Advice needed on wiring up 80 HP RPC to 400amp service

I have a 80hp RPC that I got a couple years ago when I bought out another company. I have not needed it until now, I am getting a new Doosan lathe in next week and since I already have this RPC I want to try and use it.

Already know I will have to start it with a pony.

My 400amp service is split into 2 200amp breaker boxes and is probably 50' of wire length away from my machine/ machine room.

The Doosan specs for power requirements is 72.95 amps at full capacity. It is a LSYC lathe so 20hp main, 5.5hp sub and 5hp rotary.

I attached the specs plate pic off the RPC, but it is rated 13.6 Idle amps.

So, not sure how to wire this beast up!

The RPC I want to be right next to the main service panel boxes. Keeps the distance down for wire as well as having to hear it from my machine room.

Not sure of the best way to wire it into my dual 200amp breakers/boxes. What size breaker it will need in the single phase side. How many amps total should I anticipate the system using with the RPC and machine combined? After the PC, should I run to a disconnect box in my machine room? In the future I plan to get a bigger mill and run off this PC as well, but thats a few months off probably.

Thanks for any help!

Can you show us a picture of the inside of the RPC panel?

I think you could probably get away with powering the RPC with 100 A Circuit to generate the wild and then single phasing another 100 A breaker to the machine. I don't think you'll need more than 200 A, but the picture would be more helpful. Or call 800-268-2624.

Matt Matt said:

Can you show us a picture of the inside of the RPC panel?

I think you could probably get away with powering the RPC with 100 A Circuit to generate the wild and then single phasing another 100 A breaker to the machine. I don't think you'll need more than 200 A, but the picture would be more helpful. Or call 800-268-2624.

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Here is a few pics...

beansdiesel said:

Here is a few pics...

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You don't have a start circuit, So you will have to Pony Start. I would be more happy to see it balanced from both sides of the single phase lines. What you have in there are just balancing run capacitors.

What is written on the cans in mf size? 100 µF? Those cans may need to be replaced. I have seen worse working just fine though.

How are you going to pony start it? I don't see any shaft.

Matt Matt said:

You don't have a start circuit, So you will have to Pony Start. I am glad to see it is balanced from both sides of the single phase lines. What you have in there are just balancing run capacitors.

What is written on the cans in mf size? 100 µF? Those cans may need to be replaced. I have seen worse working just fine though.

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Got one new machine to deal with now, another one not far off, I'd want to clean that up with new caps just on the principle you have a lot on your plate, and it will not be a happy-time if they go tits-up or confetti-time later, when the machine is trying to hit production deadlines.

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With a right serious-sized 80 HP of idler pony-ing up, I would also want that ponying process to be simultaneously 'leaking' mains current into the idler windings so it aligned itself pretty closely, phase-wise, with the supply by the time you were ready to slam full-power to it. Sort of a cross between pony and soft-start. Or at least phase-match indicator lamps as used for syncing gen sets.

Could otherwise get noisy at the breaker if the full power and the motating 80-hoss idler - hardly a baby kitten - happen to be the better part of a half-wave in phase disagreement when you make that cutover.

@Monarchist , I suspect this to be originally a secondary (slave) Idler in a system. It probably had a motor starter upstream with a bigger RPC or it was an old style three phase balancing system.

Not that it matters much, I do believe it's a 75 hp idler from its model number

Matt Matt said:

....
How are you going to pony start it? I don't see any shaft.

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There is the end of a shaft visible in pic #1. Presumably the cover is off. May be able to put a rope start on the accessible end, attach a pony connection, or, add a start circuit.

JST said:

There is the end of a shaft visible in pic #1. Presumably the cover is off. May be able to put a rope start on the accessible end, attach a pony connection, or, add a start circuit.

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Lol, did you zoom in on that picture??? It looks to be about 5/16 diameter protruding from a 2 inch diameter. The 2 inch looks pretty flush to me.

Matt Matt said:

Lol, did you zoom in on that picture??? It looks to be about 5/16 diameter protruding from a 2 inch diameter. The 2 inch looks pretty flush to me.

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Good eyeball calibration, Matt.

NEMA size for a 75 - 80 HP frames would put it around 2 1/8". Might be as much as a 2 3/8", no less than 1 7/8".

Either way, some machining needed to get a Lovejoy, pair or quad of dowel-holes, or a cross-slot for a drive-tab into place to couple to a pony motor or its clutch.

Jerry? I'd call this one a tad weighty to be rope-starting ...unless one has a gravity tower handy - of the sort once used to launch gliders, or at least a straight driveway long enough to give a fast pickup-truck a good run!

Matt Matt said:

You don't have a start circuit, So you will have to Pony Start. I would be more happy to see it balanced from both sides of the single phase lines. What you have in there are just balancing run capacitors.

What is written on the cans in mf size? 100 µF? Those cans may need to be replaced. I have seen worse working just fine though.

How are you going to pony start it? I don't see any shaft.

