Only 2 legs for 3 phase service...

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AltonToth

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Vancouverish, BC, Canada
Got an interesting question. I'm an electrician who owns a retail store in a shopping mall, and I had ASSUMED that each of our units was fed with a 240V 3W service based on the panel in our unit, the label, and the fact that it's only a 2 pole main breaker. However, in measuring between lines recently, I'm getting 208V, so I'm assuming that they have a three phase distribution for the mall...

My neighbour is having a ice cream cooler installed, and the compressor in this cooler has a 3 phase motor in it. Given that he's in the same situation as me supply wise, what would be the preferred method of running this? A new compressor isn't financially viable in this case. I'm thinking an inexpensive VFD might be the way to go...? :-/ that of some capacity setup to create the third leg?

It's weird, I know. I'm sure it made sense once upon a time. Given that we're retail shops I suppose we don't REALLY need 3 phases in 99% of cases.
 
If he can get the third phase pulled in economically, that would be the way to go, but that is unlikely.
If he is committed to the three phase motor, then a VFD (or equivalent phase generator without the frequency control) would seem to be the way to go.
 
Unfortunately our units are all fed with NMD (I've worked for contractors in malls where feeds were intelligently run through conduit) and the electrical room is a decent distance away. Even pulling in a new supply would result in having to change the panel out for a 4W panel. :-/

To change out the compressor on the freezer would be about $1500-2000. At least based on what the now one-year old compressor in the unit cost the last owner.

5HP VFDs are fairly reasonable in price, and I have some experience with using them as phase converters for my father in laws woodshop as well as his neighbours car hoist. I know they're kind of overkill just for phase conversion, but it's nice to set them up with start-up ramping and overload protection.
 
The VFD idea is only viable if you can get into the controls and replace a starter with the VFD. You can't just use the VFD as a phase converter for something that will switch on and off on its own, it will damage the VFD.

A variation though it a device called a Phase Perfect that uses VFD-like technology for adding only the missing phase. They can be used like that, although you need to ensure that your controls are coming from the real phases.
 
AltonToth said:
Unfortunately our units are all fed with NMD (I've worked for contractors in malls where feeds were intelligently run through conduit) and the electrical room is a decent distance away. Even pulling in a new supply would result in having to change the panel out for a 4W panel. :-/
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Not sure how long a "decent distance" is and not sure how many amps are required, but I was wondering why you couldn't just add a run from electrical room to a small 3 phase panel in the unit such as this one:

https://www.platt.com/platt-electri...ug/Eaton/3BR1224L125/product.aspx?zpid=269801

No need to rip out the existing panel. If it's 500 feet or less shouldn't be that expensive.
 
ptonsparky said:
I believe that is what a local POCO has done for a semi remote farm customer, although that ended up being a corner ground 480.

Do you have a drawing for that connection?
Click to expand...
I believe this will work...
open wye to open delta.jpg

Check output voltage across open legs. If north of 240V, reverse the connections of one transformer, primary or secondary.
 
Smart $ said:
I believe this will work...
View attachment 17782

Check output voltage across open legs. If north of 240V, reverse the connections of one transformer, primary or secondary.
Click to expand...

Thanks.

Looks like we end up with ground fault detection or a corner ground.

I suspect the VFD is still the easier/cheaper way to go given the OP knows how the control needs to change.
 
cowboyjwc said:
We're talking about pulling another wire, but has anyone even checked to see if the main is three phase?
Click to expand...

AltonToth said:
... However, in measuring between lines recently, I'm getting 208V, so I'm assuming that they have a three phase distribution for the mall...
Click to expand...
With 208 L-L and (presuming) 120V L-N, it pretty much has to have 3 phase somewhere on the property, so I think it's a safe bet that the mall service is 3 phase and they sub out single phase 208/120V to the tenants.

But if the mall owner only has a single phase meter bank for the different tenants, you will not be able to just run another wire out to your neighbor.

For a one-off machine like that, I would tell him to just go buy a Phase Perfect unit and pay you to hook it up for him. It's not exactly cheap, but nothing will be.
http://www.phaseperfect.com/p/t/overview
 
The main is three phase. We have a brand spanking new 600-208 transformer installed in the brand new electrical room (they had to move it for a new tenant).

The entire compressor and controls set for the freezer is mounted separately from the freezer, and currently it appears that that cooling compressor runs continuously as the cable to feed everything runs straight through a schneider electric overload block and straight to the compressor. Other things, like the radiator fan and defrosting heater are tapped off of the overloads. Of course I may just be misinterpreting the wiring in place currently, but I see no manual on/off on it (its been a couple years since Ive worked electrical regularly and I've had very limited motor controls experience.

