Tripping caused by touching neutral and earth

[buns]

Related to a comment below - given that an RCD/MCB will trip if you accidentally connect neutral to earth in a wall socket even with the MCB switched off(I discovered), is there any danger involved with only the live being isolated or is it just annoying?

 

[plugwash]

Normally the voltage on the neutral will not be high enough to cause danger.

There is a potential danger if a neutral becomes disconnected before the isolation point. It's a pretty low risk though providing the wiring up to the CU the circuit is fed from is in good condition.

 

[TicklyT]

Although the voltage between N & E should be low, there is a possibility that the current could be high.

 

[buns]

thanks

 

[ricicle]

The earth forms a parallel path with the Neutral back to the Star point. If there is current flowing in the installation and a Neutral of an isolated circuit (line only) is touched to earth then there is a possibility that some current will flow back along the earth path from that point, which means less in the Neutral. This causes imbalance in the coil of the RCD and will cause it to trip

 

[ban-all-sheds]

More than a possibility - all the neutrals are connected at the CU, so they all get a path to earth.

 

[Softus]

Although the voltage between N & E should be low, there is a possibility that the current could be high.

So if the N-E voltage is, say, 10 Volts, what do you reckon would be the highest current that would flow through a human body that was inserted in the N-E path?

 

[rebuke]

Obviously on a circuit protected by a 30mA RCD, the maximum that could possibly flow is 30mA (roughly speaking). If there was no RCD, then I guess it comes back to Ohms Law: I = V / R, so presumably it will depend on the resistance of the human body?

 

[Softus]

Although the voltage between N & E should be low, there is a possibility that the current could be high.

TicklyT, please could you define the words "low" and "high" in your sentence?

 

[holmslaw]

..

 

[securespark]

Although the voltage between N & E should be low, there is a possibility that the current could be high.

TicklyT, please could you define the words "low" and "high" in your sentence?

Softus, turn it around, please!

If you think TT's advice is misleading or wrong, would you be so kind as to tell us all what he should have written or indeed define "low" and "high" for us?

 

[ricicle]

More than a possibility - all the neutrals are connected at the CU, so they all get a path to earth.

Edited now - are you happy now

 

[ban-all-sheds]

Well I wan't going to persist, but since you ask, no.

there is a possibility that some current will flow back along the earth path from that point

It's more than a possibility that some current will flow back along the earth path - it's guaranteed.

 

[ricicle]

The earth forms a parallel path with the Neutral back to the Star point. If there is current flowing in the installation and a Neutral of an isolated circuit (line only) is touched to earth then there is a possibility that enough current will flow back along the earth path from that point to cause a significant imbalance in the coil of the RCD and will cause it to trip

 

[ban-all-sheds]