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When would you need overcurrent protection on the neutral Conductor?

Why would anyone want a double pole RCBO, with overcurrent protection in the Neutral as well as the Line?

Well this was a great questioned posed by one of our subscribers on a previous video:

In this video @william.winter discusses how RCBOs are classified and when you would need to consider OCP on a Neutral conductor.


0:00 Intro

0:42 When do you need overcurrent protection on the Neutral conductor?

1:25 How RCBOs are categorised

2:14 Do you ever need overcurrent protection on a neutral?

2:29 When don't you need overcurrent protection on the neutral?

2:56 When do you need overcurrent protection on the Neutral?

4:01 This weeks winner announcement

5:10 Outro

Other videos you may find useful:

Are all Mini DP RCBOs really Double Pole?

Verso Type B Video

Video Summary

Lets first re-cap on how RCBO’s are classified but this time in a little more detail.

RCBOS are classified based on two sets of criteria:

  1. How many poles have overcurrent protection

  2. Current Paths

So Single Pole devices (SP), including those with a switched Neutral only have overcurrent protection on the Line side of the device.

Double Pole devices (DP) such as RCCBs and DP RCBOs have overcurrent protection on both the line and the neutral.

The reason single pole RCBOs can be categorised as SP+N whether they have a switched neutral or not, is because it highlights the fact that the device has a singular overcurrent pole as well as an additional current path.

A nice grey area of misinterpretation there for everyone. Which is why it is always very important to check. Diagrams on the device will help you with this and also you should be able to access a datasheet from your manufacturer just to be sure.

So now we are clear with the terminologies and the reasons behind them, why and when do we need OCP on a Neutral Conductor? Is there any point in DP RCBOs?

The answer is yes but rarely on domestic settings.

If the cross sectional area or CSA of the neutral conductor is equal or greater than the CSA of the phase conductor, no specific protection is required on the neutral because it is protected by the phase protection.

Swap that around however and if the CSA of the Neutral is lower than the CSA of the Phase conductor, the neutral conductor needs to be protected against short circuit.

So this is why true Double Pole RCBOs are not as common but are very different to the Single Pole counterparts.


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