Thread Starter


Joined Jun 17, 2006
Hello again to everyone,

This time I have two questions. To begin with, when my grandfather would explain some things to me, he would always include the term "isolated". For example, he would say, "you must isolate the circuit", and I would have somewhat of an idea of what he meant. My question is, in a fully explained way (haha), what does the term "isolated" mean and how do you go about doing it?

Also another grounding question that arose this morning (at least morning in America!). Why couldn't one ground the 'hot" side of a circuit to ensure its safety?

Thanks a lot!


Joined Apr 20, 2004

Isolating the circuit is kind of a flexible idea. Removing a circuit board from an instrument is a form of isolating a circuit, for instance. When checking individual devices like transistors, it's often necessary to remove them from the pc board - another form of isolation. The idea is to make it possible to check some portion of a circuit without confusion as to what contributed to your meter readings.

Yes, grounding a hot line will make it considerably safer. It will also pop the protection device - or melt the wire - making it hard to have it supply a load. Some degree of risk is a part of life.


Joined Oct 28, 2005
If you are in the context of Electrical line voltage power distribution (United States), the terms, "isolated" and "grounded" refer to how the circuit breaker housings are to be treated. The service entrance to your house is usually "grounded" via a copper rod driven into the ground, a connection to reinforcment bar in the concrete foundation, or a connection to the cold water supply. Subsequent circuit breaker panels (Sub-panels) are "isolated" which means they are grounded through a green or bare copper wire.
Isolation may also refer to the fact that low voltage control circuits are "isolated" from ground since neither lead of the secondary side of the transformer are connected to the case of the equiptment.
Beenthere's statements are also all true -- the "hot" wire coming from a transformer is defined as any lead that is not grounded. Connecting one of the secondary leads from a single phase transformer to ground defines it's voltage at zero, and the other one to have the maximum voltage potential of the transfomer. Connecting both of the leads coming from the secondary of a transformer to ground is the same as connecting them together, and that's called a "short circuit" Most transformer windings cannot handle this condition as it causes the maximum amount of current available in the secondary.
Hope this helps.