small transformer

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T. tam

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this is my first post, i am mostly a residential electrician, but now getting into a little commercial stuff. my question is on a HS12F1.5AS Transformer. it has 277 volts feeding primary and load needs 120 volts from secondary. it is hooked up according to the information on the front of the transformer. the load is several acctuators for HVAC dampers. my question is, does the secondary need to be grounded? the tech support said it can be done either way. if it is not grounded, would it have an effect on these acctuators? several of them don't work anymore, and i am wondering why. these acctuators have a built in transformer to knock it down to 25 volts. thanks for your advice.
 
Ground the Secondary

Ground the Secondary

I would recommend grounding the secondary. I've seen a lot of issues with floating secondaries. I believe grounding it will help prevent a build up of charges when lightning is in the area.
 
thanks for the information. i will run a wire from the secondary side of transformer to the ground bar in the panel. so doing this should give me 120 volts to ground on one leg and 0 volts to ground on the grounded leg. right? where before i was getting 120 volts between the 2 legs on secondary side but only around 50 or 60 volts to ground on each leg. this transformer has been installed for a few years ungrounded, has anyone else experienced this having any effect on the load. when up at the acctuator j- box and only getting 60 volts from black wire to ground just doesnt seem right. now i should have that issue solved.
 
T. tam said:
has anyone else experienced this having any effect on the load. when up at the acctuator j- box and only getting 60 volts from black wire to ground just doesnt seem right. .
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No, the load is not connected to ground so it does not matter to the load what the voltage to ground is.

The load is only connected line to line so the line to line voltage is all that matters to the load.
 
iwire said:
No, the load is not connected to ground so it does not matter to the load what the voltage to ground is.

The load is only connected line to line so the line to line voltage is all that matters to the load.
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As long as the ungrounded system does not somehow get pumped to a high voltage with respect to ground. That could break down the insulation in the loads even though the line to line voltage is nominal.
Now it is unlikely that the ungrounded system will move that far from ground, but certain arcing events can "pump" up the voltage to ground to be several times greater than the line to line voltage.
 
T. tam said:
thanks for the information. i will run a wire from the secondary side of transformer to the ground bar in the panel. so doing this should give me 120 volts to ground on one leg and 0 volts to ground on the grounded leg. right? where before i was getting 120 volts between the 2 legs on secondary side but only around 50 or 60 volts to ground on each leg. this transformer has been installed for a few years ungrounded, has anyone else experienced this having any effect on the load. when up at the acctuator j- box and only getting 60 volts from black wire to ground just doesnt seem right. now i should have that issue solved.
Click to expand...
Although your plan will indeed "ground" one leg of your transformer secondary it is not the Code permissible method of grounding a transformer. Under certain conditions, including the transformer being not more than 1000 va, grounding to the transformer frame is an acceptable grounding means. Since your transformer exceeds 1000va, to meet Code, you would need to follow 250.30.
The outcome will in all honesty be the same, but I hate for you to get advice here that indicates the method is Code compliant.
 
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