# Thread: Wiring up a 30HP rotary phase converter

1. ## Wiring up a 30HP rotary phase converter

I don't have it yet, it's being shipped as we speak. I hope to have it next week. In light of this, I have started this thread since I've never seen one in person, nor wired it up. The unit is a 30HP from Southern Phase Converters in Texas. The unit is "new", but I bought it 2nd hand since I was able to save a few hundred.

In the meantime while it gets here, I wanted to talk about power input. To do that, I think we need to look at anticipated power consumption, which will be at most 36A (I1max) @ 230V while on 3-Φ (from the ►machine electrical spec sticker◄). By my calculations, that is equivalent to 14.4kW. The ►motor spec sheet◄ says 93.6 efficiency. So it would at most consume 15.4kW. Working backwards, that seems to indicate that it will pull 63A from the 240V 1-Φ supply side.

Do I have that correct thus far?

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## Re: Wiring up a 30HP rotary phase converter

I come up with the same figures. I'd be worried about the inrush to start current that motor in the phase converter though, since it's rated for so much more than you'll be running it at. Does it have ratings for that?

3. ## Re: Wiring up a 30HP rotary phase converter

I didn't see such a rating on the spec sheet. Are you talking about the in-rush to initially get it up to speed when it is flipped on? Or something else?

4. ## Re: Wiring up a 30HP rotary phase converter

Highly unlikely you will feed it with 240 volts. If your voltage even occasionally falls far below, efficiency will change sharply. Lets factor 225 volts, 80% efficiency.

This is a motor, we size motor circuit conductors at 125%.

The reality is you bought a BIG phase converter.

Wait a minute! Three phase, 1 HP is about an amp at 600 volts. At 230 volts Full load current is about 80 amps.

I'd figure 80 amp output. X 80% efficiency. Effectively 100 amps for conversion purposes at 80% efficiency gives you rated output. roughly 100 amps (a bit less)

Full load of something close to 173 amps. Don't panic, you won't likely pull full load.

Keep in mind 1 HP at 100% efficiency is 746 watts. 30 HP X 746 is 22380 watts You won't power 30 HP at 746 watts per, There is some waste in the motor. 1000 watts is a conservative estimate, or 30,000 watts. At 230 volts that'd be 130 amps. But we factor Three phase at 1.73 so 75 amps output.

30,000 At 230 volt single phase is 130 Amps.

I would expect your converter is overrated. Regardless, you won't likely power 30 hp motors

I will be interested in the installation instructions. I have a 6 horsepower vacuum cleaner draws 12 amps single phase 120. 6 X 746 = 4476 watts. Actual draw is 1440 watts. Somebody is fibbing!
Last edited by Willie B; 05-06-2020 at 07:49 PM.

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## Re: Wiring up a 30HP rotary phase converter

Oscar,
The 30 hp phase converter is good for 15 hp of load.

I would size the input at near full rating.

#1's from panel to the converter A and B single phase inputs and 100 amp breaker.

From A, B and C from converter panel to the idler you would use #8s.

Then from your A and B inputs and the C coming back from idler you feed your 3 phase panel with #4's.

>>>> NEVER use the A and B for the idler for anything else but converter panel to the idler ONLY.

If not using a panel to split up loads or set your self up for future then just run what your powering with only the size wire it requires. Be sure to provide proper over current protection as soon as you leave the phase converter. Smart to have some way to kill power at the machine too if the panel or disconnect is far from the phase converter.
Last edited by danielplace; 05-06-2020 at 07:52 PM.

6. ## Re: Wiring up a 30HP rotary phase converter

Originally Posted by Willie B
Highly unlikely you will feed it with 240 volts.
You're right about this. It's actually 245V coming into the house. It is a very solid supply.

I know you want to cover a whole lot of ground as your mind races through the subject to give an all-inclusive lecture/lesson, but you haven't actually helped me. This will be specifically to power my TIG welder. The link to it's spec's I already listed. The motor spec I also linked, so a lot of the speculation you did could simply be avoided if you click the links. All your talk about full load means nothing. I only want to power the TIG welder. If you want to help, I'd certainly appreciate it. Please revisit my 1st post and comment specifically on my calculations, based on my criteria, not wild mental ramblings. Thank you.
Last edited by Oscar; 05-06-2020 at 07:59 PM.

7. ## Re: Wiring up a 30HP rotary phase converter

Originally Posted by danielplace
Oscar,
The 30 hp phase converter is good for 15 hp of load.
Well that's not good. I figured I could squeeze a lot more than 1/2 it's capacity! Isn't that typically more so for starting other motors, since they start a lot "harder"? So you're saying I would not be able to squeeze out all the amperage out of my welder with it??
Last edited by Oscar; 05-06-2020 at 08:07 PM.

8. ## Re: Wiring up a 30HP rotary phase converter

They are typically rated for single motor horsepower & multi motor. It might be rated at 30 hp cumulative, but 11 or 12 single. Do you have a 30 HP machine to power?

