Discuss MCB sizing in the Electrical Forum area at ElectriciansForums.net

Reaction score
11
Welcome to ElectriciansForums.net - The American Electrical Advice Forum
Head straight to the main forums to chat by click here:  American Electrical Advice Forum

Is there any issues in having 10amp breaker if the circuit is pulling just under 6 amps? I know the breakers there to protect the cable and the cable is 2.5 3 core armour. Just curious.
 

Taylortwocities

-
Esteemed
Arms
Reaction score
2,683
You have answered your own question. For 2.5mm SWA you could have an MCB of up to 25amps. If you need to limit the current at the delivery end of the SWA - maybe because there’s lights there using smaller wiring, or because the instructions state a fuse is needed - then fit an FCU with an appropriately lower rated fuse.
 

Wilko

-
Esteemed
Arms
Reaction score
6,369
If you know the load is 6A then with 2.5mm conductors the 10 MCB may be a reasonable choice :).
 
Last edited:

Zerax

-
DIY
Reaction score
1,081
Or could be... Iz≥In≥Ib or Ib≤In≤Iz

(just showing off as I've just discovered how to do those symbols)
(still working on how to do subscript on here)
 

radiohead

Esteemed
Arms
Reaction score
761
Fixed loads do not necessarily require overload protection, as long as fault current protection is met by the device a device rating may exceed the CCC of the cable and still be compliant.
 
Reaction score
11
So when is over load protection needed? In theory you could run a lighting circuit of a 16amp breaker then as long as the cable is correct for 16 amps?
 

Risteard

-
Esteemed
Arms
Reaction score
3,401
So when is over load protection needed? In theory you could run a lighting circuit of a 16amp breaker then as long as the cable is correct for 16 amps?
BS 7671 specifically stated that ceiling roses etc. can be connected to a circuit with a protective device rating not exceeding 16A, so yes - it's in black and white that you can do it.
 
Reaction score
55
So when is over load protection needed? In theory you could run a lighting circuit of a 16amp breaker then as long as the cable is correct for 16 amps?
1.5mm cable on a 16a breaker will work perfectly fine. It's how they do it in some other countries.
 

Reply to MCB sizing in the Electrical Forum area at ElectriciansForums.net

Electrical Forum

Welcome to the Electrical Forum at ElectriciansForums.net. The friendliest electrical forum online. General electrical questions and answers can be found in the electrical forum.
Top