Tie wrapping RCBO neutrals.

[tank]

Hi guys, if 16 RCBO neutrals are tie wrapped together for neatness, are there any thermal considerations such as grouping factors to be taken into account?

 

[pc1966]

Theoretically yes.

In practice probably not. What is the sum of all RCBO capacity, and how much of it is actually usable? If you have, say, 200A RCBO total and a 100A supply I can't see the cables getting anywhere near a troublesome temperature.

 

[tank]

Ah yes I see. your point. The RCBO total is 244A on 100A supply.

 

[Deleted account]

Theoretically yes.

In practice probably not. What is the sum of all RCBO capacity, and how much of it is actually usable? If you have, say, 200A RCBO total and a 100A supply I can't see the cables getting anywhere near a troublesome temperature.

I never thought of it that way! Very clever.

 

[loz2754]

I wouldn't do it though because if an RCBO needs to be swapped later on it will be a bit of ball ache.
If the neutral cables are too long, I usually cut and ferrule the ends.

 

[Dustydazzler]

One little tie wrap for neatness won’t hurt

 

[tank]

Ball ache if you've come to work without your snips. ? I have the ferrules to fit too. I like things to be neat.

 

[loz2754]

One little tie wrap for neatness won’t hurt

True

 

[telectrix]

One little tie wrap for neatness won’t hurt

just another tenner on the bill.

 

[Dustydazzler]

just another tenner on the bill.

Twenty

 

[pc1966]

Twenty

Twenty guineas, my dear fellow...

 

[Lucien Nunes]

In practice probably not. What is the sum of all RCBO capacity, and how much of it is actually usable? If you have, say, 200A RCBO total and a 100A supply I can't see the cables getting anywhere near a troublesome temperature

I never thought of it that way! Very clever.

It's often possible to reduce the grouping factor due to supply limitation. We do this a lot in theatre lighting where there are often large numbers of circuits, only a fraction of which can be used at once. E.g. 60A 3-phase supply serving 72 circuits of 10A each. Only six circuits on each phase can be fully loaded at once, so if they are in three separate trunking runs, the grouping is for six circuits, not 24.

The worst case is always when the total supply current is carried by the smallest cross-section of copper or the smallest number of circuits, so with the above example, if 12 circuits on one phase are loaded to 5A each, the conductor temperatures will be lower than with six at 10A.