240V and 120V? 2

[Jakelian]

Dear users,

I am not an engineer but the industrial designer of a new product but I need to know the answer to a technical issue, to keep up with the technical people here, I really appreciate your attention:

I see in some web pages of American sauna/hottub builders that little models require 120V but bigger ones require 240V. In Europe, when we need more power, we make a model that uses 3 phase system (3x230) . How does it work in the US? Is 240 the way to upgrade the outlets? Or do you have something like 3x120?

thanks in advance,

Sunchallenger

 

[itsmoked]

Nope Hot-Neutral-Hot is what we use here.

Or 120-Neutral-120.

If you connect between the two 120s you get 240V.
Houses are typically supplied with either 100A or 200A services these days.

40 to 70A at 240V single phase is generally more than adequate for any hot tubes.

3 phase is generally not allowed in US homes.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[edison123]

Keith

That's odd. In India, home owners are mandated to go for 3 phase if their load exceeds 5 KW.

Why would US frown on 3 phase home connection ?

 

[wareagle]

I would say that the vast majority of homes are single phase.If the home is large enough to require a 5 ton A/C or larger, then the service may require a 3 phase service. The utility will provide 3 phase if the load is large enough to require it.

 

[tinfoil]

Distribution companies in N.A. typically run only single-phase feeders onto residential streets.

Since there is not usually 3-phase available, it's difficult to give 3-phase to the homeowner.

Commercial and industrial areas (and trunk feeds into residential areas) will usually have three-phase primary available.

 

[Kiribanda]

sunchallenger,

I think it is related to concept,safety and cost too. In NA only three wires (L1,L2 &N) given for 99% of houses.So any heavy loads (dryer,washer,hot tub etc)are connected to L1L2(220V) whereas all other loads are connected to L&N (110V).Therefore, only one simple distribution panel.

In contrast, in Euorope, ME & the EAST you can see three individual distribution boards installed inside the house where the house is provided with 3-phases.From my experience,normally in these countries (especially EAST)voltage drop was a problem and therefore most users were asking for an additional phase,so the utilities also providing 3-phases to keep the customers happy.Now it has become a tradition that even in an area where the power supply is very stable, you cannot sometimes sell your house if you donot have 3-phase installation.

In my opinion,NA method is more straight forward,simple and cost effective.

 

[waross]

Hi edison;

That's odd. In India, home owners are mandated to go for 3 phase if their load exceeds 5 KW.

Why would US frown on 3 phase home connection ?

Just a matter of scale. In North America replace 5 kW with 50 kW or so.
At one time, three phase was more common for residential air conditioning loads but single phase A/C condenser units are now available in much larger sizes than in years past, and residential three phase is rare.
200 Amp single phase services are common with 48 KVA available.
225 Amp single phase services are sometimes used with 54 KVA available.
400 Amp single phase services are available in many areas for 96 KVA.
sunchallenger;
If you are going to market in North America, be aware that large apartment buildings and condominiums (an apartment building that has a strata title where occupants ow their apartments, and have more liberty to install improvments than renters) often use three phase 120/208 volt systems.
Although the building main service is 120/208 three phase, the individual occupancies utilize single phase panels and are fed from two phases. Many residents are unaware that they are supplied with 208 Volts rather than 240 Volts but electric cooking devices, water heaters and space heaters have less output and are slower to reach operating temperature.
Be aware of this and try to design your equipment to function on either 208 Volts or 240 Volts for the North American market.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[edison123]

Thanks Bill. I agree it's the scale. Keith said 3 phase is generally not allowed, hence my question.

 

[itsmoked]

I was told by my city's electrical department [!]- Verboten -[/!] .

They equate 3ph with business, machinery, etc., which wouldn't be allowed in a residential setting anyway.

Of course this leads to things like me running a VFD in my living room.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[Jakelian]

cfhh

 

[edison123]

gotcha keith.

 

[Jakelian]

Dear members, thanks a lot!

I see that there are a lot of variations in the US, more confusing for me...

We developed a new sauna system that uses a different heating system, no stove, no infrared rods, no carbon heaters, none of those things! But we still have some different type of heaters of course: For the European market, the sauna uses 9 of those new heaters, 475 W at 230V, approx 2 amps each. We distribute those heaters to 3 phases (9/3=3 heaters per line, 1425 W per line). Then all ends in one Notr.

The market is wealthy homes, gyms, spas, clubs, hotels etc.

Question is: I see a lot of spas sold over there which run with 240. Is there any way to run our device in the US and Canada with the existing 230 V heaters?

