transformer for 208V 1-ph. to 480V 1-ph.?

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donw

Senior Member
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Arizona
I have a situation where we are replacing an existing 240V 1-ph. service with a 208V 3-ph. service. The parking lot lighting is apparently at 480V 1-ph. because it is being fed with a 10 KVA 240V-to-480V 1-ph. transformer from a 40A two-pole breaker (I assume the individual light poles are fused). I can't find a 208V 1-ph.-to-480V 1-ph. transformer off the shelf. What would you do?
1. Use a 208V 3-ph. to 480V 3-ph., but only use two phases of it
2. Use an autotransfomer from 208V to 240V, into the existing 240V 1ph.-to-480V 1ph transformer
3. Order a custom 208V 1-ph-to-480V 1-ph transformer
Any other ideas?
 
donw said:
I have a situation where we are replacing an existing 240V 1-ph. service with a 208V 3-ph. service. The parking lot lighting is apparently at 480V 1-ph. because it is being fed with a 10 KVA 240V-to-480V 1-ph. transformer from a 40A two-pole breaker (I assume the individual light poles are fused). I can't find a 208V 1-ph.-to-480V 1-ph. transformer off the shelf. What would you do?
1. Use a 208V 3-ph. to 480V 3-ph., but only use two phases of it
2. Use an autotransfomer from 208V to 240V, into the existing 240V 1ph.-to-480V 1ph transformer
3. Order a custom 208V 1-ph-to-480V 1-ph transformer
Any other ideas?
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All possible solutions.

my guess is that a universal xfmr can be wired to do the job as well. call the transformer company direct and ask them what is the cheapest answer. did you check to see if there are any usable taps on the existing xfmr?
 
petersonra said:
All possible solutions.

my guess is that a universal xfmr can be wired to do the job as well. call the transformer company direct and ask them what is the cheapest answer. did you check to see if there are any usable taps on the existing xfmr?
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No taps, and at most taps would only be 2.5%.
 
How many circuits to the parking lot lights? 10kVA is low enough value @ 480 volts it very well may only be one circuit, but if you can balance across three phases easily then using the 208-480 three phase transformer may be worth looking into. 10KVA is not really that big of a unit for three phase units. I think standard sizes are 9 and 15.

Changing taps at the luminaire sounds simple, but if you can do that you likely will have undersized circuit conductors.
 
As far as I can tell, there is only one circuit. 40A 2-pole breaker, 240 1-ph, #8CUx2---->transformer---->underground #8CUx2 to pole fixtures.
 
donw said:
As far as I can tell, there is only one circuit. 40A 2-pole breaker, 240 1-ph, #8CUx2---->transformer---->underground #8CUx2 to pole fixtures.
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What kind of distance to the light poles, I was expecting smaller conductors for what appears to be about a 20 amp max load, and are luminaires capable of tap changes for other voltages? Conductors appear plenty large enough to run @208 volts if voltage drop because of length doesn't get in the way. That is just based on the fact you said you have a 10kVA transformer, actual load may be less which only helps us out a little more.
 
kwired said:
What kind of distance to the light poles, I was expecting smaller conductors for what appears to be about a 20 amp max load, and are luminaires capable of tap changes for other voltages? Conductors appear plenty large enough to run @208 volts if voltage drop because of length doesn't get in the way. That is just based on the fact you said you have a 10kVA transformer, actual load may be less which only helps us out a little more.
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I'm the design engineer, so I don't really have the equipment to check the fixtures for taps. Distance from transformer to the first pole is about 250'. There are 10 poles with one fixture each (I'm assuming 400W fixtures).
 
donw said:
I'm the design engineer, so I don't really have the equipment to check the fixtures for taps. Distance from transformer to the first pole is about 250'. There are 10 poles with one fixture each (I'm assuming 400W fixtures).
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How much will you pay me to come check for you? I could use a vacation to AZ.:)
 
donw said:
You would like today's weather - high of 69 deg:D
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Actually has not been too bad here this week, but not quite that warm. high's 45-55 most days, but has been kind of windy, which makes it feel colder than it is if you are not sheltered from wind.
 
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