Single Phase Load, Three Phase Service?

[bobs your uncle]

I have three phase power separately metered from my main single phase service at my workshop. The three phase is 3 wire and is dedicated to one motor/hoist. I don't know if the transformer is a delta or wye, but I'm assuming it's a delta. There is no neutral. The disconnect for the three phase says "220v 3ø" although my meter reads about 208v between any of the three phase conductors. I didn't detect a "high leg" or "b" phase conductor if that helps. It's an older building, all three conductors are black.

Can I use two of the conductors in a "line -to- line" connection to supply a 208v single phase load, and if so, how do I distribute the load evenly across the phases to keep the system balanced? I know I can't derive 120v single phase as there is no neutral.

cocktail frank? Pharma? you out there?

 

[PharmaCan]

Man, I'm just an old wire puller, this is a bit over my head. All the 3 phase I've ever worked on was PowCo power going into a 3 phase panel. Different voltages are then achieved by using the three hot legs in different combinations. Single phase power is one hot and one neutral, so for single phase 208 volt you'd need one wire with 208 volts coming out of it. (Take your meter, put one probe on a hot wire and the other probe on a ground, that'll tell you how much power is coming out of each individual wire. In your case it should be 104 volts.) Beyond correcting your terminology, which in reality was done just to make me look a little less like a dumbshit, here's the best I can offer.

Hey Frank - Need some help here!

What kind of appliance are you trying to power?

PC

 

[DIGITALHIPPY]

What kind of appliance are you trying to power?

PC

im hoping a grow-light... or bunches...

why not just tap your 'other box' for a neutral??? id wait for more replies im not a sparky.

 

[hoosierdaddy]

This may help:
http://www.3phasepower.org/1phaseloadson3phasepower.htm

 

[00420]

i used to rent a small warehouse it had 3 black lines and a ground/neutral bar (my guess was it was 3P).... i just hooked 220 up to it like it was any reg power box never had any probs there was 120 lines off of the box wired into the place allready so my thoughts where if there running 120 lines 240 should be fine and it was..... the box was just like a house box except it was a incoming line was every 3rd bar as to every other bar for the breakers....

now knowing what i do i should have done some research

 

[PharmaCan]

i used to rent a small warehouse it had 3 black lines and a ground/neutral bar (my guess was it was 3P).... i just hooked 220 up to it like it was any reg power box never had any probs there was 120 lines off of the box wired into the place allready so my thoughts where if there running 120 lines 240 should be fine and it was..... the box was just like a house box except it was a incoming line was every 3rd bar as to every other bar for the breakers....

now knowing what i do i should have done some research

Actually, that's what those kind of panels are designed for. It's the same kind of panel I was talking about. You need special breakers for 3 phase, but, aside from the fact that they're 3 breakers wide, they look and work like a residential panel.

PC

 

[cocktail frank]

high

you can run anything 220v off that service you want, but you are correct, no 120v.

only way to evenly distribute the load would to have 3 double pole breakers for even usage.
1 DP across a-b phase
1 DP across b-c phase
1 DP across a-c phase

but yeah, you could use this for 220v ballasts or anything that doesnt require a neutral
and dont do what DH said, dont take a neutral from a seperately derived system.
thats BAD

 

[bobs your uncle]

Thanks everybody, for the replies.

CF - What are the repercussions of not balancing the load across the phase conductors? Will I be getting a visit from the Utility Co. asking why their transformer is out of whack. And when sourcing a sub-panel for the three DP breakers, what should I be looking for ? Any recommendations? I'm trying to visualize the conducting blade arrangement inside said sub that would allow this to work. I can visualize three "blades" side by side for A-B and B-C but what about A-C? I'm sure it will be real obvious when I take a look at some panels.

About the 208v... At first I was thinking I would need to get a buck-boost transformer to bring that 208v up to a useable 240v, but when testing my main 120/240 1ø service, the 240v was actually about 208v. That just goes to show that there is a range or "window" of voltages that most appliances will run on. All my 240v woodworking tools have been working fine on the 208 or 210v that they have been getting for the past decade, so I think I'll pass on the buck-boost.

One last thing...

What's up with the all black conductors in older buildings? This isn't the first time I've come across this legacy mono color scheme in old properties. At least it's not the cloth insulated (again, all black) wire I find laying dormant in old raceways when doing remodeling. But still, what where they thinking? Did they pull one cable at a time and connect it immediately so as to not to get confused when the next two or three black wires come through the conduit and guessing which one is a neutral. No white tape, paint or other identifying markings, just three fat ass black cables.

 

[cocktail frank]

if you dont balance the load equally, youll just lower your efficiency, not a huge deal.
dont kno what kinda wattage your running, if the panel is close enough, you might just run a few 240v lines from the panel directly.
or maybe you got a timer setup off a dryer cord, i dunno.
all depends on variables.

the power company wont care as long as your a paying customer.
its only when u steal power or dont pay the bill will they pay attention to you.

 

[bobs your uncle]

Thanks Frank. Talked to another electrician about the unbalanced load and he said pretty much the same thing. Ideally, you want to try and spread the load over the 3 phases, but it's not dangerous if you don't, just not as efficient.

Thanks again for your input.

