Loop into Fan

Improver · May 6, 2024

Hi all new to the forum

Learning the trade as an improver, trying to get my head round something.

When taking a feed from the light switch to the fan.

Normally I would P live in Com and SL in L1

So had to attach a three core then up to fan, so does permanent stay in Com or go down to L1 has anyone got a simple scenario. I just can’t see atm

oscar21 · May 6, 2024

Where is the loop connection? No good taking a 3 core to the switch if is wired in 3 plate at the ceiling rose.

westward10 · May 6, 2024

oscar21 said:
Where is the loop connection? No good taking a 3 core to the switch if is wired in 3 plate at the ceiling rose.

Maybe it isn't.

timhoward · May 6, 2024

Welcome to the forum.
Simple scenario 1, traditional ceiling rose wiring with just PL and SL at switch:

Scenario 2 - Loop in and loop out at the switch with N and PL at the switch:

In both cases:
Grey is sleeved blue, and takes N to the fan via isolator (see below)
Brown takes PL to the fan via isolator.
Black takes switched live to the fan via isolator.

The 3 pole isolator simply interrupts all of them to allow maintenance of the fan..
CPC omitted from diagrams

Does that help?

timhoward · May 7, 2024

I should add, before someone else does, that some manufacturers specify a 3 amp fuse before the fan too.

bayleydave4 · May 7, 2024

Improver said:
Hi all new to the forum

Learning the trade as an improver, trying to get my head round something.

When taking a feed from the light switch to the fan.

Normally I would P live in Com and SL in L1

So had to attach a three core then up to fan, so does permanent stay in Com or go down to L1 has anyone got a simple scenario. I just can’t see atm

Hi Mate you would also require a Neutral and by default a cpc.
Is the relevant light fitting wired as a 3 plate (loop) system? If so you will have all the connections you need for a fan, including a timer version.
If not you will have to source a neutral from the same circuit and through a 3 pole isolator.

Improver · May 7, 2024

oscar21 said:
Where is the loop connection? No good taking a 3 core to the switch if is wired in 3 plate at the ceiling rose.

timhoward said:
Welcome to the forum.
Simple scenario 1, traditional ceiling rose wiring with just PL and SL at switch:
View attachment 116290

Scenario 2 - Loop in and loop out at the switch with N and PL at the switch:

View attachment 116291

In both cases:
Grey is sleeved blue, and takes N to the fan via isolator (see below)
Brown takes PL to the fan via isolator.
Black takes switched live to the fan via isolator.

The 3 pole isolator simply interrupts all of them to allow maintenance of the fan..
CPC omitted from diagrams

Does that help?

Improver · May 7, 2024

Thankyou all for reply’s! Wiring
G diagrams are brilliant.

From a 3 plate pendant I get that no issues.

It’s more when taking from the switch PL still stays in the common? Let’s say converting a normal bathroom light. Which has PL in common neutrals in block. SL in L1.

Do these cables stay where they are, before introducing the 3 core. I get the isolator part that’s find

Improver · May 7, 2024

Right ok think I can see it now from diagram what I’m asking the loop will now stay in the common always.

brianmoooore · May 7, 2024

An alternative to the triple pole isolator is to fit a switched FCU into the supply to the bathroom light circuit. This provides the necessary isolation and the often specified 3A fuse.
Downside is that the fan can't be isolated and the light remain on, or, alternatively, the upside is that the occupants can't use the shower without the fan running and cover the walls in mould.

mhar · May 7, 2024

I have posted this years ago, it is the way I wire fans which gives the fusing required by a lot of manufacturers and the isolation required allowing the light to operate when the fan is isolated, a lot more convenient at night if you only want the light on.
Really only for new work or very straightfoward to do if there is an easy route from switch to existing isolator. It looks busy but the only difference between this and what is usually done is that instead of running a 3c from switch to isolator you run 2 x 2c, one is taking the supply l & N, the other is a switch wire for the now fused L to and from the switch