3 Phase Service Question

[Doubled33]

I am planning for a small shop and the utility company has 3 offerings for power that are within a few hundred dollars of each other.

The space is about 6k SF.

Nameplates for most loads 2 hp motors etc… show they work on single phase 208-230v.

Will have lights, battery, smaller welder, metal lathe, drill press, etc.

There will be two 10 hp motors.

Will also have AC.

Nothing runs continuously except stuff like lights and the AC.

The options are
3PH delta 120/240 4 wire
3PH wye 120/208 4 wire
3PH wye 277/480 4 wire.

 

[sparky 1971]

Get 120/208. The Delta will eliminate 1/3 of the breaker spaces available for 120 unless a single phase subpanel is installed using A and C phases while leaving B phase at the main panel. 277/480 is great, but unless you have a need for 480, it's not going to do you any good and the price of the transformer to get you down to 120/208 won't be cheap.

 

[mike93lx]

480v is pro-level ****. I'd stay away from that

 

[Norcal]

480v is pro-level ****. I'd stay away from that

It also means more expensive breakers, disconnects, & so on, plus buying transformer(s), & paying for their losses, 208Y/120V is the best choice.

 

[theoldwizard1]

Get 120/208. The Delta will eliminate 1/3 of the breaker spaces available for 120 unless a single phase subpanel is installed using A and C phases while leaving B phase at the main panel. 277/480 is great, but unless you have a need for 480, it's not going to do you any good and the price of the transformer to get you down to 120/208 won't be cheap.

Also simplest to understand for non-professionals !

There will be two 10 hp motors.

Those are big boys ! What does the label say about current ?

 

[Dagny]

1 or two unless there are some bigger motors in you future.

 

[sparky 1971]

Those are big boys ! What does the label say about current ?

While its not the nameplate, the SQD cheat sheet says a 10HP motor has a 32 amp running load at 208 three phase o it really isn't that big of a deal. I have a customer running two 10HP compressors, A 20HP vacuum, and in the winter, A 10,000 watt heater off of a 200 amp feeder. It's impossible for the compressors to start at the same time and since the vac is fired up first thing in the morning and runs all day, it's next to impossible for it to start at the same time as a compressor.

 

[micromind]

A 10HP motor is a fairly small load for a 200 amp 120/208 service.

As noted above, even though I personally like the 120/240 ∆ system, if I were you, I'd go with the 120/208 system. Far less chance of blowing something up if you're not careful and/or don't understand the ∆ system.

I've never had problems with motors on a 208 system.

 

[wyliesdiesels]

208Y/120 by a long shot

240D/120 is only useful if you have to have 240 3p and 480Y/277v will just waste your money as said above.

 

[tool_scrounge]

Have you checked the monthly charges for 3 phase? Not a problem if you small shop is for a business. But it may be a bit high compared to single phase for home use.

On Oahu, Hawaii, the minimum monthly charge for three-phase power is $98.20, according to the Hawaiian Electric Schedule TOU-J.This is in addition to other charges like a demand charge based on kilowatt usage. Additionally, residential customers have a minimum bill of $25.

Here's a breakdown of the key charges:

• Customer Charge (for three-phase service): $98.20 per month.
  
  
• Demand Charge: $13.00 per kW of billing demand, which is added to the customer charge.
  
  
• Minimum Bill: Hawaiian Electric specifies a minimum bill for residential customers, which may vary.

 

[mm08822]

Not certain 10 hp motor is 3 phase. It could be single phase with fla's @ 43a @208v.

Do they both start simultaneously or randomly or even interlocked?

Hopefully they are 3 phase.

Service size is one thing. What is upstream of that is another.

POCO needs to be aware of these 2 motors as well as total load.

 

[Doubled33]

Also simplest to understand for non-professionals !


Those are big boys ! What does the label say about current ?

I don't have these motors yet, but will be a baldor or similar 1750 rpm motor. They will run my Quincy 370's (which I do have).

 

[Doubled33]

Have you checked the monthly charges for 3 phase? Not a problem if you small shop is for a business. But it may be a bit high compared to single phase for home use.

