Wiring rotary phase converter

[PT Doc]

I will be wiring up a commercial rotary phase converter. Here is some pertinent information about my setup.

240v input power: 50 amp breaker with 6 gauge wire (currently wired as a dryer plug, so 4 wires at this location. Plug is on interior attached garage wall and was installed by builder since I asked for this)
Idler motor: 10hp

I need to have a cutoff switch that feeds the whole rotary phase converter. My plan is:

***Wall to 60 amp motor rated switch: Hardwire 3 strands through 1/2” nonmetallic liquittight conduit to motor rated switch: THHN 90C 6g
***From motor rated switch to RFC input: THHN wire 6g in non metallic 1/2” liquid tight
***RFC converter to 10 hp idler motor: THHN wire 10g in 1/2” liquid tight
***RFC panel to internal 30a breaker: THHN wire 6g
***Internal 30a breaker to 30a Leviton twist lock plug: THHN wire 10g

The wire choices above might be more than what is needed but I would rather not have 4 different gauges of wiring left over.

Any issues the plan? Thanks in advance.

 

[matt_i]

The 10awg seems wrong to me. 10hp x 745 W/hp x 1.25 / 240vac = ~38A.

I think it would be easier to use 3/4" liquidtight as well.

 

[PT Doc]

The 10awg seems wrong to me. 10hp x 745 W/hp x 1.25 / 240vac = ~38A.

I think it would be easier to use 3/4" liquidtight as well.

This is a 10 hp 3 phase Baldor/Gentec motor. According to Baldor the FLA is 28a @230v.

I have another Baldor 3 phase motor in the shop and at 230v this 3 hp motor has an amp rating of 8.2. So this hp to amp ratio seems to be consistent. 3 phase motor seems to be the key.

Thanks

 

[930dreamer]

What rpc did you go with?

 

[alfredeneuman]

10hp x 745 W/hp

That's based on 100% efficiency.
No machine is 100% efficient

 

[PT Doc]

What rpc did you go with?

https://www.americanrotary.com/products/view/ad-digital-smart-series

 

[TRWham]

I would follow the supplier's recommendations. This is not a standard motor installation so the usual methods may not be appropriate.

 

[matt_i]

That's based on 100% efficiency.
No machine is 100% efficient

Interestingly, if you take out the 1.25 factor,

10hp x 745 W/hp / 240vac = 31.0 A

Yet the manufacturer's FLA = 28 A

So its delivering the 10hp on only 28A, hence running at higher than 100% efficiency......this should help solve some of our world problems (lol)

The math is just a way to estimate. I typically use 750W/hp since its easier to think about.

It still seems odd that it takes 50A single phase input to deliver 30A 3phase output. I get that rotary converters are not fully efficient, but that seems quite low...there would be a *lot* of heat generated in constant running. Like enough to almost run a 5kW heater....

 

[TRWham]

Interestingly, if you take out the 1.25 factor,

10hp x 745 W/hp / 240vac = 31.0 A

Yet the manufacturer's FLA = 28 A

So its delivering the 10hp on only 28A, hence running at higher than 100% efficiency......this should help solve some of our world problems (lol)

The math is just a way to estimate. I typically use 750W/hp since its easier to think about.

It still seems odd that it takes 50A single phase input to deliver 30A 3phase output. I get that rotary converters are not fully efficient, but that seems quite low...there would be a *lot* of heat generated in constant running. Like enough to almost run a 5kW heater....

No, it's a three phase motor, so you cannot calculate power that way. The factor to calculate power from 3 phase is 1.73 times the current times the voltage. 50A at 240V single phase provides 12.0kVA while 28A at 240V 3 phase provides 11.6kVA.

In any case, none of that applies to this motor in this application. An idler is more like a single phase motor plus a single phase alternator in one frame. The idler only produces the missing third phase, while being rotated by power from the 2 input phases. Those 2 are also wired directly to the outputs.

 

[BLUE72CAMARO]

Why not follow american rotary's instuctions???
https://www.americanrotary.com/pdfviewer/PIDS-1531234818_6461.pdf

I installed this exact unit per instructions last winter and been working perfect for my lathe and mill so far.

 

[PT Doc]

Why not follow american rotary's instuctions???
https://www.americanrotary.com/pdfviewer/PIDS-1531234818_6461.pdf

I installed this exact unit per instructions last winter and been working perfect for my lathe and mill so far.

That is the plan for sure. Just wanted to pass my plan by the group. The recommendation to use 3/4” liquidtight was a good one.

How do you like your setup?