 

[00420]

Cf..... How do u get a neutral on a 3P set up so u can run 120v?
When I rented the warehouse there was 120 wired in the whole building hooked to the 3P box just like a house had a neutral/ground bar in it..... ...

I'm thinking like if one wanted to buy a 3P diesel gen n do a off grid grow one would not want to buy 240 fan's/pumps..... Or would u just run a 2nd gen that's 1P ??

 

[luciano28]

Cf..... How do u get a neutral on a 3P set up so u can run 120v?
When I rented the warehouse there was 120 wired in the whole building hooked to the 3P box just like a house had a neutral/ground bar in it..... ...

I'm thinking like if one wanted to buy a 3P diesel gen n do a off grid grow one would not want to buy 240 fan's/pumps..... Or would u just run a 2nd gen that's 1P ??

It was probably a Wye 4 wire connection 208/120v, there are a few different connections for 3 phase. UncleBob has a Delta 3 wire setup.

Heres a generator that would give you what you want 10kw

http://www.electricgeneratorsdirect...le&utm_source=froogle&utm_medium=shop+portals

 

[PharmaCan]

Cf..... How do u get a neutral on a 3P set up so u can run 120v?
When I rented the warehouse there was 120 wired in the whole building hooked to the 3P box just like a house had a neutral/ground bar in it..... ...

I'm thinking like if one wanted to buy a 3P diesel gen n do a off grid grow one would not want to buy 240 fan's/pumps..... Or would u just run a 2nd gen that's 1P ??

Three phase isn't some kind of special electricity, it's essentially just another hot leg that can be used in combination with the two other hot legs to achieve various voltages. Just because you have three phase doesn't necessarily preclude having a neutral. When buying a generator, you would buy one that has the correct voltage(s) for what you want to do. The hardware that makes the various voltages available is expensive, so it would be pointless to buy a genset with any more, or any less, than what you need.

PC

 

[cocktail frank]

it all depends on the trans setup that the power company provides.
if you have a straight delta like bob, then u have no neutral, just 3 hotlegs, strictly for 3phase motor loads.

if the service in the warehouse you mentioned only had 3 wires entering thru the service, you have no neutral for 120v coming in.
unless it was stepped down via transformer, it wasnt right.

 

[luciano28]

There could of been a converter, a dry off the shelf transformer, or even an induction motor too somewhere in that warehouse to be getting their 120v. Lots of ways to skin a cat with 3 phase to get what you want out of it.

 

[00420]

Heres a generator that would give you what you want 10kw

http://www.electricgeneratorsdirect...le&utm_source=froogle&utm_medium=shop+portals

I was thinking more like 75-100 kw but I get your point thx


Thx pc i knew it was not special other then the 3rd line n was kinda confused on the 3/4 wire deal we had 4 wire 3 hots n a neutral... I did not no there was more then 1 3P I never really researched it but alleays wanted to do a 50+ light setup 3p would be the only way n that much should be off grid IMO

Thx cf.... It was a pro set up multi warehouses in a row all the meters where in the same spot at the end of row n all the buildings had 120 for office's I was just confused on the 3/4 wire delta wye thing .....

 

[pro engineer]

bobs

It sound like you have a 3 wire Delta 3 phase 208 volt system. This system does not have neutral. It's not used much any more due to the fact it has no neutral. The voltage should be 208 between any two wires. The metal conduit is the system ground, to test put one probe of your meter on one of any legs and the other to the metal conduit. You should have about 120 volts if not your system may be ungrounded and may not be safe to used. A fix is to pull a new neutral and ground wire.
The Delta is a 3-wire system which is primarily used to provide power for three phase motor loads. The system is normally ungrounded and has only 1 (one) three-phase voltage available. The lack of a system ground makes it difficult to protect from ground faults. Often, a ground detection scheme, employing ground lamps, is used to provide an indication or alarm in the event of a system ground. The delta system is sometimes corner grounded to protect from ground faults on the other 2 (two) phases.

PE

 

[pro engineer]

bobs

A few other things.
Your Delta system should not have a high leg.
There is No safe way to get 120 volts from this system.
Yes some 230 volt 3 phase motors will run on 208 volts 3 phase.
A slightly unbalance will not hurt anything.
Also some but not all lighting ballast can be wired to run on 208 volts.

PE

 

[luciano28]

I was thinking more like 75-100 kw but I get your point thx


Thx pc i knew it was not special other then the 3rd line n was kinda confused on the 3/4 wire deal we had 4 wire 3 hots n a neutral... I did not no there was more then 1 3P I never really researched it but alleays wanted to do a 50+ light setup 3p would be the only way n that much should be off grid IMO

Thx cf.... It was a pro set up multi warehouses in a row all the meters where in the same spot at the end of row n all the buildings had 120 for office's I was just confused on the 3/4 wire delta wye thing .....

Whoa! Big Ballin!


I seen a big ole John Deere for around $35k when I was looking earlier.

I bet that setup was a Delta-Wye connection, the secondary wiring(off the Xfmer) being the Wye 4 wire. These are real common in commercial buildings I believe, when I first was out of school I worked for a contractor who did a few of a local chain of bakeries, they had a 208Y/120 with 208v to run their mixers and whatnot and 120 for routine appliances or whatever.