Dual Earth Sockets

[AyresomeBoro]

Can anyone please explain to me the theory of dual earth (MK rockers on the outside) sockets installed in an office environment with regards to IT equipment?

I know it is to do with earth leakage and possibly if you were to loose one cpc connection you would still have the other connection present but it has never been explained to me clearly.

Also, if you had 15 double sockets on a ring in an office, some for computers and some for general use, am I right in thinking all 15 sockets need to be dual earth to gain the desired effect?

 

[Leesparkykent]

If it is known or reasonably expected that the protective conductor current will exceed 10mA in normal service for a final circuit supplying sockets then high integrity earthing will be needed.

With the high protective conductor current there is a risk of electric shock should the protective conductor become disconnected.

Out board rockers are usually installed in offices so it's easier for people with limited movement/mobility to use the sockets. The other consideration is not to use white sockets on white walls..so people with limited eye sight can distinguish the socket from the wall. If you google part M sockets you will find grey sockets with white outboard rocker switches for the reasons mentioned above. This is taken into consideration in offices etc as it's not known who will be using the sockets and switches.

 

[123]

Funnily enough I was just going to say the same thing as Lee

 

[Pete999]

Can anyone please explain to me the theory of dual earth (MK rockers on the outside) sockets installed in an office environment with regards to IT equipment?

I know it is to do with earth leakage and possibly if you were to loose one cpc connection you would still have the other connection present but it has never been explained to me clearly.

Also, if you had 15 double sockets on a ring in an office, some for computers and some for general use, am I right in thinking all 15 sockets need to be dual earth to gain the desired effect?

Socket circuits for equipment with a high leakage I thinks it's around 10ma not sure 7671 is not with me so I can't check the exact figure, require a special circuit design. RFCs require the cpc to be connected in 2 terminals at each socket and separate terminals in the DB, hence the need for the sockets you are asking about, a radial socket circuit is treated similarly only the cpc will go to each socket connected the same as the RFC and at the last socket a cpc only will be required to run back to9 the DB to form a ring for the cpc, in other words the radial will be a radial but the cpc will be in the form of a ring, hope that explains things, it's all explained in either the OSG or BS 7671 none of which do I have with me to give more details.

 

[AyresomeBoro]

Thanks for the quick replies!

So if you have 10 standard sockets and 5 dual earth sockets on the same RFC it is a bad design as 5 of the CPC's will be terminated separately and 10 will be terminated together, therefore not following with the theory?

 

[Pete999]

Thanks for the quick replies!

So if you have 10 standard sockets and 5 dual earth sockets on the same RFC it is a bad design as 5 of the CPC's will be terminated separately and 10 will be terminated together, therefore not following with the theory?

Correctamundo, but has the circuit with the different types of sockets been designed for electronic equipment that will cause high cpc current? could be that someone has just used the available socket he has, without any thought of the cpc current.

 

[Pete999]

Thanks for the quick replies!

So if you have 10 standard sockets and 5 dual earth sockets on the same RFC it is a bad design as 5 of the CPC's will be terminated separately and 10 will be terminated together, therefore not following with the theory?

PAGE 81/82 7.5 OSG Earthing requirements for the installation of equipment having high protective conductor current.

 

[westward10]

It used to be listed as a Special Location, Section 607 but that has been removed.

 

[Deleted member 26818]

The double Earth terminal sockets are for use where 2 CPCs are installed.
Each CPC should be terminated at separate terminals.

 

[Pete999]

PAGE 81/82 7.5 OSG Earthing requirements for the installation of equipment having high protective conductor current.

Socket circuits for equipment with a high leakage I thinks it's around 10ma not sure 7671 is not with me so I can't check the exact figure, require a special circuit design. RFCs require the cpc to be connected in 2 terminals at each socket and separate terminals in the DB, hence the need for the sockets you are asking about, a radial socket circuit is treated similarly only the cpc will go to each socket connected the same as the RFC and at the last socket a cpc only will be required to run back to9 the DB to form a ring for the cpc, in other words the radial will be a radial but the cpc will be in the form of a ring, hope that explains things, it's all explained in either the OSG or BS 7671 none of which do I have with me to give more details.

Socket circuits for equipment with a high leakage I thinks it's around 10ma not sure 7671 is not with me so I can't check the exact figure, require a special circuit design. RFCs require the cpc to be connected in 2 terminals at each socket and separate terminals in the DB, hence the need for the sockets you are asking about, a radial socket circuit is treated similarly only the cpc will go to each socket connected the same as the RFC and at the last socket a cpc only will be required to run back to9 the DB to form a ring for the cpc, in other words the radial will be a radial but the cpc will be in the form of a ring, hope that explains things, it's all explained in either the OSG or BS 7671 none of which do I have with me to give more details.

PAGE 81/82 7.5 OSG Earthing requirements for the installation of equipment having high protective conductor current.

 

[Deleted member 26818]

The OSG (as I have pointed out a number of times) is not BS7671.
There are two options listed in BS7671.
One is to use 2 CPCs terminated at separate terminals at each accessory and at the DB, the other is to use a single CPC with a CSA of copper equivelance minimum 4mm2.
I also do not have a copy of BS7671 to hand.
I don’t bother with OSGs now, too many errors.

 

[Strima]

I don’t bother with OSGs now, too many errors.

Only time I use the OSG is for the cable resistances and number of cables in conduit etc.

 

[westward10]

Not got one and would never use one.

 

[Deleted member 26818]

Purchased one for my 16th edition upgrade course.
Got given a red 17th edition one.

 

[Ian1981]

I buy one every time it changes and I still don’t know why?
It has useful parts like the conduit capacity tables and cable resistances but a better resource for that stuff is the guidance notes I’d say especially GN1.
It’s still good information for up and coming sparks like apprentices I feel.

 

[Wilko]

Suggest having a read of 543.7.1 and 2.
The reliability benefit of individually terminating the CPCs as described does strike me as a bit of a stretch, in that now there are twice as many things to go wrong (?). But as it says "shall be terminated indendantly" that's what I do .

 

[AyresomeBoro]

I suppose it can be useful for some lunch time reading!

Thanks again.