On Oahu, Hawaii, the minimum monthly charge for three-phase power is $98.20, according to the Hawaiian Electric Schedule TOU-J.This is in addition to other charges like a demand charge based on kilowatt usage. Additionally, residential customers have a minimum bill of $25.

Here's a breakdown of the key charges:

• Customer Charge (for three-phase service): $98.20 per month.
  
  
• Demand Charge: $13.00 per kW of billing demand, which is added to the customer charge.
  
  
• Minimum Bill: Hawaiian Electric specifies a minimum bill for residential customers, which may vary.

I am in HI, but this will be built on the mainland.

Our power here is a little over 50 cents a KwH which is ridiculous. But everything here cost way more than it should. For example I purchased solar and 2 Tesla batteries for my house here. My electric bill went from almost 400 bucks to minimum fees of 30 bucks with that being off set by selling back power to HECO. My solar was 42K all in for a 7kw system. State and federal rebates got me down to 20K out of pocket. The math makes sense here. It never made sense on my house in SoCal (Pasadena) which I still own.

 

[Doubled33]

Not certain 10 hp motor is 3 phase. It could be single phase with fla's @ 43a @208v.

Do they both start simultaneously or randomly or even interlocked?

Hopefully they are 3 phase.

Service size is one thing. What is upstream of that is another.

POCO needs to be aware of these 2 motors as well as total load.

They will be 3 phase. Looking at what I want to purchase they show to work on a 230 to 460v but the current at voltage shows 208, 230 and 460. 27, 25, and 12.5 respectively.

They will not start at the same time.

 

[mm08822]

How have you determined them to be 10 hp?

 

[Doubled33]

How have you determined them to be 10 hp?

Looking at buying two of these.

 

[mm08822]

That's the motor cut sheet, but how do you know that you need 10 hp vs 7.5 hp, etc.?

 

[Doubled33]

That's the motor cut sheet, but how do you know that you need 10 hp vs 7.5 hp, etc.?

Quincy's data for the 370 shows around 40 cfm with 10HP. They show the pump to be driven by a 7.5 to 15HP motor.
What I did not mention above is that I have a glass bead cabinet as well.

 

[DaChev]

I wouldn't go 208. A lot of equipment that is rated for 208 or 230 is given that nameplate, but runs like trash at 208. It very well might overheat or the Ip will cut out the power. If the voltage sags on the island it might not run at all, see rural NY. If you do go 208 make sure the equipment was designed for 208, not was designed for 230 and also runs on 208.

I test 3 phase equipment for a living.

 

[wyliesdiesels]

Define runs like trash

 

[KenC]

All I can say is that I'm very happy with me 120/240delta. Shop was built in the 60s with a 240v single phase service, but with a separate breaker box and entrance panel. The entrance panel had the main breaker and the 240 breakers, the additional box had all the 120v breakers. Don't know why it was done that way, but it was.

The original main breaker failed open. I had a stack of Square D 3 phase stuff I bought at an auction. Used it to replace the entrance panel. I wanted a 3ph compressor and table saw and took the opportunity to upgrade the service. City did the service build at no cost!! The electric foreman was a woodworker and just did it for me.

Just be sure to label the high leg, land it in the right place, and put blanks in the appropriate slots of the panel. Even knowing better I managed to fry a DSL modem as I wired its recept with the cover off and tried it out before replacing the cover. Oops'!

I've had 208 in other buildings, and it may be my imagination but motors seem to start faster/easier under load on 240.

 

[Dagny]

any larger motors in the future?

 

[Dagny]

might not be worth the extra expense for two motors but 3 phase motors have less problems.

 

[mm08822]

I wouldn't go 208. A lot of equipment that is rated for 208 or 230 is given that nameplate, but runs like trash at 208. It very well might overheat or the Ip will cut out the power. If the voltage sags on the island it might not run at all, see rural NY. If you do go 208 make sure the equipment was designed for 208, not was designed for 230 and also runs on 208.

