Rotary phase converter: local ground or all the way to the panel?

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Ok. Thanks for everybody's help in the earlier thread. The 20HP rotary phase converter is working, but I now need to place it in the garage, about 70+ feet wiring run distance from the main breaker panel.
Given the cost of copper wire these days, my inclination is to run just the two hots to the panel and to put a grounding rod close up to the garage and run a local ground to it. I see no reason to run a neutral line from the panel (the machines are all 3 phase).
I know that I could run a ground line to the panel AND run a local grounding rod, but is it a bad idea to just do a local ground?
What gage wire for a 20HP RPC, but the main/biggest load/machine will be a 10HP spindle and a couple of 2HP machines, never all at the same time? ($ signs get much bigger with the wire gage/diameter :-)
Anybody near San Jose, CA have a spool of #4 or larger gage for cheap? :-)
Thanks in advance!
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bad idea it can create a ground loop and hazardous vlotages between grounds, install a ground rod, but definetely bond it to the main building ground.
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On Wed, 27 Feb 2008 09:04:23 -0800 (PST), rpseguin

I used 6/3 SO cable for mine. For that 70+' distance however, you might be better off with 4/3. The SO cable might cost a little more, but it makes for a clean installation. Unless you plan to run conduit.
Also keep in mind, if you run wire instead of SO cable, your ground doesn't need to be as big as the hot wires. A #10 ground wire will work.
Matt
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On Wed, 27 Feb 2008 18:09:10 GMT, Matt Stawicki

Forgot to mention...... Go all the way to the panel with the ground.
Matt
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That is illegal and unsafe. I assume the "primary" side is a 240V motor? You need an equipment ground conductor all the way back to the 240V service. If one of the hots shorts out to the motor case, for example, you need this bonding path to carry enough current to trip the breaker. You can not rely on the earth for the bonding path, its resistance is too high.
As for the secondary side, you need to look up in the NEC how to wire a "separately derived system". You can also look up how to wire motor loads to determine the size of the feeder conductors for the primary side.
Cheers, Wayne
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SO cable is not for permanent installation, you need to use SER or UF cable.
Wayne
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On Wed, 27 Feb 2008 09:04:23 -0800 (PST), rpseguin

You can get by with #10 Green..but...
Go all the way to the panel.
While life is cheap, replacing you can be expensive
Gunner
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copper is costly but why install something you know wouldnt pass code, or a future home inspection.
do it right do it once then relax and forget about it
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I'll do it the right way and run it to the panel.
I'm just renting the house, which, by the way, doesn't have any grounded outlets other than a couple of GFIs in the bathrooms. The landlord did put 3 prong grounded receptacles in, even though there's no ground wires in any of them.
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| I'm just renting the house, which, by the way, doesn't have any | grounded outlets other than a couple of GFIs in the bathrooms. | The landlord did put 3 prong grounded receptacles in, even though | there's no ground wires in any of them.
They don't make very many 2-prong ungrounded GFCI receptacles, even though such things would work and can even do a self-test without a ground wire.
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True. But to clarify: three prong GFCI receptacles that aren't grounded are legal. Ungrounded three prong outlets _downstream_ of a GFCI are also legal (as a retrofit), as long as you use the stickers saying "ungrounded outlet" on them.
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|> |> | I'm just renting the house, which, by the way, doesn't have any |> | grounded outlets other than a couple of GFIs in the bathrooms. |> | The landlord did put 3 prong grounded receptacles in, even though |> | there's no ground wires in any of them. |> |> They don't make very many 2-prong ungrounded GFCI receptacles, even |> though such things would work and can even do a self-test without a |> ground wire. | | True. But to clarify: three prong GFCI receptacles that aren't grounded | are legal. Ungrounded three prong outlets _downstream_ of a GFCI are | also legal (as a retrofit), as long as you use the stickers saying | "ungrounded outlet" on them.
How about one of those grounded plug adapters ... the kind where you have 3 holes on one end to plug in a grounded plug, and only 2 prongs on the other end to plug into a legacy 2-hole no-ground outlet ... that integrates GFCI protection as part of the adapter? I've seen GFCI cord sets, but only with a grounded plug. How about with an ungrounded plug?
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The GFCIs look grounded to my tester. I haven't bothered to open them up and look if there is a ground wire in there. What I was trying to say is that all of the "normal" (non-GFCI) 3 prong outlets are just hot and neutral with no ground wire in there. Landlord did the cheap thing, although I don't know of any easy and inexpensive way to retrofit a ground in to a lot of outlets (say 20+).
As for my sub-panel and 3 phase panel things, I've just ordered a 500' spool of #1 aluminum wire. It is _WAY_ less expensive than copper. I will be certain to read up and make certain that I bond everything correctly, use anti-corrosion goo and make certain all connections are torqued down properly. The RPC and all of the machine loads will be made using some copper THHN that I already have.
I've acquired a Cutler Hammer 3BR1224L125 125 amp 3 phase circuit breaker load center panel and now I need to find some CH BR3xx plug/ stab-in breakers. 3 pole breakers are pricey new! Anybody have some Cutler Hammer compatible breakers like these: BR360 BR350 BR340 BR330 BR320 BR315 BR310
Thanks!
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I'm not absolutely certain of the full nuances[+] of "plug connected device" w.r.t. CEC or NEC, but strictly speaking I don't think NEC or CEC applies in this case.
_However_, UL and CSA do. In particular, 2 two pin to 3 socket adapter (without GFCI) will not pass CSA, and is illegal to offer for sale in Canada. I do not believe such a device will pass UL either, but UL doesn't have power-of-law as CSA (or legislatively equivalent) does in Canada.
Conversely, if it has non-fraudulent UL or CSA markings on it, it will be legal unless overruled by local ordinance.
[+] I'm meaning edge-cases here. 2->3 plug adapters that simply make the third pin connect via pigtail to the outlet cover screw are illegal and covered by both NEC and CEC I believe. As the ground wire is screwed on, I think they're considered "permanent wiring". Or something. I dunno for sure. They're certainly illegal in Canada because they won't be granted CSA approval.
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rpseguin wrote:

