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gazdkw82

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Installed some new floodlights/pir and switches today. All tested fine, however on power up it was evident I had got something wrong. Upon investigation I had the neutral in the switched live of the PIR. Kicked myself but mistakes happen.

Corrected the mistake but still nothing was working as it should. Spent over an hour chasing the fault. Got to the metal clad RCD spur I had installed, live - cpc =245v, live - neutral = 110v, neutral - earth = 38v.

I got to the point of just having a piece of flex on the load side of the RCD and still getting the same results. Measurements are fine if you disconnect the cable. Fair to say I was stretching my head. Disconnected the RCD F/spur and tested the circuit again. All comes back ok. Wired all the lights up (bypassing all sensors/switches) and all works ok.

Has anyone come across a RCD behaving like this? Could my initial neutral/live fault have broken it? If so, how come a simple piece of flex causes these readings but no flex doesnt?
 
Best guess is that you have blown the neutral conductor somewhere.

Could be the N connection through the rcd. A volt measurement between live in and live out, followed by N in and N out will help track it down.
With a load attached, you should measure 0v from in to out on either the L or N
Any voltage showing, means a damaged unit.
 
You might have been lucky here. If the RCD is open-circuit in the neutral as it seems, it might have saved you from blowing up the PIR with the crossed connections.
 
Yep, neutral is open circuit.

Could I link out the neutral supply and load? As long as the rcd tests ok on the load side?
RCD measures the current in both L & N to detect anything missing. Bypass N and it would trip immediately I'm afraid as all L current would be seen as "missing" since it is not seen to come back via the local N.
 
Well, I'm a little overwhelmed here. Been over today to change rcd, test and commission the lights.

Getting some strange problems and I dont know if I'm missing the obvious. I cant think straight now. So here's the story.

As said earlier, I had a neutral on the switch return of 1 of the PIR sensors yesterday. Fault rectified but rcd was not working right. Not sure if it worked correct before the fault or now.

Today, upon a few hours of head scratching I found that the 3 way switch was not actually switching the load of the switch return from the PIRs. I tried a regular 1 way switch on the PIR switch and the motion sensors switched the lights as they should. Put the 3 way back on and the pir switch return was showing in terminal 1 but not actually passing it through to common. What are the chances. Left the 1 way switch on and all lights and sensors worked as they should.

After that, I decided to put an rcd spur back on the circuit. Circuit tripped immediately. The rcd just wouldn't hold in. The rcd was showing 115v on the load side even though the rcd would not hold in...

I disconnected the rcd and testing the circuit again. Maximum Zs I got on the circuit was 0.55ohms. Insulation resistance line and neutral to earth >200Mohms. Voltage on the circuit 254v between line and neutral, line and earth and nothing between earth and neutral. Put the lights back on the circuit and did a milliamps clamp reading on the earth. 0.08mA when lights not on, 0.69mA when all lights on. 0.48A on both neutral and line.

I'm really stuck here. I feel like I missing the obvious but because iv been mulling over it so much I cant think straight.

Any ideas?
 
When you say three way switch do you mean a 3gang switch mate or are you talking about a 2 way with auto/manual override positions ? Can you do a little drawing of your setup ?
 
When you say three way switch do you mean a 3gang switch mate or are you talking about a 2 way with auto/manual override positions ? Can you do a little drawing of your setup ?
A 3 position switch. L1, l2 and common.
 

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Thanks, on my previous post I uploaded a photo of the setup.

I have 2 of these set ups running to 2 independent 3 position switches. 1 for the side and 1 for the back.

I cannot see any issues with the design of the set up?
 
So you have a change-over switch with centre-off position? Changing over between permanent L and PIR SL out to feed the lights? So far so good. You say L1 was not apparently making contact to common as the PIR output was not reaching the lights. Did you check its resistance?

The RCD tripping seems to be a completely separate fault. Your tests seem to show an intact circuit so either you've misread something, or there's an intermittent, or you clear the fault when manoeuvring the switch etc to get the test leads on.
 
So you have a change-over switch with centre-off position? Changing over between permanent L and PIR SL out to feed the lights? So far so good. You say L1 was not apparently making contact to common as the PIR output was not reaching the lights. Did you check its resistance?

The RCD tripping seems to be a completely separate fault. Your tests seem to show an intact circuit so either you've misread something, or there's an intermittent, or you clear the fault when manoeuvring the switch etc to get the test leads on.

Thanks Lucien, I didn't check resistance on the switch, just continuity which was open circuit no matter what the switch. Switch must be a duff. Could have been caused by the original fault.

I am back there on the 12th and plan to find this fault.

This is my method of attack.

Break circuit down.

Test and confirm the supply to switch in off position. Confirm rcd is holding in. Gradually introduce circuit a little at a time. Testing and then energizing. Side lights through switch in perm position, front light through (new) switch in perm position. Then both sets of PIRs.

One thing I did notice, the robus PIRs have a max LED loading of 150w. On the fronts I have 4x50w LED floods. Obviously this is over the max rating per PIR, would having 2 PIRs in parallel cause an issue like this?
 
this is over the max rating per PIR

Not good. If the inrush is too high, the relay in the PIR might weld closed, rendering it useless. The 150W rating is a bit arbitrary because unlike tungsten lamps (which all behave much alike, allowing the makers to calculate what tungsten load their product will handle) there's no direct relationship between LED wattage and inrush. Manufacturers can only estimate and prove by testing that 150W of typical LED drivers will create a level of inrush that the relay can be survive for an adequate number of switching cycles over the expected lifetime of the PIR. With your 200W load, it might last its full rated lifetime, or it might weld after 6 months. It probably won't fail tomorrow but if and when it does, you can't send the PIR back as faulty with a clear conscience, although I suppose a lot of people try.

There's no significance to how many PIRs are in parallel. The first unit to trigger when the lights are off has to bear the full inrush; the other unit might as well not be there.
 
Not good. If the inrush is too high, the relay in the PIR might weld closed, rendering it useless. The 150W rating is a bit arbitrary because unlike tungsten lamps (which all behave much alike, allowing the makers to calculate what tungsten load their product will handle) there's no direct relationship between LED wattage and inrush. Manufacturers can only estimate and prove by testing that 150W of typical LED drivers will create a level of inrush that the relay can be survive for an adequate number of switching cycles over the expected lifetime of the PIR. With your 200W load, it might last its full rated lifetime, or it might weld after 6 months. It probably won't fail tomorrow but if and when it does, you can't send the PIR back as faulty with a clear conscience, although I suppose a lot of people try.

There's no significance to how many PIRs are in parallel. The first unit to trigger when the lights are off has to bear the full inrush; the other unit might as well not be there.

As usual, golden pieces of information
 

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