Query about Belkin surge protector

[4kruby]

Hello,

I have a belkin surge protector with 3 pins.
https://www.belkin.com/in/chargers/surge-protectors/home-office/na/p/p-f9e300-1.5m/

The MOS and thermal fuse has been damaged (burnt). So, I replaced them.
After replacing, I noticed that when plugged into power, the following happens :
1. When onboard switch is ON, I can sense the line on line socket and nothing on neutral and earth socket (using a 100 to 250v tester)
2. When onboard switch is OFF, I can sense the line on both line and neutral socket and nothing on earth socket (Edit : I measured the voltage between neutral and line - its around 1 volt).

It is working when appliances are plugged in. I understand that if  both line and neutral are hot, the effective voltage should be nil and so, appliance will not work. But is this a common way of design? or is there any flaw in this power strip?

I am not sure whether this was the behavior before I opened it.

Thanks.

[4kruby]

I found that the line and neutral is swapped on the plug outlet. I guess the surge protector switch is doing something with the neutral line. May be its shorting neutral with line when OFF ?

Because the above behavior does not happen if it is plugged into the socket where line and neutral are not swapped (line on right and neutral on left)

[Whales]

The switch on the picture looks like a single pole switch, ie it only switches one wire.  Two situations:

(1) If it's wired to switch the active wire: appliances will turn on/off as expected.

(2) If it's wired to switch the neutral wire: appliances will turn on/off as expected BUT the sockets will still be hazardous when turned off (don't go poking metal in them!).  Additionally some (poorly designed) appliances plugged into the "off" power strip will become hazardous even though they appear to be off.

If your house wiring has the active and the neutral swapped (edit: looks like you have a powerpoint with this?) then situation (2) probably occurs.  You will measure full mains voltage (240V/120V/etc) between outlet and ground even when the switch is turned off.


Also be wary of "phantom" or "high-impedance voltages".  A properly turned off socket can still read 10 or 100 volts AC if you use a normal high-impedance multimeter.  This is from electricity leaking through the capacitance of the switch and wiring insulation.  This voltage disappears if you plug in an appliance or other load. 


Obligatory safety

* Please use a properly rated DMM to do these tests.  Do not use one of those screwdrivers-with-neon-bulbs, they are rarely properly tested or rated, I would not consider them safe.

* Make sure to replace the fuses, including thermal fuses, with the same type (slow/fast), temp rating (degC), max voltage and max breaking current (hundreds or thousands of amps)

* If the original design didn't use solder: it's probably for a good reason.  I've seen some thermal fuses welded or crimped instead of being soldered.

[Whales]

I found that the line and neutral is swapped on the plug outlet. I guess the surge protector switch is doing something with the neutral line. May be its shorting neutral with line when OFF ?

I doubt the switch will be shorting anything, but I could be wrong.

The surge protector will have some internal loads (resistors, inductors, capacitors, etc) between active, earth and neutral.  These will have subtle effects on your (high-impedance) multimeter readings when the switch is in the off position.

As a simple workaround: leave a resistive load plugged into the power strip (eg a electric kettle with no brains/timers/LCD/other electronics) and turned on whilst making these measurements.  This will get rid of the phantom voltages and things might make more sense.

[4kruby]

Thanks for your reply!.

Only to this power outlet (3pin socket), the neutral and line are swapped (probably the electrician did it by mistake or ignorant).

I was wondering like why should both line and neutral output some voltage when the power strip switch is switched off. For example,
I measured the voltage between the terminals and found their values to be this when the switch is OFF.
1. Line to neutral - 1v
2. Line(neutral) to earth - 200v
3. neutral(line) to earth - 80v

I mentioned in the brackets because, they are swapped (inside brackets are the designated ones and outside brackets are the actual ones).

Please note that the switch I am mentioning above is the switch on the power strip. Not the switch switching the power outlet itself.

Thanks.

[Whales]

Please note that the switch I am mentioning above is the switch on the power strip. Not the switch switching the power outlet itself.

Yes, that's the one I'm referring to as well.

I was wondering like why should both line and neutral output some voltage when the power strip switch is switched off. For example,
I measured the voltage between the terminals and found their values to be this when the switch is OFF.
1. Line to neutral - 1v
2. Line(neutral) to earth - 200v
3. neutral(line) to earth - 80v

200V will probably be the full mains voltage.  That pin is live and dangerous (due to a combination of your backwards wiring and the single-pole switch).

80V will probably be a phantom or "high impedance" voltage.  You will only see this when measuring using a high-impedance tool (like a multimeter in volts mode).  If you plug in an appliance to the powerstrip (like I suggest) then it should instantly disappear.  Technically also if an earthed human touched the wire (don't do this!  I may be wrong!) it would also disappear to below 10VAC or so.



Switches do not perfectly ever turns things off or on, they have limits:

- In the ON position: the switch is a small resistive load (milliohms).

- In the OFF position: the switch is a very high resistive load (likely dozens of megaohms or more) with some capacitance in parallel (perhaps a few dozen pF or so).

Additionally any insulation that separates the live and neutral wires also acts as a small capacitor.


A little bit of current leaks through this capacitance when the switch is OFF.  When you use a high-impedance measurement tool (like volts mode on most multimeters) then you end up with a circuit like this:

   240VAC mains -- unintended capacitances (~100pf) -- multimeter (~10Mohm resistive impedance) -- 240VAC mains

With these approximate numbers: you would read about 50VAC on the multimeter. 

[4kruby]

Thanks very much for taking time to explain in detail.

I guess the line and neutral have a difference of 1v instead of 200v because of the phantom voltage you mentioned. Or may be due to the separation capacitance. I shall connect a load to it and measure once more when it is in OFF condition.