Killed a PIR, fluorescent lighting

[Pretty Mouth]

Actually managed to kill 2 PIRs in succession yesterday. The first I got SL and N mixed up (who uses the black core of a 3C+E as neutral? honestly), which killed it dead, tripping the breaker in the process. Schoolboy error.

The second, well I don't feel it's 100% my fault.

The PIR I had been asked to change had stuck permanently in the on position, and the client had turned off the breaker until it was replaced. It was controlling 2 twin 6ft fluorescent tubes in a garage, so 280W of fluoro lighting. I replaced it with an Eterna PIR, which instructions state good for 300W of fluorescent lighting.

However, on re-energising, I had the same problem - the new PIR was stuck on permanently. You could hear a faint click 'on' when it sensed motion, and again click 'off' after the time delay, but the SL terminal remained live. I noted that the starter for one of the twin fluoros had gone, so the tubes were flickering indefinitely as they attempted to light up.

What I guess happened is the constant start up current due to the failed fluoro starter caused the contacts in the PIR to weld closed. Can anyone confirm that this is likely to be the case, or if they have come across a similar problem before?

 

[Deleted account]

Yep grey is always the neutral to me.

 

[Mikegh]

Just seems like bad luck all round on the day there

 

[buzzlightyear]

Oooops. You lean by your mastakes.

 

[Pretty Mouth]

Yeah, I guess so. I can't help feeling that starter failure on fluorescents is inevitable, and if it is that that killed the PIR, it should at least be warned against in the instructions.

 

[Sparkgap]

The PIR is rated for 300W inductive load (fluor), does that include surge on start or just continuous loading? And if you are running 280W load off it anyway you are pretty close to the full rating. Personally, I would have looked for something with a higher rating just for peace of mind.

 

[Vortigern]

I think the welding bit may be correct on the PIR. It is definitely a problem with contactors of all kinds the inrush currents. Most manufacuturers give inrush current data. But notionally I think you are in the range of 10x to even 100 times inrush current. Even at the lowest estimate that's enough to nuke the delicate contacts in a PIR. Of course that would be times 2, maybe use a suppressor?
non-compensated ferromagnetic ballast - 10-15 x In for 5-10ms
compensated ferromagnetic ballast - 20-60 x In for 0.5-1ms
electronic ballast 30-100 x In for 0.5ms

 

[Pretty Mouth]

The PIR is rated for 300W inductive load (fluor), does that include surge on start or just continuous loading? And if you are running 280W load off it anyway you are pretty close to the full rating. Personally, I would have looked for something with a higher rating just for peace of mind.

It just says max 300W for fluorescent load, no more info than that

 

[Mikegh]

I'd be the same , I'd be wary of maxxing out the fluorescent rating on the pir

Wouldn't trust it

 

[Pretty Mouth]

I think the welding bit may be correct on the PIR. It is definitely a problem with contactors of all kinds the inrush currents. Most manufacuturers give inrush current data. But notionally I think you are in the range of 10x to even 100 times inrush current. Even at the lowest estimate that's enough to nuke the delicate contacts in a PIR. Of course that would be times 2, maybe use a suppressor?
non-compensated ferromagnetic ballast - 10-15 x In for 5-10ms
compensated ferromagnetic ballast - 20-60 x In for 0.5-1ms
electronic ballast 30-100 x In for 0.5ms

Thanks @Vortigern . I've not had to use a suppressor before, what sort of thing should I use?

Do you think that the fluorescent starter being defective would have worsened the problem (I assume the problem was the starter, as both tubes of the pair were failing to light up properly).

I have suggested changing to LED, although the max load for that is even lower, 200W max 8 lights.

 

[Vortigern]

@Pretty Mouth just google inrush suppressor. I imagine you are going to get a cycling of the inrush as the starter was not working but I am not sure that would make matters worse as the circuit does not finally excite.

 

[Pretty Mouth]

@Pretty Mouth just google inrush suppressor. I imagine you are going to get a cycling of the inrush as the starter was not working but I am not sure that would make matters worse as the circuit does not finally excite.

Thanks for this @Vortigern . I had a read up on NTC thermistors, and while I now get the idea of them, I wouldn't know how to select one for this purpose, or what considerations there are for installation. For a low value job such as this, I'm not going to pursue it any further - they can have a manual switch instead! Cheers

 

[Vortigern]

Inrush Current Protection for LED Lighting Retrofits

LED lighting retrofits require inrush current limiters to prevent damage to existing electrical equipment. Simple calculations are provided for selection.

www.ametherm.com

May be of help. Not particularly easy!