"Bunching"

[petesparks1]

A job I was working at recently had a 16A mcb with 2 x 2.5mms leaving the breaker.
The CU was in the middle of the office block and one cable served 3 x FCUs to the left and the other cable served 3 x FCUs to the right (Air con fans @ 3amp)
Another spark told me that when he had that situation during his nic assesment the lovely nic chap told him that "Bunching" was bad practice and the nic dont like it.
I cant see a problem.The FCUs were labelled with the circuit No. and if it was wired on a single radial you would use more cable hence less current rating etc etc

Thoughts?



Pete

 

[Sintra]

Have a read at reg 523.8 conductors in parallel. In my opinion 2 seperate radials unless you can comply with this.

 

[davelerave]

but they are not paralleled?

 

[Mark42]

No, not paralleled!

Maybe it looks ugly to have two conductors in one MCB, and (possibly) potentially confusing, but I can think of no reason why it should not be electrically acceptable.

As the OP says, doing it this way reduces cable length and hence Volt drop, and it could be argued that it is always good practice to consider this. (Not that voltage drop would be significant with this load).

How about if all six FCUs were wired on one run, then the run fed by a single 2.5 from the MCB to the nearest FCU (which would then contain three wires)? Would that satisfy a sensitive inspector?

Or fit a junction box for the 2 x 2.5's just outside the CU, then feed this from a single 2.5? What difference would it make electrically? (Answer: none, beyond unnecessarily having the whole load on a single length, which in my opinion would be thoughtless practice in this case.)

 

[davelerave]

suppose the disadvantages are that the cables are under-utilised if the load is split and the 2 wires may be considered messy or confused with rings certainly no reason why they can't be separated anyhow would be interested to know the rules on it

 

[mogga]

one circuit one MCB 2 circuits 2 mcbs each radial should be in its own MCB

 

[havoone]

petesparks..... have a look at reg 314 Division of installation and 314.4 in particular.

 

[pevvers]

petesparks..... have a look at reg 314 Division of installation and 314.4 in particular.

Have a look at the definition of a final circuit,

 

[davelerave]

so what are the rules on this?

each radial it's own mcb i think prob best-no confusion then

 

[havoone]

Have a look at the definition of a final circuit,

dont see your point pevvers ?

 

[havoone]

so what are the rules on this?

each radial it's own mcb i think prob best-no confusion then

yes, each on own protection

 

[davelerave]

ya prob no worthwhile reason to 'bunch' circuits

 

[pevvers]

dont see your point pevvers ?

No?

Well as with all things with the regulations, you sometimes have to read between the lines. Regulation 314.4 says that each final circuit is connected to it's own overcurrent protection, or similar (I'm away from my regs at the mo), so you could read that as each CABLE (disregaring rings of course) needs its own overcurrent protection. But if you were then to have a look at the definition of a final circuit, you will see that there is nothing to say anything about amounts of cables, all that is said is that a final circuit is a collection of electrical equipment protected by a single overcurrent device.

Parallel cables are just that, parallel cables, i.e. two cables, running exactly the same run. Two radials, going to different places are not in parallel are they?

As long as the termination at the overcurrent device is designed to take the amount of cables, and 314.1 - minimising inconvenience in the event of a fault is not contravened, then there is nothing wrong with two radials (or more) protected by one overcurrent protective device.

 

[davelerave]

yes 'bunching' and 'paralleling' are not the same


dont work in the UK but looks like 314.4 takes precedence ie:1 cable 1 mcb for radial

bit confusing

 

[pevvers]

but looks like 314.4 takes precedence ie:1 cable 1 mcb for radial

Where does it say CABLE?!