Isolation Transformers

[gregpowell]

I am in the process of designing a product which will allow operators to make final adjustments to television sets. It is general practice to use an isolation transformer with an ungrounded neutral when performing these adjustments to protect against the high voltage potential to ground. Does anyone know if this practice is documented in any published standard (ANSI, OSHA, IEEE, TV manufacturers association, etc.)? I am also looking for a NEC code exception that allows an ungrounded circuit to be used in this application.

Any assistance is appreciated.

Thanks
Greg

 

[jbartos]

Suggestions: Check
1. NFPA 70 latest edition, National Electrical Code
for 517-160 Isolated Power Systems. (Isolation is often used in Health Care Facilities.) There is no explicit statement pertaining to your application in NFPA 70. The ungrounded systems are known for the detection of ground faults within the isolated transformer secondary branch circuits.
2. OSHA

http://www.osha-slc.gov/OshStd_toc/OSHA_Std_toc_1910_SUBPART_S.html

(electrical - general)

http://www.osha-slc.gov/OshStd_data/1910_0306.html

(somewhat related)

http://www.osha-slc.gov/OshStd_toc/OSHA_Std_toc_1910.html?General+Industry=General+Industry

(general + industry)
3. ANSI and IEEE standards do not focus on the personnel safety very much, if at all.
4. TV Manufacturers Association
Please, clarify.

 

[don01]

hi greg
yeh I think we've all got an isolating trany somewhere for working on TVs so I just had a quick look in the Australian standards and they do in section 5.3 acknowledge the use of isolating trnsformers
provided :-
the frame of the device is earthed
the device is connected by flexible lead
only one device is able to be used at a time
and the transformer complies with AS 3108 or AS3126

Now this leads me to an idea (pardon the pun).
If Mr Bartos's post hasn't given you the answer already ( and usually he does)
Check out the literature on some isolating tranies. They should tell you they comply to standard xyz now check out that standard if it doesn't refer directly to what you want it should call the standard you want.

Keep us posted
Don