Room for extending Circuit?

[claret73]

Fairly straightforward, just wish to check my theories...

Have been asked to put a PIR Security light outside a Garage for my Sister. Best way would be to take the feed off the garage light itself. To determine if I have sufficient allowance on the circuit to do this, would I use a Clamp Meter to read the current ampage with all lighting on for that circuit & then determine if sufficient room by doing the design current calc for the PIR?

Or (possibly getting lost here) take a ZS reading & determine from that figure according to Regs for allowance by adding to circuit?...

 

[Guest123]

Hi.

To determine existing loading you could as you say, turn on all loads on that circuit and check with a clampmeter on line conductor at the MCB for that circuit.

Just add the load of your pir to the existing and see if there is scope, it is though highly unlikely that all lights on one circuit will all be on at the same time from day to day so bear that in mind.

As for Zs, you can check but I wouldn't have thought it will be an issue at all, nor VD.

 

[claret73]

Thanks Lenny
Much appreciated. I know it seems a bit overboard but I'd rather check rather than just add to the circuit without really knowing. Could do diversity calc I suppose against a physical check.
Cheers again

 

[flukey]

how many lights on existing circuit

 

[claret73]

I'm not sure yet Flukey? Just summarising approach to ensuring I'm not overloading...
It's a 3bed so I'd imagine usual arrangements of:

Lounge (I know there are wall lights in place of ceiling points)
Dining Room
Hall
Kitchen
Porch
Garage
Back Garden external?

 

[flukey]

I'm not sure yet Flukey? Just summarising approach to ensuring I'm not overloading...
It's a 3bed so I'd imagine usual arrangements of:

Lounge (I know there are wall lights in place of ceiling points)
Dining Room
Hall
Kitchen
Porch
Garage
Back Garden external?

if its a normal set up there should be plenty of room for extending

 

[cornburn]

If you're doing it by the book and counting lamp holders on the circuit you should also assume that each has a 100W bulb in (so unless you have more than 14 lamp holders on a 6A breaker no need to even worry about diversity). As has been said, in a domestic setup it's unlikely there'll be enough on the circuit to worry about it.