Home>Discussions>ELECTRICAL & LIGHTING>Light fixture only dims when switched off
8 posts / 0 new
Last post
NYhighlander
Light fixture only dims when switched off

Hi, My bathroom light fixture all of a sudden would not switch off. It would only dim slightly when the wall switch was turned off. I replaced the switch first and then tried a new fixture. Neither changed anything. Before I start pulling my wall apart looking for a short or a crossed wire or call an electrician does anyone have any insight?

jdevlin
Re: Light fixture only dims when switched off

Loose connection or open neutral somewhere on the circuit. Look for loose wirenuts in any junction box on the circuit.

canuk
Re: Light fixture only dims when switched off

By chance ..... was there any other electrical work done elsewhere in the home?

KKelly
Re: Light fixture only dims when switched off

I've run into this in many older homes that have fixtures "hot wired".

"Hot wired" means that the fixture always has a "hot" voltage wire running to it and the wire to the switch only shuts off the ground. The problem with that wiring, besides the expected safety problems, is that the fixture is always hot no matter what position the switch is at, the switch shuts off ground, and it can still be hot if the ground to the fixture runs through any other fixtures or receptacles, which in bathrooms, is often the case. So, if that fixture runs through any receptacle that has something plugged into it or another light or anything else, that "other" becomes a resistor to power (your ground current has to go through something like another light bulb to get to home) and you get that dim effect.

Today, the switch is normally wired to hot, so shutting off the switch, assuming it's working properly, shuts of the power or any opportunity for power to reach the appliance/light/thing. So, shutting off a switch, in a properly wired home, should effectively shut the power to that item completely. In a properly wired home, every single fixture should be continuously wired to ground, never to hot. A ground short would, normally be extremely obvious.

In older homes in particular, there are often many electrical shortcuts taken in bathrooms and kitchens which should never have been taken.

Turn off your light switch and use a voltage detector to check for hot wires in the fixture. I'd bet it's still hot. If it's not, you have feedback current of a few volts from somewhere else which is an entirely other problem, and it means a short or, more likely, a short in something that acts as a resistor to current and feeds to the fixture you have the problem with. ...Which, I'm guessing, is why "canuk" asked if there was any recent work done.

If the problem started without any recent work being done, and without a hot wired house and, if it is hot wired, without any new appliance having been connected recently, then it's most likely a short or, more likely, partial short which is rare. I've seen this when someone connects a bathroom heater and runs a hair dryer to a poorly wired system.

NYhighlander
Re: Light fixture only dims when switched off

First, thanks for all the responses, I appreciate it. First, there was nothing new added or changed within the last two months or so. I will have to check to see if the fixture is hot wired or not. I don't believe it is. I am going to work on it today so I will let you know what the outcome is today.

NYhighlander
Re: Light fixture only dims when switched off

Well, I started the work today and being short on time I did not pull the wall apart today. It turns out that the fixture must have orginally being hot wired and had its own switch. It was bypassed at some point and a switch was run from that connection to connect a fan switch as well and then back to the fixture. There must be a short somewhere along the line running back and forth from the switch to the fixture. I didn;t want to pull open the wall because I am not ready to and it is paneling over sheet rock so it would have been messy. I am planning on a complete makeover of the bathroom next summer so I took the easy way out today. Since the hot wire was at the fixture I simply ran an external counduit out of it to a new switch directly wired to the fixture so it is a short term solution.

jdevlin
Re: Light fixture only dims when switched off

If it worked before it should work now. The problem is likely one of the neutral connections in the fan or switch box is probably apart.
If it never worked from the switch then the problem is someone tapped into a switch loop for the fan. The fan and light fixture are now wired in series.

chadchappell
Re: Light fixture only dims when switched off

i have the same problem and can't get it figured out. My shed lights only dim when turned off, this just started. the light wires are run into the fuse box then run to a switch, so assuming "run hot". The switch was old so i did change that out with a brand new one, didn't change anyghing. only thing on this circuit is 2 lights

TV Listings

Find TV listings for This Old House and Ask This Old House in your area.