WRS 80/2 RCD - HELP!!

[Bastion]

Please clear up something for me. The above mentioned RCD has a 30mA short circuit current - right, and the 80 means that it can withstand a maximum of 80A - right? So how can u use this in a domestic installation whereyou normally use 2.5mm at the most.
I am led to believe there will come a time when someone comes along and connects too many appliances on the same circuit, then you gonna have some fried wires?
My thinking is that the max. size mcb on a domestic installation is normally around 32A, so why the need for a RCD with 80A Imax, surely you cold use 16A RCD 30mA?
PLease help, so confused.[/b]

 

[sparkydude]

The reason it has an 80A current rating is that it should normally be used in the tails of a fuseboard protecting the whole board, or as the main switch inside a split load consumer unit supplyingmore than one circuit, for example, downstairs sockets,shower and shed supply, these would or could be on 32A fuses so therefore the rcd needs to handle this current.

hope this clarifies it a bit.

The rcd is rated at 80A but it is not a fuse , it is an earth leakage device and will not trip out in a short circuit situation.

Nick

 

[davy_owen_88]

Please clear up something for me. The above mentioned RCD has a 30mA short circuit current - right, and the 80 means that it can withstand a maximum of 80A - right? So how can u use this in a domestic installation whereyou normally use 2.5mm at the most.
I am led to believe there will come a time when someone comes along and connects too many appliances on the same circuit, then you gonna have some fried wires?
My thinking is that the max. size mcb on a domestic installation is normally around 32A, so why the need for a RCD with 80A Imax, surely you cold use 16A RCD 30mA?
PLease help, so confused.[/b]

I'm equally confused, but at your logic...

The RCD does not provide overload protection, that is the MCB/RCBO's job. It provides earth leakage protection to a number of separate MCB's each with their own rating. If you have even a single 32A MCB why would you use a 16A RCD?

 

[Bastion]

Davy_owen wrote,

If you have even a single 32A MCB why would you use a 16A RCD?

The regs state that u should use an RCD on handheld/portable appliances. Having a 32A MCB does not eradicate the need for a RCD, whose main purpose is to avoid electric shock due to a CURRENT imbalalnce between PHASE and NEUTRAL.

My question is if you use a 80A RCD in place of and MCB(whatever rating) on a ring main, could that result in the wires frying?
My assumptions were based on the fact that I have never come across a WRS 80 RCD.
The reason for my question is that I am working for the council as an operator for out of hours repairs(TEMPORARILY), the electrician says that many of the recently refurbed houses are having their wires burnt. COULD THIS BE THE REASON.
I hope this clears things up.

 

[bernardgreen]

My question is if you use a 80A RCD in place of and MCB(whatever rating) on a ring main, could that result in the wires frying?

If there is only and RCD and no MCB then a live to neutral short or overloading by appliances could result in wire frying.

The RCD does not limit current, an 80A RCD is designed to carry 80 amps with out problem. It would probably carry 160 amps without anything more than getting warm ( do NOT try it ).

The MCB on each circuit limits the current.

So without an MCB that trips at a current below the maximum permitted for the cable the wires can fry.....

 

[davy_owen_88]

The regs state that u should use an RCD on handheld/portable appliances. Having a 32A MCB does not eradicate the need for a RCD, whose main purpose is to avoid electric shock due to a CURRENT imbalalnce between PHASE and NEUTRAL.

The regs state that an RCD should be used on any circuit likely to supply outdoor equipment. RCD's detect earth leakage (possibly due to a person undergoing a hair raising experience) and an MCB's job is to detect overloads.

My question is if you use a 80A RCD in place of and MCB(whatever rating) on a ring main, could that result in the wires frying?
My assumptions were based on the fact that I have never come across a WRS 80 RCD.

An RCD should never replace an MCB. An RCBO (combined MCB/RCD) is a suitable substitute but only if all circuits requiring an RCD are replaced with RCBO's.

The reason for my question is that I am working for the council as an operator for out of hours repairs(TEMPORARILY), the electrician says that many of the recently refurbed houses are having their wires burnt. COULD THIS BE THE REASON.

If an 80A RCD has been used to substitute multiple MCB's then you have a problem and during overloads/shorts damage is going to be caused to the cables.

Davy

 

[Bastion]

Thank you all for your responses, they are mush appreciated.

I sent the sparky in to investigate a property whose RCD (previuosly mentioned) would not stay up. This RCD was used for all sockets in the house. All other circuits eg. lighting were protected via MCB. The fridge stove etc. are all hard wired (ie. no removable plugs) something I have never come across, so he could not unplug all those appliances connected to the circuit.
As I know from past experience, fridges esp. old ones can cause nuisance tripping.

Could this be the problem.Since the 80A RCD30mA is being used in this application.

 

[Spark123]

Every appliance should have some way of being disconnected, are you saying they are fed from fused spurs? Are these switched fused spurs?

 

[Bastion]

THx Spark,
I have not been to the site, so Im just going on what I've told.
If I had to guess I would say they were on switched spurs, as I cant think that someone would permanently connect kitchen appliances without a way switching them off directly -primary isolation.

As I will not have achnace to visit the site, I thinks its best to put the matter to rest in the hope that whoever did th re-wire were not winging it.

Its always a pleasure to be in the company of such great minds.

Peace and Love 2 all