Machine earthing problem

**Vernonv** · 28th December 2010, 03:05 PM

Originally Posted by .RC.

If you installed a second earth (to it's own earth stake) wouldn't it then bypass the ELCB and create a risk?

No. An ELCB/RCD only monitors the active and neutral conductors and trips if there is an imbalance. So regardless of which path the "leakage" finds to earth, it should still trip.

**.RC.** · 28th December 2010, 04:05 PM

OK, Thanks... I thought it monitored the earth and if any current flows through it it trips...

**Vernonv** · 28th December 2010, 04:49 PM

Originally Posted by .RC.

OK, Thanks... I thought it monitored the earth and if any current flows through it it trips...

If it did work like that then it wouldn't trip if current found another path the earth other than the earth cable eg. person standing in a puddle of water, or touching a steel fence post.

The beauty of the way RCD's work is that they will trip whenever they detect "missing" current regardless of where it went (and that includes if it went to another circuits neutral or active conductor - hence why you need to be careful when you have 2 circuits going to the one machine).

**eskimo** · 30th December 2010, 11:41 AM

Originally Posted by Vernonv

If it did work like that then it wouldn't trip if current found another path the earth other than the earth cable eg. person standing in a puddle of water, or touching a steel fence post.

The beauty of the way RCD's work is that they will trip whenever they detect "missing" current regardless of where it went (and that includes if it went to another circuits neutral or active conductor - hence why you need to be careful when you have 2 circuits going to the one machine).

But they do not protect if you are insulated from earth...if you touch active to nuetral with no contact to earth, you'll get fffffffrizzzzzzzzzzzzzzled

nothing like safe wiring!!!

**Stustoys** · 30th December 2010, 11:54 AM

Originally Posted by eskimo

But they do not protect if you are insulated from earth...if you touch active to nuetral with no contact to earth, you'll get fffffffrizzzzzzzzzzzzzzled

nothing like safe wiring!!!

How is that effected by two earths to one machine?
Active to neutral applies to everything in your house, including isolation transformers.
Getting across active and neutral is always a risk but it is much harder to achieve than active to earth.

**eskimo** · 30th December 2010, 12:19 PM

Originally Posted by Stustoys

How is that effected by two earths to one machine?

it doesnt, but some people have the mistaken belief that they will be protected in all instances of something going wrong.

Dave J · 30th December 2010, 12:40 PM

My mill turned up with the main earth wire not connected in the elec box,

I don't know how they missed that, but I am glad I found it before anything happened.

Dave

**Stustoys** · 30th December 2010, 12:56 PM

Good

A little knowledge can be a bad thing.........unfortanatly, thats where I am most of the time, hence the questions. Of course its hard to know what you dont know.

Stuart

**elkangorito** · 10th March 2011, 01:32 AM

Stustoys, what did you end up doing?

**Stustoys** · 10th March 2011, 10:18 AM

I went with two earths. (Thats two earth wires both earthed at the same point, not two earth points)
Stuart

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