Armoured Cable seems to have no earth

Miked83 · May 9, 2020

I have been helping my dad in the garage and we have an armoured cable with 4 wires.
Red - Live
Yellow - live via a switch
Black - neutral
Blue - is just taped at the end these were connected to an old garage consumer unit. There does not seem to be a earth wire?
Testing with a light :
Red and black - light on
Yellow and black - light on via switch
Blue and and black - no light
Red/Yellow with blue trips the fuse.

is it right that this would imply that there is no earth?

thanks for any help.

telectrix · May 9, 2020

the blue may be earth. also the steel wire armour should be earthed. suggest you get an electrician to check it out, meanwhile isolate at MCB in main CU.

Miked83 · May 9, 2020

telectrix said:
the blue may be earth. also the steel wire armour should be earthed. suggest you get an electrician to check it out, meanwhile isolate at MCB in main CU.

Yes will do just want to check. Thanks for the advice.

pc1966 · May 9, 2020

Better safe than sorry!

As telectrix said, the armour should always be earthed (though sometimes a conductor is used as well). This would be done via the proper glands that grip the steel wire of the armour, but in turn it has to be certain the gland is properly connected to earth. Sometimes that is just relying on the metal box it is clamping, but best practice is to have a dedicated earth wire to the gland fixing arrangement.

The fact that a light test to the blue tripped the circuit would suggest it is earthed, but it is slightly odd to be earthed at only one end, usually if used for earth it would be at both ends. Also there should be some indication if the conductor is earth by sleeving the cable with green/yellow so its function is clear.

davesparks · May 9, 2020

The armour of the armoured cable is the earth, this hold be connected via brass armoured cable glands and a suitable means of connecting an earth flylead to it.