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Topic Title: changed pir for day/night sensor and mcb trips?
Topic Summary: Could it be a surge?
Created On: 04 December 2017 04:59 PM
Status: Read Only
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 04 December 2017 04:59 PM
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ady1

Posts: 839
Joined: 19 April 2005

Hi
As the title suggests..
The supply to the pir is a switched live from a switch in the hall.
Been working great...switches on about 14 5w led's.
The customer asked me to change it to a day/night sensor.
Now every time I switch it on in the hall - the 6a mcb trips !!
Could it be a surge ?
Kind regards
Ady

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Resistance is futile.
 04 December 2017 05:33 PM
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mikejumper

Posts: 2466
Joined: 14 December 2006

If it is a surge then wouldn't it have been happening when the PIR switched the lights on, after all you havn't changed the load, just the switching method.
 04 December 2017 06:39 PM
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ady1

Posts: 839
Joined: 19 April 2005

Hi Mike
I have considered that, however...
A pir is not closed circuit non energised, but a photo cell is, therefore upon switching on, the load is now direct, but wasn't before.
Tomorrow, I shall just link it through and see if it trips... I also will change the head.
Cheers
Ady

-------------------------
Resistance is futile.
 04 December 2017 08:46 PM
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mikejumper

Posts: 2466
Joined: 14 December 2006

Not sure if I've understood that.
Wouldn't both methods of switching have to open until triggered to close by whatever means.

Linking through should at least check if the photocell is the problem.
 04 December 2017 08:54 PM
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ady1

Posts: 839
Joined: 19 April 2005

Hi. Actually no, A photocell is closed circuit on the relay when not energised, so live feed and live out are short circuit.
Whereas a pir is is open circuit till energised.....
Its the only difference - so, yes linking through will confirm if the photocell id the problem.
Cheers
Ady

-------------------------
Resistance is futile.
 05 December 2017 12:28 AM
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mapj1

Posts: 9689
Joined: 22 July 2004

If it really fires every time rather than sometimes, I'd be looking for something else first, like double checking that it is not now switching an LN short due to some terrible confusion about the wiring colours on the sensor module, before assuming inrush which tends to be hit and miss.

-------------------------
regards Mike
 05 December 2017 05:10 AM
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leckie

Posts: 4439
Joined: 21 November 2008

I'm sure I am being really thick here but.....

how does that work then? The photo cell is closed circuit you say until energised? So do you mean that the photo cell is N/C with no power on, then you feed it, perhaps via a time switch, then it switches on the load momentarily until it detects daylight, and then goes open circuit?

I would have thought that if a PIR was there previously it would have been permanently fed, so if you replaced that with a photo cell then so would that? Can Ady, or someone else, explain what he means please?

Regarding the MCB tripping, that sounds like a cell that has a short on it, or its connect wrong, probably N in the Sw terminal.
 05 December 2017 10:44 AM
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AJJewsbury

Posts: 16095
Joined: 13 August 2003

I'm sure I am being really thick here but....

Me too. My best guess is that ady has noticed that the MCB trips as soon as his wiring is supplied with power, rather than being OK until an "event" happens (i.e. darkness falls in the case of the photocell or something moves in the case of the PIR).

I don't quite follow the thinking though, as all the PIRs I've worked with always turn their output "on" as soon as they get power when switched on from cold - so the same thing should have happened with the previous PIR. Even then the actual switch-on surge should have been identical whether the initial switch on was due to supplying power or by PIR or photocell trigger - unless of course there were preciously multiple PIRs, each switching a sub-set of the lights, so there was some natural staggering of switch-ons.

- Andy.
 05 December 2017 07:50 PM
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ady1

Posts: 839
Joined: 19 April 2005

Hi.
Maybe i'm missing something - because i'm not as bright as many of you guys on this forum.
Firstly; Yes, the relay is closed between live in and live out on a photo cell non energised. When energised the load is on for about 10 seconds (during the day) then the relay open circuits to turn the lights off and await darkness.... So when its dark the relay is then closed again etc etc.
Secondly; I found the problem today. My apprentice had put a screw through one of the additional lights on the load side a few days earlier. Surprisingly the additional lights we fitted did work fine, but the resistance of the fault had obviously got lower in time and along with the original lights was just enough to trip the mcb. Coincidence with the timing though !
Thankyou for all the replies.
Kind regards
Ady

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 05 December 2017 08:53 PM
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leckie

Posts: 4439
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Well I must admit I have never measured across L and Sl of a photocell with no supply. I will give it a try but I would imagine that I'd it's daylight it would be OC. I thought they just thought that some types went SC when power was first applied; like a test run sort of thing!

I have a couple of spare photocell heads so I will give them a test when I get a minute and see what I get.

However, it doesn't matter much because Ady has sorted it out. He has blamed the apprentice! Only joking Ady, glad you got it sorted out, things like that can drive you a bit potty!
 06 December 2017 04:08 PM
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Zoomup

Posts: 3428
Joined: 20 February 2014

Originally posted by: leckie

Well I must admit I have never measured across L and Sl of a photocell with no supply. I will give it a try but I would imagine that I'd it's daylight it would be OC. I thought they just thought that some types went SC when power was first applied; like a test run sort of thing!



I have a couple of spare photocell heads so I will give them a test when I get a minute and see what I get.



However, it doesn't matter much because Ady has sorted it out. He has blamed the apprentice! Only joking Ady, glad you got it sorted out, things like that can drive you a bit potty!


I remember the old Royce Thompson photo cell switches that were used on lighting columns. The cell was on top of the light column head. The relay was located at the base of the column. It had a rocker switch marked TEST or AUTO I seem to remember. The relay was thermally operated. Initially when first powered up the output was there on the output terminals. After a few minutes the bi-metallic strip opened the contacts in the daylight. After dark the contacts closed. Perhaps the new electronic relays work in the same way. When first powered up in daylight they provide an output until they have settled down to an open contact situation, awaiting darkness.

P.S. Blinkin ek, they are still using the same bases with a new design relay unit. I suppose that makes sense as there must be millions of the old bases installed in lamp columns still in use.

http://www.lightinglocations.c...-cell-70lux-1660.html

Z.

Edited: 06 December 2017 at 04:17 PM by Zoomup
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