 

[PT Doc]

Interestingly, if you take out the 1.25 factor,

10hp x 745 W/hp / 240vac = 31.0 A

Yet the manufacturer's FLA = 28 A

So its delivering the 10hp on only 28A, hence running at higher than 100% efficiency......this should help solve some of our world problems (lol)

The math is just a way to estimate. I typically use 750W/hp since its easier to think about.

It still seems odd that it takes 50A single phase input to deliver 30A 3phase output. I get that rotary converters are not fully efficient, but that seems quite low...there would be a *lot* of heat generated in constant running. Like enough to almost run a 5kW heater....

Just to clarify I didn’t say that it takes 50a input for this setup. This is the setup that I have in the garage. It’s a standard 4 wire 240v 50a circuit that the builder supplied. If I keep the appropriate wiring up till the 30a breaker that is in the RFC panel then I can keep the existing circuit as is.

 

[BLUE72CAMARO]

That is the plan for sure. Just wanted to pass my plan by the group. The recommendation to use 3/4” liquidtight was a good one.

How do you like your setup?

So far mine has ran great but hasnt seen a ton of use as all I was powering was my lathe until about a month ago when I got my full size mill and was able to ditch the enco round column I had been using. Still in the process of getting tooling for it though. LOL The only issues I had with mine was a high pitch noise from the idler motor when it was really cold out this winter. I tightened up the bolts on the motor and it went away though.

 

[wyliesdiesels]

I will be wiring up a commercial rotary phase converter. Here is some pertinent information about my setup.

240v input power: 50 amp breaker with 6 gauge wire (currently wired as a dryer plug, so 4 wires at this location. Plug is on interior attached garage wall and was installed by builder since I asked for this)
Idler motor: 10hp

I need to have a cutoff switch that feeds the whole rotary phase converter. My plan is:

***Wall to 60 amp motor rated switch: Hardwire 3 strands through 1/2” nonmetallic liquittight conduit to motor rated switch: THHN 90C 6g
***From motor rated switch to RFC input: THHN wire 6g in non metallic 1/2” liquid tight
***RFC converter to 10 hp idler motor: THHN wire 10g in 1/2” liquid tight
***RFC panel to internal 30a breaker: THHN wire 6g
***Internal 30a breaker to 30a Leviton twist lock plug: THHN wire 10g

The wire choices above might be more than what is needed but I would rather not have 4 different gauges of wiring left over.

Any issues the plan? Thanks in advance.

Why are you using a 30a dryer plug (NEMA 14-30) on a 50a circuit?

Shouldve used a NEMA 14-50....

 

[PT Doc]

The receptacles are indeed 14-50. I should not have called it a dryer plug.

 

[PT Doc]

Since 8g THHN is rated for 55 amps @90C, I will likely use this for the wiring up till the 30a internal breaker. This will allow me to use 1/2” liquidtight for the 3 strands of 8 gauge since 3is the max fill for 8g. Don’t think I will end up pulling the neutral wire at this time. From there I’ll use 10g for the rest.

When would this neutral wire ever be used in the future? If I end up with more 3 phase equipment that will not be on a vfd, I would install a 3 phase load center and a few appropriately sized plugs oil less than 3 hp and hardwire if 5hp.

Thanks for all the comments.

 

[TRWham]

... Don’t think I will end up pulling the neutral wire at this time. From there I’ll use 10g for the rest.

When would this neutral wire ever be used in the future?...

You would never need the neutral for the phase converter. The voltage between the incoming neutral and the outputs of the RPC is not useful and there are big warnings that the outputs should never be grounded, and the incoming neutral is tied to ground. RPC outputs are configured in a Delta with no neutral. If you are connecting a 3 phase load that needs a neutral, then you need to add a Delta-Wye transformer that provides a neutral from its three incoming lines. That transformer would also need to drop the RPC output voltage to 208V line to line, otherwise the line to neutral would be too high for a 120V load.

 

[Bert_]

You would never need the neutral for the phase converter. The voltage between the incoming neutral and the outputs of the RPC is not useful and there are big warnings that the outputs should never be grounded, and the incoming neutral is tied to ground. RPC outputs are configured in a Delta with no neutral. If you are connecting a 3 phase load that needs a neutral, then you need to add a Delta-Wye transformer that provides a neutral from its three incoming lines. That transformer would also need to drop the RPC output voltage to 208V line to line, otherwise the line to neutral would be too high for a 120V load.

Like any 240v delta service two of the lines are 120V to ground and totally usable for 120V loads if you have a neutral. Only one leg has a higher voltage to ground, ~210V, and should only be used for line to line loads. All lines are 240v phase to phase although the generated leg will tend to vary with load.

