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doctor demo
01-09-2010, 05:06 PM
A friend of Mine that does some hoby wood work in a single car garrage with minimal electrical outlets asked if I would help install a small sub panel and run a few more circuts in the garage.
When I looked at the stuff he had, I noticed that the sub panel is for three phase. I know that electricaly it will work, without 1/3 of the breakers being used .I can't find anything that forbids doing this in the NEC but I'm sure it does.
What do You All think?

Steve

JoeFin
01-09-2010, 05:14 PM
Will I guess it wouldn't be "Modifying the Panel" which is strictly forbidden.

And I have seen numerous 240/120 Delta (Stinger Leg) panels used for 120 v lighting minus all the breakers on the wild leg.

Chances are however if he ever goes to sell the place they'll pick it up on the termite report and the buyer will seek to deduct the cost of changing it out. ($1200 est.)

BTW: How much is a 125 amp sub over at Home dippo these days?

Doozer
01-09-2010, 05:23 PM
" Home dippo ".

I love it!

--D

SteveF
01-09-2010, 06:16 PM
Subpanel should be around $50 plus cost of the breakers. Small price to pay to not have a hassle selling the house.

Steve.

doctor demo
01-09-2010, 06:30 PM
Will I guess it wouldn't be "Modifying the Panel" which is strictly forbidden.

And I have seen numerous 240/120 Delta (Stinger Leg) panels used for 120 v lighting minus all the breakers on the wild leg.

Chances are however if he ever goes to sell the place they'll pick it up on the termite report and the buyer will seek to deduct the cost of changing it out. ($1200 est.)

BTW: How much is a 125 amp sub over at Home dippo these days?
Yeah I got My sub panel at HD a few years ago for under a hundred.
I don't think there will be a sale any time soon, and I doubt a inspection will catch it based on the inspections I've seen.

Steve

doctor demo
01-09-2010, 06:38 PM
Subpanel should be around $50 plus cost of the breakers. Small price to pay to not have a hassle selling the house.

Steve.
Not My house, not My hassle. I was just asked to help and saw the panel was 3ph and was curious, never thought much about it befor now and couldn't find any NEC reference to it.

Steve

Carld
01-09-2010, 10:17 PM
I don't see where it would hurt anything. You will be feeding two legs from the service panel and using breakers on those buss connectors and the third buss will not be hot.

You do need to check national code and local and state code to see if the box has to have a ground rod and if the mechanical grnd buss and white wire buss have to be paired or isolated. I ran a sub panel to my pole barn and had to have a ground rod and the white and green had to be grounded to the box.

J Tiers
01-09-2010, 10:37 PM
A 3 phase box may or may not have a neutral actually in it. While it would have been provided, it might not be with it now, since I am assuming the box is a 'take-out" from somewhere else. Since the "bond" from neutral to ground should only be in the main service box *, you'd need a separate neutral for the 120/240 usage.

if it's a 120/208 box, there will be no problem with missing neutrals etc.

A cursory examination of the NEC doesn't turn up anything past a general "suitable for" consideration, which is arguable either way, I suppose. Something nags at me that there might be an issue, even so.

One issue with a "take out" box is that the three adjacent breaker spots cover the three phases, and that means the box may have open spots unless more breakers are assigned to one line by hooking two phases to it. That way there could be no missing spaces, but more branch circuits will fall on one of the 120 lines, which is generally not good practice.

* Outbuilding grounding and bonding is another matter, and local vs national codes may differ. Some local codes forbid bonding on a "sub feeder" regardless, and others require it.

Carld
01-09-2010, 10:43 PM
J Tiers, do you think he could just use single pole 120 breakers and two pole 220 breakers in the box?

JoeFin
01-09-2010, 11:15 PM
I ran a sub panel to my pole barn and had to have a ground rod and the white and green had to be grounded to the box.

Should not have grounded the Nuetral at the subpanel. That is a BIG No-no in the NEC and every code enforcing authority in the country.

The ONLY time you are allowed to Bond the Grounded Current Carrying Conductor is at the Service Entrance or a Seperately Derived System - meaning the secondary side of a transformer.

doctor demo
01-09-2010, 11:26 PM
The box is from ? and does have two 120V 20A 1ph breakers at the top and one 30A 208/230V 3ph breaker at the bottom, so it would need a blank cover added if the 3ph is switched out to 1ph 230V. The few other breakers would have to be placed properly to avoid having to add more blank covers.
Worse case I guess I could have three single phase breakers in a row and lable the one on the empty leg as a spare .
It does have a neutral and a ground buss in the box and a jumper between the two , as I understand it the jumper has to be removed.

Still can't find any specific code violations and reading the book is frustrating at best.
Thanks for the replies guys!
Steve

J Tiers
01-09-2010, 11:42 PM
Should not have grounded the Nuetral at the subpanel. That is a BIG No-no in the NEC and every code enforcing authority in the country.

The ONLY time you are allowed to Bond the Grounded Current Carrying Conductor is at the Service Entrance or a Seperately Derived System - meaning the secondary side of a transformer.

Remember, it was an outbuilding.... and the local rules DO seem to differ on that. I agree, the most I have seen personally was that the equipment grounding conductor had to be supplemented by a local rod.

