Balanced power

[scott1972]

Roughly ten years ago I installed a balance power transformer from equi-tech in a recording studio, we followed all engineers specs, installed a ground triangle, isolated ground plugs with an external ground wire (there was old steel two wire bx and it was easier to add a ground wire then to replace), and followed the code. The system worked great, no noise at all.That was until we did some upgrades, about a month ago we changed the panel to allow for 10 additional circuits, we ran aluminum m/c with two grounds one equipment (dirty), and one to the center tap with all the other isolated grounds which led to the ground triangle (clean). The system now has a little noise not much, but not like before. We checked everything, however when we plug into the old outlets we get no noise and when we go to the new outlets there is some noise :blink:? If anyone has input it would be great, the NEC article on balance power is 647.
Thanks

 

[brian john]

Is this a grounded system with a neutral 120 VAC to Neutral and ground or a 60 VAC to 60 VAC with a grounded center tap?

Did you megger the branch circuits when you installed them?

 

[infinity]

Roughly ten years ago I installed a balance power transformer from equi-tech in a recording studio, we followed all engineers specs, installed a ground triangle, isolated ground plugs with an external ground wire (there was old steel two wire bx and it was easier to add a ground wire then to replace), and followed the code. The system worked great, no noise at all.That was until we did some upgrades, about a month ago we changed the panel to allow for 10 additional circuits, we ran aluminum m/c with two grounds one equipment (dirty), and one to the center tap with all the other isolated grounds which led to the ground triangle (clean). The system now has a little noise not much, but not like before. We checked everything, however when we plug into the old outlets we get no noise and when we go to the new outlets there is some noise :blink:? If anyone has input it would be great, the NEC article on balance power is 647.
Thanks

Sounds like the old receptacles we'ren't really grounded if they were connected solely to an electrode.

 

[romex jockey]

“Technical Equipment Ground” via 647.6 B is a new one on me

what is the dif betwixt technical and isolated here?

~RJ~

 

[scott1972]

Balance power

Balance power

This is a 60volt to ground system with a 120volt between both legs, and I misspoke in original post there is noise across all outlets, it is not just on the new ones but the old ones as well

 

[mbrooke]

My guess is that stray current is some getting on the EGCs from another power source (that outside the isolation transformer) Just a guess though- I am mystified as well.

 

[Andy Delle]

Sounds like the old receptacles we'ren't really grounded if they were connected solely to an electrode.

Agreed! The secondary centertap should be grounded back to the service. Otherwise you have a floating system and that's not what NEC647 balanced power is about. IIRC, only some medical installations may be floating and those have specific ground fault monitoring.