Why does my MCB trip ?

Last summer I installed a set of PIR controlled outdoor halogen lights on driveway and inside a group of garages. Idea is that you are lit up as you drive down to garages and park in them with no switching required. Wired all lights up and tested the system using 13 amp plug with 13 amp fuse and extension lead. All worked fine over a period of some months so have now laid on permanent supply to garages terminating in Screwfix Garage Consumer unit. This has 40 amp 30 mA RCD and two MCBs, one 16 amp and one 6 amp.Have wired up power point to 16 amp MCB but this circuit is very rarely used. Lights are connected to 6 amp MCB and used daily. As you drive towards and inside the garages you activate a series of lights 6x150 and 1x500 watts so the total load is 1400 watts.I make that about 6 amps at 230 volts and usually all works fine but about once a week as the second or third light in the series comes on the 6 amp MCB trips and you are in darkness. The RCD never trips it is always the 6 amp MCB. Why does this trip on a random basis and not every day ? Do PIR Halogen lights draw a heavier current as they start up ? Would my best bet be to upgrade the 6 amp MCB to a 10 amp version ? Many thanks in advance for any helpful answers. John Chapman
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
John Chapman wrote:

Because you're running right up to the limit of the MCB, and occasionally going over that limit. The difference could be lower bulb temperature or higher main voltage.

Nothing to do with PIR. All incandescent bulbs, including halogens, draw more current when first switched on. As the filament heats up, it's resistance increases, and it draws less current.

Yes.
--
Grunff

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Knock the power of the lamps down -- 1400 watts is one hell of a lot for outdoor lighting. Start by replacing the 500W halogen with a 200W or 300W, or a GE 225W energy saver halogen.
--
Andrew Gabriel

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

I`ve got 540W in my kitchen alone - and it`s not a big kitchen :-}
--
Please add "[newsgroup]" in the subject of any personal replies via email
* old email address "btiruseless" abandoned due to worm-generated spam *
  Click to see the full signature.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
On 25/01/2004 John Chapman a wrote :

It sounds like you are probably just enough over the limit at times to trip it. Any lamp, when first switched on cold, will draw a little more than its rated current.
You can either increase the MCB rating assuming the cable is suitably rated, or split the lighting load onto two MCB's.
--

Regards,
Harry (M1BYT) (Lap)
  Click to see the full signature.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

than hot. So indeed, with the trip already supplying say 4A for the first two lamps, the third one coming onstream could be just enough to trip the 6A MCB during the, oh, one-third-of-a-second-or-so the lamp takes to come up to final resistance (of course while it's warming up its resistance is increasing so the current is going down to the steady-state value all the time).

replacing the 'B'-characteristic MCB which he probably has with a 'C'-characteristic one. This will allow a higher switch-on surge than the B. An electrickle trade-supply place will have these off the shelf. For full safety, the earth loop impedance for the size of wiring (1.0mmsq? 1.5mmsq?) should be checked; reference to the OnSiteGuide's Table 7.1 suggests you're OK for a circuit length up to 38m in 1.0mmsq and tor 59m in 1.5.
Better than any of the above, though, would be to replace the 500W bulbs under PIR control with 300W ones (same length as 500W, so no need for new fittings). Little more than half the energy consumption, a bit less light scattered into the once-dark skies, no PIR popping, and naff-all effect on how well-lit the scene is by comparison to the pitch black. Further down this line of reasoning is to put up, say, 8 or 10 bulkhead fittings, fitted with say 3 60W incandescents for instant-on lighting and the rest fitted with say 15W compact flourescents. The larger number of lower-intensity sources gives more even lighting without the sharp shadows you get from a small number of spots, and makes bulb replacement less urgent (you can wait till the morning if what you've lost is just 10% of your light). That's the approach I've gone for in lighting up the areas around our house, and it's much less jarring than the "Colditz Effect" the previous occupants' single PIR spot fitting created.
HTH - Stefek
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
Harry Bloomfield wrote:

Make that a heck of a lot more, actually.

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
Harry Bloomfield retched Why does my MCB trip ? onto my recliner:

Good idea.
--

Phil K.

http://philkyle2003.reachme.at /
  Click to see the full signature.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

That sounds more like runway lighting than a driveway. Don't you have headlights? Your car headlights are 120W total and show enough to travel safely at 70 mph. Why do you need 1.4kW when you are parking?
Christian.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Problem is that headlights are only fitted to front of our cars both of which need to be manoeuvred a few times in a restricted space before being reversed into garages to ensure safe exit on to road next morning. In addition the garages are made of a vicious pebble dashed reinforced concrete which we do not wish to scrape as we reverse in. Hence need for copious illumination. John Chapman
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
John Chapman wrote:

Yes, especially when bloody cold.

If the cable can take it, yes. Or a 'slo blo' type?
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Related Threads

HomeOwnersHub.com is a website for homeowners and building and maintenance pros. It is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.