Three Phase Power - Is it worth the expense?

[radiationroom]

Writing up my studio and shop specs so I can pull building permits. Made a call to the co-op to discuss the electric service and was told that they need to add a new pole and transformer because the existing transformer on my block was maxed out. To make things interesting, the co-op manager then offered me three-phase power.

Here's the deal: If I go with a standard single-phase 120/120 service (I'm in North America) the co-op pays for the new pole transformer and a single cut-out. If I do three phase I pay for the (three phase) transformer (or alternately three single phase transformers) and the five cut-outs needed to pull and terminate the two additional phases up the block (currently there is a single cut-out for the existing phase). I pay for a new pole in either case and the co-op pays the labor to install everything.

Is it worth the expense and what would you do?

Which service type is better? 208Y/120 or 240 "delta" with a 120/120 center tapped phase?

Or just standard 120/120 single phase and forget about it?

NOTE: In addition to my A/V gear I also have shop equipment with three phase motors that I am running off of a rotary phase converter, still at my old location. The phase converter is noisy as hell and it would be nice to be rid of it.

NOTE: I have professional experience in electrical work and am quite familiar with a substantial chunk of the 2008 NEC.

[jhharvest]

NOTE: In addition to my A/V gear I also have shop equipment with three phase motors that I am running off of a rotary phase converter, still at my old location. The phase converter is noisy as hell and it would be nice to be rid of it.

Seems like you answered your own question.

Basically I would have said: what do you plan on running? But since you need three phase leccy anyway then surely it's a moot. As to which configuration you should go with I can't help as I'm only used to 230/400V (and I'm not an electrical engineer anyway...).

[Scodiddly]

Do you need 120/240 for anything? Say maybe a stove in your kitchenette?

[goose134]

If your shop machinery takes 3 phase it might be worth looking into getting the 3 phase service. As to which one, I can't say which is better. High leg systems are great for motors, but you'll be leaving an awful lot of spaces open for lights and outlets. I really don't know what the economics are in terms of service charges. I'm pretty sure you'll be paying a monthly service charge for the additional 3 phase.
The only thing I would say might be a minus about 120/208 is that the neutrals from your service would be bonded to the existing neutral for the building. It might be worth your while to investigate the grounding/bonding in your system now. 3 phase problems like harmonics and general neutral problems with poor and improper bonding/grounding may give you more headaches than you bargained for.
Maybe invest the money in a chemical ground for your service only?

[radiationroom]

The building is being gutted to the exterior walls and roof and everything inside floor to ceiling is being built from new including all electric wiring back to the pole ground rods and all. Since the building is zoned commercial I can not put in a full kitchen without jumping through some major hurdles including restaurant type fire suppression, so no stove (not even a microwave although a fridge is OK). Why? The zoning department sez so.

Thanks for your replies!

[Rod Gervais]

Which service type is better? 208Y/120 or 240 "delta" with a 120/120 center tapped phase?

What are your existing needs?

Equipment designed for 208 volts does not generally like 240 - and equipment designed for 240 will not appreciate 208........

Your power design should be based on the equipment you are connecting to it - especially when you already own the equipment..........

Rod

[goose134]

Which service type is better? 208Y/120 or 240 "delta" with a 120/120 center tapped phase?

What are your existing needs?

Equipment designed for 208 volts does not generally like 240 - and equipment designed for 240 will not appreciate 208........

Your power design should be based on the equipment you are connecting to it - especially when you already own the equipment..........

Rod

While this is true, I think most of his equipment was shop tools, which are motors. Motors will take the high leg service just fine. High leg is just B phase 240 to ground. A and C are 120. A and C to B measure 230. Service was designed with motors in mind.

Audio stuff, not so much.

[radiationroom]

Equipment designed for 208 volts does not generally like 240 - and equipment designed for 240 will not appreciate 208........

Your power design should be based on the equipment you are connecting to it - especially when you already own the equipment..........

Thanks for the reply Rod. I just ordered your book on studio design and am looking forward to reading it.

My rotary phase converter outputs 240 delta, which my three phase motors run on just fine. Knowing that, let me rephrase my question:

Are there audio/video advantages and/or disadvantages to having three phase power?

Thanks again in advance.

[Ron Obvious]

Single Phase 120 VAC is THE ONLY PROPER WAY TO GO.

I've designed a few studios over the years. http://www.mts.net/~lakemail/bio-cv.html In these studios I had the electricians install a large 240 VAC to single phase 120 VAC / 100 amp isolation transformer. A separate Master Audio AC panel is now fed from this 120v. ALL AC PLUGS in the studio & control room area are fed from this panel. The panel also has an isolated ground connection installed with copper rods outside the building. This is all "legal". I.E. "Hospital grade AC". No you don't need to use the expensive orange plugs.

Also in the control room I would still have some regular "house" AC plugs for the plug in room lights, lava lamps, client laptop AC adapters, coffee machine, etc.

