Dual earth socket fronts

RF Lighting

RF Lighting

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Hi, one of my jobs this week is to replace all the socket fronts in a school computer room to sockets with dual earth connections (we will be using MK K2746 WHI)

Can someone tell me why dual earth terminals are required in a computer room, and what the difference is between dual earth terminals Vs both wires into the same terminal.

I know the question will come from my apprentice and I want to be ready with the answers so I look super clever and like some sort of oracle of electrical knowledge.
 
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as far as i know its just in case one earth becomes detatched,something to do with the leakage currents on it equipment
 
If one earth becomes detached, there will always be a return earth path.

It kit has, by nature, a high protective conductor current. If you disconnect the earth, depending on how much curent was flowing, a potential will exist between the 'lifted earth' and real earth. The higher the current, the higher the PD would be.

It is basially to negate the potential shock hazard.

The circuit must be wired as a ring, with the earths terminated into different terminals at all sockets AND the CU.

OR

Two radials with the two last sockets earth terminals linked with a single earth conductor.

OR

The last socket of a radial having a return of earth cable back to the CU (or utilising the armour of a cable, galv trunk etc).
 
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With Class I (earthed) equipment, if the earth continuity disappears, any current that would have travelled down the CPC can travel through a person touching conductive parts of the Class I equipment.

If the available "touch current" is high enough, it can kill. There doesn't need to be a further fault in the equipment to achieve this if the "touch current" ("protective conductor current") is high enough.

There needs to be two methods of protection against shock. The first was providing the earth. The second needs to be a second earth, or some form of insurance that loss of earth continuity is unlikely, or automatic disconnection if continuity is lost.

Therefore, with high earth leakage currents ( 10 mA was decided on), you need to either provide 10 sq mm CPC (risk of loss of CPC continuity is minimised), or provide two conductors, each to separate terminal (a knock-on effect from using 2.5 / 1.5 sq mm solid) or automatically disconnect the supply if earth continuty is lost (earth monitoring system).

Jaymack
 
Cheers guys.

I'm going to sound so knowledgeable :D


(hope he asks the question now)
 
Am I missing something here? Maybe I am. Surely the reason for dual earth is for a clean earth supply for the computers. This would go back to a seperate Earth terminal at the mains. This stops fault spikes from damaging Computers. Ive never heard of a second earth in case the first one gets disconnected. If thats the case, how about a third one...just to be sure :LOL:

I'll get flamed for this I think :cool:
 
Job_n_knock said:
Am I missing something here? Maybe I am. Surely the reason for dual earth is for a clean earth supply for the computers. This would go back to a seperate Earth terminal at the mains. This stops fault spikes from damaging Computers. Ive never heard of a second earth in case the first one gets disconnected. If thats the case, how about a third one...just to be sure :LOL:

I'll get flamed for this I think :cool:
Click to expand...


dual earth sockets dont provide a clean earth,they are two different methods
 
I am yet to a see a clean earth socket with a dual terminal on the socket pin earth :rolleyes: They usually just have a terminal for the plug pins, and a terminal for the socket screw lugs.
 
Lectrician said:
I am yet to a see a clean earth socket with a dual terminal on the socket pin earth :rolleyes: They usually just have a terminal for the plug pins, and a terminal for the socket screw lugs.
Click to expand...

The misconception is they are not clean earth sockets they are "high integrity" earthed sockets.

Before the twin earth sockets were introduced 7671-section 607 called for single sockets to be used for these application. Because it was only a single socket without breaking BS-6396 you could not plug enough high earth leakage equipment into the outlet to cause any harm if the earth became disconnected.

However, a double socket allows twice the amount of high earth leakage equipment to be plugged in so if the earth on the socket became disconnected you could have twice the leakage present on the users earth which could cause a problem, hence the twin earths to minimise the risk of this happening.
 
Im havn't "mis-concepted"!

I am aware of the two very different things we are talking of here. I was just saying that when you run some sockets in for some computer kit, and wire to the regs with dual earth for high protective conductor currents, also incorporating a clean earth supply could prove difficult.

I suppose aslong as the sockets are in plastic dado, and are supplied from a clean board, or earth bar in a board, then there is not really a problem.

Clean earth sockets where used mainly where the ring circuit also fed other items of office kit - the computer dedicated ones then had a seperate earth run to them. These days, computers are vastly used, and have circuits dedicated to them.
 
D

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