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# Confusion about bathroom light/fan circuit

Sun 31 Jul, 2016 06:17 am
I have an end of the run switch that controls a bathroom light and fan. The wire going into the switch only registers hot when the switch is turned off. How does this work? Shouldn't it always register hot?
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Type: Question • Score: 2 • Views: 1,354 • Replies: 7

dalehileman

-1
Sun 31 Jul, 2016 11:48 am
@Cgelpi,
Cg, (1) what's "end of the run, (2) how any wires come to it and (3) do the light and fan come on and off together

Forgive for my ignorance of techs' terminology

My guess is that there's something wrong. (1) what are you measuring with respect to (neutral? gnd?) and (2) is the voltage abnormal (that is slightly higher or lower than line)

Quote:
Shouldn't it always register hot?
That's the way a power switch is usually wired, yes. However, if there's no malfunction it's likely there's a semiconductor unit somewhere that senses the switch position and control the lights accordingly
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mesquite

3
Sun 31 Jul, 2016 03:13 pm
@Cgelpi,
This just means that the hot wire goes directly to the fixtures and the switch is in the neutral line. With the switch open, you will see a voltage on the line coming from the fixtures.
dalehileman

1
Sun 31 Jul, 2016 04:30 pm
@mesquite,
Mes that's quite an uncommon system isn't it
mesquite

2
Mon 1 Aug, 2016 01:05 am
@dalehileman,
I have seen that setup in some older houses. I doubt that it would pass code in most places today.
dalehileman

1
Mon 1 Aug, 2016 10:51 am
@mesquite,
Yes, Mes, and one might ask how many novices electrocute themselves in such home projects
0 Replies

1
Mon 1 Aug, 2016 11:00 am
@Cgelpi,
It could be just the way you are attempting to read the circuit. A meter measures the difference in voltage between 2 sources. If they are both the same voltage then it reads as zero.

If you are attempting to read the 2 sides of a switch, it will register hot when turned off but when the switch is turned on it will go to zero because at that point you are simply measuring the same wire.

Make sure you are measuring the wires to the switch against ground. This should allow you to read one side of the switch as always hot and the other side turns on and off with the switch.
dalehileman

1
Mon 1 Aug, 2016 11:09 am
Quote:
This should allow you to read one side of the switch as always hot
Yea Para but let's not encourage Cg to suppose that's normal

Cg: Consult a friend who's good at this sort of stuff
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