Advantages in audio are.
1. Basically NO ground loops because every piece of audio gear is on the same phase and same voltage fluctuations. I.E. if the voltage drops to 116volts, every piece of gear see's 116v.

2. Isolation from all the other building's "dirty" power. I.E. flourescent lights, dimmers, cycling HVAC units, washers/dryers, photocopy machines, hot water tanks, etc.

On the cheap home studio side.

If I'm helping a client. I make sure every AC plug in the "studio/control" area is on the same 120AC phase. I move any dimmer lights, refigerator, AC unit, etc - to the other 120VAC phase on the standard North American house panel. **** Danger - Only do this if you know what you are doing. *** An electrican can sort this out in less than an hour on your house AC breakout panel.

[radiationroom]

The panel also has an isolated ground connection installed with copper rods outside the building.

That's illegal. All "grounding" and "grounded" conductors are to be tied together for safety at the point of service. Isolation transformers to derive a "new neutral" which is separate from the serivce neutral is legal, but the new neutral has to be bonded to building/service ground as well along with the transformer frame. I learned that in EE class many many years ago....

Basically NO ground loops because every piece of audio gear is on the same phase and same voltage fluctuations. I.E. if the voltage drops to 116volts, every piece of gear see's 116v.

Thank you for the reply.

Know all about ground loops from doing concert sound. Worse than a ground loop is when an amp has a hot chassis putting that 116V onto guitar strings and the player gets grounded by grabbing the microphone. Even worse than a hot chassis is when the building/generator neutral goes haywire and the two 120V legs are all of a sudden in series with each other. Instead of having 120V/120V you wind up having weird voltages depending on what the active load is on each side of the service. That can do bad bad bad things to your equipment, to your building, and to your occupants, among other very very bad bad things.... ....been there done that.... Often times that can be fixed simply by retightening the various connections inside the panel and using Noalox compound where ever one finds aluminum in the power path.

Maybe invest the money in a chemical ground for your service only?

Thank you Goose134 for suggesting this. Chemical grounds are a great idea and I don't know why they are not mandatory for new construction of all types. My only question (for the inspector) is whether or not two are required spaced six-feet apart like standard rods (inspector has not yet returned my call). I've never installed a chemical ground myself, but some of my EE acquaintances swear they are the way to go.

Now back to the three phase question. Seems like you guys say "no" other than to run my three phase motors. That's my question.

[jhharvest]

In the 230/400V systems I've seen the point is what Ron Obvious gave - you can run all your equipment even in a larger setup from a single phase which makes life generally a whole lot easier. Then you can run your other gear separately. That alone is in my experience worth the investment but then I really can't say if it's the same in 120V based setups.

[goose134]

Chemical grounds simply replace the grounding electrode, which is usually the water pipe. The advantages are apparent when anyone one the same power company transformer has an improper neutral or ground connection. On a standard electrode, you'll experience the circulating neutral currents on your grounding electrode, and consequently, on your system. As was mentioned earlier, this is required to be bonded to your neutral in the service panel.

As far as putting isolated ground outlets on a ground rod, it will never in one million years trip a breaker in a ground fault. It needs the reference to neutral that the bond provides. The earth in and of itself is a terrible conductor. Ground rods are to disperse lightning strikes to the service mast. That is all.

Isolation transformers are good, but again as mentioned, the neutrals are bonded and common. Chemical grounds are the only way to separate your system from the common ground of your neighbors ( who may be flaunting the NEC rules and creating havoc for all you know).
Required? I don't know. They are expensive, but for a pro studio, they are the only system I'd ever recommend.

[radiationroom]

Chemical grounds simply replace the grounding electrode, which is usually the water pipe.

A question since you are a pro electrician. Would a well casing work the same as a water pipe and would it be legal? I have a 250 foot deep well with a nickle-plated steel casing which goes the entire length. It is about 150 feet away from the service panel. Just asking to ask if it's doable. No public water where I'm at.

Thanks again!

[goose134]

I'll have to look at the code book. Wells are a little different. Top of my head says the code language says as long as metallic pipe extends 10 (or 20?) feet into the earth, then it can be considered an electrode if sufficiently grounded.
Let me look at section 250 and get back to you.

[goose134]

Chemical grounds simply replace the grounding electrode, which is usually the water pipe.

A question since you are a pro electrician. Would a well casing work the same as a water pipe and would it be legal? I have a 250 foot deep well with a nickle-plated steel casing which goes the entire length. It is about 150 feet away from the service panel. Just asking to ask if it's doable. No public water where I'm at.

Thanks again!

According to 250.52, if there is no other grounding electrode available, the well casing would be acceptable. One thing came up in the talks with colleagues: Is there a ufer ground? This is a type of grounding that uses the rebar structure as a grounding electrode. Depending on when your place was built, it may or may not have one. If it does, then you can use that as your primary electrode and only need to bond the well. If not, use the well casing as the electrode.
You do not need ground rods at the well. You will need two at the meter, spaced at least 6' apart.