208vac single phase?

[biggerrigger]

Hopefully someone can answer a question for me. The wife bought a piece of equipment that is wired for 3 phase 208vac but it states on the unit that it can be wired for single phase 208vac. The question at hand is can this unit be used in my home with a 220-240vac standard American single phase circuit with the addition of a step down transformer? Am I on the right track thinking that this will work with the addition of another piece of hardware? Possibly a converter of sorts? That is of coarse after I wire it for single phase operation.
Any help would be greatly accepted.

[Bill Fitzmaurice]

I doubt you need a transformer. Voltage ratings are nominal, because there's a lot of variation in the actual voltage supplied.

[LelandCrooks]

Usually under a panel somewhere will be a circuit diagram showing you how to rewire internally. If if states it will run on single phase, you don't need a transformer. And they're damn expensive.

[biggerrigger]

Thanks fella's for the info. It does have a sticker on the back stating that it is currently wired for 3-phase and right under that it has another sticker stating that it can wired for either single or three phase power. I will pull the panel today and take a pic of the info contained within before I rewire for single and before I plug it in

[Israel]

a 3 phase circuit is a more efficient use of electrical power yet it would require a 1 to 3 phase converter which will cost more or less depending on its power rating (google 3 phase converters) or ask for 3 phase direct from the grid if available, none of these will be my choice, but better to pav the road for you the equipment manufacturer let single phase wiring available thats a good thing ill go on that. About voltage all 3 phase circuits diminish the voltage when phasing (173% of 120v or 86.5% of 240v as you wish) if the equipment can be used on single phase it can handle the full 240v from line to line (+ to +) so dont worry on voltage put your mind on wiring it correctly. eye on the diagram and good luck and skill pal

[DaveK]

What kind of equipment is it? It's been about 30 years since my days of working with 3-phase power, but IIRC transformers and rotating motors are designed for a certain phase relationship between the hot legs. The 3 legs of a 3-phase feed are 120 degress out of phase. 2 phase is 180 degrees. Normally, you wouldn't mix those, but some motors, and especially transfomers, have separate lugs for 3 phase and 2 phase feeds.

BTW, 208V is the difference between each leg of a 3 phase circuit. All of them are 120V relative to neutral. In "single phase" mode does the equipment expect 240V or 120V?

[biggerrigger]

http://www.garland-group.com/docs/uploa ... 517069.pdf
This is the same exact wiring diagram that I found inside of the unit. If I am reading this right all I need to do to switch to single phase is rewire K5 as seen in the diagram. Or am I looking at this wrong?
I need to get a dryer style plug to replace the one that is on there now. I also need to run a new line back to the breaker box to feed the unit as we run on gas now and this will be an add on appliance.

[biggerrigger]

DaveK if you would be so kind could you have a look at the diagram and see if Im on the right track in rewiring K5? As I see it this is all that needs to be changed to operate in single phase mode.

[DaveK]

First the big caveat. I'm not an electrical engineer and this is not a prefessional opinion. High voltage kills and I advise you to get a qualified person to rewire your device. If you wire things wrong, burn down your house, and cause a blackout in the greater tri-state area, don't say I didn't warn you.

As a strictly academic exercise, here's what I see in the schematic you referenced.

It appears that the motor (MTR) is fed from PCB 2, which in turn appears to be fed from TR1, which is a step-down transformer from line voltage to control voltrage (24 V). You still have not said what this equipment is, but since it has an oven light, it might be some sort of oven. Thus, the motor is probably not a high horsepower one that needs 3 phase to run efficiently. Perhpas it is for turning a rotisserie or something like that. I'm guessing the motor runs on 24V, not 3 phase line voltage. Thus, no worries about changing voltage for it.

Turning attention to transformer TR1, the schematic shows 3 different input taps - 240V, 208V, and 120V. The schematic shows it wired for 208V, but if the input voltage was different it would need to be connected to a different tap to maintain the correct 24V output.

Turning to relay K5, it appears to turn on and off the heater elements. Since this is presumably some sort of oven, these are the high power elements. Relay K5 is fed from terminal block TB1, where lugs L1, L2, and L3 are connected to the 3 legs of a 208V feed. All 3 are turned on and off simultaneously by relay K5. The other end of each heater is connected to the next phase in sequence so that each heater has a 208V drop across it.

