Isolation.... (Re: is it useable?)

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "davep by way of Terry Fritz <twftesla-at-qwest-dot-net>" <davep-at-quik-dot-com>


>>        Isolate, agreed.
>>        'any' is a bit strong.  Isolation transformers, except
>>        as below, have an amount of interwinding capacitance.
>>        This leads to HF/RF (EMI) coupling via this capacitance.
>>        The conventional isolation transformer is designed for
>>        'dc' and '60 Hz'(ish) isolation.
>>
>>        Serious Work uses special transformers, with added
>>        shielding isolating the load side from the line side.
>>        Those I have seen are specifically marked.
>>
>>        I am NOT proposing it not be used.  However
>>        understanding what can be expected is commonly helpful.

> You're right in a small sense, If the core be grounded with a dedicated
> ground and the tranny is a true ISO. tranny then most RFI will be held
> within the secondary windings.

	I suggest that more critical than grounding the
	core is having a designed in shield between primary
	and secondary.

> EMI is a different story because this can be induced into the

> wiring on the primary side very easily,

	What i've referred to as 'radiate around the filter'.

> shielded BX cable with the armour flex grounded will help here.

	A bit.
	Recall the old rule:
	EMI/RFI shielding is only as good as its longest
	single opening?
	THAT, in the case of BX, is the long spiral.
	(true: tho non coiling, case:
	We were qualling a new mouse for EMI.
	Sample was fine.  Next one failed.
	'they' had switched the cable from continuous shild,
	with folded foil to an 'audio grade' shield, with no
	fold....)

	Also, the EMI can travel on, and radiate from, the
	metallic BX armor.  Grounding that will help,
	probably a lot, for coiling freqs.  For the VHF strays,
	the armor will radiate nicely as a 'long wire'.


	best
	dwp

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