I have , however, heard of other cases where a bond was required by the local bozos. When you think about it, it's not *that* bad... after all the power company grounds your neutral at the pole (and in the city, at several adjacent poles also). It's not as if you were bonding in the same building at multiple spots, which would end up carrying current on teh equipment grounding conductor within the building.

I think it comes down to the definition of a 'service". The NEC is clear, but apparently not all AHJs agree. Their argument is that the difference in potential from neutral to ground may be too big at an outbuilding some distance away. There won't be any current on the equipment grounding conductor within the building, although there will be between buildings.

We also don't know if the EGC was even carried between buildings in that case....... if fed underground, it usually is, but if overhead, it often is not on buildings I have seen.

Regardless, the NEC says the AHJ gets to call the shots, so you do what the local yokels say.

Carld
01-10-2010, 12:02 AM
Joe, I guess you better get in touch with Kentucky Utilities, and the Spencer County electrical inspector and tell them they are wrong. I did what they wanted and didn't argue.

JT, I asked the lineman that hooked my service about why they grounded the neutral at the meter panel and I had to seperate them in the home and shop service panel and bond them at the pole barn and I never really understood what he said. He and I still see each other and talk from time to time and he is friendly and helpful but I just accepted what has to be and did it.

whitis
01-10-2010, 01:11 AM
And you should probably be using 2/3 of the box, not 1/3, unless you are going to only run 110V instead of 110/220V to the box.
Normal single phase breaker box in US has 110/220V with alternating breakers (vertically) for 110V connecting alternately to the two legs and 220V circuits using dual gang breaker which connects to two adjacent legs giving 220V.

Not using 1/3 of the box isn't modifying it. Adding a neutral bus bar if you didn't already have one might be. Cutting the third phase in half so you can put half on leg 1 and half on leg 2 and use the remaining circuit breaker modifications probably would constitute modification. Wiring the entire third leg to one of the two existing ones probably would not constitute modification though you loads wouldn't be evenly divided (not that they necessarily are anyway and you might intentionally compensate for an unbalanced load elsewhere); you would also have to be careful where you installed dual gang 220V breakers as in some positions they would then connect to two copies of the same leg.

doctor demo
01-10-2010, 01:36 AM
And you should probably be using 2/3 of the box, not 1/3, .
I did say lose a third of the box so I would be using 2/3
Steve

Arcane
01-10-2010, 03:33 AM
There is one thing about not bonding the ground wire to the neutral and that is you have to rely on the ground rod/earth interface to have a low enough resistance to allow enough current to flow to trip the breaker. This is especially true for those installs where NEC says NOT to bond neutral and earth ground wire together in the panel. Here (http://home.earthlink.net/~jimlux/hv/grounds.htm) is a chart that gives the typical resistances found in various soil types. Current in amps is equal to voltage divided by resistance in ohms. As you can see, most single ground rods would not trip the standard 15 amp breaker even if you hooked it up directly to a 120V hotleg. So many people get so excited if they don't have that ground present, yet have no idea that it's more than likely just "window dressing" and provides no real safety function at all. Personally I think ground fault breakers are the way to go. Also, a 4 wire feed where the ground has it's own dedicated wire back to where the neutral and ground are bonded together works very well.

JoeFin
01-10-2010, 10:35 AM
So many people get so excited if they don't have that ground present, yet have no idea that it's more than likely just "window dressing" and provides no real safety function at all. Personally I think ground fault breakers are the way to go. Also, a 4 wire feed where the ground has it's own dedicated wire back to where the neutral and ground are bonded together works very well.

The Ground - what ever resistence it is, WILL drop 100% of the voltage across it. The Utility Distribution is of "Finite Resistence", floating with no potential until it comes in contact with earth. More resistance in the ground, that results in LESS voltage potential. Then the Utility merely changes taps in the transformer to increase the voltage. That is the reason you will see a ground connection on the secondary side of the utility transformer on the pole.

The code reads some thing to the effect You can feed an outbuilding sub panel without Ground Electrode Conductor provided the Eguipment Service is Less Then 480 volt and 1000 amp. I've always thought the limitation of "less then 1000amps was because the minimal size subpanel of 100 amps would have a nuetral conductor some where around the size of 12 1/2% (minimal ground conductor size) the size of the max feeder. So it would at least carry the fault current.

It does not say you can run a Branch Feeder for a Subpanel without the Nuetral Condutor (Grounded Current Carrying Conductor).

Where a secondary bond point run into trouble is for the exact reason Arcane pointed out. The Resistance of earth ground differs with the soil's grounding properties. IF the soil at the Subpanel has better (Less) resistence properties then the soil at the Service Entrance Point then all the Nuetral current will attempt to travel there to meet that earth ground.

Should the Sub Panel Feeder Nuetral be too small to carry the current it WILL burn out like a fuse. Now every thing on that sub panel is floating. First time you have your hand on a peice of equipment (energized merely by the electro-static charge of induced imbalance current) and a nice ground like a water pipe - you'll know about it

Number of times I've seen Nuetral Bars literally melted out of the subpanels for this very reason - 3