Lights and shower circuit linked together!

[HappyHippyDad]

Evening all..

I came across an interesting one today that I had not seen before.

I had a simple job of like for like replacement of some ceiling lights. I switched off the lighting circuit but the lights stated on, not too unusual you may think. I then switched off the rest of them one by one and the lights went off with the shower MCB. I then switched the other breakers back on and the lights came back on with the lighting circuit breaker!

I then noticed an unswitched fused spur (in 1mm) from the shower switch which supplied power to the 2 lights I was changing. Then I switched off the shower circuit and noticed that the shower was still live as it was coming through the lighting circuit and then through the 3A fuse!!

Has any one else come across crossed circuits like this? How could it occur? Why would someone do that as the lights already had power so why then give them another source?

 

[KEV 1 N]

I've come across multiple lighting circuits wired in conduit that have somehow been interlinked....yes it's funny when trying to find the MCB for the lights you want to isolate only to find none of them do, unless you have both affected circuits off together!

 

[andysparkfree]

you sure it isn't a power shower , as needs only a few amps to power the pump(so good on a 6 amp fuse i guess)

 

[ipf]

Once, installing some extra sockets on a rfc, I had no ring continuity. There was an unused t+e tucked away in the cu.
A bit of investigation and found another unused in the bathroom cylinder cupboard. All 3 were live. I'm sure you can conclude the reason. A good reason for dead testing.....never presume!

 

[Richard Burns]

Sounds very inappropriate but it may have been a DIY attempt to get the lights to come on when the shower was turned on and to have a separate light switch but without realising that the circuits would back feed each other.
At least they fused the lights down but I do not think the fuse would last long with an electric shower running through it! and it was probably lucky the circuit resistances were such that the shower did not pull 3A through the fuse.

 

[HandySparks]

Maybe someone thought it was a good way of supplying a fan from both the lights and the shower????

Edit: as above.

 

[Wilko]

Good find HHD !
Just remember how daft some folks are and then apply a dollop of DIY ... gulp!

 

[The Ghost]

I can't make head nor tail of what you are describing!

 

[Deleted member 26818]

I can't make head nor tail of what you are describing!

Has Feed from board to shower isolator.
Isolator then has separate feeds to shower and FCU.
FCU feeds lights which are also fed from the lighting circuit.

 

[The Ghost]

Got it

 

[MJPD29]

Came across this too, 9.6kw shower with 1.5 t&e straight out of the shower pull cord
(On a 45a breaker) and into a fuse spur and then on to feed a bathroom fan and 3 downlights. I was wondering why there was no light switch. 1 pull cord does all, some dodgy work

 

[Bobster]

Came across this too, 9.6kw shower with 1.5 t&e straight out of the shower pull cord
(On a 45a breaker) and into a fuse spur and then on to feed a bathroom fan and 3 downlights. I was wondering why there was no light switch. 1 pull cord does all, some dodgy work

Unorthodox, but what's wrong with it?

 

[MJPD29]

Unorthodox, but what's wrong with it?

1.5mm cable running directly off 45a mcb

 

[Strima]

1.5mm cable running directly off 45a mcb

Would the load exceed the current rating of the cable?

 

[MJPD29]

Would the load exceed the current rating of the cable?

Yes

 

[Bobster]

1.5mm cable running directly off 45a mcb

How far is between the switch and the FCU?

 

[Strima]

So was the shower running off the 1.5mm or just the lighting?

 

[Toneyz]

Came across this too, 9.6kw shower with 1.5 t&e straight out of the shower pull cord
(On a 45a breaker) and into a fuse spur and then on to feed a bathroom fan and 3 downlights. I was wondering why there was no light switch. 1 pull cord does all, some dodgy work

I had this also once without the fused spur.

 

[Dave OCD]

I've had similar, isolated a shower at DP pull switch to replace and on disconnecting the shower unit found voltage at the neutral. A timer fan had been connected straight off the shower switch with the permanent live on the mains side, more potentially lethal dodgy DIY.

 

[MJPD29]

I'm sorry i think i have worded this very badly

How far is between the switch and the FCU?

About 4metres probably