The 1PHASE inset for relay K5 appears to show an alternate schematic for 240V single phase power. The input to all 3 heaters is connected to leg 1 and the output of all 3 heaters is connected to leg 3. Thus, it appears that the designer intended for a 240V single phase feed to be connected to lugs L1 and L3 of TB1, with lug L2 unused. Note that this means the heater elements now have a 240V drop so they run a little hotter. As long as the appliance was designed with that in mind, the difference is probably within tolerences.

However, there are some puzzling things about that PHASE1 inset that I can't figure out from the schematic. First, it shows the returns from the heaters connected to the relay instead of back to TB1 like in the main schematic. I suspect it would still work either way, but it troubles me that there is a difference.

Second, the numbering of the heater returns in the main schematic is 40, 41, and 42. However, the numbering in the 1PHASE inset is 41, 42, and 43. I can't find a 43 anywhere in the schematic. My guess is that the main drawing was revised at some point, but the 1PHASE inset was overlooked. Again, somewhat troubling.

[biggerrigger]

Thats what was puzzling me as well. The item is a Garland Moisture+ Convection Oven(Tim Hortons Edition). My biggest issue thus far is the motor wiring. I cannot tell for sure from the schematic but it looks like it would be the only item that is not able to be rewired to run on the single phase circuit. Everything else looks like it would be easy to change over. I just double checked the motor and it seems as it is somewhat universal. And already wired for single phase.
voltage 200-230vac
After looking at the schematic again it appears to me that the motor is only ran in a single phase mode no matter what the main wiring scheme is.
And looking even closer it seems to me that only TR1 and K5 need to be changed for proper operation. It seems like the entire oven is wired single phase with the exception of K5. TR1 would need to be changed due to proper voltage but it too is fed single phase.

This is looking better every time I look at it.

[byacey]

TR1 would have to be re-tapped to the proper voltage - 240V, and the heating elements rewired to K5. Each end of the elements go to K5, as the contacts open both legs ensuring total isolation from the line when the relay is open; in a 3 phase scheme you would need more relay contacts to accomplish the same thing. This is why the element returns get connected back directly to the line if 3 phase is being used.

[Harley]

Dave's right. I'd be getting a registered electrician to getting that working if that were me.

[biggerrigger]

Com'mon Harley where is your sense of adventure

I will definitely have this looked over before it is put into service. But on the same note I want to learn how it is laid out and functions on an electrical scale. 120-240 I have no problems with, I wired my entire house from the meter to the outlets by myself and had it singed off on by the inspector. I actually got props from the inspector on the neatness of my work in the walls and the layout of the panel. I am quite familiar with AC power until it comes to 3 Phase.

[biggerrigger]

TR1 would have to be re-tapped to the proper voltage - 240V, and the heating elements rewired to K5. Each end of the elements go to K5, as the contacts open both legs ensuring total isolation from the line when the relay is open; in a 3 phase scheme you would need more relay contacts to accomplish the same thing. This is why the element returns get connected back directly to the line if 3 phase is being used.

That is what I was seeing as well. I just wanted to have someone else look at it and confirm what I was thinking. So at this point It can be safe to say that this unit is capable of being used on a 240 single phase circuit and I can continue on with the install of the main wiring and plugs,ect. and get this install on its way. Before it is energized I will have it looked over for proper setup.

I am trying to save myself some money here. If the electrician has to look it over for 10 min it cost me $25, If he has to get his screw driver out and move 3 wires it cost me $150

[DaveK]

Another consideration is whether the oven is designed to be field convertable to single phase. The schematic shows the alternate wiring of K1 for single phase, but that may be for use in manufacturing a different model that ships from the factory that way. The wires from the relay to the heater elements may be soldered or crimped in a way that makes them hard to change in the field. Also, the relay may be hard to access. You might want to check these before installing a circuit. In fact, if it was me I would want to have the conversion made and then test it on a temporary circuit before investing in a permanent circuit.

Although the schematic shows the heater elements wired back to K5, your electrician might decide that an easier field modification is to leave K5 alone and just move the wires at the terminal block. He or she may decide that all they need to do is take the 3 wires running from the terminal block to K5 and put all 3 in lug 1. Then take the 3 wires returning from the heater elements and put all 3 in lug 3. This would be especially easy if the terminal block has screw fasteners.