.1. Looks like the breaker box is fed single phase power through L1/T1 and L2/T2 connections, and only T3 is not provided/generated. when the converter is off. The contactor shown in the diagram does NOT cut single phase power to the breaker box when the RPC is off.

Ltk Others on this site know a LOT more than I do so I may be "off on this. I would double and triple check the wiring between the converter and the breaker - meaning that the wire identified for L1 at the RPC is identified as that at the breaker. I am suspecting that at the breaker what you think is T3 is actually T1 or T2, and that this affects the controls of the grinder. Does the grinder have a neutral wire?

 

[EmGo]

it should not be possible to turn on a 3 phase unit when the RPC is not producing output.

Agreed that it should not be possible, however, we are in do-it-yourself-land here, where anything turns out to be possible ...

You've been here longer than me, you should recognize by now that people often do things that are not exactly 'normal'

 

[kenscabs]

"Look at page 11 figure 3.2.1. Looks like the breaker box is fed single phase power through L1/T1 and L2/T2 connections, and only T3 is not provided/generated. when the converter is off. The contactor shown in the diagram does NOT cut single phase power to the breaker box when the RPC is off."


I have 2 American RPCs. The older one runs T1 T2 T3 through the contactor. The newer on (last years purchase) passes T1 & T2 through the convertor and only switches T3 in. I contacted them about this and never got a real answer. Their only response was for me to add a contactor on the output side to control all three outputs. Doesn't make sense why you'd want power to your control circuit that can switch on the motor if the T3 lead is not there.

 

[mmurray70]

I have 2 American RPCs. The older one runs T1 T2 T3 through the contactor. The newer on (last years purchase) passes T1 & T2 through the convertor and only switches T3 in.

I dont get this either. I cant see how a big company like that can design and sell phase converters without using a contactor to shut down all output power when turned off. Seems crazy to me.

 

[TDegenhart]

The contactor should not be energized if the convertor is not running. Since the control circuits are not shown, I can only surmise that power for the control circuit is drawn from before the contactor. When the convertor is turned off, that contactor should open. If the contactor does not shut off when the convertor is off, then I suspect there is a wiring error.

Tom

 

[kenscabs]

Update, the older unit only uses the contactor to pass T1 & T2. T3 off the convertor goes out without passing through the contactor.

 

[Ltk]

To attempt to answer everybody at once and clarify on the situation a little; with the main panel breaker (rotary phase converters own breaker) ON, and the rotary phase converter itself OFF, the output side is still flowing out the single phase input that is being fed to the RPC. This output is going straight into my 3-phase breaker panel and out to my machines. My lathe has a contactor on it, one side is receiving single phase input (will this hurt it?), the grinder is receiving the single phase at the start/stop switch and buzzing which I assume is not good for the machine at all.

The problem, I think, is that the RPC does not have a contactor on the output side at all, and for a $2,200 unit that is absolutely ridiculous. As far as installing one myself I have no idea where to begin or what to buy? Aside from flipping each breaker as I need each machine, which was not my intended use for the 3 phase panel, or installing disconnects at every single machine, how have you guys worked around this problem?

Thanks in advance for all the help

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[JST]

So, yes, you are correct, sort of.

The through connection ought to be controlled by the same contactor that controls the RPC idler, so the power to the idler also supplies the 3 phase output. That fixes the "off" condition problem. It does not guarantee that there is actually voltage on the generated leg.

Truly guaranteeing that can lead to a danger of drop-out when the generated leg gets pulled down too far.

Agreed that it should not be possible, however, we are in do-it-yourself-land here, where anything turns out to be possible ...

You've been here longer than me, you should recognize by now that people often do things that are not exactly 'normal'

Oh, I know that, for sure..... Starting with the 14ga aluminum wire I found after we bought this house.... running as a tap off a 40A breaker dryer outlet (wired from one hot to neutral.... we don't need no stinking ground), and going all the way across the basement to an outlet for chafing dishes etc in the dining room. THAT was fixed PDQ.

So, the "should" was that "if it is done right, that is what should happen". I have seen enough that I "get it" about what really happens.

 

[scsmith42]

I'm feeding a 400A 240 3 phase panel from a 30hp phase converter and a generator, via a transfer switch. If I need to run a lot of HP, I'll use the generator; if not then the phase converter.

The correct way to wire an RPC to a panel is to use a safety switch large enough to carry the full current output of the phase converter. The safety switch should feed both the power input to the converter, as well as the L1 and L2 input to the panel (with the converter providing the generated L3 leg). Some people will use a circuit breaker instead of a safety switch, but the safety switch is the correct method. Mine requires 125A in order to fully power the converter, panel and equipment.

