Neutral with a Buck & Boost Transformer

[jandon]

Were installing an LG dryer that opertates at 240/120 single phase. Our current servive to our facility is 208/120 three phase. We plan on running 208 through a buck and boost to get the 240V we need but the dryer also needs a neutral for the 120 side. The last time I metered the secondary side of a buck & boost being supplied by 208V, I saw 120 to ground on one leg and about 100V on the other leg. Being that a buck & boost does not provide a neutral, can we run an uninterupted neutral wire from the panel all the way to the dryer and using it as the common to the secondary leads(240V) of the buck and boost without being a hazard or a code violation?

 

[kwired]

How will that change what voltage you measured from your transformer output to ground? The neutral is at same potential as the ground with small differences because of voltage drop.

The dryer will run just fine @ 120/208 it will just not produce as much heat and will take a longer cycle to do the same work.

If you are concerned because the dryer is not marked for 208 volts consider the fact that a 5 or 7.5 Kva transformer will cost more than a different dryer. Even the buck boost will likely get close to cost of a different dryer.

 

[hillbilly1]

If you were getting 120 to ground on one leg, and 100 volts on the other, the buck/boost transformer was wired as a "buck", reducing the voltage. If wired as "boost" one leg will be higher than 120 to ground or neutal. The problem with this, is if you make the wrong "leg" the high leg, you risk burning up any of the 120 equipment that uses a neutral.

 

[kwired]

The problem with this, is if you make the wrong "leg" the high leg, you risk burning up any of the 120 equipment that uses a neutral.

Also the reason to not use it for a cord connected appliance. You may get it right on first dryer. Down the road someone changes dryer and now 120 loads are on other line - there will be problems. As I said before, the proper transformer will cost more than a dryer, and all that will be lost is a little less heat and more drying time.

 

[hurk27]

If I remember right there are buck/boost configurations that will give you 120 volts, but trying to guess which leg of the dryer is using 120 volts might be a guessing game you might not want to do, and if the dryer has 120 volt loads on both legs your sunk. adding 24 volts to the neutral voltage would put it over what most controls and electronics would take.

but as was said, the only load in the dryer that needs 240 is the heating element and it will operate just fine on 208, it will just take a couple minutes longer for the dryer to preheat, once heated it will maintain the heat just like on 240.