3 Phase problem

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dandrews1281

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Customer runs a wood working shop and wants 3 phase in the building to run only 4 of his machines. At the moment he is using a motorized rectifier to solve this problem. He would like to avoid tearing out existing 200amp single phase panel. The only way i have been able to figure a way to achieve this is A) change the service over to 3phase, install a new 3phase panel and run existing panel as a sub-panel off the new three phase panel. Space is an issue so the new 3phase panel would have to be a 24 slot. Or B) apply for a special circumstance and try to have separate 3phase service brought in, in addition to the existing single phase service. There is always option C) where i replace the old panel with a 3phase panel and bring the new service to it but i told him i would try to explore all options. Possible? Am i missing an option? appreciate the input
 
Depends a lot on POCO and how the existing and new metering might be handled.
I'd leave the existing panel and add a 3 phase panel for the new equipment. POCO can change their service drop (lateral) to 3 phase so you can pick up the old service conductors to the old panel and add your new.
If they change it to a 3 phase service its still one service. You will simply be feeding one single phase panel (existing) and one 3 phase panel (new) from the new meter (or service point if CT'ed)
 
Why not continue using the existing phase converter? Even if it's on its last legs, istm to be a less expensive and faster option/installation than new panels and a 3ph service.
 
dandrews1281 said:
Customer runs a wood working shop and wants 3 phase in the building to run only 4 of his machines. At the moment he is using a motorized rectifier to solve this problem. He would like to avoid tearing out existing 200amp single phase panel. The only way i have been able to figure a way to achieve this is A) change the service over to 3phase, install a new 3phase panel and run existing panel as a sub-panel off the new three phase panel. Space is an issue so the new 3phase panel would have to be a 24 slot. Or B) apply for a special circumstance and try to have separate 3phase service brought in, in addition to the existing single phase service. There is always option C) where i replace the old panel with a 3phase panel and bring the new service to it but i told him i would try to explore all options. Possible? Am i missing an option? appreciate the input
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I would go with A or C out of these options.

Another option is to get single phase motors or VFDs for the three phase equipment and not change the service. I would go with single phase motors if these choices are in play.
 
Like Dave I would opt for A or C. If it were my sole decision I would go with C. Will you be using 240 or 208 volts?
 
All the machines have single phase/ three phase options but they run noticeably better on 3 phase. I believe they are all 240. The phase generator is in good condition and still works but only services 3 machines out of the 4 he needs, and limits him from eventually upgrading machines to 3 phase down the road.
 
dandrews1281 said:
All the machines have single phase/ three phase options but they run noticeably better on 3 phase. I believe they are all 240.
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I am curious about this. You can switch them on the fly from single to three phase?
The phase generator is in good condition and still works but only services 3 machines out of the 4 he needs, and limits him from eventually upgrading machines to 3 phase down the road.
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Well it's not gonna cost less to move to a three phase service a year from now.
 
dandrews1281 said:
Customer runs a wood working shop and wants 3 phase in the building to run only 4 of his machines. At the moment he is using a motorized rectifier to solve this problem. He would like to avoid tearing out existing 200amp single phase panel. The only way i have been able to figure a way to achieve this is A) change the service over to 3phase, install a new 3phase panel and run existing panel as a sub-panel off the new three phase panel. Space is an issue so the new 3phase panel would have to be a 24 slot. Or B) apply for a special circumstance and try to have separate 3phase service brought in, in addition to the existing single phase service. There is always option C) where i replace the old panel with a 3phase panel and bring the new service to it but i told him i would try to explore all options. Possible? Am i missing an option? appreciate the input
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Rotary phase converter? A rectifier turns AC into DC.
 
Make sure he understands the full ramifications of getting a 3 phase service. With that, many, if not most, utilities will also add a Demand Meter, something he is totally unaware even exists if he has only seen residential services. He could be in for a rude awakening when he sees his first bill. That happens to home shop owners a lot, and the utilities are often slightly cagey about informing them ahead of time. The demand on their system is the same whether it is 3 phase or single phase, but regulatory rules don't allow them to bill residential customers for demand charges. So they actually like it when a residential customer switches to 3 phase, because they classify that as commercial. Also, the cost to do it is often very high if the utility doesn't have a nearby 3 phase transformer. They then make the HO pay by the foot to wire to the nearest one.

That's why rotary phase converters are so popular...

And by the way, as mentioned, for small machinery up to and including 3 HP,there are a lot of very inexpensive VFD options available that will accept a single phase input and give you a 3 phase output for the motor. You can do it higher than 3HP too, but it starts to cost a lot more.
 
Three phase service will likely have to be on a commercial rate, demand charges depends on the POCO. Some maybe don't have demand charges until you get over 50, 75, maybe 100 kVA supply whether single or three phase, others may have a demand charge on all commercial services. Some might even have demand charges for residential customers.
 
I also vote for VFD for each motor. Gives protection and soft starting, if allowed for the task.

The rotary phase converter just needs to be sized to start the largest motor that can run alone. You can add as many motors after that you like to run, until you exceed the service to the panel. Each motor ads to the rotating mass to start larger motors!

Of course you can exceed panel capacity and each motor still needs independent protection (starter/etc), follow NEC, etc.

I was told years ago 25 HP single phase motors were manufactured in the beginning. I can not imagine the conductor size if that was on 240! This was told to me in the 70s when I saw a 10 HP single phase motor get rebuilt.
 
Frank DuVal said:
I also vote for VFD for each motor. Gives protection and soft starting, if allowed for the task.

The rotary phase converter just needs to be sized to start the largest motor that can run alone. You can add as many motors after that you like to run, until you exceed the service to the panel. Each motor ads to the rotating mass to start larger motors!

Of course you can exceed panel capacity and each motor still needs independent protection (starter/etc), follow NEC, etc.

I was told years ago 25 HP single phase motors were manufactured in the beginning. I can not imagine the conductor size if that was on 240! This was told to me in the 70s when I saw a 10 HP single phase motor get rebuilt.
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Depending on power factor and efficiency you are looking at somewhere around a 100 to maybe 125 amp FLA.

I'm sure they could build large single phase motors there just isn't the demand for them so they are not standard stock items.

15 HP has been common for crop dryer motors for years, but they are "air over" rated motors and look to be mostly a 10 HP built motor that needs extra air flow to keep it cooled if loaded to 15 HP.

Baldor does have a 16 HP general purpose single phase motor and I have seen an occasional 15 HP by others - again mostly on crop drying applications but those were not air over motors and would work for other applications.
 
Installing a 3 phase service is only an affordable option if the customer is not far down a single phase (one phase and neutral) tap. If it's mostly a residential area, it may not have 3 phase primary. To run a 3 phase tap from the nearest 3 phase primary would be HUGELY expensive.
 
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