I test 3 phase equipment for a living.

I've seen 208-230V motors fail early when the 208Y service continuously sagged in the summer due to ac loads. After that person lost the second motor, he asked me what could be done.

I installed a buck-boost xformer on the wall with a voltmeter on the supply side of the xformer. The transformer plugged into the existing building recept. The output side had 3 recepts - +0%, +5%, +10%. Every morning when he went to start up, he would check the incoming voltage and if needed, move the motor plug to the required recept so the motor saw 208-230v. Hasn't lost a vacuum motor in 8 years or so. He runs them 8-12 hrs/day.

So the real question is, will the OP's service voltage sag throughout the year.

 

[Doubled33]

any larger motors in the future?

No two 10hp are the largest.

 

[Doubled33]

I've seen 208-230V motors fail early when the 208Y service continuously sagged in the summer due to ac loads. After that person lost the second motor, he asked me what could be done.

I installed a buck-boost xformer on the wall with a voltmeter on the supply side of the xformer. The transformer plugged into the existing building recept. The output side had 3 recepts - +0%, +5%, +10%. Every morning when he went to start up, he would check the incoming voltage and if needed, move the motor plug to the required recept so the motor saw 208-230v. Hasn't lost a vacuum motor in 8 years or so. He runs them 8-12 hrs/day.

So the real question is, will the OP's service voltage sag throughout the year.

Interesting comment on this.

Not to get into a debate but in reading I see that the general consensus is that 208 is within 10 percent of 230 so all is good. I have no opinion on this but…

I suspect this is why the nameplate usually has a range of voltage and amps shown for those that connect to a 208 service in lieu of a 230 service with an anticipated voltage drop. Basically I am saying by showing 208 on the nameplate the manufacturer is not advertising it works with a 230v service that is stressed down to 208.

But if your 208 has voltage drop you would be out of spec for the motor… or would you.

So if a motor nameplate has 208/230 on it would it still work with a 10% drop from 208 and have longevity?

I guess I am getting into the theory of how the motor was designed.

 

[gregs]

We did the Delta 120/240 when we built our commercial shop. Have had 0 issues running equipment. Yes you do loose every third slot in the panel, but it was never a problem and we put a big enough panel in to have plenty of room for the future. Since we are one of the few places out here with 3ph, we have had a couple of issues with losing the 3rd leg from the POCO. Unfortunately we do not have any type of monitor or safety shut down when this happens.

 

[Snapped-off]

I've seen 208-230V motors fail early when the 208Y service continuously sagged in the summer due to ac loads. After that person lost the second motor, he asked me what could be done.

I installed a buck-boost xformer on the wall with a voltmeter on the supply side of the xformer. The transformer plugged into the existing building recept. The output side had 3 recepts - +0%, +5%, +10%. Every morning when he went to start up, he would check the incoming voltage and if needed, move the motor plug to the required recept so the motor saw 208-230v. Hasn't lost a vacuum motor in 8 years or so. He runs them 8-12 hrs/day.

So the real question is, will the OP's service voltage sag throughout the year.

Got to see this with two sump pumps. Probably 20' of head. They would run on 208, but just wouldn't pump. After installing a buck-boost transformer to get 240, they pump great.

 

[fitter30]

480 will need a transformer for 240 & 120. 3 ph panel and 120/240 panel. To bad they don't offer either 208 or 240/ 3 ph

 

[wyliesdiesels]

Shop was built in the 60s with a 240v single phase service, but with a separate breaker box and entrance panel. The entrance panel had the main breaker and the 240 breakers, the additional box had all the 120v breakers. Don't know why it was done that way, but it was.

most likely to prevent burning up 120v equipment which can happen when someone connects it to the stinger/hi leg.

having a separate panel for 120v loads prevents the hi-stinger leg from ever being part of the equation...

 

[manwithtools]

The options are
3PH delta 120/240 4 wire
3PH wye 120/208 4 wire
3PH wye 277/480 4 wire.

To bad they don't offer either 208 or 240/ 3 ph

What am I missing here?

