Intresting Problem

Reply

  #1  
Old 04-07-09, 07:54 AM
N
Member
Thread Starter
Join Date: Jan 2008
Location: Southern New Jersey
Posts: 25
Received 0 Votes on 0 Posts
Intresting Problem

All,

I recently re-did a bath room. I put an exhaust fan/light fixture inside the shower stall. According to NJ code, I had to put this fixutre on a GFI protected circuit. OK, no big deal. I wired the fixutre off of the GFI outlet on the vanity. The circuit is as follows:

Power comes into then out of the GFI outlet on the vanity. Thus everything there after is GFI protected. Power then runs to the fan/light fixture in the shower. Then from the fixutre the circuit runs to a switch on the wall. Now I'm pretty good with electric. And I'm almost certain that the circuit is run corretly. However, when I flip the switch for the fan, the GFI outlet blows. Right now it is just the fan. I do not have the light plugged in as well. The intresting thing is that with the switch in the on position, and the GFI breaker blown, I can reset the GFI breaker by pushing the reset botton on the outlet then the fan comes on and stays on.

I'm confused. The only thing I can think of is that the inductance in the fan causes the output current through the GFI outlet to lag the input current, which causes the outlet to blow.

Has any one ever had the same problem??
 
Sponsored Links
  #2  
Old 04-07-09, 12:04 PM
I
Forum Topic Moderator
Join Date: Feb 2005
Location: Near Lansing, Michigan
Posts: 10,944
Received 42 Votes on 40 Posts
Originally Posted by nicstefa View Post
The only thing I can think of is that the inductance in the fan causes the output current through the GFI outlet to lag the input current, which causes the outlet to blow.
It's possible, but that problem is much less common with the newer GFCI devices. If you're using a store brand or an older GFCI receptacle, I'd recommend trying a new brand-name one like Pass-Seymour or Cooper.

It's also possible that your ground wire in the switch box might be touching the hot screw and when you bump the switch it could cause a momentary contact. Same goes for a pinched wire clamp at the switch box.
 
  #3  
Old 04-09-09, 08:49 AM
B
Member
Join Date: Oct 2008
Posts: 1,312
Received 0 Votes on 0 Posts
GFCI's work by measuring how much electricity is going out one wire and making sure the same amount of electricity is returning on the other wire.

If some electricity is "leaking" and going to ground, then the same exact amount of electricity will not be returning on the other wire, then the GFCI will trip.

This is what would happen if you were being electrocuted. Some of the electricity would flow through your body and to the "ground".

With that said, electric motors (fan) are notorious for leaking electricity.

So a test would be to disconnect just the fan and see if the problem stops.

And/or remove the ground from the fan and see if the problem stops. Then there would be no path to ground and all the electricity would have to return via the other wire.

If the fan motor is leaking, try blowing it out with compressed air and cleaning it as much as possible. Or if you are required to have this on a GFCI and the cleaning does not work, then get a new motor.

Reconnect the grounds after testing. Don't Touch the Fan with the Ground Removed and Power Applied!
 
  #4  
Old 04-10-09, 06:44 PM
B
Member
Join Date: Dec 2004
Location: Canada
Posts: 167
Received 0 Votes on 0 Posts
The only thing I can think of is that the inductance in the fan causes the output current through the GFI outlet to lag the input current, which causes the outlet to blow.
It's possible
I beleive this is not correct guys, current can lead or lag the voltage or voltage can lead or lag the current but output current can not lag input current. Unless there is something I have forgotton ? It has been a long while since school
 
  #5  
Old 04-13-09, 08:32 AM
I
Forum Topic Moderator
Join Date: Feb 2005
Location: Near Lansing, Michigan
Posts: 10,944
Received 42 Votes on 40 Posts
I don't believe it's necessarily the current lag that causes a trip, but more like energy lost due to inducing current in the motor frame and other tiny effects like that which briefly confuse the GFCI. If you consider that it is supposed to detect a 5mA difference in a 20A current, that's a 0.025% deviation. In that sort of tolerance, there's bound to be a false trip now and again.

I'm lumping this problem into the same category as times when I've seen GFCIs trip on freezers, door openers, etc. I've never seen in person, but have had several reports on this forum of HDTVs causing trips. Replacing the GFCI with a newer model which has more EM/RF shielding and better internal components almost always fixes the problem.
 
Reply
Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Thread Tools
Search this Thread
 
Ask a Question
Question Title:
Description:
Your question will be posted in: