PIR Yard Lights

[Graysonlad]

We have 5 in number of 500 watt floods with combined PIRs, not all on the same circuits, located on various outbuildings. For some reason these lights malfunction. Some fail to come on at night. When I check the following day electrically everything seems OK. If I trip the MCBs and reset them some of the lights come on (in the daylight) for a short period and then go off and then work correctly in the dark. Others come on but they stay on all day and night. The units and not expensive the kind available from B&Q for about £10 each.
Would anyone care to express an opinion on the following:
1: How reliable are combined units?
2:For reliability is it better to have combined or separate PIRs?
3:When the electronic bit fails on these units do the normally go short (light staying on) and open circuit (Light fails)?
4:If a light is on the same circuit with other items and a PIR fault occurs could this cause an MCB to trip? The problem for me is when I get to the job I have no way of knowing if any one else has reset the trip.
4: What is the most cost effective way of dealing with yard lights that require PIRs?

 

[Darkwood]

The Magic word there was B&Q ..... You get what you pay for...
Floods whether seperate or combined with Pirs have always been problematic, we started refusing to fit them 10yrs ago because of the problems we had, unless you going to pay a decent amount for the pir (£50)ish then youll get a box of cheap unreliable electronics.
In answer to your all questions .... 1,2,3 ,,,it varies......4a - ask if its been reset and lastly 4b - would need alot more details regarding site/yard design and size to see what best system you need.