 

[KenC]

most likely to prevent burning up 120v equipment which can happen when someone connects it to the stinger/hi leg.

having a separate panel for 120v loads prevents the hi-stinger leg from ever being part of the equation...

Note that my post stated the original was single phase. I installed the 3ph later, using one of the original panels for some 120v loads
Edit: but the original wiring was done by a guy who did mostly commercial as this was built as commercial shop back in the day, all wiring in EMT. so he may have anticipated it to be 3ph someday.

 

[LXCam]

Guess I'm the odd man out. Having 277/480 3ph was an absolute selling point to me when I purchased our 5Ksqft building. That consideration went beyond my needs but would allow sufficient capacity if someone (including myself) wanted to operate a small machine shop out of it once I was done with it.

Sparky installation cost aside, another $5-6K for that versatility upfront is marginal in the grand scheme of things.

 

[fitter30]

What am I missing here? Me my brain

 

[mm08822]

Interesting comment on this.

Not to get into a debate but in reading I see that the general consensus is that 208 is within 10 percent of 230 so all is good. I have no opinion on this but…

I suspect this is why the nameplate usually has a range of voltage and amps shown for those that connect to a 208 service in lieu of a 230 service with an anticipated voltage drop. Basically I am saying by showing 208 on the nameplate the manufacturer is not advertising it works with a 230v service that is stressed down to 208.

But if your 208 has voltage drop you would be out of spec for the motor… or would you.

So if a motor nameplate has 208/230 on it would it still work with a 10% drop from 208 and have longevity?

I guess I am getting into the theory of how the motor was designed.

The motor you linked to is rated 230/460V. No mention of 208V. So I expect it could handle 208v but that would be at 230v - 10% = 208v, which is the lower end of its low voltage range. Not to say in can't continue to run below 208v, but the actual load on the motor will determine how well and for how long of a lifetime.

There are motors rated 208-230/460v, with the corresponding amperages, but I didn't find any mfr curves for voltage variance. The curves generated reference the high voltage only. Maybe you can find other mfrs' motor specs to dig into this further.

Here is a generic curve.

 

[theoldwizard1]

I wouldn't go 208. A lot of equipment that is rated for 208 or 230 is given that nameplate, but runs like trash at 208.

True for older motors.

Newer motors run on 200VAC - 240VAC. Some even on 50Hz - 60Hz.

 

[Doubled33]

The motor you linked to is rated 230/460V. No mention of 208V. So I expect it could handle 208v but that would be at 230v - 5% = 208v, which is the lower end of its low voltage range. Not to say in can't continue to run below 208v, but the actual load on the motor will determine how well and for how long of a lifetime.

There are motors rated 208-230/460v, with the corresponding amperages, but I didn't curves for voltage variance. The curves generated reference the high voltage only. Maybe you can find other mfrs' motor specs to dig into this further.

Here is a generic curve.

The linked cut sheet shows current draw at 208v. But you are right the voltage does not list 208v.

Why would they list current at 208 if not rated for that?

Thanks for the above explanation

 

[mm08822]

The linked cut sheet shows current draw at 208v. But you are right the voltage does not list 208v.

Why would they list current at 208 if not rated for that?

Thanks for the above explanation

B/c it's a possible voltage application the motor could see. The 208v is not the problem, it's more so if the 208v sags, IMO.

 

[micromind]

The type of motor matters a lot.

A NEMA motor rated at 208-230/460 or even 230/460 will run just fine on 208. An IEC model or any other piece of junk will have problems on 208.

 

[mm08822]

The type of motor matters a lot.

A NEMA motor rated at 208-230/460 or even 230/460 will run just fine on 208. An IEC model or any other piece of junk will have problems on 208.

Sticking with NEMA motors, 208v is fine as it is the -10% value of 230v. The real question is, does any mfr build in any reserve to a motor rated 208-230 to handle 208v - 5/10%, or is the 208v value simply the lower limit of 230v and the rest is just a marketing answer to the q "can this 230v motor run on 208v?"