×
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!
  • Students Click Here

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here

Jobs

GFI protection at 80 vac

GFI protection at 80 vac

GFI protection at 80 vac

(OP)
I am planning on installing a power distribution system to provide 80 vac for 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 the circuits.
The various available units that are sold commercially seem to only be rated for use down to 102 v (120 v -15%).
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 an approved GFI for my needs?

RE: GFI protection at 80 vac

You would need special 80V heaters, too !

Wouldn't be simpler to insulate the wires with
e.g. silicon rubber and heatsink the ends of the
tubuler heaters -- where the wires enter -- to
keep them at the temperature safe for the silicon
rubber -- i.e. keep the "vacuum" away from the wiring ?

RE: GFI protection at 80 vac

(OP)
Resistance heaters will provide heat directly proportional to the line voltage squared assuming their resistance remains constant.
The heaters that I plan to use are called mineral insulated (MI) and the heating conductors are completely encapsulated by a metal sheath.
Nevertheless, we must provide limits on the voltage so that a broken sheath does not bring on a "lightning storm" which is how some describe the corona. And we need GFI protection to eliminate the shock hazard for the astronaut if the heater was broken open.

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members!


Resources