Strange fault

[gazdkw82]

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?

 

[James]

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.

 

[Dave OCD]

Could be the RCD spur not putting the neutral through , not a BG one by any chance ?

 

[gazdkw82]

Could be the RCD spur not putting the neutral through , not a BG one by any chance ?

Yeh it is. Common fault?

 

[Lucien Nunes]

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.

 

[gazdkw82]

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.

I hope so. I will find out tomorrow

 

[Dave OCD]

Yes I've had this once before with a BG rcd spur, open neutral and that's what gives you the funny readings mate.

 

[gazdkw82]

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?

 

[pc1966]

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.

 

[Dave OCD]

It's poor really, I had the same issue with a BG Rcd spur over 3 years ago and it seems they still haven't resolved it properly.

 

[gazdkw82]

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?

 

[gazdkw82]

Any ideas anyone? I'm still puzzled ?‍

 

[Dave OCD]

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 ?

 

[gazdkw82]

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.

 

[stanwelbach]

Any ideas anyone? I'm still puzzled ?‍

Best thing to do now is to take stock of what you've done, by that I mean draw out the circuit as you've actually wired and connected it then work out from your drawing what is wrong.