Live Or Dead Testing - A Question For Members

[says-les]

Apprentice87, is that not a design factor you are introducing?<br />An EICR which I am discussing here only needs us sparks to measure and record Ipscc AND the breaking capacity of each fuse/circuit breaker. The former must never exceed the latter or explosion will result in the event of a dead short adjacent to the device+! no doubt about that one, is there?

 

[steptoe]

To Steptoe, why is an RCD now to be installed, protecting sockets unless in the care of competent people? Although it is classed as additional protection, we must assume the reason is to give closer protection against shock by rapid tripping (40mS instead of 400mS as for a CB or Fuse). You cannot say that it is additional in case the CB or Fuse fails to clear an earth fault, and so you cannot say that the RCD is less reliable than the CB or fuse any more than saying that a CB is more reliable than an RCD.<br />So unless someone gives firm ruling AND logic which no one has as yet, then where are we?<br />Even forgetting the C-Type breakers. I amateurs wired this place and used b-Type breakers and Zs was high then we have the choice of adding local equipotential bonding or adding RCD in addition. We are no by doing the latter RELYING on the RCD solely as suggested by someone's logic, but rather ensuring that shock does not occur. Bad design, I know perfectly well, but who is going to tell the owners that the whole installation is badly designed? and it is!<br />Please don't think I am being argumentative. I am just wanting better logic as to why I am wrong in my logic. Put it this way, if EVERY CB was replaced by an RCBO Zs would not need to comply with Table 41.3!<br />Is there anyone out there who knows how to ask Tony Cable of the NICEIC?<br />He once gave me his card but I cannot find it.<br />Anyone not know who I am referring to?

I dont know why an RCD is to be installed, unless as a bodge for poor circuit design, so I dont know why you are directing this at me.

as for amateurs designing the circuit in the first place, pay peanuts get monkeys, this trade is full of idiots that dont know what they are doing, and, thanks to the short course colleges its getting worse by the week, [or 5 ]

BTW, RCDs are by their inherent nature very unreliable, HRCs are by far a better solution, IMHO.

L-N fault is still fault current, RCDs by their nature CANNOT detect that type of fault,

 

[steptoe]

Apprentice87, is that not a design factor you are introducing?<br />An EICR which I am discussing here only needs us sparks to measure and record Ipscc AND the breaking capacity of each fuse/circuit breaker. The former must never exceed the latter or explosion will result! no doubt about that one, is there?

and where do you get that little gem of information at?

do you actually know the process that will happen if a fault occurs that exceeds the breaking capacity of the OCPD ?

 

[ProDave]

why is an RCD now to be installed, protecting sockets unless in the care of competent people? Although it is classed as additional protection, we must assume the reason is to give closer protection against shock by rapid tripping (40mS instead of 400mS as for a CB or Fuse). You cannot say that it is additional in case the CB or Fuse fails to clear an earth fault, and so you cannot say that the RCD is less reliable than the CB or fuse any more than saying that a CB is more reliable than an RCD.

Do you actually understand WHY an RCD is fitted for shock protection and HOW it works?

If not, try this simple test.

Find a non RCD protected circuit, grab hold of the L wire, and time now long it takes for the CB or fuse to blow.  :coat

The RCD is there for a completely different reason to the fuse or CB.

 

[says-les]

Yes, if the energy let-through is greater than the manufacturer's designed maximum clearance energy, then the only thing that CAN happen is explosion.

Someone said that RCD are not as reliable as fuses, but RCD's cannot be used in place of either fuses or CB's. If you add a pod to a Mem CB it makes it an RCBO, agreed?  An RCBO can be used in place of a fuse or CB. 

RCBO has both overcurrent AND earth leakage tripping ability.  An RCD has only earth fault current protection.  By adding a pod to an existing MCB it is the pod that only detects leakage current to earth and sends trip current to the CB.

We have to test regularly to see that the RCBO is clearing within 40mS, and label it to instruct consumer to test once a quarter by pressing the trip button.  The latter instruction is to check the breaker will triop if there is unbalance in the current-balance transformer, which the button creates artificially not by causing a short to earth.

 

[says-les]

ProDave

Not sure what you are getting at here?

If there is added risk of shock then an RCD in addition to the overload device (fuse or CB) is used, e.g. socket-outlet circuits, bathroom circuits of any kind (lights included) and other places required by the Regs.

The fuse or CB will always also be present for short circuit and overload protection.

 

[steptoe]

not all test buttons create an imbalance,

some physically disconnect the terminals,

how do you circumnavigate that?

 

[says-les]

not sure what you mean.  The test button disconnects what terminals?

 

[steptoe]

ah, now we are on the same page, cos I have no idea what half of your posts are trying to convey either,

on some devices the test button simply forces apart the terminals within the RCD/RCBO , it does not actually create any form of imbalance.

 

[says-les]

ProDave

Of course the RCD is there for a different reason to the fuse.  I'm not saying the RCD can replace the fuse.

RCD - Leakage current to earth sensing ONLY

Fuse - Overload sensing AND short circuit sensing AND earth leakage sensing if Zs is to Table 41.3 modified with the 0.8 factor.

 

[says-les]

Steptoe,

Forgetting what I am trying to convey, which is the truth behind Zs and RCDs, I am getting back from some of the guys evidence of misunderstanding of various concepts.  Now you say some rcd's have a button that forces apart the terminals?????

What type are you referring to cause I have never seen them.  The whole idea is that the test button simulates an earth fault by by-passing one of the transformer windings, thus causing the same condition as an earth fault, i.e. unbalance, and proves that the CB trips instantly.

 

[Sidewinder]

les,

The test button on an "RCD" only proves the mechanical operation of the device.

There is no more to say.

 

[Sidewinder]

Yes, if the energy let-through is greater than the manufacturer's designed maximum clearance energy, then the only thing that CAN happen is explosion.

Sorry les you are wrong with respect to this in a big way.

 

[says-les]

Enlighten me please, Sidewinder

 

[steptoe]

Steptoe,

Forgetting what I am trying to convey, which is the truth behind Zs and RCDs, I am getting back from some of the guys evidence of misunderstanding of various concepts.  Now you say some rcd's have a button that forces apart the terminals?????

What type are you referring to cause I have never seen them.  The whole idea is that the test button simulates an earth fault by by-passing one of the transformer windings, thus causing the same condition as an earth fault, i.e. unbalance, and proves that the CB trips instantly.

really,?

and where did you find that standard at?

les,

The test button on an "RCD" only proves the mechanical operation of the device.

There is no more to say.

thank you, that is what I was trying to convey, albeit in not so a fluent manner.

 

[steptoe]

Enlighten me please, Sidewinder

you do understand the maximum PFC/PSCC of PME is 16kA , and a 1361 is 16.5kA

upstream protection ?

 

[says-les]

I agree with you. I was only offering an explanation of how it did so.

 

[says-les]

Yes

 

[steptoe]

so where is this explosion of yours coming from then?

 

[says-les]

les,

The test button on an "RCD" only proves the mechanical operation of the device.

There is no more to say.

That is correct.