The RCD only protects against a fault to earth
What you had was a short circuit in a faulty lamp, this would not produce a
fault to earth and therefore not operate the RCD. This fault would product a
current sufficient to operate the fuse in the CU.
Hope this helps
--
Ellis Greensitt
Supplychain(Doncaster) Ltd.
www.supplychain.org.uk
01302 761205 : Tel
01302 761206 : Fax
"Dundonald" wrote in message
ups.com...
Radial spur off of main consumer unit in garage. The spur feeds
exterior lighting via a dusk till dawn unit - 3 x 40 watt halogen lamps
and 1 x 150 watt halogen security lamp. It was cheaper for me to buy
an RCD plug than a separate RCD and fuse box so I simply plug the
exterior lighting in to the radial spur using the RCD plug.
When I first plugged in the circuit the consumer unit fuse tripped, but
the RCD didn't cut out. I'm not sure I understand why, can anyone
help? I thought the RCD would cut out before anything else and
therefore protecting the main consumer unit.
In attempt to find out the cause of the fuse trip on the consumer unit
I checked every single connection on the dusk till dawn, junction
boxes, and lamps, and they all looked fine. So I flicked the switch on
the fuse and this time I heard a pop outside and again the fuse
tripped. One of the lamps had popped - identifiable from a black ring
on the brick around the lamp. Again I checked the connections in the
junction box leading to that lamp and again also inside the lamp. They
all are fine, but I noticed more carbon around the manufactured
attachments where the cable runs in to the lamp unit. So I'm figuring
the lamp is faulty. I'll be replacing this lamp unit and of course I
do not leave the circuit on. But that said, strangely, I flicked the
trip switch on the fuse in the consumer unit back to on and the circuit
works fine now - not sure why either!
So my questions are -
1. why didn't/doesn't the RCD trip before the fuse on the consumer unit
2. any ideas what the likely cause of the problem is with the lamp -
just out of interest? Like I say I'll just get a replacement from B&Q
anyway but just curious.