Radial Circuit Voltage drop from 230V to 7V under load

Thread Starter

Connordidit

Joined Apr 5, 2021
1
Hi All,

First time posting in here!

I have wired 6 LED downlights in my kitchen each rated at 5W 220VAC-240VAC using 1mm T&E flex in a radial circuit, they do NOT need a transformer/control module to operate. I have tested the last LED in the chain (easiest one to remove and refit as there's only one wire going to it) by connecting it to an existing ceiling pendant and it worked just as it should.

Back in the kitchen I have the old Red and Black T&E flex coming out of the wall into the single pole switch, using a voltmeter I can see that with the MCB "ON" the old cable is reading 227VAC and with the MCB "OFF" it reads 0VAC. So far, so good.

I have connected the new Blue Neutral wire to the old Black Neutral wire using a twin Wago connector. I have then switched the Line and connected the CPC from the old flex to the back box (clipped the CPC in the new flex as it isn't needed for the LED's).

When the Line is switched "ON" I am seeing the voltage drop from 227VAC to around 7VAC which seems odd to me. I hope it's not a short somewhere between the switch and the consumer unit/

During all of this I had another downstairs light on which stayed on the whole time just to make sure the MCB nor the RCD tripped.

I'm not an electrician and understand that it's usually best to call someone trained when dealing with live line connections however I feel that my knowledge on the subject should be sufficient to hook up a few lights.

Any thoughts on the matter would be appreciated.

Regards

Connor
 

AlbertHall

Joined Jun 4, 2014
11,129
It would appear that you a poor connection between where you are measuring the voltage and the MCB. That could be either the Line or Neutral wire.
 

wayneh

Joined Sep 9, 2010
17,058
It's tough to follow your description without a diagram. But, from experience, I can tell you that it's easier to have a bad connection than you might think. In a typical home circuit, a bad neutral line can cause some very odd symptoms you'd never dream of.
 

Ian0

Joined Aug 7, 2020
1,618
Measure live and neutral voltages with respect to earth. If you live voltage falls w.r.t. earth, then the break is in the live.
If the neutral voltage rises, then the fault is in the neutral.
 

wayneh

Joined Sep 9, 2010
17,058
One tool I find useful is a lightbulb on a cord to test for power. Sometimes a meter will read a "phantom" voltage but you can't fool the lightbulb. Obviously you have to be careful where you stick the wires when testing live circuits. I try to put the neutral or ground connection solidly in one place and probe for the hot with a single wire.
 

Ian0

Joined Aug 7, 2020
1,618
Miniature Circuit Breaker (the usual DIN-rail mounted 17.5mm wide sort)
Circuit Protective Conductor - what's wrong with calling it "Ground" or "Earth" - the meaning is obvious regardless of which side of the Atlantic you live!
Residual Current Device = Residual Current Circuit Breaker = Ground Fault Interruptor
When it was a Residual Current Circuit Breaker (formerly an "Earth Leakage Trip") we knew what it did - now it's a "device" which conveys less meaning.
I hate some of these new names and acronyms - why change from the descriptive "Fuse box" to the completely meaningless "consumer unit"?
 
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