 

[wyliesdiesels]

Since 8g THHN is rated for 55 amps @90C, I will likely use this for the wiring up till the 30a internal breaker. This will allow me to use 1/2” liquidtight for the 3 strands of 8 gauge since 3is the max fill for 8g. Don’t think I will end up pulling the neutral wire at this time. From there I’ll use 10g for the rest.

When would this neutral wire ever be used in the future? If I end up with more 3 phase equipment that will not be on a vfd, I would install a 3 phase load center and a few appropriately sized plugs oil less than 3 hp and hardwire if 5hp.

Thanks for all the comments.

You cannot base breaker size off of the 90* c column as that is for derating purposes only.

 

[PT Doc]

You cannot base breaker size off of the 90* c column as that is for derating purposes only.

https://www.cerrowire.com/ampacity-charts

https://www.homedepot.com/p/Southwi...anded-CU-SIMpull-THHN-Wire-20488399/204632883

For 8g, both of the above state 55 amps at 90*C. You are saying that this is not to be used? The 75*C column on the Cerrowire site states ampacity for 8g is 50 amps. If the 75*C is the column to look at in my case, then since the breaker is 50 amps for this 240v circuit, I should be code compliant.

Thank you for the help.

 

[wyliesdiesels]

https://www.cerrowire.com/ampacity-charts

https://www.homedepot.com/p/Southwi...anded-CU-SIMpull-THHN-Wire-20488399/204632883

For 8g, both of the above state 55 amps at 90*C. You are saying that this is not to be used? The 75*C column on the Cerrowire site states ampacity for 8g is 50 amps. If the 75*C is the column to look at in my case, then since the breaker is 50 amps for this 240v circuit, I should be code compliant.

Thank you for the help.

yes the 90* c column is only to be used for derating purposes.

For example, lets say you have a conduit that runs through a hot attic that has 9 #8s.

You would start with 55a then derate the conductors for both ambient temperature and number of conductors in pipe.

If youre using THWN and no derating is involved then you use the 75* c column.

 

[Bert_]

To add a bit to the discussion, the column that you can use is determined by the type of wire and the connections at each end. For example, most breaker and 50 amp plugs have terminations rated 75* C. 15 and 20 amp outlets in are only rated 60*C. There are some crimp connectors rated 90*C but they are not something you see for home use.

You final ampacity cannot be higher than the temp rating of the lowest part.

 

[PT Doc]

To add a bit to the discussion, the column that you can use is determined by the type of wire and the connections at each end. For example, most breaker and 50 amp plugs have terminations rated 75* C. 15 and 20 amp outlets in are only rated 60*C. There are some crimp connectors rated 90*C but they are not something you see for home use.

You final ampacity cannot be higher than the temp rating of the lowest part.

Thank you for providing clarity. Easy to understand too.

https://www.homedepot.com/p/AFC-Cab...llic-Liquidtight-Conduit-6003-22-00/100027081

This 3/4 liquid tight conduit states good to 140F. So do I have to use the 60C column on this chart?

https://www.cerrowire.com/ampacity-charts

If yes, then another question. Since I have a 50a breaker and this will feed a rotary phase converter, I have to keep the 50a wire rating until the rotary phase converters internal 30 a breaker that feeds a 30 a plug, then I have to use 6g wire because of the 60C column that is good for 55a? Using 8g wire and the 60F column shows into only good for 40a, so no good.

Thank you for your help.

 

[wyliesdiesels]

Why are u using LT indoors? U could use FMC- flexible metal conduit/greenfield....

 

[PT Doc]

Why are u using LT indoors? U could use FMC- flexible metal conduit/greenfield....

I could use fmc but I have a bunch of the liquidtight. Have no fmc. Used fmc in the past and it’s not as flexible with install. Used LT for compressor hardwiring and it was easy to work with. And if LT gets stepped on it no big deal. Thanks for you help. I greatly appreciate it.

 

[TRWham]

Like any 240v delta service two of the lines are 120V to ground and totally usable for 120V loads if you have a neutral. Only one leg has a higher voltage to ground, ~210V, and should only be used for line to line loads. All lines are 240v phase to phase although the generated leg will tend to vary with load.

The question was whether you should carry the incoming neutral to the RPC. The people who make these things are quite adamant that you should not ground the outputs, and tying any line to the incoming neutral (aka the grounded conductor) does just that. Yes, I suppose you could create a delta neutral on the outputs, but if you need 120V on the output side it is recommended that you create a wye neutral using a transformer for isolation. Line voltage to a neutral formed in a wye connection of all three lines will be 138V if the line to line is 240V.

