I am working with a Dayton 2YU39. The name plates states that it has to be powered by 208 volt system. There's a 3-phase panel and a single-phase panel. The 3-pahse panel L1 to ground is 118 volts. L2 is a high leg with 209 volts. L3 to ground is 118 volts. This panel phase to phase is 236 volts (even with the high leg). Now the single-phase panel L1 to ground is 117 volts. L2 to ground 118 volts. Phase to phase is 237 volts. This heating unit specifically states that before you energize, voltage must be checked to make sure that the voltage coming from the panel matches the voltage on the name plate. Several of my co-workers seem to believe that it is sufficient to hook this sytem up to the 3-phase system although this system does not match the voltage on the name plate of the unit. My superviser advised me to order the 2YU36, which has a voltage rating of 240 volts. Is it safe to hook up a system with 208 volts to something that carries a higher voltage of 240 volts?

single phase 240VAC. data late will have info. 3 phase usually has 12 leads.

Do not purchase it because parts are obsolete.

A one phase 3 wire system has a center tap. Two hots and a neutral. Typical 120/240 volts.
A three phase 4 wire system has Three hots in a Y or Delta. The Y system has three hots and the neutral comes from the center of the Y, this is the neutral and grounded conductor, 120 volts from hot to ground and 208 volts hot to hot. In a 3 phase system the voltage is not doubled hot to hot as in a single phase system because the hots are 120 degrees phased from each other and the square root of 3 is the factor, multiply the 120 volts by 1.73 to get 208 volts hot to hot. Multiply 208 by the reciprocal of 1.73 and get 120 volts. Your exact application is not given so it is not known. A delta system is a triangle and the angle of each triangle is a hot wire, one angle would be grounded or the center tap of one of the sides of the triangle. Y is the configuration of the windings of the alternator or transformer and Delta is the configuration as a triangle of the windings of the alternator or transformer where the power supply is.

With a three phase home service, you can only connect two hots from your single phase generator, and the neutral. One of the house's hot does not get connected and any three phase loads in the house should be switched off and kept from energyzing or a circuit breaker or fuse serving that 3 phase load may trip.
Only one power supply can be connected at a time. The power company power must not be connected at all while using an alternate power supply unless your power supply has means to synchronize the alternating cycle.

It is adviced that the loads be kept within 10% of their rated voltage, especially motors.

Sounds like this maybe a three phase unit and you are powering it off on single phase power. Most can be converted to single phase but will draw three times the current and requires some wiring changes. It needs to be on a three section breaker for 3 phase.

My limited research indicates this heater is designed for USA electrical systems. That would mean single phase, 240/208 volts, 60 Hz. The drawings I reviewed shows a 2 pole, 240 volt breaker feeding each heating circuit. That means no "neutral wire" goes to the heater and therefore no 120 volts is needed. This is good. Kenya's system is single phase, 240 volts, 50 Hz. The heater should work reasonably well on the African system. Connect the power just like you would in the US.

208 Volt 2-wire is generally achieved by pulling two hot wires off 3-phase 120/208 Wye or 208 Delta, or Highleg to center tap off high leg delta.
http://waterheatertimer.org/How-to-wire-3-phase-electric.html
http://waterheatertimer.org/images/3-phase-timer-diagram3-T104-208-240.jpg

Since each of these three phase systems also offers 120volt for lights, and a dimmer can be used for lights, then I wonder what you are using dimmer for?

208 volts.can be controlled by turning off one hot of the two hot wires.
Install dimmer on one of the hot wires, and see what happens.
Is the dimmer rated for 208 volts?

Add a comment and say what you discover.

If you need further help, I’m available over the phone at https://www.6ya.com/expert/gene_9f0ef4df2f9897e7

You'd need to supply a "Buck-Boost" transformer to do this properly. Technically, the 265 VAC is one hot leg and neutral of a 480 VAC 3 Phase Y system that measures 277 VAC. The 265 number comes from this:

265 is the standard nameplate voltage for a 277 volt motor or AC unit.

230 is standard name plate for 240.
200 is standard name plate for 208
460 is standard name plate for 480.
110 is standard name plate for 120.

Most electricians call the hot leg / neutral circuit "277V AC".

Some popular "Buck-Boost" transformers will convert 208 to 240 and 240 to 208 volt systems, and 240 to 277 and 277 to 240 volt systems - among many other variations. These are auto-transformers as the primary secondary windings share a connection. KVA ratings differ significantly from name plate because of this fact. You should contact a qualified electrician to not only size, but wire the transformer for you. Failure to install a Buck-Boost transformer - and running this unit on 240V AC mains will cause premature failure of motors - fans and compressor due to overheating. This can also result in a fire hazard.

I hope this helps and good luck!

Doubtful that voltage is the issue.

It is single phase. Either 208 volts 3240 watts or 240 volts 4316 watts. Unfortunately, its difficult to know which one you have. It can be ordered either way. Here's the deal, For no apparent reason, some buildings have 208 volts, some have 240 volts. If you know when you buy new equipment, you specify which voltage you have. So if your building has 208 volts and the machine is 240, it will still work, maybe a little slower to heat up. If it is the other way around, your building has 240 volts and the machine has 208 elements, it will heat up much faster, but the life of the elements is drastacally reduced becuse they burn out much quicker. You can call Lang at 314 781 2777 ask for technical assistance and they may have a way to find the voltage if the tag is missing.

if its a single phase panel you will only have 120/240 v.a.c. you can wire it for 240 volts and it will heat faster anyway the only way you could have 208 volts would be if you had 3 phase delta or open delta 3 phase or buy a special "dry-type" transformer for 240 volt to 208 volt step-down,otherwise it will be red-& black will be your 2 hot phases of 120 volts each/white-neutral/and green or green-yellow will be the case safety ground