For now he's reached out to a local refrigeration company. They may be willing to give him a good deal on swapping out that compressor to a capacitor start/run one so we can feed it single phase, or at least off 208V two wire, especially since the current compressor is only a year old or so old.

I didn't think about hooking up a couple transformers. Given that I need a 20A supply or so I'll have to investigate the cost of that as an option.
 
Jraef said:
The VFD idea is only viable if you can get into the controls and replace a starter with the VFD. You can't just use the VFD as a phase converter for something that will switch on and off on its own, it will damage the VFD.
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Exactly, chances are there is more then just a single motor in the machine for loads. It may not damage most modern drives when switching on a load, but will trip on protection features when you try to add another load to an already running drive.

ptonsparky said:
I believe that is what a local POCO has done for a semi remote farm customer, although that ended up being a corner ground 480.

Do you have a drawing for that connection?
Click to expand...
That is exactly what they do for nearly all open delta services

ptonsparky said:
Thanks.

Looks like we end up with ground fault detection or a corner ground.

I suspect the VFD is still the easier/cheaper way to go given the OP knows how the control needs to change.
Click to expand...
Use a transformer with a center tap on one of the secondary sides (or leave one center tap "floating" if they both have a center tap). You will have a high leg on the secondary system.



Seems to me the best thing to do is sell the three phase machine and buy a single phase machine.

If owner thought they got a steal on their purchase it is because they didn't know what they were buying and what it may cost to get it to run for their application. Restaurant and food service machines that are three phase often do sell cheap compared to new machines. It is those that are first starting a business that don't know any better and just see dollar signs when they go to purchase a machine, then if they don't have the right system to power it find out it cost more then they paid for the machine just to be able to make it run.
 
Jraef said:
With 208 L-L and (presuming) 120V L-N, it pretty much has to have 3 phase somewhere on the property, so I think it's a safe bet that the mall service is 3 phase and they sub out single phase 208/120V to the tenants.

But if the mall owner only has a single phase meter bank for the different tenants, you will not be able to just run another wire out to your neighbor.
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So, if you have A and B phase and he has C and A phase couldn't you let him use your B phase? :blink:

Tongue planted firmly in cheek........ ;)
 
Thanks guys. Ultimately the unit belongs to the supplier, so it hasn't cost my neighbour anything yet. All the compressors, cooling fans, etc are externally mounted, and everything is two wire, EXCEPT the compressor itself, so rewiring a couple controls to be upstream of the VFD should be no problem. I should even be able to tie in these controls to fire the VFD up automatically rather that start it as a phase converter and walk away and hope it doesn't trip with a thousand bucks worth of gelato in it.

This was basically confirmation of what I thought / figured, I was just wondering if there was a different approach I should consider.
 
AltonToth said:
Thanks guys. Ultimately the unit belongs to the supplier, so it hasn't cost my neighbour anything yet.
Click to expand...

I don't understand. If the freezer belongs to the supplier (as is often the case where a store agrees to sell their product- the supplier provides a cooler/freezer/merchandiser as long as the store only uses it for their product. See Coke, Pepsi, Snapple, Dolly Madison etc.) Why are you or the store owner worrying about this? Just tell the supplier to provide the correct freezer, it's not like it's yours or anything. Sounds like they screwed up to me.

-Hal
 
hbiss said:
I don't understand. If the freezer belongs to the supplier (as is often the case where a store agrees to sell their product- the supplier provides a cooler/freezer/merchandiser as long as the store only uses it for their product. See Coke, Pepsi, Snapple, Dolly Madison etc.) Why are you or the store owner worrying about this? Just tell the supplier to provide the correct freezer, it's not like it's yours or anything. Sounds like they screwed up to me.

-Hal
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I agree. it is the supplier's problem to fix this.
 
hbiss said:
I don't understand. If the freezer belongs to the supplier (as is often the case where a store agrees to sell their product- the supplier provides a cooler/freezer/merchandiser as long as the store only uses it for their product. See Coke, Pepsi, Snapple, Dolly Madison etc.) Why are you or the store owner worrying about this? Just tell the supplier to provide the correct freezer, it's not like it's yours or anything. Sounds like they screwed up to me.

-Hal
Click to expand...
Count me in on asking the vendor to supply a machine that will operate on single phase.
 
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