isolation

[BCK]

Many people have these in there homes. Maybe I'm wrong, but isn't it against code to directly bond a neutral to ground in a residence other than at the Service Entry Panel? Are transformers an exception?

 

[BCK]

Dereck, I'm actually wondering myself what I am looking for. Even though this has gotten a little crazy it's been very helpful. After reading this I think I should be in the market for something else.

 

[ELA]

I agree that isolation transformers still provide enhanced noise rejection even when the secondary center tap is bonded to ground. The secondary is no longer considered gavanically isolated because of the bond but you still get noise rejection. Although you lose the feature of breaking a ground loop when the secondary bond is present.

A transformer with a farady shield between windings then further helps prevent capacitive coupling as a means for noise to couple between windings.

I have to admit that I have used the unsafe methods of using an unbonded isolation transformer or floating the ground lead on a O'scope in the past.(when measuring ac circuits that are referenced to ground).

Once you have witnessed the ground lead burnt off of a scope probe when measuring without isolation you get very cautious.

Of course I was very careful in making my measurements not to touch the scope case and ground at the same time.

I loved it when DC powered and isolated scopes came out so I did not have to deal with "floating the scope" (or the a-b differential measurement) anymore.

 

[dereckbc]

Many people have these in there homes. Maybe I'm wrong, but isn't it against code to directly bond a neutral to ground in a residence other than at the Service Entry Panel?

Yes, but you are confusing the issue. You are not bonding the neutral comming from the service panel with the transformer input. You are creating a completely new seperately derived system on the secondary side, and a new ground reference point.

After reading this I think I should be in the market for something else.

Yes I believe so from what I can gather. You are looking for one of the four methods I posted before this one, like a new scope with built in isolation.

Most scopes have the common input referenced to the chassis of the scope, which makes it impossible to take bridged or balanced measurements without using something like a differential input mode, a add-on isolation amplifier, or dangerous modifications like cutting the groud pin off.

 

[quogueelectric]

Isolation xformer

Isolation xformer

Most Isolation Xformers I have seen are used in operating rooms for surgical equipment. Also there is a common ground for which all metalic equipment to come in contact with the patient has a special ground connection to make sure all equipment is at the same potential to ground and each other. Most of The panels have ground fault monitoring alarms on them allso.

 

[LarryFine]

I'm actually wondering myself what I am looking for.

After reading this I think I should be in the market for something else.

Okay, I think I've held back long enough.

BCK, just what are you looking for, that an isolation transformer might or might not be the solution for?

Is it for personnel protection or signal-reference isolation for test equipment?

 

[iwire]

Is it for personnel protection

As far as I am aware the only place that the NEC allows a truly isolated ungrounded system for personal protection is as described in Part VII of Article 517 Health Care Facilities.

Ungrounded Delta systems are not installed for personal protection.

or signal-reference isolation for test equipment?

I do not believe the NEC ever allows an ungrounded system for that type of isolation. I also think OSHA would take a very dim view of eliminating the connection to earth putting technicians and test equipment at risk especially when as Dereck and Jon pointed out there are ways to get around this problem in a safe and code compliant manor.