Another hot tub wiring question (long) - best 3-phase service?

[Beachcomber]

This rather long question is directed to electricians and engineers
who are familiar with wiring and service installation requirements for
a commercial hot tub business. The question is what is the best type
of service class (voltage - # of phases) for a U.S. installation with
6 or more hot tub units.

With the exception of some 120 V. installations, virtually all of the
residential hot tub units in the USA specify single-phase 240 V. four
wire service (usually at 50 or 60A). This consists of two hot wires,
a neutral, and a safety ground wire. The code requirements specify a
hefty Ground Fault Circuit Interupter for each unit.

The problem I am encountering in a commercial installation is as
follows. When combining six or more of these units, it is presumably
desirable to connect to a commercial size three phase service entrance
in such a way that all of these large current-drawing pump motors and
electric heaters present a balanced load to the incoming feeders. The
problem is that even the commercial tubs require 240 volt single phase
4 wire service + the GFCI. Hot tub pump motors that operate on 208V
single or 3-phase are non-standard inventory and difficult to obtain.
The same applies to the factory standard electric heaters which expect
240 volts and take a performance hit if the only voltage available is
208.

Given the standard services available in the USA (Edison split-phase
120/240, 3 phase wye 120/208, 3 phase High Leg Delta 120/240, and
others, etc.) each present difficulties to these requirements.

Standard Edison split-phase 120/240V service would require wiring all
6 hot tubs to one (or two if Delta primary) service phases and create
a highly imbalanced situation as far as maximum current draw. I
suspect that the power company would not be happy with this if the
entire building were loaded onto one phase.

3 phase wye 120/208 service does not match with the required 240V.
that the tubs specify for pumps and heaters.

3 phase High Leg Delta 120/240V service provides for the proper 240
voltage, but the problem is that two sides of the Delta do not have a
center-tapped neutral, thus causing difficulties with the code
requirements for a neutral and the GFCI.

My guess would be that the 3 phase wye 120/208 with three boost
autotransformers to step up the 208 to 240 volts would be the best way
to go, but I'm not an expert and certainly not as familiar with the
code as some of the participants in this newgroup. The goal is a safe
installation that meets and exceeds the NEC requirements at the lowest
possible cost.

I will be doing further investigations and talking to my electrical
contractor and the power company for advice, but I was wondering if
anyone out there had all ready encountered a similar installation and
perhaps could describe how they did it.

Incidently, this seems to be the one example I've found where the
European System (High Leg at 240 V., current carrying neutral, and
safety ground) seems to present an advantage over the US 3 wire split
phase system. If the former were allowed in the USA, we would specify
wye connected transformers with 240 volt secondaries, use Euro style
tubs with their own GFCI's and evenly distribute the load on each
phase. I'm not sure if the US code would permit this, however....

Beachcomber

 

[SQLit]

This rather long question is directed to electricians and engineers
who are familiar with wiring and service installation requirements for
a commercial hot tub business. The question is what is the best type
of service class (voltage - # of phases) for a U.S. installation with
6 or more hot tub units.

snipped
, this seems to be the one example I've found where the

European System (High Leg at 240 V., current carrying neutral, and
safety ground) seems to present an advantage over the US 3 wire split
phase system. If the former were allowed in the USA, we would specify
wye connected transformers with 240 volt secondaries, use Euro style
tubs with their own GFCI's and evenly distribute the load on each
phase. I'm not sure if the US code would permit this, however....

Beachcomber

The 240 volt service, with high leg may create more problems that the GFI.
If you mistakenly get the controls on the high leg,,, poof you have let all
the magic out of the unit.

We ran into this a long time ago with 3 phase services to apartments. Water
heaters were 240 and the service was 208. We just pulled the covers off the
water heaters and raised the temps. They worked just at a reduced output.
Same for the ranges. I doubt that anyone even noticed.

As for the utility and the load on a 240v service they do not give a damn.
They will just charge the crap out of the owner for demand. The load for
these tubs will not even make the utilty lines sneeze. Now if you had 3-4
200 MVA loads they would be talking to ya immediately.

