Hi all
You still get RCBO's with the the earth sensing wire, these provide for loss of supply neutral protection which in domestic installations is important where you rely on the Neutral for your means of earthing, IE TNCS or PME. They are the ones I would always fit and the four Sneider type B's I purchased three days ago all have the white wire and no indication window! In an industrial/office enviroment fitting RCBO's without the earth sensing wire is ok because the means of earthing is TNS.
You also get type C RCBO's and for your Steeple board
https://www.denmans.co.uk/den/root-category/Distribution/Consumer-Units-&-Devices/Domestic-RCBOs/Type-C-RCBO-|-20A-|-SP-|-6kA-|-30mA/p/2500549699?showBackLink=false
or if Wylex fit then screwfix gives you the choice of with and without earth sense in type C
Eaton RCBOs | Eaton Memera RCBOs | Screwfix.com
As I said before, unless you have a multifunction tester then get the electrician to inspect because you are not going to resolve without his knowledge.
Hi Roy...a bit of a dissertation.... You wrote " in domestic installations is important where you rely on the Neutral for your means of earthing". Is this an English situation? If so I'm surprised. The concept of a neutral being used as an earth may be a misinterpretation of the UK PME/TNCS concept.
It is true that all properties/devices along a supply are a cumulatively part of 'the supply system' however each property has to ensure its protection is adequate notwithstanding any others.
Bonding earth and neutral at supply or at distribution board ("MEN") is not to use a neutral as the earth but to reduce any differential voltage between them. That the neutral is connected into the earthing system whether at supply or at db does not make it 'the earth'. Were it so then earthing would be no more than a back-up and be required to be the same c.s.a. as the neutral.
The potential differential between terrain earth and supply neutral can be substantial (as well as between earth and active ) and caused some swimming pool deaths until the 240V lighting systems were abolished and equi-potential bonding made compulsory..
A differential example, Effectively 'earthed' kneeling on the bath edge I cut a bathroom shower pipe in one case and as the pipe parted it drew a substantial arc. Surprise , I measured across the gap...75volts...could have been nasty for me. These days in Australia all such metal must have continuous and effective earthing (e.g. pipes in kitchen, at HSW and so on).
For RCD to function, 'in spec' earthing loop impedance has to be not so much 'to code maximum ' impedance but must be of a value which ensures the leakage differential and any other protective device can do its job.
The neutral for RCD is isolated from the earth link ...or conversely if you wish; (the MEN system). Hooked together in the RCD circuit the RCD will trip instantly when activated.
RCD's are intended to protect only active to earth leakage...for example through insulation deterioration, other faults or through a body. They do not protect an active to neutral 'hookup' of a person. You know all that...I'm just including it for those that may not.
It is possible however to have a neutral fault which sees he electrician servicing a 'not working' problem carrying neutral current to earth when the appliance is 'on' and the person contacts the faulty neutral and earth/earthed metal simultaneously.
Where not 'MEN', neutral and earth are completely isolated (ignoring terrain conduction via other nearby earthed premises) until back at authority supply source.
The loss of supply neutral in the MEN (Multiple Earth Neutral) system leaves the earthing carrying the load otherwise carried by the neutral. The loss of neutral forward of the db should make no difference to the earthing. they should be entirely isolated at least >1 Megohm and more likely will be >10 meg ohms or even 'infinity' on test.
Neutral/Earth service situations I have experienced have been where from time to time the electricity authority bloke (or errant sparkie) perhaps does not tighten that incoming mains neutral. (more likely there to give problems than at the closer fitting sub-mains neutral link). In one case he hadn't even put the neutral tail back into the authority link before closing and sealing the case.
When not tightened with the physical shock (current caused) of heaters, aircond, cooking appliances being turned 'on' the loose connection jumps/deteriorates/gives high resistance contact. If the situation continues the MEN earthing carrying the sub-circuit current in excess of its rating via the terrain back to supply neutral may send the earthing smoking.
If not MEN all that will happen is intermittent or 'no' operating. It's a high risk for death for inexperienced sparkies who for some reason when called to fix the problem then unhook the main earth from the neutral link and treat it as benign holding the link in one hand and perhaps contacting the copper tail with the other whilst withdrawing it.
Interesting effects can come from 3 phase system with a bad or broken neutral connection but I'll leave it there.
