Help me understand correct method to use a control transformer
Help me understand correct method to use a control transformer
(OP)
I have a machine that is single phase 240vac operation. Power in is L1,L2, and the grounding conductor. I would like to step down the voltage to 120vac so i can power a single convenience outlet meant to only power a small ionizing fan that is to be used on the unit.
The control transformer is 240/440 primary with 120vac secondary coil (single coil). From what i have read is you are supposed to obtain the grounded (neutral) conductor by bonding X2 of the secondary to ground. My questions are as follows:
1. Is this the correct method? From what i have always understood was that the grounded and grounding conductors are only ever tied together at the main panel.
2. If it is how you do it, can it be bonded directly at the place of installation? does it need a dedicated groundING conductor all the way to the main power entry of the machine?
3. Does it need a neutral? can the voltage be "floating". If so, what are the benefits and negatives of this?
The control transformer is 240/440 primary with 120vac secondary coil (single coil). From what i have read is you are supposed to obtain the grounded (neutral) conductor by bonding X2 of the secondary to ground. My questions are as follows:
1. Is this the correct method? From what i have always understood was that the grounded and grounding conductors are only ever tied together at the main panel.
2. If it is how you do it, can it be bonded directly at the place of installation? does it need a dedicated groundING conductor all the way to the main power entry of the machine?
3. Does it need a neutral? can the voltage be "floating". If so, what are the benefits and negatives of this?






RE: Help me understand correct method to use a control transformer
2) You should use the ground that came with the 240Vac you mentioned, that way there will not be any potential difference between the two grounds in your machine/system. You can ALSO then ground locally if you still desire.
3)No! And not allowed in the USA.
Keith Cress
kcress - http://www.flaminsystems.com
RE: Help me understand correct method to use a control transformer
"You measure the size of the accomplishment by the obstacles you had to overcome to reach your goals" -- Booker T. Washington
RE: Help me understand correct method to use a control transformer
But Keith, 250.21 allows for the choice to ground or not ground the secondary of a CPT circuit if it is used just as control power. Whether or not a light fixture inside of a control panel is "control power" or not might be debatable however. But still even so, just because you can doesn't mean you should...
"You measure the size of the accomplishment by the obstacles you had to overcome to reach your goals" -- Booker T. Washington
RE: Help me understand correct method to use a control transformer
I did not recall 250.21! Seems ridiculous anyway to leave it all so ambiguous.
Keith Cress
kcress - http://www.flaminsystems.com
RE: Help me understand correct method to use a control transformer
"You measure the size of the accomplishment by the obstacles you had to overcome to reach your goals" -- Booker T. Washington