I believe that what you are experiencing is that your panel is fed by L1 and L2 even if the converter is turned off, so two of your three legs are hot even with the converter off.

If you use a safety switch to supply combined power to both units, your 3 phase panel will either be totally hot, or totally cold. Not the partial situation that you currently have.

 

[mmurray70]

The problem, I think, is that the RPC does not have a contactor on the output side at all, and for a $2,200 unit that is absolutely ridiculous. As far as installing one myself I have no idea where to begin or what to buy?

Exactly, you shouldnt have to worry about that kind of stuff. When I started shopping for a phase converter I looked at American Rotary units, but with some hesitation I bought a used RPC that was made by small company here in Canada based on some advice from a friend. That unit has been bulletproof. Starts nice and easy for a 35hp, shuts off all output power when turned off and even came with an isolation transformer. Ended up being a way better purchased than I realized at the time. I love the fact that when its off, everything is off. Cant imagine having it any other way. If I had an AR unit I would find a way to add a contactor too it somehow.

 

[JST]

An output contactor is not always required. But having the entire 3 phase circuit dead if the RPC is off, is a requirement.

That can be done with an output contactor, but is also possible using an input safety switch, or an RPC start contactor that shuts off both the RPC and the "pass through" wiring.

I have a disconnect (safety switch), and then a motor starter that controls the RPC as well as the pass-through. That provides a power-fail "off" condition, and prevents a "single phase" condition as long as the RPC is actually working.

You can put in a set of lights to assure that all phases are "up", if you like. Schemes to cut power if the RPC output drops, etc, are possible, but starting a heavy load may cause false trips if the generated leg drops, even if it does not "fail".

 

[dalmatiangirl61]

Can we get a schematic of how you have wired this? I'm not familiar with how AR wiring is done, not quite understanding how you are supplying power to L1 and L2, yet the converter is OFF. On my rpc suppling power to L1 & L2 powers on the converter, generating L3. I use a manual switch on both legs of the incoming single phase power.

 

[JST]

Can we get a schematic of how you have wired this? I'm not familiar with how AR wiring is done, not quite understanding how you are supplying power to L1 and L2, yet the converter is OFF. On my rpc suppling power to L1 & L2 powers on the converter, generating L3. I use a manual switch on both legs of the incoming single phase power.

On his, the 2 wires go "past" the RPC switch, so the RPC is actually on a tap off of them. So if the RPC is off, those two wires are unaffected.

If the wires to the panel are moved to AFTER the switch, then it will be "dead" in all the 3 phase wires unless the RPC is switched on. That assumes the switch (or contactor) is rated for the load plus RPC input.

The simplest way to wire it and not have the problem is shown in this tech note from Phase-A-Matic

https://phaseconverters.phase-a-matic.com/Asset/RB.pdf

 

[neilho]

One possibility: instead of a switch, you have a magnetic contactor? One side of the single phase is reaching the contactor coil and there's a wonky connection to ground/neutral somewhere on the other side of the coil? Just a possibility.

Agree with Dalmationgirl that a posted schematic is in order, otherwise, we is all just speculatin'.

 

[scsmith42]

On his, the 2 wires go "past" the RPC switch, so the RPC is actually on a tap off of them. So if the RPC is off, those two wires are unaffected.

If the wires to the panel are moved to AFTER the switch, then it will be "dead" in all the 3 phase wires unless the RPC is switched on. That assumes the switch (or contactor) is rated for the load plus RPC input.

The simplest way to wire it and not have the problem is shown in this tech note from Phase-A-Matic

https://phaseconverters.phase-a-matic.com/Asset/RB.pdf

That's a great link to the Phase-a-matic wiring diagram. My converter is their R30 model. It's been a good one.

 

[TDegenhart]

Also keep in mind that you need a way to prevent automatic restarting in case of a power failure. A magnetic contactor with a holding circuit will accomplish this.

Tom

 

[scsmith42]

Also keep in mind that you need a way to prevent automatic restarting in case of a power failure. A magnetic contactor with a holding circuit will accomplish this.

Tom

I respectfully disagree.

The OP's question is regarding the power supply to the panel - ie an RPC, not power supply to individual equipment.

Re the benefits of magnetic starters on equipment, by all means yes regarding your recommendation.

But your recommendation to put a contactor on the RPC - in essence you're saying that the main power supply to your building should be on a contactor so that your load centers are not reenergized following a power outage. That's not how it works.