9. ## Re: Wiring up a 30HP rotary phase converter

Originally Posted by Willie B
They are typically rated for single motor horsepower & multi motor. It might be rated at 30 hp cumulative, but 11 or 12 single. Do you have a 30 HP machine to power?
......
Originally Posted by Oscar
...from the ►machine electrical spec sticker◄....

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## Re: Wiring up a 30HP rotary phase converter

You want that last 50 amp from 350 to 400 ?

You have 40 amp to spare and welder only needs 34-35 amp on 240 ? approx.

Last edited by danielplace; 05-06-2020 at 09:31 PM.

11. ## Re: Wiring up a 30HP rotary phase converter

Originally Posted by danielplace
You want that last 50 amp from 350 to 400.

You have 40 amp to spare and welder only needs 34 amp on 240 ? approx.

Yes, that is what I figured, just slightly less than 36A since I have a good solid 245-247V coming into the house.

So back to my initial investigation, how do my calculations look?

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## Re: Wiring up a 30HP rotary phase converter

Originally Posted by Oscar
Yes, that is what I figured, just slightly less than 36A since I have a good solid 245-247V coming into the house.

So back to my initial investigation, how do my calculations look?
Oscar,
The single phase amps is close to 1.5 times the amps of three phase you intend to deliver.

Using the 1.5 of 35 it is like 53 amp
.
The input wire size and amp I believe they suggest for that RPC is actually 130 amps on #1's I believe.

#1's or #2 on a 100 will run that machine I believe and still have some breathing room.

I say 100 but if that panel has a 125 available that will go in it then go 125. What brand/model panel is it you will be feeding the RPC from ? How many amps is the service feeding the panel ? How much existing load is on the service ?
Last edited by danielplace; 05-06-2020 at 10:42 PM.

13. ## Re: Wiring up a 30HP rotary phase converter

I’ve been running a Phase-a-matic 30 hp RPC in my shop for around 10 years. It powers a 22hp wide belt sander, a 5 hp dust collection blower, a 10hp air compressor, 5 hp radial arm saw and a 5 hp jump saw. Typically I’m running the wide belt sander and the dust collection system at the same time.

Mine requires at least a 100A breaker. Occasionally it will trip the breaker if there is a lot of load on the belt sander. The current in-rush is significant when starting the converter.

As Willie B indicated, there will likely be a voltage drop when you have the equipment running. My meters read 240 when only the lights are on in the shop, but when the RPC is running the voltage has dropped to around 228. With the wide belt sander also running, I’ve seen it below 220.

14. ## Re: Wiring up a 30HP rotary phase converter

Originally Posted by danielplace
Oscar,
The single phase amps is close to 1.5 times the amps of three phase you intend to deliver.

Using the 1.5 of 35 it is like 53 amp
.
The input wire size and amp I believe they suggest for that RPC is actually 130 amps on #1's I believe.

#1's or #2 on a 100 will run that machine I believe and still have some breathing room.

I say 100 but if that panel has a 125 available that will go in it then go 125. What brand/model panel is it you will be feeding the RPC from ? How many amps is the service feeding the panel ? How much existing load is on the service ?
I'm not following you, as to where you are getting the 1.5 factor from, nor where you are getting 130A on 1awg for this RPC. Exactly where are these numbers/calculations coming from?

The panel is a Cutler-Hammer rated at 200A max in the garage. It is getting power from the main panel via 100A breaker with 2awg. It powers the majority of the house except for A/C,range (the largest item on that garage sub-panel is the water heater, which is relatively small, about 40gal). Even then, if I'm in the garage using a welder, there is nothing going on at all inside the house, so the extra load on that panel will be very very low. The conductors are 90°C rated, which I believe are sufficient for more than 100A if I'm not mistaken.
Last edited by Oscar; 05-07-2020 at 12:23 AM.

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## Re: Wiring up a 30HP rotary phase converter

You can't use 90° rating on wire. Once it terminate in a lug of lesser rating the entire circuit must be downgraded. You just use the 60° to be safe even though there may be more 75° terminations available but surely no 90° at all.

The 30 hp they say is good for approx 42 amp with that type of load.

Similar to starting a single 15 hp motor. But if that is all you ever anticipate ever needing out of it I do believe a 60 amp with #6 or #4 would function perfectly.

Based off charts supplied by a manufacturer of similar 30hp rotary phase converters.

Your subpanel panel size is your answer. Use it all. Install a 100 amp and #2 and call it maxed and know you can't ever do it any better without busting the bank.

If your looking for the least install then go 60 - 70 amp with #4's
Last edited by danielplace; 05-07-2020 at 12:58 AM.

16. ## Re: Wiring up a 30HP rotary phase converter

Thanks for the info, duly noted. I got a hold of the instructions from the seller. Sheet says 80A breaker with 4awg, so I guess that would be the absolute bare minimum. I can always upgrade since it's a very short run from the main panel to the sub-panel. It's only about 15ft.

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## Re: Wiring up a 30HP rotary phase converter

I would take advantage of all you have. 100 in 100 out.

Put a 100 on it and #3's(or #2's if wanted) and know you did all you could without subpanel feeder upgrades at least. I honestly think that is best route to go.