THANKS!

 

[waross]

Hello sunchallenger;
The system voltage is 240 Volts, however motors are rated at a utilization voltage of 230 volts. This is to allow for voltage drop between the distribution transformer and the point of use.
Gyms, clubs, spas and hotels may all have three phase 208 volt service. It is common to use 230 and 240 Volt rated heaters on 208 Volt systems.
Your 475 Watt heaters will develop about 517 Watts on a full 240Volts and only about 356 Watts on 208 Volts.
The experience with electric stoves and electric water heaters on208 Volt systems is that the initial warm up time is greater but once the temperature control takes over and starts cycling the element to hold it at the desired heat the performance is good.
An option you may explore is using 120 volt rated elements in series with the neutral point connected. This would give you 120 volts on either a 120/240 volt system or a 120/208 Volt system.
Please note that in North America the neutral is defined as the conductor which carries the unbalanced current between two circuits in series.
As I understand the European convention, 230 Volts single phase is derived from one phase of a 230/400 Volt system.
Fair enough. We do the same with to derive 120 Volts from 120?208 volt systems, 277 Volts from 277/480 Volt systems and in Canada 347/600 volt systems.
Where the misunderstandings arise is from the practice of sometime using a center tap on a 230 Volt transformer to develop 115 Volts, but still grounding one end of the transformer winding rather than the center point. In this case we would consider L1 to be the grounded conductor and consider the center tap to be the neutral. By North American codes we must use the neutral (by our definition) for the grounded system conductor, if a neutral exists.
We could use a 240 Volt transformer and ground one line, but once there is a center tap we must recognize that as the neutral and ground the system there. Not all of our systems must e grounded however if by grounding a neutral the voltages on the hot lines may be limited to not more than 150 Volts to ground then the neutral must be grounded by our codes.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[Jakelian]

Thanks Bill!

The problem is we dont have the 120V version of this element yet and it is too much work and research and expense to build it (they are made in Sweden, very safe and top quality but of course, expensive!). Since I am not an enginner, I am having difficulty understanding those technical definations. But as a partner of this new venture, I am trying to find a way to use the existing 230V versions for the US if possible.

Cabins are made of glass, teflon and stainless steel, NO wood, so they are very strong. And air temp of 36,5 C (your body's own temp) is enough for persipiration! But with this setup:

208 is perfect but 240 might be dangerous for us; because:

If the device loses all its control measures, (everything gets broken, or software makes a mistake, or probes move away from theirs locations, etc., as a result, we lose the control ability of heater temperature). We have 3 additional control measures that cuts of the power in that case. But, in case those also fail, then the heater that runs at 60 C gets out of control and becomes 120 C (248F) and destroys itself. Unfortunately , there is no repair possibility, we have to give the customer a whole new cabin, which is very expensive! I am not even mentioning legal stuff!

It is kind of unbelievable to learn that voltage differs like this all around the States... When we visit the gyms etc, what are we going to find there, 208 or 240 or? What choice do you think is the best to run this system?

Thanks!

 

[waross]

Facilities in residential areas are more likely to have single phase.
Smaller stand alone clubs and gyms may have single phase.
Hotels, and facilities in larger buildings and strip malls and shopping centers are more likely to have three phase.
An anecdote to illustrate the prevalence of 120/208 systems:
Several years ago I was renting an apartment in a large building with a 120/208 Volt service. The manager was a retired industrial electrician. One day I casually mentioned something about the 208 volts. He was not aware that the building had three phase power. I suggested that he stick his volt meter in the range receptacle. He was surprised to find 208 volts.
The point is that most 240 Volt rated household equipment runs well on 208 Volts.
The most noticeable difference is that clothes driers take a little longer.
Back to your issues:
You should be designing for the highest system voltage which is 240 Volts.
I doubt that you will be able to have your device approved unless and until you have a dependable high temperature safety shut down system. Once you cross that hurdle, you may find that your system performance is adequate on 208 Volts.
BTW IEC guys, what is the standard Voltage in Sweden?

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[dpc]

If you want to sell your product for US residential use, it will have to operate on 120V or 240V single-phase 60 Hz AC. There are no other options.

Nothing prevents you from installing a small autotransformer to convert 240V to 208V for internal use. But it will all have to be UL approved as an assembly to be sold anywhere in the US anyway.

"Theory is when you know all and nothing works. Practice is when all works and nobody knows why. In this case we have put together theory and practice: nothing works... and nobody knows why! (Albert Einstein)