You could put in a buck boost transformer and raise the voltage to 240.
Sounds like a lot of money for nothing to me.

 

[Beachcomber]

You could use three 208 to 120-240V single phase transformers (not
autotransformers) and feed three seperate single phase sub panels. But
this is getting expensive.

Thanks for the suggestions. One question though... If I did as you
suggest above with three single phase 120-240 transformers, I have
concerns about the derived neutrals. Since the primaries would be
coming from different phases, it would seem to me that there would be
a potential difference between the neutrals of each sub panel if each
neutral were connected to the center-tap of the secondaries. In other
words, is a neutral truly a neutral if it is not grounded somewhere?
If everything were isolated, it would be as though the appliance were
operating through a full isolation transformer and would lose the
benefits of a safety ground? Does the code allow this?

Hence I thought that by using autotransformers, the original
continuity of the (grounded) neutral at the center of the wye would be
preserved.

I hope I am expressing this clearly. It seems to be a complex issue.

Beachcomber

 

[Beachcomber]

3 phase pumps are certainly available and heaters just have to be sized to
reflect the voltage available, as the other poster pointed out.
Residential spas are usually the "skid pack" 50a unit you refer to but a
commercial spa can easily be field assembled.

If you want to sell this in the US you had better use 240/120 volts 1-phase
3 wire or 208/120 volt 3-phase 4 wire.
These are the standard voltages and phases. Try anything else and you are
asking for trouble.

Actually, the standard is 240/120 volts 1-phase 4 wire (Hot, Hot,
Neutral, Safety Ground) for most residential "skid pak" hot tubs.
(Some will run on 120V if that is all that is available). The code is
rather stringent about the use of a GFCI for any residential
installation. (Siemens makes 50A and 60A GFCI's for this purpose.

Agreed, three phase pumps and three phase hot tub heaters would be
better, cheaper, more efficent, quieter, and probably last longer.
The problem is that, as far as I can tell, the hot tub industry
manufacturers do not stock them as standard equipment. Of course it
is possible to build a custom system using 3-phase pumps and 3-phase
DHW heaters are certainly available. There are increased costs and
warranty issues for the custom construction option, however.

Beachcomber

 

[Beachcomber]

On 12 Feb 2004 08:51:03 GMT, [email protected] wrote:>

[be sure to display with a fixed width font, such as Courier]

A-----*------------------------------------------------------*
B-----|--------------*----* |
C-----|--------------|----|--------------*----* |
N--* | | | | | |
| | 208 | | 208 | | 208 |
| \/\/\/\/\/\/\/ \/\/\/\/\/\/\/ \/\/\/\/\/\/\/
| ================= ================= =================
| /\/\/\/\ /\/\/\/\ /\/\/\/\ /\/\/\/\ /\/\/\/\ /\/\/\/\
| | 120 | 120 | | 120 | 120 | | 120 | 120 |
| *--------|--------|-|--------|--------|-|--------|--------|-- X1
| | | *--------|--------|-|--------|--------|-- Y1
| | | | | *--------|--------|-- Z1
*----------*--------|----------*--------|----------*--------|-- N
*-------------------|-------------------|-- X2
*-------------------|-- Y2
*-- Z2

Phil:
Thanks for a most impressive diagram. Now I'm wondering if I can
just order my service this way from the power company. (In other
words... they would configure the secondaries according to your
diagram, using a primary voltage of whatever the incoming lines are
set for...

I've not seen a diagram like this before. Would this be considered a
standard class of service? The only thing that causes me to have
concern about your circuit is that I've lived in condo buildings that
only provided the common wye 208/120 V. (single phase service to each
unit - 3-phase incoming service). I'm now wondering why I could not
get the more desirable 240/120 V. service (as per your diagram).

Are you saying there is no issue with the three center tapped neutrals
all bonded together like that? It would seem that even with no load,
you would have current flowing in the neutral even though it might all
sum to zero.

Beachcomber

 

[Beachcomber]

That depends on if his building is already wired for what configuration of
power. I've seen the effect of switching things from 240/120CT to 208Y/120.
If the building is already wired up for 208Y/120, then it is probably cost
effective to just leave it that way.
--

Thanks to all for a good discussion. The spa building is still in the
planning stages (without existing service) so that will figure into
the specifications. Much useful input was given from these
discussions.

