208 vs 230 volt motor

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bh

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I am providing a new service to a multi-apartment building. The old service was fed at 120/240 single phase from 167kva transformers on each floor. I want to use 120/208 3 phase and put in a large padmount for the whole building. Will the older AC units (which will not be replaced) run at 208?
 
If they won't handle 208, I believe you can put in a buck boost transformer set up from Cutler Hammer, Square D, et. al. They give you a nifty chart in their catalogs that has you look up how many phases, wye or delta, Vin and Vout, and power. It's a bit daunting at first. Basically you're tacking a line Voltage primary to a 12, 24, 16, or 32V secondary transformer on the end of the line. They also provide hook up diagrams.

If all else fails make their sales rep explain it - if he wants the sale, do his job.

You'll have to delve into the code a bit on this connection too, article 440 or 450? They tend to get heavy as the power goes up, but the prices aren't bad - not as much as a new AC unit. I had a few that weighed about 60lbs each for a 40A load 208 to 240.

The "secondary" lead wires will be quite fat since it's really a line to low Voltage transformer, but just have an assortment of wire nuts on hand.

I've used them on motors when 208 w3-phase wasn't quite enough. No smoke, no fires.

Check your local & state codes too, and find a good place to mount them if it's allowed.

Matt
 
If they (motors) run OK at 208-volts, I would check to see if the wire size is large enough. You are talking about a 10% increase in the motor amperage.

So, install a lower voltage source, use the same conductors, have a larger amperage, .....

I bet voltage drop calculations might raise an eyebrow.
 
I believe HVAC units that are dual voltage (208/240) have a jumper or some other setting inside them you have to change. The motor/compressor will probably work at either voltage, but the 24V control voltage sometimes falls too much to pull in contactors. I think the jumper puts this 24VAC back up to 24V instead of 21V when being fed from 208V.

If its old and not designed for 208V, then you may have to use the buck/boost option someone else mentioned.
 
On top of being a licensed Electrical Contractor, I am a licensed A/C Journeyman. Not that that means much, (if anything) but I have been around the block a little.

On split systems, I have connected several A/C condensers that were labeled for 208 / 240 volts. The 24 volt transformer is usually connected with the furnace.

Sounds to me like bh is replacing window (or motel) type units. Those units usually have built in thermostats.

At any rate, follow what Larrfine said - Look at the label.

(For what it's worth, I have NEVER installed a buck/boost in this type of application)
 
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Thanks for the insight. It is an large occupied apartment building so I can't get in to look at the nameplate on every unit. I have been told that most of the AC units are fairly new and will operate on the 208 volt system. For those that cannot operate at this voltage they will be replaced.
The tenants just need to know that it will take a little longer to bake a cake when the 208 volt system is installed :)
 
Engineer Says "Tenants be Damned"?

Engineer Says "Tenants be Damned"?

It seems like you are disregarding the needs of customers (tenants) when you decide to install a system to put them on 208 Volts instead of 240.

Heating elements of all kinds will produce only 75% of what they would produce at 240. Does the owner supply hot water, or do tenants have electric water heaters? Do any of them have the "Instant hot water" type that will be decreased to 75% of capacity?

Who is going to pay for replacing the ACs if they need to be replaced? Who pays for any service calls to change over from 240 to 208 Volts?

If there are circuits that are just within the code limits for current, those Air Conditioner circuits are going to exceed the code rating when the current increases to meet the power requirement, and there will be greater conductor losses.

Who pays for all the service calls that will be generated when the lower voltage affects operaton of their equipment?

If I were a tenant adversely affected by the change, I would be getting together with my fellow tenants to recover damages.
 
Bob NH said:
Heating elements of all kinds will produce only 75% of what they would produce at 240. Does the owner supply hot water, or do tenants have electric water heaters? Do any of them have the "Instant hot water" type that will be decreased to 75% of capacity?
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Almost all residential appliances stoves, water heaters etc are dual rated for 208 or 240 operation.

Yes it will take longer to heat soup on the stove but that is a just a fact of life for any residence running on 208.

In some areas the power company supplies single family homes with single phase 208 services.
 
iwire said:
In some areas the power company supplies single family homes with single phase 208 services.
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Although I haven't done any residential work since 1980, I never saw this before. Actually, I've never seen single phase 208.

I'm with Bob. I don't like 120/208 being delivered to a home. If one had it, I would not buy it.
 
In the Boston area often the power company will install a 3 phase transformer or a bank of single phase transformers to provide 208Y/120 3 phase.

From that transformer they will supply many homes with single phase 208/120.

First house on phases A-B, next on B-C, next on A-C etc and on it goes.

Homes supplied this way require a different seven jaw meter socket.

Any larger multifamily building I have worked on is supplied with a 208Y/120 3 phase service to modular meter stacks supplying each apartment / condo with 208/120 single phase.

IMO there is no reason from a design standpoint not to supply dwelling units at 208/120.

I say that even though when I lived in a 208 volt supplied apartment I considered adding a buck boost to my range to provide faster heating of the stove top elements. :)
 
hardworkingstiff said:
A Vega (wow I'm old) will get you from point A to point B, but I would not own one.
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LOL I remember Vegas have even driven them.

Owning or buying is different from designing how many Vega designers drove Vegas.

In this area I have not seen the power company provide a large single phase service.

You get what they give or you make your own.;)


How about a Vega with a V-8? :)
 
There Is an Owner/Renter Contract!

There Is an Owner/Renter Contract!

"Any larger multifamily building I have worked on is supplied with a 208Y/120 3 phase service to modular meter stacks supplying each apartment / condo with 208/120 single phase.

IMO there is no reason from a design standpoint not to supply dwelling units at 208/120."

I don't have any problem with installing 208/120 3-phase service in multifamily residences, or even in single family homes, as long as the customer can make the initial purchase of equipment to match the voltage.

You can buy cooking ranges, ovens, air conditioners, and water heaters that are designed for 208 Volts.

My concern is the disregard of the customers (in this case, renters) by CHANGING from 240 Volts to 208 Volts, thereby diminishing the capability of the equipment that they are using as part of the contract (lease) that they entered into when they rented the apartment.

The owner is saving a few bucks on the upgrade at the expense of inconvenience to the renters who have an expectation that the livability will not be diminished by making them wait longer for their water heater or range to deliver the energy that they had reason to expect when they signed the lease.

The owner might be sued by the renters when they figure this out, and the engineer may want to be sure that his Errors and Omissions insurance is paid up.
 
But the answer the OP was looking for is: YES, the older A/C units WILL work just fine on 208 volts.

However, you will have to decide if it's worth loosing Bob as a potential tenant. :D
 
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