to earth or not to earth.

[IQ Electrical]

I'm out.

 

[Paul.M]

so does a rcd not work without a cpc?

NO IT WILL NOT WORK

I'm off for a lie down.

 

[SimpleSimon]

Just come back to this thread.
As IQ stated RCD is almost pointless without an earth as there is nothing for fault current to flow to to create an imbalance.
You may have seen places without earths, doesn't mean it's always right.

Hate to say this mate but I strongly advise going over your books, BS7671, GN3 and GN8. This is basic stuff and without having a full grasp on it your going to compromise Someones safety.
By all means ask away but please read it yourself to get a real good understanding.

 

[Engineer54]

What's the saying?? ....You can lead the horse to water!!..... lol!!!

 

[mayfair]

So if the horse was drinking water, and the water was acting as a conductor the horse would be earthed DOH...

What's the saying?? ....You can lead the horse to water!!..... lol!!!

 

[IQ Electrical]

A mane earth

 

[mayfair]

you got it in one m8

A mane earth

 

[Deleted member 26818]

Appears that some people are getting quite wound up over this discussion. Don't quite understand why?
Anyway, RCDs will operate without a CPC. The only problem being, that a person will most likely become part of the earth fault path in order for the RCD to operate.
Wheras with a CPC, the RCD will hopefully operate without the need for a person to be involved. I say hopefully, because RCDs are not the most reliable of devices, which is why BS7671 still considers them to be additional protection (one of the reasons at least).

 

[SimpleSimon]

People are getting wound up Spin because numerous examples have been given already but OP has ignored them all and carried on asking the same question!

 

[dekachad]

I have a good understanding of earthing systems and this is why i am asking "do we need an earth" a rcd will work without an earth, it detects an inbalance between neutral and live, which would occur in any shock situation, unless you grabbed hold of live and nuetral at exactly the same time, and the presence of an earth in this situation would be useless too.

 

[telectrix]

is it time now for an actual test involving a live body, an RCD and 230v, sod the theory, let's go and grab some live cables, show the videos on youtube or you've been framed. last one to fibrillate is a cissy.

 

[dekachad]

Also, the numerous examples given....I questioned but no definitive answers were given. its all college and regs stuff.

 

[Deleted member 26818]

Chad, what's your date of birth?

 

[dekachad]

whats that got with a discussion????

 

[SimpleSimon]

Yes. Although no earth wire (or cpc) is present, it can still be earthed by direct contact from a person. Eg, a washing machine with no earth/cpc conductor develops a fault, the live wire inside touching the metal casing would not trip a mcb as it would now be part of the circuit with no way to get to earth until someone comes along and touches it and grounds it via your body. The earth will take as much current as the resistance can carry until the flow superseeds the rating of the mcb.

A rcd monitors the out going current on the live/line wire and the return current if the neutral and if the live and neutral go beyond 30mA (30/1000 of an A) it will operate and trip.

The earth/cpc is to allow a path to earth faster than a person. This in turn will request a much higher current than the rating of the mcb. Eg you cut a twin and earth 1.5 rated at 6A, current then flows from the live to the cpc back to earth in milli seconds. Because of the connection to the cpc the earth can take a much higher load than 6A and trips the mcb. If there wasn't a cpc it would travel via the neutral with the same effect. Another way a mcb trips is for it to be overloaded. Multiple loads on a circuit higher than the rating of the cable Thers why we rate the mcb at the same current capacity or lower than the cable.

In a rcd circuit continuously compares the current in live and neutral. If the circuit is healthy the two will be equal until a live to cpc occurs and when 30mA leaks to earth via the cpc or a person the rcd will trip.

Hope that gives you a better description of the two. Both are needed and a cpc/earth is also vital.

An earth-free system in a domestic property would be almost impossible to implement due to extraneous conductive parts etc. introducing earth potential into the location.

The cpc has absolutely nothing to do with overcurrent protection.

Even using a TN supply system, you would be 'importing' an earth via the earthed neutral conductor which in the event of a neutral fault to an exposed conductive part, would earth the equipment.
Earth-free local equipotential bonding can be used but requires careful planning and supervision to ensure that the specialist requirements are adhered to.

"Rules and Regs aside" Look at it this way.

An RCD supplies a circuit with 1 socket outlet.

If you stick your finger in the live and you've got your insulated boots on, you won't get a shock because you are not earthed.

If you stick your other finger in the neutral you WILL get a shock (Big time ) because you have now become the load, but the RCD won't trip because the current passing through the L & N , and your body, is keeping the RCD in balance, You need to take one of your fingers out and touch the earth and then the RCD will trip immediatly because the resistance of your body is enough to cause an imbalance in the RCD of more than 30Ma.

If you can keep hold of the live and neutral long enough, and by now your hair is on fire, the MCB will trip because an overcurrent will be going through your body.

Earths are good!

Appears that some people are getting quite wound up over this discussion. Don't quite understand why?
Anyway, RCDs will operate without a CPC. The only problem being, that a person will most likely become part of the earth fault path in order for the RCD to operate.
Wheras with a CPC, the RCD will hopefully operate without the need for a person to be involved. I say hopefully, because RCDs are not the most reliable of devices, which is why BS7671 still considers them to be additional protection (one of the reasons at least).

Also, the numerous examples given....I questioned but no definitive answers were given. its all college and regs stuff.

These are all examples, college stuff is what is going to happen to you in the field if the regs on these matters are defied. The Regualtions are based on logic. I can't understand what else your asking for?
You've had some very good basic replies from some well respected members on here.... what else are you asking?