I guess the factor is closer to 1.9 X 3 phase load for the standard rotary type. 36 X 1.9 = 68.4 of single phase input roughly.

The 80 would just give you the 36 you want and a bit more but the 100 would give you some decent head room.

Does your Cutler hammer take BR or CH breaker type ?

Are the breaker handles black or grey ? 99% of time Black are BR Grey ones are CH

It is a lot easier to source a 100 amp for that panel most likely than a 80 amp. Home Depot most likely carries a 60 and then a 100 nothing in between. They do have BR and CH in 80 amp available you just may have to go to a electrical supply that carries the Cutler Hammer stuff if you did want to use 80.
Last edited by danielplace; 05-07-2020 at 02:05 PM.

18. ## Re: Wiring up a 30HP rotary phase converter

Duly noted.

it takes BR type breakers, handles are black.

On a separate but similar note, I was reviewing ampacities for wire gauge sizes in an online reference chart.

4awg: 21mm² can carry 70A using the 60°F rating.
10awg: 5.4mm² can carry 30A using the 60°F rating.

Insulation aside, we know that the current carrying capacity is largely determined by the cross sectional area of the wire. I noticed that it would take four 10awg wires to roughly make up the cross sectional area of a single 4awg wire. Then technically barring other factors like undesireable heat-dissipation conditions, would that imply that four 10awg conductors be able to carry 120A because they have more surface area from which to dissipate heat than the 4awg wire that has the same cross-sectional area? The combined surface area per-unit-length of four 10awg conductors is 31.7mm², where as for a single 4awg conductor it is 16.3mm²; roughly double, even though the cross-sectional areas are roughly identical.
Last edited by Oscar; 05-07-2020 at 02:44 PM.

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## Re: Wiring up a 30HP rotary phase converter

You are right about your idea's on cross section but irrelevant for wiring though because you don't parallel a wire smaller than a 1/0 and you can't put more than one wire in each hole in a lug.

20. ## Re: Wiring up a 30HP rotary phase converter

Originally Posted by danielplace
you don't parallel a wire smaller than a 1/0 and you can't put more than one wire in each hole in a lug.
Why?.

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## Re: Wiring up a 30HP rotary phase converter

Originally Posted by Oscar
Why?.
It is illegal and against code.

Proper wiring isn't done that way. There are reasons. Many.

You and know it would be fine but I still very highly suggest you go get the proper wire for every thing.

The lines in just use #3 cheapest that will get it done.

#8's to the idler

#6 or #8 with a overcurrent device at 60 amp or 45 amp respectively . Small 60 amp 3 phase disconnect with cartridge fuses is what I would use for load size protection.

You are going to protect the welder with overcurrent I hope. It isn't just protecting the load but your phase converter too.

I mean trying to make large wire out of several small wires is a real junky stunt so now you got me worrying about you. Lol.
Last edited by danielplace; 05-07-2020 at 04:14 PM.

22. ## Re: Wiring up a 30HP rotary phase converter

Got it. I didn't know it would be illegal/against code. In the car audio world, maniacs with 100kW worth of amplifier power typically parallel wire to achieve the necessary current carrying capacity (to transferhundreds of amps of current) from the front of the vehicle to the rear where the amplifiers are traditionally installed. Obviously that is different from building wiring, which is why I asked "why".

23. ## Re: Wiring up a 30HP rotary phase converter

What do you think about a DIN Rail 3-pole breaker for the 3-phase OCP between the welder and the RPC?

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## Re: Wiring up a 30HP rotary phase converter

Originally Posted by Oscar
What do you think about a DIN Rail 3-pole breaker for the 3-phase OCP between the welder and the RPC?
Nope not like that. If you were building a cabinet with controls in it maybe but you don't need any. Get a disconnect that includes the enclosure.

More like this.
https://www.homedepot.com/p/Square-D...322N/205071143

3/4" or 1" greenfield with 3 #8's and a #10 from RPC to disconnect and then hardwire welder straight into it or mount your receptacle just below it or add so SJ cord and make a 20 foot drop then receptacle or something like that may be nice to give little more mobility.

You will be using the breaker feeding RPC to shutdown so the disconnect is just protecting from something going to ground mostly but if fused properly with 40 amp fuses it will offer the welder some protection if it was drawing more than it should for some reason.

You could also put a small panel then you would be setup for future loads without much hassle and it would be much more. Panels are relatively cheap. A main lug only panel you could even use for this so it would be less expensive. You start adding panel, main breaker and welder breaker it will add up.
Last edited by danielplace; 05-07-2020 at 07:28 PM.

25. ## Re: Wiring up a 30HP rotary phase converter

But then would I not be missing an OCPD if I didn't have a breaker (in between the welder and the RPC)? I'm almost 100% sure I will go with a 100A breaker with 2awg from subpanel-to-RPC, but surely that isn't considered OCPD for the welder?

edit: nevermind, didn't read properly about " if fused properly with 40 amp fuses it will offer the welder some protection if it was drawing more than it should for some reason."

Looks like the RPC will be here tomorrow. That was fast. I need to make space in the garage!
Last edited by Oscar; 05-07-2020 at 08:00 PM.

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