Put the converter right near the entrance panel so the highest current only has to run the short distance. Then run smaller wire to the remote 3 phase loads. Requires an additional lead but the lower current req. should work out a lot cheaper. Now as to "remotely developed grounds" This was legal when we did a bunch of "cabins in the woods" supplied from a main lodge back quite a few years ago (I havent checked the code since). We ran the power with two direct burrial wires and installed a standard grounding rod at each cabin. This was all code compliant (at that time). ...lew...
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Lew sez:
"Put the converter right near the entrance panel so the highest current only has to run the short distance. Then run smaller wire to the remote 3 phase loads. Requires an additional lead but the lower current req. should work out a lot cheaper."
Not a good idea and not even remotely close to any "code". A RPC consists of one or more idler and load motors. The combination comprises a sort of electrical network. Complex circulating currents flow between the idler and load. It is not like there is a "generator" side and a "load" side. The same current circulates throughout the network; wiring should be sized accordingly.
Bob Swinney
rpseguin wrote:

Now as to "remotely developed grounds" This was legal when we did a bunch of "cabins in the woods" supplied from a main lodge back quite a few years ago (I havent checked the code since). We ran the power with two direct burrial wires and installed a standard grounding rod at each cabin. This was all code compliant (at that time). ...lew...
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Yes, for the reasons expressed by others.

Remember that there are losses in the RPC. A 10HP spindle actually loaded to 10HP (as opposed to an unloaded 10HP motor) is going to present something more like 12-13HP on the RPC. So, you're going to have to factor in 20-30% losses.
Secondly, yeah, wire is expensive. You may wish to consider using aluminum instead. Done correctly (to-code connectors and conductive grease for the application), it's just as safe, to-code, and a lot cheaper.
When I installed the 100A subpanel to my detached garage (100' of burial), I saved something near $300 by using aluminum instead of copper, and the inspector was perfectly happy with it - despite catching the electrician forgetting the grease on the subpanel end... ;-).
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Chris Lewis,

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Folks:
I gotta say, when you start tossing 20HP rotary convertors and 10 hp motors into the pot, economy starts to shed its meaning. Best to do the job right. If a 10 hp motor can't pay for its own infrastructure it might as well go to pasture. I'd say this even goes if the motor is for recreational use -- fun does have value, but fun can turn bad if you cut corners. Don't skimp on your hot sticks when turning on your Tesla coil.
But, man, ten horses...some people have big fun, I guess.
A P
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Don't know your actual installation plan, but you may be able to pick up a coil of #4 AL triplex from the local power company - some of it gets scrapped, either from teardown, or a leftover chunk off of a reel. Ken.
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<Ken Sterling (Ken Sterling)> wrote in message

Shhh but in a pinch I've used a "strand"--twisted together from 3 individual pieces of #12 or 14 copper.
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