Household Electrical Question

[8ntruck 7,777]

Here is a question for you sparky guys out there that know more about sparky stuff than I do:

 

We have a GFCI outlet and the vanity light switch in the wall next to the bathroom sink.  Both were installed at least 25 years ago.  The GFCI will frequently trip when the vanity light is switched off.  The only thing the GFCI is protecting is the outlet.

 

What could cause that?  Is it possible that the GFCI has aged out, and reacting to some sort of spike that happens when the light is turned off?

 

The snap that the GFCI makes when it trips scares my wife.  My gut feeling is totrplace the GFCI equipped outlet and see if that solves the issue. 

[WHX?? 51,696]

I would replace it. 25 years it don't owe ya nothing. 

I would also go through the wiring behind it and check connections. Make sure everything is wired as should. 

Check neutrals GFIs like bad neutrals.

[JPWH 6,337]

Before you replace the GFCI check for loose wires on the device and the connections  in the box. If the wires or terminals have any corrosion then moisture is not helping the situation so when you replace the device install a w.p. device(real pricey) or at least a gasket behind the plate. 

[squonk 43,731]

Yup old GFCI's will cause issues. 

 

Working in an OLD school kitchen. Cloth wiring , the works. Got a call that a steam cooker wasn't working. I get there and it's fine. Can't find anything wrong. Get called several times over the year. Same thing.

 

Turned out they had an old Bunn Coffee pot that apparently had a small internal leakage to ground. One of the later arriving lunch ladies would make coffee everyday with it and it would trip a GFCI, so she would move it to another plug until it tripped again. She never told anybody and we would get calls that another piece of equipment wasn't working. She or someone else would reset the outlet before we got there. Turned out several non GFCI outlets were connected to GFCI outlets including this steam cooker that  haunted me for a year! 

Edited May 22 by squonk

[Achto 29,368]

10 hours ago, 8ntruck said:

The GFCI will frequently trip when the vanity light is switched off.  The only thing the GFCI is protecting is the outlet.

 

If the light is wired through the GFCI outlet then it will also be protected by the outlet.

[Gasaholic 286]

41 minutes ago, Achto said:

 

If the light is wired through the GFCI outlet then it will also be protected by the outlet.

Yep. Can also depend on HOW it is wired - I installed  Combo (Top is a light switch, bottom is a GFCI Outlet) - came with instructions how to wire it so that the light switch works independently of the GFCI protection (With a jumper wire)  GFCI works based on detecting any power surges, and sudden loss of load can cause voltage spike enough to trip the GFCI. (GFCI is also a problem in shops/garages where a VFD powered device is used - VFD and GFCI do not like each other.... Oh yeah, VFD = Variable Frequency Drive for variable speed electric motor powered stuff like lathes, drill presses, end mills, etc.) 

[rmaynard 16,290]

Try the simplest thing first. Replace the old GFCI. When my house was built in 1978, it was common practice for the bathroom GFCI to power not only the bathroom, but the kitchen counter outlets within arms reach of the sink, the outlet on the deck, the front and back porch lights, and for some reason the outlet in the master bedroom that shares a wall with the bathroom. I have replaced it twice in 47 years.

[Mickwhitt 5,114]

I did some work building a false wall style paneled feature wall in our bedroom.

There was a lighting circuit which was fed from a downstairs fuse box and had provided a light for a now removed staircase. 

I thought it would be useful to use that feed to power a standard lamp so that we had a bedside switch for it. 

Wired everything up with no problem.  

Fitted the boards to the framing, not knowing I had trapped a twin and earth cable between them. 

I found out when the downstairs fuse board tripped out and would not reset.

The RCCB would not reset until I removed a lighting neutral from the bus bar. So it was a neutral to earth fault, I had clearly pierced a cable building the wall. But where?

Took a while to find but the trapped cable was the culprit, and a 1mm air nail I had scored a bullseye with on it.

 

 

Thankfully not too great a chore to free the trapped wire and cut out the damaged section. 

Just tells you to check and check again with any wiring installation. 

This is the completed wall ready for finish painting. Bed will sit between the reading spot lights. Sockets are higher than usual to allow bed side units. 

 

[wh500special 2,262]

What kind of lamps are in the vanity light, and were they recently replaced?

if they’re not incandescent…

 

Non-resistive loads can throw a pulse back when switched off. Same phenomenon as a spark plug firing when the points open.  If that’s the case, the GFCI can see this pulse as a current imbalance and open.   Might not happen every time. 

Fluorescent lamps can do this as they themselves are capacitive and their starters can also store energy. So can LEDs as they have drivers in them upstream of the lighting diodes (it’s these power supplies that fail making the bulbs not last as long as they should). 
 

You can soak up the pulse with a properly sized Metal Oxide Varistor (MOV) shorted across the switch contacts, but this is rarely to never implemented on household stuff.   I used to have a MOV in a plug that I plugged into the hallway outlet of my house when I used the vacuum cleaner.  Without it, 100% of the time when I turned off the vacuum it opened the arc fault breaker in the breaker panel in the basement.  With it, it suppressed the arc and kept the breaker closed.  I have a different vacuum now and it doesn’t induce the fault anymore…no idea where I put the plug or I’d open it up for a picture. 

 

GFCI devices can change their behavior over time too.  Replacement is the easiest way forward. We just had a GFCI spontaneously go bad on us on a piece of brand new equipment we manufacture at work.  This was one brand new one out of about 1000 of them that we installed over the last six months.  

 

  If you happened to relamp the fixture recently with something other than incandescent lamps, it’s possible if you can go back to whatever was in there before that the issue will resolve.  Maybe even just a different set of lamps will cure it. 
 

It happens. 

 

Steve

Edited May 24 by wh500special

[8ntruck 7,777]

The vanity light Is a single fluorescent tube fixture.  Nothing has been replaced lately.  Then again, this is not a new issue, but it is happening more frequently lately.

[rmaynard 16,290]

If the fluorescent light uses a ballast, that could be your problem. I have seen it before in older homes that were retrofitted with GFCI's.

[wh500special 2,262]

Likely a product of the lamp type.  Might be possible that over time the surge that spits back when turning off the switch has burned the switch contacts enough to cause the opening event to last longer and make the GFCI more apt to catch it.  Easiest things to do are replace the GFCi and the switch.  And cross fingers. 
 

Steve