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hotater

08:12PM | 09/18/04
Member Since: 09/17/04
3 lifetime posts
Bvelectrical
Hello folks, blame Google for me finding you.

I live at a very remote hot springs that came with two 30Kw diesel gensets producing three-phase 120/240 power.

I've now finished a restoration project on an old 15Kw diesel named Little Enos (because of its half-stature similarity to the big ones like the Smokey and the Bandit character).

I'm about to wire my machine shop to Little Enos by way of a Siemens three-phase service panel.

The generator has four service wires, L1, L2, L3, and L0. The L0 leg is neutral.

I get 120v from L0-L1, L0-L2 and 208V(!) from L0 to L3. (I don't understand that)

240volts are obtained from L1-L2, L1-L3, and L2-L3.

I think I understand a tiny bit about single and three phase 240, but 120v single is a puzzle.....and the issue of grounding has me thinking of Yellow Pages and a $300 service call.

The question is, since the generator is not grounded (or should it be?), do I ground the service panel? If it's not grounded by wire should it be insulated from accidental ground?

My plan is to wire the four generator wires to a weatherproof pin and sleeve Hubbel female. Then plug in 30 feet of 6-4 SOOW cable wired directly to the 100a 3ph service panel hung inside the building. From that box will hang a Medusa of ten foot SOOW cables with waterproof female connectors (thanks ebay) that will plug into smaller distribution boxes for lights, workbench plugs and for the four pieces of three phase machinery, plus and air compressor and coolant pumps, etc. (I'm a one man band, 15Kw is plenty.)

On three prong 120v plugs I would assume either L1 or L2 for power and L0 for neutral, and the ground?

My gut feeling is to treat the generator frame as ground and consider the L0 lead to be attached to it...hmmm. Have to check that....

BUT, I'm nervous about attaching a generator lead to a service panel frame, too! And if lightning strikes Little Enos between the eyes....what happens to ME that's hanging onto a lathe handle?

FWIW, I checked on bringing in power....it's $199,700 higher than a service call.

Turning diesel into mega-bytes and broadcasting by satellite.

Tom O

05:18AM | 09/19/04
Member Since: 09/17/02
477 lifetime posts
There are more issues here than just the grounding issue. The proper reply to your questions & some other issues would be a lot more than I'm willing to type.

Try the experts area or spring for the $$$ it takes to get a professional set of eyeballs out to look at Little Enos.

Tom


sadickers

08:11AM | 09/19/04
Member Since: 02/20/04
52 lifetime posts
It would seem as though little Enos has some generator issues. A 3 phase gen set if wound as a 4 wire "Y" configuration should provide 208V leg to leg and 120 V leg (any) to neutral (center point on the "Y"). The other configuration is the Delta and there should be 240V between any two leads. There is no neutral so no 120V, at least without a transformer. You best bet as Tom says is to have someone familiar with 3 phase generators look it over.

HomerS

09:51AM | 09/19/04
Member Since: 03/20/04
24 lifetime posts
Your generator is configured for 3-phase, 4-wire, center-tapped delta.

It is not a 4-wire WYE or 3-wire DELTA as sadickers suggests.

http://www.bmillerengineering.com/elecsys.htm

This is why you get 208V between the "High/Wild/Crazy/Stinger" Leg and Neutral while the other legs give 120V to Neutral.

With a 4-wire, center-tapped delta you must be careful of the High Leg. It must be identified with Orange tape and you must not use it for 120V single phase loads. (It's really 208V as you've found out.)

Homer


sadickers

10:50AM | 09/19/04
Member Since: 02/20/04
52 lifetime posts
Yep, I did some research and Homer you are so right. I am wondering if this is very common? I have heard of the "Wild Leg but never really paid much attention as I've never run across a situation where all the legs weren't balanced. Is this just a cheap way to get 120V off of a Delta 3 phase? I would guess that this configuration would also apply to a Delta 3 phase xfmr? I don't work much with 3 phase but do run across it on ocassion so will comit this to memory.

Steve

Tom O

03:27PM | 09/19/04
Member Since: 09/17/02
477 lifetime posts
I'm basing my comments on the National Electrical Code. I don't know of any books that make it easy to understand, especially since you also need an understanding of the relationship that one article might have to another one. (or two or three)

Some of the things that come to mind are proper grounding, which might not be possible if you use a 4 wire cord & connector from the generator (this is off the top of my head, I didn't research it), properly marking & installing the wild leg, improper use of flexible cord,possible listing violation if you connect 2 pole breaker to the high leg.