Transformers are interesting, seemingly simply devices... In reality
however, they are quite complex, like a game of chess, in terms of a
theoretical analysis of the basis underlying principals.

For those interested in a little bit of history...

The inventors of the transformer (Lucien Gaulard & John Gibbs)
experienced years of difficulty with their invention because they kept
on hooking up their circuits with the primaries in series instead of
parallel. The end result was that they could transmit power for long
distances, but the practicality of the invention suffered due to poor
load regulation. The parallel primary connection (for multiple
transformers) that seems so obvious to us today, was not perfected
until a theoretical understanding was applied by men like Tesla,
Stanley, and Westinghouse.

Lucien Gaulard was born in Paris in 1850. Gaulard was a French
scientist, primarily interested in chemistry of explosives, but later
he shifted his interests to electrotechnics. He developed a
thermochemic battery and he is particularly known for his work with
induction coils (transformers). In 1882, Goulard and his English
colleague Gibbs patented a system of distributing power using
alternating current and two-coil induction devices. They used devices
(then known as secondary generators) of the Ruhmkorff type in the
first alternating current distribution system and had a 1:1 ratio and
were used with their primaries in series.

A power transformer developed by Lucien Gaulard and John Gibbs was
demonstrated in London in 1881, and attracted the interest of
Westinghouse. Transformers were nothing new, but the Gaulard-Gibbs
design was one of the first that could handle large amounts of power
and promised to be easy to manufacture. In 1885, Westinghouse imported
a number of Gaulard-Gibbs transformers and a Siemens AC generator to
begin experimenting with AC networks in Pittsburgh. In hands of
Westinghouse the transformers received really practical
implementations.

Gaulard's transformers were successfully presented in 1884 on the
international exhibition in Turin. The farthest lamp fed, on the
Torino-Lanzo railway line, was at 40 km distance from the 2,000 V
generator with 133 Hz frequency. The series connection led to
unsatisfactory regulation unless all the transformers were equally
loaded. However, these transformers were in use until 1912.

Gaulard was ingenious, but unlucky inventor. During his life his work
was not recognized in France. Gaulard fell in depression state and
seems he went mad, was sheltered in clinic where 1888 died the 26
November. Now Gaulard fame is memorized with tombstone in the railway
station of Lanzo, there is also a street with his name in Paris.

This man was the co-inventor of one of the world's most revolutionary
inventions that gave the world the ability to transmit electric power
for long distances, but for some reason he just couldn't get the
connections correct.

Beachcomber

Reference: (excerpts from)
http://chem.ch.huji.ac.il/~eugeniik/history/gaulard.html

 

[Beachcomber]

<snipped>

My first inclination would be to ask why you want to install hot tubs
rated for residential use in a commercial installation?

I thought I stated it earlier, but perhaps I did not make myself
clear., these would be commercial units. Most, if not all of the
commercial units available would still be rated for 240V. (same as
residential).

Beachcomber

 

[Louis Bybee]

[email protected] (Beachcomber) wrote in message

<snipped>

My first inclination would be to ask why you want to install hot tubs
rated for residential use in a commercial installation?

Presumably you have 120/208/4w coming in already. I'd be inclined to
buy transformers and make 240v/3w (i.e. - three 208 to 240 center
tap). They won't be real cheap or something you can get at home depot
tomorrow, but acme or some other xfmr mfr can make them up pretty
quick these days.

I am not a big fan of buck/boost xfmrs, having seen way too many of
them applied improperly, just to save a few bucks.

That could be said about almost any installation of any product!

The problem you've seen is crap installations not the Buck-Boost Xfmr
proper. Properly specified, and installed, a Buck-Boost xfmr installation is
neither complex or unreliable. Just the opposite is usually the case. Proper
application can extend the life of the connected components due to operating
within a proper voltage window.

There are ample sources to guide the proper application of a Buck-Boost
application. A Google search is just one of many.

Louis--
*********************************************
Remove the two fish in address to respond

Louis