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I am going to attach a pulley to one of the ends of the shaft for the pony to start it.

I will get the specs on the caps tomorrow. It had some burnt ones so i had a local electric motor guy go through it all. Pretty sure even if it had a start circuit i wouldnt be able to start it without a pony anyway. It draws almost twice as many amps as i have coming in the building lol.

The guy i got it off of said he used it all the time and would pump the breaker to get it started and watch all the lights in the area dim. I am guessing thats why it had burnt caps.

So, what if it IS flush? I expected that it was, never saw any extension on it, but if there is one it would help.

I'd have a stood-off pulley on there in a short time. Little peg or point to go in the centering (if it has that) or a recess for that stub, if it has one. Three or four screws in the end to hold the pulley and filler/standoff, and you can run any pony you want.

Bound to be cheaper in shop time than a nice new 80 HP (40HP?) RPC.

I see Beans was typing at the same time...

The start current should come through OK, the breakers have a time delay, so long as it DOES start.

Rope start? Sure. All you really need is to get it rolling at a few rpm to bias it (the more rpm the better, of ĉourse), the motor will take off from there. Better than "pumping the breaker", but a decent start circuit would naturally be even better

beansdiesel said:

The guy i got it off of said he used it all the time and would pump the breaker to get it started and watch all the lights in the area dim. I am guessing thats why it had burnt caps.

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BTDTGTTS, 100 hoss GE @ 416 Wye off a 100 kay-dub (145 BHP motor) diesel. Stand on a 5-Ton's tire and plywood, push breaker with a dry board. Repeat, repeat, usually OK on the fourth go.

But that was at Long Binh, 1960's.

As to burnt caps? Well we were 3-Phase all the way, Marathon gen-set head onward, no converters nor caps, anywhere.

You gots to figure slamming contacts that way and having them pop-back open, spikes of around four times the supply voltage happen - sometimes more - and they ain't exactly "low-energy under the curve" ones, either, so the breaker can have a short life as well.



You got a shop to run. You can surely do better, easier, and less 'dramatic'.

JST said:

Rope start? Sure. All you really need is to get it rolling at a few rpm to bias it (the more rpm the better, of ĉourse), the motor will take off from there.

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Sure 'nuf. RPM is too low when you throw single-phase at it, big sumbich that size just locks up and hums.

Strong as an ox whilst doing that, but it thinks its an electromagnetic brake and a short-lived space heater, not an idler motor.

That deal about pumping the breaker.......

Could be the balance caps were not totally balanced and so acted like start caps a bit. In that case it might pop a few times until it got enough speed going to have back EMF and the breaker would hold as it accelerated.

If you know which way it wants to go, you rope it that way, and get a head start. It won't lock up, and it may start first try with no breaker futzing.

JST said:

That deal about pumping the breaker.......

Could be the balance caps were not totally balanced and so acted like start caps a bit. In that case it might pop a few times until it got enough speed going to have back EMF and the breaker would hold as it accelerated.

If you know which way it wants to go, you rope it that way, and get a head start. It won't lock up, and it may start first try with no breaker futzing.

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75-80 HP rope-a-dope?

Y'do know I've been trying to be more polite lately, so I'll just take a leaf from an earlier Pilgrim:

You sure don't sweat much for a fat girl!

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75HP RPC Feeder Size Requirements

"beansdiesel,
So, not sure how to wire this beast up!

The RPC I want to be right next to the main service panel boxes. Keeps the distance down for wire as well as having to hear it from my machine room.

Not sure of the best way to wire it into my dual 200amp breakers/boxes. What size breaker it will need in the single phase side. How many amps total should I anticipate the system using with the RPC and machine combined? After the PC, should I run to a disconnect box in my machine room? In the future I plan to get a bigger mill and run off this PC as well, but thats a few months off probably."

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I would suggest that before you go too far you have a good look at your service size, and utility transformer size. A 75HP RPC and a 1st load of 30HP is no small feat for a residential service, let alone additional loads.

Looks like you only got half of the RPC, the motor and cap box. Controls are missing in action. The manufacturer offers a soft start package for this model that can start with 250A starting current, I would call and see how much they want to build the controls for it. It could save you some grief making your own system and the trial and error. I wouldn't want to be pumping a breaker to try and start it, that could be hazardous to you and the breaker.

Here's the rest of the package:


And the specifications:
Remco Electrical Manufacturing | Phase Converters

If you want full power from it the tag calls out 250FLA that is more than you can get from either of your panels, as your likely to only have 100A breakers to fit in your existing panels. Not to mention that the service transformer might be a tad small for this load.

Some numbers to consider.
Doosan 73A 240V 3Φ, 73A x 1.732 = 126.43 FLA @ 240V 1Φ

Then add the load for the RPC.
PRC, 123.43A x.666 (2/3)= 84FLA
Generating 2 of the 3 phases.

126A + 84A = 210A FLC of the combined load on 1Φ

Then adding the 25% for starting surge and overload conditions as required by the NEC.

