GFI for non-standard voltage 1

[rlaft]

I am planning on installing a power distribution system to provide 80 vac for lighting and heating inside vacuum chambers. 80 vac is the accepted limit to prevent the occurence of corona which occurs violently with higher voltages as the absolute pressure is being decreased. These chambers may be "inhabited" by a human being (astronaut) for testing purposes. So, I need to provide GFI protection for all circuits.
I am sure I could design a GFI which uses a separate control circuit to sense the output of the current transformer etc. but this would surely be expensive. Obviously it would also lack industry approvals.
So where can I find a GFI for my needs?

 

[jbartos]

Comment: The GFI of the shelf is fine-tuned to certain ground fault currents associated with certain voltages. Please, would you clarify the "..higher voltages.." in your post. There could be a need for transient voltage suppressors.

 

[rlaft]

The higher voltages are in excessof 80 vac (RMS). They can initiate the corona under certain low absolute pressures. To prevent corona we typically use 120 vac fed variacs with a mechanical stop at 80 vac. This is an expensive solution and therefore, I am hoping to have a transformer custom wound (affordably) and then will have the gfi problem.

 

[jbartos]

It appears that a regular ground fault interrupter for 120VAC, 60Hz could be safe since the power supply from the utility may drop to 80VAC, 60Hz for some reason or other. This would imply that the standard off the shelf GFI would be unsafe, which is not the case.

 

[rlaft]

I have looked at several manufacturer's specifications for voltage levels. The lowest I have found is 92 volts. Just now I looked at Hubbell and theirs are 120 v +10%/-15%. I sent them an e-mail and they simply said it would not work at lower voltages. If I was representing a manufacturer, I would dispute your conclusion that a GFI was unsafe if it failed to operate at voltages lower than that specified.
As I recall, the typical design relies on a electro-mechanical relay to energize to break the circuit and I think 66% of design voltage would be insufficient to pick up the armature.
Have you personal experience with a particular model to support your expectation?

 

[WoodrowJWeen]

Have you considered using a 120V system with midpoint ground, giving only 60V line to neutral. This system was used in the audio industry.

 

[CHDean]

A standard US made GFCI breaker most likely will not function below 107VAC. The internal electronics will become unreliable and at some point not operate.

 

[stevenal]

Two and a half years latter he gets answers. Do you really think he cares now?

 

[jbartos]

Suggestion to rlaft (Electrical) Mar 23, 2001 marked ///\\I have looked at several manufacturer's specifications for voltage levels. The lowest I have found is 92 volts. Just now I looked at Hubbell and theirs are 120 v +10%/-15%. I sent them an e-mail and they simply said it would not work at lower voltages. If I was representing a manufacturer, I would dispute your conclusion that a GFI was unsafe if it failed to operate at voltages lower than that specified.
///I beg your pardon, this was not my conclusion. My conclusion was:

jbartos (Electrical) Mar 21, 2001
It appears that a regular ground fault interrupter for 120VAC, 60Hz could be safe since the power supply from the utility may drop to 80VAC, 60Hz for some reason or other. This would imply that the standard off the shelf GFI would be unsafe, which is not the case.

Clearly, I stated at the end: ".., which is not the case." This implies that the standard off the shelf GFI is safe for lower voltages; however, down to certain voltage level only.\\
As I recall, the typical design relies on a electro-mechanical relay to energize to break the circuit and I think 66% of design voltage would be insufficient to pick up the armature.
Have you personal experience with a particular model to support your expectation?

///As a professional engineer, I often have to use technical data from manufacturers and elaborate on them as required.\\\

 

[jbartos]

Suggestion: Visit

http://www.nssltd.com/pdf/15 amp plug.pdf

http://www.nssltd.com/pdf/Reptacle GFCI.pdf

for:
Operating voltage range:
From 85% to 110% of rated, i.e. 102V to 132V of 120V rated.