Am I missing something here or am I looking into this to hard

I don't know if I am looking into this to hard.

I am in the middle of adding some external relays and alarms to all of our machines.

I go to the plc check voltage on the card to make sure it has 120 volts ac and not wired dc becouse here colors don't always mean anything.

1 lead to ground 1 lead to hot wire 46 volts ac
So I think I have a short loose conection ect.

I unhook all 120 vac wires 1 at a time check it nerver changes.find no issues

at the transformer the readings seem weird
x1 to x2 120 vac
x1 to ground 54 vac
x2 to ground 290 vac

The transformer has 480 vac at the top been running for a while and no wires moved

so why would x2 read 290 vac to ground

souldn't x2 have a ground wire hooled to the neutral at the transformer?

It's obvious they did not ground it or the grounding connection is now missing. Check the machine schematics.

On a 480 x 120 VAc Step down Control Transformer X2 is you neutral for 120 volt devices connected to that transformer

X2 should not be connected to another neutral. If it is this could be part of the problem.

X2 should be tied to earth ground also so that you do not have a floating neutral. Othervise your voltage reading will vary quite a bit.

The ground to X2 needs to be connected to the ground bar and the incoming feeder ground if possible. Bonding the X2 to ground via the panel interior plate is not the best bethod but it will work.

Looks familiar Like the wye secondary with goofy voltages like yours. Found the star point was not bonded to ground. Doing this will fix problem

Dan Bentler

bernie_carlton said:

It's obvious they did not ground it or the grounding connection is now missing. Check the machine schematics.

Click to expand...

I once encountered a system where the 120 control voltage was not bonded to ground. What they did have is an alarm system, two separate bells one was hooked to X1 the other was hooked to X2 the other wire from each bell was hooked to ground. When they had a ground fault in the 120 control system one of the bells would ring until the ground fault was removed. I have no idea how long the system was setup this way, but the facility has existed since the 20's.

Note: The bells were constantly vibrating but the gong never touched the bell when there was not a fault.