 

[Bert_]

Thank you for providing clarity. Easy to understand too.

https://www.homedepot.com/p/AFC-Cab...llic-Liquidtight-Conduit-6003-22-00/100027081

This 3/4 liquid tight conduit states good to 140F. So do I have to use the 60C column on this chart?

https://www.cerrowire.com/ampacity-charts

If yes, then another question. Since I have a 50a breaker and this will feed a rotary phase converter, I have to keep the 50a wire rating until the rotary phase converters internal 30 a breaker that feeds a 30 a plug, then I have to use 6g wire because of the 60C column that is good for 55a? Using 8g wire and the 60F column shows into only good for 40a, so no good.

Thank you for your help.

I believe the 140* rating is for ambient temp only. The conductors can use their full rating.

The question was whether you should carry the incoming neutral to the RPC. The people who make these things are quite adamant that you should not ground the outputs, and tying any line to the incoming neutral (aka the grounded conductor) does just that. Yes, I suppose you could create a delta neutral on the outputs, but if you need 120V on the output side it is recommended that you create a wye neutral using a transformer for isolation. Line voltage to a neutral formed in a wye connection of all three lines will be 138V if the line to line is 240V.

We aren't talking about grounding an output. We don't need to "create" a neutral, the output from the phase converter is not isolated from the input so the neutral can be carried straight though...

The output from these phase converters is delta, there is no 138v anywhere. Only 240v between any of the phases, two lines with 120v to ground and one line ~210V to ground.

 

[TRWham]

...
We aren't talking about grounding an output. We don't need to "create" a neutral, the output from the phase converter is not isolated from the input so the neutral can be carried straight though...

The output from these phase converters is delta, there is no 138v anywhere. Only 240v between any of the phases, two lines with 120v to ground and one line ~210V to ground.

Neutrals are created all the time, and in many locations, usually very close to the load. They are not all created equal, however. There are 3 phase machines (usually ones with complex controls or ancillary equipment) that require the use of line to neutral connections on all three phases, and you cannot simply use a neutral created between 2 phases (whether delta 3 phase or split single phase) for that. Rather, you need to create a neutral equal between all 3 phases, and you can use a delta-wye transformer for that. If you simply connected 240V to the delta side of a delta-wye xformer without voltage reduction, the voltage between any of the three lines on the wye side and the wye neutral would be ~138.7V. Therefore, it needs to be dropped to 208V line to line to result in a 120V line to neutral voltage. This is same reason 4 wire 3 phase service is 208V/120V rather than the 240V/120V we are accustomed to in a typical split-phase residential service.

 

[wyliesdiesels]

Neutrals are created all the time, and in many locations, usually very close to the load. They are not all created equal, however. There are 3 phase machines (usually ones with complex controls or ancillary equipment) that require the use of line to neutral connections on all three phases, and you cannot simply use a neutral created between 2 phases (whether delta 3 phase or split single phase) for that. Rather, you need to create a neutral equal between all 3 phases, and you can use a delta-wye transformer for that. If you simply connected 240V to the delta side of a delta-wye xformer without voltage reduction, the voltage between any of the three lines on the wye side and the wye neutral would be ~138.7V. Therefore, it needs to be dropped to 208V line to line to result in a 120V line to neutral voltage. This is same reason 4 wire 3 phase service is 208V/120V rather than the 240V/120V we are accustomed to in a typical split-phase residential service.

Apparently youve never heard of 3 phase 4-wire 120/240 Delta which is called hi-leg or stinger leg or red leg delta.

We have many of them out here...

 

[Sincerd]

Apparently youve never heard of 3 phase 4-wire 120/240 Delta which is called hi-leg or stinger leg or red leg delta.

We have many of them out here...

So that's what I need? Is Transformer best way to accomplish this?

 

[wyliesdiesels]

So that's what I need? Is Transformer best way to accomplish this?

Seeing as how this thread is 5yrs old and I have no clue what your use case is or what equipment youre powering, I have no idea what you need.

Best to start a new thread and give more details

 

[Norcal]

The NEC has a article covering RPC's, it should be consulted together with manufacturers instructions.

 

[Sincerd]

Yeah sorry replying to the wrong thread.

Adding three phase sub panel to Suburban garage

A couple years ago I added a 220 single phase sub panel in the garage. Everything is worked well, but now I'm starting to get three phase equipment. I plan to get a phase perfect, 7.5 horsepower or 10 horsepower version. After that connection, I want to run it to a subpanel. And I just found one...

www.garagejournal.com