It is usually cheaper to invest in the electrician before doing the work since replacing materials already installed can get expensive. Leave the generator techs be, find an electricain that likes the great outdoors & get him to come out.

Tom

hotater

04:40PM | 09/19/04
Member Since: 09/17/04
3 lifetime posts
Thanks folks--

Here's what I've learned:

My generator is an Onan 15.0RDJC-5DRSpec. 1280AA, Serial # H750971877.

The rough translation is: 15.0 Kw

Radiator, Diesel, model JC. The '5DR' means four wire, 120/240 3 phase.

The "H 75" means it was built in August, 1975. Also hidden in the serial number is the '18' that denotes series delta 12 wire connection to get the four wire 120/240 3 ph.

Inside the control box the wires from the bus are colored T1=Orange, T2=Blue, and the high leg L3 is Yellow.

I used all weather marking pens of the same colors to mark the tops of the bus bars in the service panel to be sure I don't vaporize the coffee (and pot) or cause excitement. It's too far to the hospital from here!

The L0, neutral wire is NOT connected to the frame as a ground. All four wires are connected to busses but only the L1, L2, and L3 are breaker/switched.

I'll drive a ground stake to hobble Little Enos to in case the lightning tries to fry my grits and drive another one for the service panel in case a cord gets mashed or something.....but there are only four wires....

I still don't see how this system can be safe.

Assume for a minute the power wire, L2, breaks or wears through the insulation inside the machine and rubs up against the lathe innards.

The lathe is on rubber vibration dampners...... If I've got a handfull of cast-iron crank handle and standing on concrete what keeps me from becoming the conductor on a fast train to the Great Beyond with incandescent nose hair?

Should I tie everything together with ground straps and stake the whole works down to earth? OR, is the L0 lead grounding the machine TO the generator and everything becomes a return line so no ground is needed?

Here's the science on it, but I haven't been able to completely grasp all the qualifiers and (apparent) ambiguities.

http://www.imsasafety.org/journal/marapr/ma5.htm

THANKS!

Turning diesel into mega-bytes and broadcasting by satellite.

sadickers

11:39AM | 09/20/04
Member Since: 02/20/04
52 lifetime posts
You got my interest in this up and I spoke with a Fellow I know from work. He is a master electrician and works entirely commercial/industrial stuff. He was quite familiar with the 4 wire delta configuration or as he put it 3 phase delta with a wild lead. As he described it to me the L0 or centertapped lead is off one of the 240V windings.This is a neutral lead for the 120 v circuits and should be connected to a neutral buss bar in the panel. DO NOT connect it to ground!!! You need a seperate ground to the panel and to the generator frame as well as connecting any load equipment back to the ground buss in the panel. For your 120V loads they should be balanced between the 2 L lines that provide 120V to the L0 lead, they well be the two ends of that center tapped winding. Any 240V 1 phase loads should be split between the remaining L lead (the one that has 208 V to the L0 lead) and one of the other 2 L leads (not L0). Three pase loads will connect to the L1,2,3 leads, keeping in mind that the connection pattern determines direction of rotation of the motor. When I asked if there were any ocassions where a load would be connected using the L0 to 208 V lead he said there were some very special application motors that do use that lead. They are 1 phase motors that require an extra kick to their starting capacitors to get them started, then disconnect. I didn't go into detail on that with him. Anyhow aparantly this delta configuration is not that uncommon in industrial applications.

Your original question has allowed me to learn something new so I thank you>>

He also said general practice is to code the high lead Orange. Just don't make it red, black or blue as those are used commonly for standard 3 phase. Looks like you have that issue under control already.

Steve

Tom O

01:29PM | 09/20/04
Member Since: 09/17/02
477 lifetime posts
At some point, the neutral from the generator must be bonded to a metal enclosure and it must be grounded. Otherwise, there will be no ground fault return path.

The bonding connection can be at the generator or at the panel, but not both. You will need 5 conductors from the generator to the panel, regardless of where you do the bonding.

Now do you see why I recommend an on site visit by an electrician? Find one that is familiar with separately derived systems.

Tom

HomerS

02:44PM | 09/20/04
Member Since: 03/20/04
24 lifetime posts
I have to agree strongly with Tom about hiring an electrician who's experienced in seperately derived systems.

We have helped you determine that what you have is working as expected.

Panel bonding with a seperately derived system is not something that a DIY'er should attempt.

That bonding if done properly will help protect you from any HOT to chassis appliance faults.

If not done properly, you may be creating a hazardous condition where current splits between your neutral and grounding conductors. This can lead to voltage appearing on exposed "grounded" metal surfaces.

This is a "Hot Spring", so I imagine there's plenty of water nearby.

Homer


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