210A FLC x 1.25 = 312A min required overcurrent device and wire size.

That's over the size of your panels and maybe your service transformer. So I would investigate here first.

How is your service supplied, and what is the transformer size feeding the building?

SAF Ω

Monarchist said:

You sure don't sweat much for a fat girl!

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Hey. That's my favorite line. You been reading my joke book ?

(Except I heard it, "Y'all don't sweat much for a big ol' fat gal." Same result tho, I bet )

SeaMoss said:

Hey. That's my favorite line. You been reading my joke book ?

(Except I heard it, "Y'all don't sweat much for a big ol' fat gal." Same result tho, I bet )

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Dunno what Province you are based in, PRC side of the Pacific, but Guangdong, Macau, Hong Kong any of the many other places I have been in China or anywhere else in Asia, a "fat lady" is very-damned-seldom a 'local', anyway. Yew-Ass or Yew-Kay tourist, usually. Most European Continental's, Latins, African, Indian,s and even Canadians are more fit and slender than British "Beef Trust" or KFC 'merican 'Hog Women' and their mates.

Tragicomic is second-plus generation Asians raised on Cola-sugar, Big Mac salt, greasy, salty fries, hormoned-up fried chicken, and greasy, salty, starchy 'Frozen Dinners' that become pudgy little porkers, right here in the USA. Their GRANDmothers are more fit.

Monarchist said:

many other places I have been in China or anywhere else in Asia, a "fat lady" is very-damned-seldom a 'local', anyway.

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Getting to be some waddlers here. Nothing like the US still, but more. The assistant and I have running bets going; when I see a fat Chinese person I say 'two kuai, three kuai, five kuai' depending on how fat. She gets the foreigners.

So far I'm about 36,000 rmb behind

Yew-Ass or Yew-Kay tourist, usually. Most European Continental's, Latins, African, Indian,s and even Canadians are more fit and slender than British "Beef Trust" or KFC 'merican 'Hog Women' and their mates.

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Want a shock ? Go look at some US street photos from the sixties or seventies. Normal-size humans. What the hell happened ?

Tragicomic is second-plus generation Asians raised on Cola-sugar, Big Mac salt, greasy, salty fries, hormoned-up fried chicken, and greasy, salty, starchy 'Frozen Dinners' that become pudgy little porkers, right here in the USA. Their GRANDmothers are more fit.

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Happening here as well and it's not just western food (which is what all Chinese love to claim.) Food in Skankhai is pig slop and it's slathered in oil. Just floating in the effing stuff. I hate it. And tasteless. Zhejiang has the world's worst food.

The part that really shocked me was, about fifteen or twenty years ago food was THE most important thing in a China person's life. Just for fun I'd freak people out and say "Okay, let's get on this right now" at about fifteen minutes to lunch. They'd almost cry And the food was excellent. Fresh, locally grown, tasted great - the test of a civilization is the tomatoes. And China tomatoes were like we had in the fifties in the US. I couldn't imagine they'd give this up, ever,

Yeah, well ... now it's all supermarket-style garbage. Just shit.

While we're here, could someone tell me who did the breeding on strawberries, to develop these huge, bright red, delicious-looking pieces of cardboard ? All looks, no taste. I won't even touch the things, they are such a disappointment.

Watermelons are still mostly good tho, now that they quit exploding.

Anoth3er reason for the change in weight is that important people drive cars, they don't walk. So that's gone. And old buildings had to have elevators if they were over six floors, so most buildings were six floors. Going up and down three or four floors a few times a day will work off some fat. Now they are all twenty or so, so everybody rides the elevator.

They'll be as fat as US porkers one day soon, but it's not KFC's fault. Food quality has gone to shit and exercise in daily life disappeared.


Back on-topic, I can't even imagine "ponying" a 100 amp breaker. When they trip, they lose a little current-carrying capacity from the contacts pitting ... seems like you'd run through the breaker's entire life in about a week this way.

SeaMoss said:

Getting to be some waddlers here.

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Noted. "Glow-ball" i-zation of bad choices. Sad.

Back on-topic, I can't even imagine "ponying" a 100 amp breaker. When they trip, they lose a little current-carrying capacity from the contacts pitting ... seems like you'd run through the breaker's entire life in about a week this way.

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Dunno about the general ruck, but at least ONE of Schneider's many, many legacy brands - Square-D - has published specs for interruption cycles of their breakers.

If anyone bothers to look them up, it is soon clear they were NOT meant for that sort of service atall. I have 60 & 100 A disconnects, fused and otherwise, 60 A 'transfer' switches here, one of them a Cummins/Onan branded automatic unit for the gen set.

Any of those take up about 40 times the volume of a 100A breaker. ONE set of contacts is near-as-dammit the size of an entire QO breaker.

I'd not be masturbating an ordinary breaker to switch that pig.

Proper set of contactors, good arc-chutes, etc. rated for the task, rather. Big, yes. Cheap, not.