setp up transformer

[grumpy11]

i got a 3 phase setp up transformer 208 to 480v

im being told that the voltage on two legs is 480 volts to ground.

if the wiring was crossed in the transformer where the higher voltage was connected to the x/o terminals not the h terminals would that cause the strange voltages

 

[infinity]

i got a 3 phase setp up transformer 208 to 480v

im being told that the voltage on two legs is 480 volts to ground.

if the wiring was crossed in the transformer where the higher voltage was connected to the x/o terminals not the h terminals would that cause the strange voltages

That's because it's likely a corner grounded Delta secondary. Is the X0 on the primary or the secondary?

 

[kwired]

i got a 3 phase setp up transformer 208 to 480v

im being told that the voltage on two legs is 480 volts to ground.

if the wiring was crossed in the transformer where the higher voltage was connected to the x/o terminals not the h terminals would that cause the strange voltages

My guess is there is no neutral for the output and it is a grounded phase system. Common when backfeeding a transformer to get 480 volts instead of ordering one designed for step - up.

 

[augie47]

If your 480 side is delta and one phase is grounded, you will measure 480 to ground on the other two phases.

 

[grumpy11]

step up transformer

step up transformer

twp phses going into an ac unit each phase at 480 volts why

 

[infinity]

twp phses going into an ac unit each phase at 480 volts why

3?, 1 grounded, other two 480 v to ground.

 

[kwired]

twp phses going into an ac unit each phase at 480 volts why

Give us some more specific details of what you have, but I'm guessing you have a grounded phase system.

How many wires from the transformer to first disconnect. Where is the bonding jumper and which system conductor is it connected to. Chances are there is no HO terminal in the transformer just H1 H2 H3 (maybe some voltage % taps but no HO). There is no choice with this system but to ground a phase or use as ungrounded system - which requires ground fault detection equipment if you go with ungrounded system.

 

[templdl]

Give us some more specific details of what you have, but I'm guessing you have a grounded phase system.

How many wires from the transformer to first disconnect. Where is the bonding jumper and which system conductor is it connected to. Chances are there is no HO terminal in the transformer just H1 H2 H3 (maybe some voltage % taps but no HO). There is no choice with this system but to ground a phase or use as ungrounded system - which requires ground fault detection equipment if you go with ungrounded system.

I second this emotion.

 

[brian john]

I have often taken a stance against 208/120 wye step up to 480 delta, or the often called back fed transformers. This is why; few electricians realize what they are facing when they see what the OP saw. On two different occasions we have responded to calls where uninformed electricians shut sites down in a panic as they had a corner grounded system. On a few other occasions we have had ECs call us wanting to know how to derive a neutral for lighting.


At a minimum the installing electrician should label the equipment. I prefer a 208 delta to 480/277 wye.

But it is legal per the NEC and I would not change that. Maybe a bit more education in apprenticeship?

 

[texie]

I have often taken a stance against 208/120 wye step up to 480 delta, or the often called back fed transformers. This is why; few electricians realize what they are facing when they see what the OP saw. On two different occasions we have responded to calls where uninformed electricians shut sites down in a panic as they had a corner grounded system. On a few other occasions we have had ECs call us wanting to know how to derive a neutral for lighting.


At a minimum the installing electrician should label the equipment. I prefer a 208 delta to 480/277 wye.

But it is legal per the NEC and I would not change that. Maybe a bit more education in apprenticeship?

Agreed. I've seen more of these improperly done than I care to think. And they never seem to understand how important it is to not ground/bond the wye input. There are many of these installs out there that are accidents waiting to happen.

 

[grumpy11]

turns out after checking it out more today its a corner ground delta

 

[meternerd]

As stated in other posts, I think corner grounding 480 is a bad idea. Any ground on the ungrounded phases is a phase to phase fault. Any accidental contact with an ungrounded phase when you are standing on or touching ground means you are getting zapped by 480. Ungrounded delta can be much more forgiving as long as the required ground dectection equipment is installed. Just my opinion, having worked around 480 to over 35 years.

 

[kwired]

As stated in other posts, I think corner grounding 480 is a bad idea. Any ground on the ungrounded phases is a phase to phase fault. Any accidental contact with an ungrounded phase when you are standing on or touching ground means you are getting zapped by 480. Ungrounded delta can be much more forgiving as long as the required ground dectection equipment is installed. Just my opinion, having worked around 480 to over 35 years.

And unless you are in an industrial place with qualified persons how long does the ground detection show a fault before something is done to fix the problem (in most cases). If nothing stops working many people will just ignore it, and not really know what the situation really is all about either. A corner ground is definately going to open an overcurrent device and something will stop working, and someone will need to fix the problem if they want to continue to use things.

 

[meternerd]

Good point. Guess I'm used to the industrial world.