One Wire Too Many (in PIR lamp) (Ed.)

[DaveH1954]

Hi, I’m trying to replace an old outside light with pir function with a newer version which also has pir function inbuilt. I was expecting to see three cables - L,N & E but there are four wires connected to the old light. Picture attached shows existing wiring - as the new light only needs three, should I simply leave one of the original four disconnected (in a Wago connector) and which should it be?

 

[opps]

I suspect one is a switched live, plus a permanent live, a neutral and an earth.

If so, put the switched live in the Wago. You can additionally isolate it in the light switch.

 

[DaveH1954]

Many thanks opps. What’s throwing me is that two of the wires have had tape added. The white wire has a piece of blue tape and I’m assuming this is neutral and the black wire has a piece of brown tape which I’m assuming is the switch live.

 

[opps]

Do you not have access to a multimeter or voltage pen?

You could turn off the supply in the consumer unit, put a wago on the potential switched live and then wire up the rest and see what happens.

BTW, I am not an electrician, but that is what I would do. Don't forget to isolate the switched live in the redundant light switch later.

Edit---- you hadn't posted your image when I first replied. I think you are correct about each of the wires.

 

[DaveH1954]

Many thanks opps. Yes to both. I’ll follow your suggestions as to isolating the SL and wiring the three remaining cables.

 

[JohnD]

The SL enables you to turn it off (and, usually, by flicking, on) manually from indoors when needed.

Why would you want to deprive yourself of that ability?

 

[DaveH1954]

So what would the wiring look like if I retained the switch live functionality and would it override the PIR and keep the light on permanently if the switch is in the on position?

 

[JohnD]

as the new light only needs three

What do the instructions say these three connections are?

 

[nero44]

Why would you want to deprive yourself of that ability?

I would definitely agree to this. If the switch is already there, connect it even if only infrequently used. Else also maybe some future owner will think... WTflip is this for... When I moved into my current property I had such an inactive swtich and it took a long time for me to find out what it intially meant to do and to get it reconnected.

Switches for PIR can either act as double pole isolation (when you need to replace a bulb), or as force overrride ON. But typically the second is part of the actual PIR function, so would need to check the manual. If your PIR does not have that functionality, then I would still retain the switch as isolation.

 

[opps]

The SL enables you to turn it off (and, usually, by flicking, on) manually from indoors when needed.

Why would you want to deprive yourself of that ability?

Not all PIR lights will let you do the double flick though. But yeah, if the OP's one does, I guess he could isolate the perm live and use the switched live instead.

 

[JohnD]

What do the instructions say these three connections are?

There's a fair chance that the lamp has N, L and SL

And so does the cable.

In which case it can work as intended.

 

[opps]

There's a fair chance that the lamp has N, L and SL

And so does the cable.

In which case it can work as intended.

The OP said that that there are only three connections- live, neutral and earth.

 

[JohnD]

live, neutral and earth.

Did he?

 

[opps]

Did he?

Post number one, the OP says that the new light only needs 3 cables. He seems to be smart enough to know that one of them is a (required) earth. That only leaves a live and neutral.

 

[JohnD]

Post number one, the OP says that the new light only needs 3 cables.

Yes, that's what he said.