B
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
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